# Haldex Problem - back wheels won't stay engaged



## All_Euro (Jul 20, 2008)

So, I tried having a little AWD fun in the snow and got nothing but FWD action so I propped the car up on jack stands and all four wheels are spinning... and they accelerate fine with some throttle but when load is applied, the back wheels stop and it's just the fronts turning. There is a bit of a rubbing/skipping sound from the back like the wheels are trying to engage but are slipping out.

Replaced the Haldex fluid just to be sure and the old stuff came out clean. No electrical issues to worry about as my system is full time 50/50 and simply turns off and on with the ignition.

Seems like an issue with the diff - thoughts...?


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## Gonzalo1495 (Feb 2, 2015)

oh boy.

Sounds like a bad precharge pump to me. Could be on it's way out (from the continuous 50/50 demand). However I'm not sure what you mean by 50/50 since it's wired to the ignition. I vaguely remember reading your set up in the haldex thread, could you restate what it is exactly? Are you running the insert + constant current to the precharge pump?


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## All_Euro (Jul 20, 2008)

Gonzalo1495 said:


> oh boy.
> 
> Sounds like a bad precharge pump to me. Could be on it's way out (from the continuous 50/50 demand). However I'm not sure what you mean by 50/50 since it's wired to the ignition. I vaguely remember reading your set up in the haldex thread, could you restate what it is exactly? Are you running the insert + constant current to the precharge pump?


Yes, I'm using an insert and the pre-charge pump turns on with the ignition - which fully engages the Haldex system. The pump is connected to a 5A fuse in the fuse box and the fuse is good. When all four wheels are in the air they spin so that confirms the pump is working and that all driveshafts are connected.

The issue is the back wheels want to turn but they don't stay engaged under load. So insufficient pressure from the pre-charge pump might have this symptom - the pump is only a few months old though so I doubt it's that...


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## Gonzalo1495 (Feb 2, 2015)

Did you buy the pump new or used. Or did you use the pump rebuild kit from yourhaldexworks?

It's either the pump or you've significantly damaged something inside the haldex unit itself. I wouldn't suspect the controller. 

Lastly, I'm not going to pretend I know how the precharge pump functions via voltage. Does it use a certain voltage to determine how much it needs to pump? Is that how you maintain "50/50 all the time" by wiring it up to a 12v source which I would assume is the max, in this case the ignition being the source?

There's not really a whole lot that can go wrong with the haldex. It's either the clutch packs, pump, controller or maybe a driveshaft. My $ is still on the pump. There's no resistance in the air for the pump to generate just enough to rotate the tires, where as on the ground it would need to be operating at almost full capacity to spin the tires, hence why I think it's the pump.

Final question, how long have you had the insert in the controller?


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## lite1979 (Sep 9, 2005)

I believe the insert is what makes it 50/50 all the time.

http://auditttuning.org/2013/09/19/...mprove-your-haldex-first-generation-traction/

"Working pressure in a Haldex unit is not created by the pre-charge pump and whatever you use your Haldex stock, electronically or mechanically upgraded or with the Powertrack Insert, the pre-charge pump do its job the same way with no difference and no more stress applied on it."


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## All_Euro (Jul 20, 2008)

Gonzalo1495 said:


> Did you buy the pump new or used. Or did you use the pump rebuild kit from yourhaldexworks?
> 
> It's either the pump or you've significantly damaged something inside the haldex unit itself. I wouldn't suspect the controller.
> 
> ...



It was a new pump from a TT enthusiast in Polad - his pump was only about $30 more than the repair kit from those other guys... http://www.ebay.ca/usr/haldexpart

The controller isn't hooked up at all. It's in place but completely bypassed - only need it if you're switching percentages of applied power.

In the OEM system, the pump is on too but the controller adjusts a pin that controls fluid pressure to the clutch-packs. With the insert, as soon as the pump turns on it pressurizes the Haldex fluid and fully engages the clutch packs - they stay engaged until the key is off and the pump depressurizes.

These AWD conversion parts that I installed are used and from a lightly damaged TT 225 so I don't know for sure how solid each of components are - visual inspections only get you so far. Just wondering if there is something in the diff that could be going wrong. Maybe the clutch packs but with how grippy they are I don't suspect the soft disengagement sound is coming from them - it is possible though. Driveshafts are solid - I know the sound when they come out of the hub...

I suppose it is possible the pump is only holding a minimal amount of pressure... and then it would be the clutches that are slipping and not allowing the wheels to hold power under load. Hmm... the insert and pump have been installed for the summer and very end of last winter.

I do know it isn't one of the multiple Haldex related sensors malfunctioning though


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## Gonzalo1495 (Feb 2, 2015)

lite1979 said:


> I believe the insert is what makes it 50/50 all the time.
> 
> http://auditttuning.org/2013/09/19/...mprove-your-haldex-first-generation-traction/
> 
> "Working pressure in a Haldex unit is not created by the pre-charge pump and whatever you use your Haldex stock, electronically or mechanically upgraded or with the Powertrack Insert, the pre-charge pump do its job the same way with no difference and no more stress applied on it."


No. The insert makes it so the haldex distributes 50/50 instead of whatever percentage the controller would dictate normally. But what OP is saying is that he has fulltime 50/50 awd.

The insert basically makes it so whenever the haldex is told to engage, the haldex controller is bypassed and instead you get a 50/50 split.

@all_euro

Honestly I'm not sure. So many variable as this is really a custom set up you've got. I would never dare to bypass the controller (or why for that matter, since fulltime awd is understeer city on turns). 

If you have vcds, run the awd "tests", and see if you can hear your precharge/cargo pump whining when the test engages it. If it's very faint or not audible at all you have found a problem.

Considering you've eliminated the controller, your pump must be fully operational always. I'm pretty sure the haldex system is meant to have periods where it can bleed off pressure, which in your case it would not have. Also could be clutch packs since they're always engaged.

Check the pump and go from there honestly.

Other than that, it's quite the predicament. I'll closely be following this thread, very curious on how it plays out. Wish you luck man


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## TheDeckMan (Sep 26, 2004)

If having slippage issues in the rear then it could be that the clutches and clutch plates are shot, can happen from too much heat or not changing the Haldex fluid often enough. Since your running a plug to jam the clutches into full engagement all the time I would put my money on needing a clutch pack set. I think they are $300-400 and require pulling the rear end out to replace.


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## All_Euro (Jul 20, 2008)

TheDeckMan said:


> If having slippage issues in the rear then it could be that the clutches and clutch plates are shot, can happen from too much heat or not changing the Haldex fluid often enough. Since your running a plug to jam the clutches into full engagement all the time I would put my money on needing a clutch pack set. I think they are $300-400 and require pulling the rear end out to replace.


With the unknown condition of the clutches when they were installed, they could be toast. When I drained the fluid it was nice and clear so, at this point, I don't suspect it's anything I've done... will probably just pull the diff out and have a look inside since the only external issues could be pump or axles. Axles are good and I'm pretty sure the pump is ok.


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## TheDeckMan (Sep 26, 2004)

Looking at the fluid is not really a good way to tell on the condition of the clutches. Pulling them out once the diff is out takes 20 min or so, but be careful as there are all the ramp bearings that want to fall out as well. They should look like these GTR units










If they are very smooth then that means that the friction and heat has worn them down. Part number for them is 02D 525 565


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## All_Euro (Jul 20, 2008)

Just went and double checked that the Haldex filter was tight and hadn't been leaking - all is good on that front.

The vent on top of the Haldex portion of the rear end looks like it's been letting some oil vapour out though - not sure if that's normal. The rubber vent on top of the diff seems dry...


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## All_Euro (Jul 20, 2008)

TheDeckMan said:


> Looking at the fluid is not really a good way to tell on the condition of the clutches. Pulling them out once the diff is out takes 20 min or so, but be careful as there are all the ramp bearings that want to fall out as well. They should look like these GTR units
> 
> 
> 
> ...


Cool, thanks for the info Noah. I post what I find as I work through this.


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## TheDeckMan (Sep 26, 2004)

All_Euro said:


> Cool, thanks for the info Noah. I post what I find as I work through this.


:thumbup: Good luck! Let us know what you find. This happens a lot on Porsche differential clutch packs, they wear out and no longer have any pre-load.


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## asiwa (Dec 18, 2014)

This is an interesting thread, but I'm a little confused as to how this "permanent" 50/50 system works. 

The Haldex drive train isn't capable of operating at a continuous 50/50 distribution under really any circumstances. There will be some point - at least one moment - during any driving situation where the rear wheels will be disengaged. The only way you can possibly work around that is by installing a no-longer-available competition controller, which maintains rear wheel engagement under braking. The issue is that the clutches will not - and I mean legitimately will not - operate unless you have a functioning controller. 

The clutch packs operate when hydraulic pressure is applied to them; that is the function of the Haldex controller. The precharge pump acts as a fluid circulation device so that engagement of the clutch pack is more instantaneous when the controller needs to do so. The insert mentioned above alters the flow of the fluid through the controller so that when the controller receives a signal to transition power to the rear wheels, the distribution is instantly 50/50 as opposed to slowly ramping up to that distribution over a short period of time depending on demand.

Your problem is that your controller is not hooked up. I know that you insist that your system is full-time 50/50, but that is literally impossible on this car without physically modifying the clutch pack (i.e. welding the clutches together). All of the legitimate Haldex modifiers on the market (notice the word "legitimate") all require a working controller. Whether we're talking about the Unitronic flash, HPA's TouchMotion system, or the older Haldex-branded Blue/Orange/Silver controllers, they all have the same feature in common.

I had *exactly* the same problem on my car for almost two years before I figured out the problem earlier this year. My controller had gone bad and needed to be replaced, and I was magically back in business. Before that I had gone through all of the fixes: ABS module, ABS sensors, precharge pump rebuild, Haldex fluid drain/refill (multiple times) and more. My pump was working fine and all four wheels would spin when the car was off the ground, but would cease spinning when reasonable throttle was applied or the car was on the ground. Trust me, I was legitimately stumped. A $200 replacement controller off a TT with 30k miles solved the issue.

And if you plug the controller in and you still have the same issue, we know what the issue is; at that point you'll be in the market for a replacement. At this point they are easy to find on places like car-part.com; just make sure you find one off the lowest-mileage car you can find.

Edit: To answer more concisely, you still need a working controller even with a Powertrak insert. The controller doesn't get "bypassed", it just becomes modified in its overall operation.


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## All_Euro (Jul 20, 2008)

Thanks for the idea - I would prefer to just wire up the Haldex controller and not have to pull the driveshaft, rear axles and diff out of the car. The insert that's installed completely bypasses the need to have the controller adjust the pin in the Pressure Regulating Valve - it's just fully pressurized whenever the ignition is on. You're right, though, the stock or flashed OEM systems need the controller (among other things) to be fully functioning.

When airborne, all the wheels spin through various speeds and under lighter loads - not just at idle. It's when a heavier load is applied to the back wheels that they stop. And there is a bit of a skipping sound coming from the diff when they do... plan to pull it tomorrow...


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## All_Euro (Jul 20, 2008)

TheDeckMan said:


> :thumbup: Good luck! Let us know what you find. This happens a lot on Porsche differential clutch packs, they wear out and no longer have any pre-load.


I've got the rear diff out and partially disassembled - the clutch discs don't feel super grippy but do have well defined square ridges. Not sure how these should look/feel...


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## Marcus_Aurelius (Mar 1, 2012)

asiwa said:


> The Haldex drive train* isn't capable of operating at a continuous 50/50 distribution under really any circumstances*. There will be some point - at least one moment - during any driving situation where the rear wheels will be disengaged.* The only way you can possibly work around that is by installing a no-longer-available competition controller*, which maintains rear wheel engagement under braking. The issue is that the clutches will not - *and I mean legitimately will not - operate unless you have a functioning controller*
> .


How do these work then? 
http://www.sqsracing.com/produkt/314:406:haldex-regulator-controler-valve


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## TheDeckMan (Sep 26, 2004)

All_Euro said:


> I've got the rear diff out and partially disassembled - the clutch discs don't feel super grippy but do have well defined square ridges. Not sure how these should look/feel...


Those look pretty good, what do they measure? How do the other plates look?


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## TToxic (Nov 15, 2008)

Marcus_Aurelius said:


> How do these work then?
> http://www.sqsracing.com/produkt/314:406:haldex-regulator-controler-valve


You've not heard ? Its Magic!


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## All_Euro (Jul 20, 2008)

TheDeckMan said:


> Those look pretty good, what do they measure? How do the other plates look?


Feeling the discs without so much fluid on them, they do have some grip - I was imagining a bit more though. The rest of the discs are in the same condition and back when I changed the original filter it was clean.

My digital callipers have a dead battery but the sintered disc thickness is about 2.5-2.7 mm... the other discs are nice and smooth - no scoring or anything. Didn't measure those though.


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## TheDeckMan (Sep 26, 2004)

So the thickness of the discs check out even better than the spare set I have kicking around at 2.4mm. Guess the next thing is to clean the passages on the Haldex. One of the ones I pulled apart had tons of metallic slim in it from my guess being from bearing, clutch and cooked Haldex fluid.


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## All_Euro (Jul 20, 2008)

TheDeckMan said:


> So the thickness of the discs check out even better than the spare set I have kicking around at 2.4mm. Guess the next thing is to clean the passages on the Haldex. One of the ones I pulled apart had tons of metallic slim in it from my guess being from bearing, clutch and cooked Haldex fluid.


Ok, that's reassuring - I'd say the clutch discs are good. They're back in place and I was just thinking of pulling the Haldex control unit aprart... was thinking one of the pressure valves might be weak but I don't have anything to test them with. I'll try cleaning the fluid passages :beer:


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## asiwa (Dec 18, 2014)

Marcus_Aurelius said:


> How do these work then?
> http://www.sqsracing.com/produkt/314:406:haldex-regulator-controler-valve


No need to be snide about it; I've seen those SQS controllers lots of times online but have seen very few cases (and never in person) where people actually used them, and when they did it was typically to disastrous results. That being said...

They're just crude versions of the stock Haldex controller. They even have a model with a brake/handbrake disengagement safety to lessen the chances of you royally messing with your rear end because they must understand the clear and present issues with a mechanical-only system. Great, they're manually adjustable. We'll check me being wrong off the list on that one.

Regardless of the method, mechanical modifications to the original electric-hydraulic system take the parts where they weren't meant to go. The system was designed a certain way to increase longevity of the mechanical parts, so why go and make that system unintelligent? People tracking their cars would use that as a reason but frankly the original system is still better for that as the low rear power distribution on straightaways reduces drag from the drive train. We're talking about fractions of a second between slip and grip and I would barely call it slip. Sorry - just my take on things in that department. In fact I know that Marcus had similar words in another conversation along these lines 

*Regardless* (my apologies for momentarily hijacking this one) to address the OP: your clutch disks look to be in normal if not superb condition. If you dig around on the R32 forum a little you can find some pictures of toasted clutch disks and they sure aren't pretty :laugh: There are also some pretty severe signs associated with that sort of failure, like tons of brass flakes in your oil and burnt looking/smelling oil to boot. 

With all of this in consideration I am also stumped on your issue. Regardless of the system, your problems align pretty closely with what I was experiencing and that is why I pointed you in the controller direction. I see some others have mentioned dirty fluid passageways. That would probably be the next thing I would look at, although with all of your symptoms and the condition of the internals I'd say the chances there are pretty slim. It's fairly difficult for those passages to become clogged but it isn't unheard of. 

Keep us posted; I'm interested to see what's ailing your rear end


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## All_Euro (Jul 20, 2008)

Pulled the controller apart and the electrical areas were nice and dry - I'm not using them but it's still nice to see the oil is staying where it should. Pulled the electrical pieces off, sopped up the existing oil and blew some compressed air through the oil passages...











Double checked the insert was actually long enough - same dimensions as the original except the 5mm extension at the bottom. When inserted it blocks almost all of the oil passage that the pin in the Regulating Valve normally would...











Pulled the pre-charge pump and Haldex filter just to check - they were both clean. Ran a bit of compressed air through the different exposed oil passages - they were all good. Found a little opening on the bottom of the diff that seems to lead into the bearing area of the bottom of the stack of clutch discs - is this a vent or should it have a tiny little plug (think mini frost plug) like the one by the Haldex filter? It's in the upper right portion of the picture by one of the bolts that attach the Haldex unit to the differential...


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## ticketed2much (Feb 18, 2012)

Mine has that hole too, no plug. Probably for some type of pressure relief. Of course mine is sitting in the shed and I have not used it yet!

If you don't find any other obvious cause I would skip the friction modifier when you refill and see if it makes a difference. I realize some people have used it successfully including yourself, but it may be a bit too slippery.

Thanks for documenting everything so well, it's great to see everything up close.


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## TheDeckMan (Sep 26, 2004)

Valve









Grime


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## All_Euro (Jul 20, 2008)

ticketed2much said:


> Mine has that hole too, no plug. Probably for some type of pressure relief. Of course mine is sitting in the shed and I have not used it yet!
> 
> If you don't find any other obvious cause I would skip the friction modifier when you refill and see if it makes a difference. I realize some people have used it successfully including yourself, but it may be a bit too slippery.
> 
> Thanks for documenting everything so well, it's great to see everything up close.



Seems like a vent then - I was thinking all the vents would be on the top of the diff but good to hear someone else has it too.

Originally I was going to start with no friction modifier and then add some to cure the binding I was sure would happen but I added a little right from the start so I wouldn't have to mess around trying to add a little later. I think I'll try straight Haldex fluid like you're saying and see what happens.

Fill capacity is 0.42L and the tubes VW sells are a touch over 0.25L to allow for spillage - if I drain all the fluid out of the Haldex coupler, should the first fill be 0.42L and the services 0.25L or are they all done at 0.25L?


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## All_Euro (Jul 20, 2008)

TheDeckMan said:


> Valve
> 
> 
> 
> ...



Thanks for the pics Noah - that's one of the valves I was talking about... might as well clean everything while it out


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## Marcus_Aurelius (Mar 1, 2012)

asiwa said:


> No need to be snide about it; I've seen those SQS controllers lots of times online but have seen very few cases (and never in person) where people actually used them, and when they did it was typically to disastrous results. That being said...
> 
> They're just crude versions of the stock Haldex controller. They even have a model with a brake/handbrake disengagement safety to lessen the chances of you royally messing with your rear end because they must understand the clear and present issues with a mechanical-only system. Great, they're manually adjustable. We'll check me being wrong off the list on that one.
> 
> Regardless of the method, mechanical modifications to the original electric-hydraulic system take the parts where they weren't meant to go. The system was designed a certain way to increase longevity of the mechanical parts, so why go and make that system unintelligent? People tracking their cars would use that as a reason but frankly the original system is still better for that as the low rear power distribution on straightaways reduces drag from the drive train. We're talking about fractions of a second between slip and grip and I would barely call it slip. Sorry - just my take on things in that department. In fact I know that Marcus had similar words in another conversation along these lines


I simply asked a question you know, a question to understand how you came up with the statements you posted about the system being completely incapable of physically operating in maximum rear engagement "under any circumstances". Bringing up why it's not advisable (even if I totally agree and have said it myself many times), is totally irrelevant. "Not a good idea" and "physically impossible under any circumstances" are not the same thing. 

Anyway, there is no point in arguing the principle and clog a good thread.


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## Marcus_Aurelius (Mar 1, 2012)

All_Euro said:


> Thanks for the pics Noah - that's one of the valves I was talking about... might as well clean everything while it out


I believe there are internal pressure bypass valves in the coupling, while you have it apart, check to see of one isn't stuck open. 

If that fails, this what I would suggest: put everything back together, and instead of using the controller gasket, make a block off gasket to block the fluid pressure bypass. If your pre-charge pump is in fact working, you should have full time rear engagement. If not, you're not building enough pressure for the system to operate under load (which would explains the why you have all 4 wheel spinning in the air, but not under driving conditions). This scenario points out to bad pre-charge pump (even if new, it's possible).


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## All_Euro (Jul 20, 2008)

Checked the pressure limiting valve which was clean. Checked for the "grime" next - finally found something...









Cleaned the magnet and housing up...


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## TheDeckMan (Sep 26, 2004)

Yummy!


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## All_Euro (Jul 20, 2008)

Marcus_Aurelius said:


> I believe there are internal pressure bypass valves in the coupling, while you have it apart, check to see of one isn't stuck open.
> 
> If that fails, this what I would suggest: put everything back together, and instead of using the controller gasket, make a block off gasket to block the fluid pressure bypass. If your pre-charge pump is in fact working, you should have full time rear engagement. If not, you're not building enough pressure for the system to operate under load (which would explains the why you have all 4 wheel spinning in the air, but not under driving conditions). This scenario points out to bad pre-charge pump (even if new, it's possible).


Hmm, I'll have a look for those bypass valves. I was trying to check the two pressure valves beside the pressure limiting valve (19mm socket) that are held in with snap-rings... haven't been able to get them out yet but will give it another try. Not sure if sludge around that magnet could be the sole cause of my Haldex woes. Every other passage, valve, filter was clean but I'll see what else I can get at.

Before disassembly, the pre-charge plump was audible and pumping - wheels stopped with the fuse out. Wonder if it could be pumping but only a minimal amount...

Good idea for the block-off plate - I'll try that if need be :thumbup:


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## All_Euro (Jul 20, 2008)

Didn't have any success with the various snap-rings so I left the other valves alone for now. Decided to reassemble the coupler assembly and will power the pre-charge pump up once fluid has been added.

Rollers back in their slots...









Thick washer over the rollers and then final thick washer over the discs - you can see the two odd teeth fit in the keyway just right of the bottom centre...









Bearing on top of the stack of washers / clutch discs...









Washer over the bearing with the raised lip inward...










I don't have a Bentley yet but here's a clutch DIY thread I found useful during disassembly / reassembly... http://forums.vwvortex.com/showthread.php?6760419-DIY-for-Haldex-Clutch-Replacement


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## All_Euro (Jul 20, 2008)

All_Euro said:


> ...Fill capacity is 0.42L and the tubes VW sells are a touch over 0.25L to allow for spillage - if I drain all the fluid out of the Haldex coupler, should the first fill be 0.42L and the services 0.25L or are they all done at 0.25L?


Fill level from completely empty is 0.42L and the service changes are done at 0.25L - although the tubes are 0.275L. Fluid level is supposed to be even with the inspection hole which is the first arrow in the service illustration above.

Same housing that holds the magnet...


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## All_Euro (Jul 20, 2008)

Pulled the diff apart just to be sure nothing fishy was happening in there. Nothing was so I cleaned the inside out and reassembled - clean magnet this time...











Once everything was back together, and fluids were filled, I powered up the pump which ran fine... clutches were engaging but not holding loads still. Made a block-off plate (as Max suggested) out of some thin hard plastic that an unopened tool was in...











Bolted the controller back on and fired up the test rig - finally holding pressure


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## All_Euro (Jul 20, 2008)

Marcus_Aurelius said:


> I believe there are internal pressure bypass valves in the coupling, while you have it apart, check to see of one isn't stuck open.
> 
> If that fails, this what I would suggest: put everything back together, and instead of using the controller gasket, make a block off gasket to block the fluid pressure bypass. If your pre-charge pump is in fact working, you should have full time rear engagement. If not, you're not building enough pressure for the system to operate under load (which would explains the why you have all 4 wheel spinning in the air, but not under driving conditions). This scenario points out to bad pre-charge pump (even if new, it's possible).



So with the block-off plate allowing the clutches to hold pressure - this means the pump and accumulator are working but pressure is being bled off via the pressure limiting valve? Anyone happen to have a part # for this faulty valve?


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## All_Euro (Jul 20, 2008)

TheDeckMan said:


> Valve



This is what I've been referring to as the pressure limiting valve - I just pulled it out and the ball under the spring that seals the bottom face does push in pretty easily with an awl... that normal or should it be pretty solid?


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## jsmith2015 (Mar 7, 2015)

Some one aught to sticky this thread. Lots of good pics and info. Nice work.and good luck.

Sent from my Torque using Tapatalk


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## Marcus_Aurelius (Mar 1, 2012)

All_Euro said:


> This is what I've been referring to as the pressure limiting valve - I just pulled it out and the ball under the spring that seals the bottom face does push in pretty easily with an awl... that normal or should it be pretty solid?


I would assume it should be pretty solid in tension due to the kind of operating pressure in this system. As a limiting valve, the ball should not be easily manually moveable I'd assume. I never handled one these valves firsthand so I'm not much of a help, but I think you're on the right track. The clucth pack is fine, the system can build pressure, so now you have to figure out why/where it's bleeding pressure under load. 

For some reason, if it's not a pressure bypass valve that failed, I feel it's the dummy controller with insert combo playing tricks on you. I think (it's a theory) YHW at some point revised the length of the insert from the original ones that fully blocked all bypass. So if you're using an insert that allows some amount of bypass without an operating controller, you won't get full pressure under load.


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## TheDeckMan (Sep 26, 2004)

The valve I pulled did take some effort to push the ball back in. Another possibility of a future issue for us will be if these valves being plastic start to fatigue. Something I just thought about, especially if they are over tightened back into the housing. I'll have to grab one out of the spares and take it apart and see what the spring pressure is. Might be useful to know and perhaps even test to pressure test to ensure no cracks in the plastic.


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## All_Euro (Jul 20, 2008)

Marcus_Aurelius said:


> I would assume it should be pretty solid in tension due to the kind of operating pressure in this system. As a limiting valve, the ball should not be easily manually moveable I'd assume. I never handled one these valves firsthand so I'm not much of a help, but I think you're on the right track. The clucth pack is fine, the system can build pressure, so now you have to figure out why/where it's bleeding pressure under load.
> 
> For some reason, if it's not a pressure bypass valve that failed, I feel it's the dummy controller with insert combo playing tricks on you. I think (it's a theory) YHW at some point revised the length of the insert from the original ones that fully blocked all bypass. So if you're using an insert that allows some amount of bypass without an operating controller, you won't get full pressure under load.



Ya, it's a definite step in the right direction - there are a few pressure valves but I'll start with this one and go from there. A guy on my local forum had a good idea to seal off the valve I think is bad and leave the other passageway open - think I'll give that a try.

I bought the insert (and then pre-charge pump) from a Polish company but the guy running it turned out to be pretty cool so I can just ask him it need be.


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## All_Euro (Jul 20, 2008)

TheDeckMan said:


> The valve I pulled did take some effort to push the ball back in. Another possibility of a future issue for us will be if these valves being plastic start to fatigue. Something I just thought about, especially if they are over tightened back into the housing. I'll have to grab one out of the spares and take it apart and see what the spring pressure is. Might be useful to know and perhaps even test to pressure test to ensure no cracks in the plastic.


Ok, mine went in pretty easy... not 100% on what 4 bar on the end of an awl should feel like though  Any chance you know the part # for this valve or the others?

Good point about the plastic sleeve that's over the spring. Didn't see any cracks on mine but it's worth another look. That'd be awesome if you can test a spare - I'll try to find something to test mine with too :beer:


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## TheDeckMan (Sep 26, 2004)

All_Euro said:


> Ok, mine went in pretty easy... not 100% on what 4 bar on the end of an awl should feel like though  Any chance you know the part # for this valve or the others?
> 
> Good point about the plastic sleeve that's over the spring. Didn't see any cracks on mine but it's worth another look. That'd be awesome if you can test a spare - I'll try to find something to test mine with too :beer:


I'll grab two of them tonight. One I know is good and the other is questionable. Sure I can figure out a way of making a testing fixture. I have an idea that I need to try out on how to test it.


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## ma2kster (Jun 4, 2010)

Awesome work and great detail, i've been following with a lot of enthusiasm. While i dont know the part number of the valve you are seeking, i wanted to contribute with the following schematic and link. I also suggest you call Bernardi Audi parts and talk to Emile or Chris. They always find what i need. 800 924-1884 is their number. You might need the VIN number for a more accurate determination.

http://www.partsbase.org/audi/audi-...-unit-for-four-wheel-drive-pre-charging-pump/


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## All_Euro (Jul 20, 2008)

jsmith2015 said:


> Some one aught to sticky this thread. Lots of good pics and info. Nice work.and good luck.


Thankfully others with experience have been chiming in and helping out - hope we can stockpile a little more Haldex info that isn't readily available :beer:



ma2kster said:


> Awesome work and great detail, i've been following with a lot of enthusiasm. While i dont know the part number of the valve you are seeking, i wanted to contribute with the following schematic and link. I also suggest you call Bernardi Audi parts and talk to Emile or Chris. They always find what i need. 800 924-1884 is their number. You might need the VIN number for a more accurate determination...


Thanks. Good diagram too - I was checking vagcat.com but the nice thing about your link is you don't need to create an account to use it. The exchange rate is scaring me away for shopping south at the moment but thanks for the contact - always good to know people like that :thumbup:


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## All_Euro (Jul 20, 2008)

Marcus_Aurelius said:


> ...For some reason, if it's not a pressure bypass valve that failed, I feel it's the dummy controller with insert combo playing tricks on you. I think (it's a theory) YHW at some point revised the length of the insert from the original ones that fully blocked all bypass. So if you're using an insert that allows some amount of bypass without an operating controller, you won't get full pressure under load.


I did try to isolate the pressure limiting valve today by placing some of that hard clear plastic directly under the ball/spring but was unsuccessful - the fluid squeezed past. I think I'll pull the controller apart again to see just how much clearance there is at the bottom of the insert. If I completely plug that oil passage and the clutches won't hold then it should be the pressure limiting valve...




TheDeckMan said:


> I'll grab two of them tonight. One I know is good and the other is questionable. Sure I can figure out a way of making a testing fixture. I have an idea that I need to try out on how to test it.


That'd be awesome. I checked with my OEM parts supplier and he couldn't find a # for that valve - seems like you have to buy the top half of the housing just to get the valves that are in it *02D 525 577A*

I did get one of the circlips out of the top of a pressure valve beside the pressure limiting valve. The circlip landed somewhere on the other side of my basement but I picked up a 1/2" snap ring from Lowe's that fit perfectly. Just a weak ball and spring assembly in that one or those two. The plastic threads and sleeve on the limiting valve are in good shape though...


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## ma2kster (Jun 4, 2010)

> That'd be awesome. I checked with my OEM parts supplier and he couldn't find a # for that valve - seems like you have to buy the top half of the housing just to get the valves that are in it 02D 525 577A


That's what i was afraid of. The diagram i shared yesterday didnt show a seperate valve either. It is worth talking to a seasoned/reputable parts person. Sometimes Audi amends these with repair kits, and those are hard to find in the parts catalog. It seems quite expensive to get that half housing. $340 per link below.
http://audi.bernardiparts.com/Audi-COVER__02D-525-577-A.aspx


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## All_Euro (Jul 20, 2008)

I pulled the controller apart again to have a better look at how much of the Regulating Valve is being blocked by the pin and insert... when the system if fully pressurized, the pin completely blocks off the lower valve opening and covers about 1/2 of the upper opening. The insert blocks about 7/8 of the upper valve opening and leaves the lower opening untouched.

Pin blocking lower valve opening only...









Pin fully extended so the lower opening is blocked and the upper valve opening is about 1/2 blocked...









Pin fully retracted so lower valve opening is clear and insert fully seated is blocking 7/8 of top opening...










So compare these pictures with the flow diagram that Noah posted - for the clutches to be fully locked, the return path to the accumulator needs to be cut off. As long as the Pressure Limiting Valve is closed, this only happens when fluid is allowed to pass through the top opening in the Regulating Valve.

As Max pointed out, this insert is allowing some fluid to escape and since the controller isn't adjusting the Regulating Pin in the valve - the system is only able to partially pressurize the clutches.


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## All_Euro (Jul 20, 2008)

Kind of helps to see the assembly laid out the same way it's installed in the controller.

Snap Ring - Aftermarket Insert - Regulating Valve - Spring - Regulating Pin - Toothed Plastic Tail for the Adjusting Motor...









I wanted to try to replicate the OEM pin position when the clutches are fully locked - so with the pin blocking the lower opening and about 1/2 the upper opening as well. I found a spare bolt that was about the same thickness of the toothed plastic piece that clips on to the bottom of the pin and then dremelled the head off so it could sit under the plastic tail... I don't have the controller hooked up so the pin can't move anyway.

The "pin extension" is 6mm wide and, in this picture, 11.5mm long. I trimmed is down to 11mm and the assembly seated and locked into place nicely. OEM insert went back in as well...


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## All_Euro (Jul 20, 2008)

The holes at the top right and bottom left are for bolts but here are how the openings in the controller housing relate to the Regulating Valve - top opening in the valve feeds the top and bottom openings in the housing. Lower opening in the valve feeds the middle opening in the housing which is where the point of the awl is...




















So with the lower opening in the valve or the middle hole in the housing blocked, full pressure / clutch lock should happen. The initial test went well - the clutches locked up as I was hoping and when I checked the clutches about an hour later they had depressurized... will try again tomorrow and then hopefully install and test for real.


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## All_Euro (Jul 20, 2008)

ma2kster said:


> That's what i was afraid of. The diagram i shared yesterday didnt show a seperate valve either. It is worth talking to a seasoned/reputable parts person. Sometimes Audi amends these with repair kits, and those are hard to find in the parts catalog. It seems quite expensive to get that half housing. $340 per link below.
> http://audi.bernardiparts.com/Audi-COVER__02D-525-577-A.aspx


Good tip - I'll stop by Audi and ask their parts guy about the housing and possible replacement valve(s)... junk yards sell the entire Haldex Coupling for about $250 so I'll probably try that first if need be.


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## All_Euro (Jul 20, 2008)

Clarification: when I checked the clutches before install they did have pressure on them still. Not full pressure but it took some effort to move the driveshaft so not ideal.

Stepped out into my garage yesterday to install the diff...











Install went well and the subsequent test drive resulted in some tail-happy cornering... nearly shed a tear I was so happy. Really slow U-turns are a touch grabby. It's minor but it is there so I'll add a bit of viscosity modifier to the Haldex oil when I have a chance.


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## TheDeckMan (Sep 26, 2004)

Great to hear!


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## All_Euro (Jul 20, 2008)

TheDeckMan said:


> Great to hear!


Thanks Noah - if nothing else, we have a baseline on these clutches to judge wear over time from permanent 50/50 Haldex operation :beer:


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## All_Euro (Jul 20, 2008)




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## Marcus_Aurelius (Mar 1, 2012)




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## ticketed2much (Feb 18, 2012)

All_Euro said:


> Clarification: when I checked the clutches before install they did have pressure on them still. Not full pressure but it took some effort to move the driveshaft so not ideal.
> 
> Stepped out into my garage yesterday to install the diff...
> 
> ...


Thanks for putting so much time and information into this thread! Glad its working. You should really just wire in the system like factory at some point, when its not snowing If you already have traction control, and since its a GLI it probably does, its relatively easy compared to what you have already done.


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## All_Euro (Jul 20, 2008)

Marcus_Aurelius said:


>






ticketed2much said:


> Thanks for putting so much time and information into this thread! Glad its working. You should really just wire in the system like factory at some point, when its not snowing If you already have traction control, and since its a GLI it probably does, its relatively easy compared to what you have already done.


Happy to help and glad others have been supportive :beer:

I may wire the controller up in the future but I actually want full time 50/50 so I'll try this out first and just keep an eye on things. ABS is handy because of the icy conditions in my area but I'm not really a fan of the other driving aids that are available for this generation VW/Audi.

Yes, working on the car outside in the winter is less than ideal - need to time these things a little better! Almost done for the winter... sort of...


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## ChoctawSlideTeam (May 10, 2010)

Thanks for the documentation here! I've just read through and appreciate the valuable info! Please keep advised of the clutch wear you experience! :beer::thumbup:


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## All_Euro (Jul 20, 2008)

ChoctawSlideTeam said:


> Thanks for the documentation here! I've just read through and appreciate the valuable info! Please keep advised of the clutch wear you experience! :beer::thumbup:


Thanks - I'm not keen to pull the clutch packs apart again right away but was thinking of sending the oil in for analysis next time I change it... this should show any abnormal wear but we'd need to have something to use as a reference. Maybe someone else can do the same with their oil so we can compare...


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## Ptr34 (Mar 10, 2021)

All_Euro said:


> So with the block-off plate allowing the clutches to hold pressure - this means the pump and accumulator are working but pressure is being bled off via the pressure limiting valve? Anyone happen to have a part # for this faulty valve?


where do this plate go? I'm trying to do it now and don't see any pictures


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