# brake proportioning valve



## bobsright (Oct 28, 2008)

I have a '95 Jetta w/rear drums. Anybody use the disc brake proportioning vale on a drum brake system? Been told it works fine-and is cheaper.


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## germancarnut51 (Mar 23, 2008)

*Re: brake proportioning valve (bobsright)*

Whoever told you that the disc brake proportioning valve is less expensive then a rear drum brake proportioning valve is an idiot.
The disc brake part is more expensive both new or used, and is much harder to find used than the drum brake part.
MKIIs use the same proportioning valve for rear drum or disc brakes. MKIIIs have different parts for rear drum or disc brakes because the caliberation is different for disc and drum brakes. I can't tell you how your car with drum brakes will react if you were to install the rear proportioning valve for a disc brake car. I can only tell you that in a MKIII with drum brakes, if you were to install the proportioning valve from a disc brake car, the car would not brake the same way as it did with the correct drum brake proportioning valve.
So if you have drum brakes on your MKIII, and need to replace the proportioning valve, then you need one for a rear drum brake car.


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## bobsright (Oct 28, 2008)

*Re: brake proportioning valve (germancarnut51)*

I'm the idiot who said the disc brake proportioning valve is cheaper than the drum brake one. Check it out. If you find a valve for drum brakes lower or even the same price let me know.


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## spitpilot (Feb 14, 2000)

*Re: brake proportioning valve (bobsright)*

Since the disc brake is more powerfull..I'd say using a disc valve on a drum car would give you under utilized rear braking power...pressure to rear brakes would be reduced more than necessary for proper brake balance...in swappin out brake parts keep in mind that the answer to the ?.."will XYZ part work on this other car?"...might be yes as far as fit and function goes, but NO in terms of overall brake system safety...proportioning valves are meant to reduce risk of spin out in heavy braking by reducing pressure on rear brakes..if you put in a valve that doesn't do that right...it may work just fine..untill you slam on the brakes in the wet some day..


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## bobsright (Oct 28, 2008)

*Re: brake proportioning valve (spitpilot)*

Yes but-1. if you have less pressure at the rear wheels ,you have less chance of a spinout.-2, It's my understanding , according to the manual, that the valve is adjustable. It would be a matter of trial and error as to the correct setting. There are no markings for adjustment. Therefore I believe the only difference in the valves , is the factory settings. Which begs the question-why such a wide difference in the price? So back to my original question-has anybody tried a disc brake valve on a drum brake car?


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## germancarnut51 (Mar 23, 2008)

*Re: brake proportioning valve (bobsright)*

I stand corrected. I checked the priced everywhere last year as I started collecting parts for my rear disc brake conversion. Disc brake proportioning valves were running $175-$235 everywhere I checked.
I just went down the list of Online Suppliers that I use, and the price for the rear disc brake proportioning valves has fallen drastically to the point where they are the same price or lower than the drum brake proportioning valve. GAP (germanautoparts has them priced about $.40 apart (both at $93.XX).
So if you still want a new drum brake proportioning valve, GAP looks like the cheapest place to buy one. Just make sure that you're getting a Genuine ATE part, and not a Chinese made clone. Three of the online places of the five I checked have the disc brake version at around $93.XX.


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## bobsright (Oct 28, 2008)

*Re: brake proportioning valve (germancarnut51)*

Thanks! That's cheaper than any place I've searched. I've found the disc one for 79 and change,but the drum ones where all over 100!


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## GTijoejoe (Oct 6, 2001)

*Re: brake proportioning valve (bobsright)*

I'm not an expert on VW proportioning valves but I will give you some FYI:
It would be best to use the OEM valve for the brake spec.
Not all proportioning valves are created equal, yes they all serve the same purpose but different valves can have different pressure ramp rates.
This being most important from disk to drum brake differences. It is a common misconception than disk brakes are "more powefull" than drum, and that is certainly untrue. Drum brakes can achieve much higher effectiveness than disk brakes, mechanically have the ability to self energize much much more than conventional disk brakes, thus also making it harder to control braking torque vs pressure.
This being said, it would be very easy to under utilize or over utilize RR drum brakes if improperly tuned based on a range of weight loading and decel conditions.


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## magyarbetyar (Sep 30, 2003)

*Re: brake proportioning valve (GTijoejoe)*

Kind of off topic, but when I did the rear disk brake conversion on 85 Scirocco I never added or swapped out any kind of proportioning valve and it worked great.


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## bobsright (Oct 28, 2008)

*Re: brake proportioning valve (magyarbetyar)*

Well, as an update, here's what I did. I went and got the disc brake proportioning valve. @$79 from autohause it was the cheapest option. Guess what? Ya can't tell the difference! Now maybe in certain situations like lock up, or in the rain it might show up, but, so far so good. If anything out of sorts happens will let you know.


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## ChinkyVdub (Jul 18, 2003)

*Re: brake proportioning valve (bobsright)*

bump from the dead.
just a FYI.
I did some research on this as I too wanted to do this. Just remember on a drum system. There is addition reservoir in the drum brakes. On a disc system there no reservoir, therefore the valving on the proportioning valve is different.
The only way to know is to do a pressure test on the actually lines. 
The following data is from alldata standard.
Drums
Rear @ 435-508 psi
740-812 psi
Disc
Rear @ 406 -493 psi
711-798 psi
note that there are two sets of numbers and they are slightly different. because of the distance of the caliper to the pressure module. What happens is when you have a drum setup and install a disc setup, you can "technically" get a away without changing the prop. valve. The pressure from a drum to disc is somewhat the same. The range is similar. Now, that doesn't mean its the right way, but suggested that you change the valve. It may cause a slight drag on your disc, therefore increase pad wear. I did read that the prop. valves are adjustable. Now to test this is the real question. I suggest not on a busy street.







enjoy hope this helps.


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## ricardo (Feb 19, 1999)

*Re: brake proportioning valve (ChinkyVdub)*

here is my







I did not change the proportioning valve form the original drums when I did my rear disk brakes.. car brakes work fine..... I did panic brake one time and the rear lock faster than the fronts... had that set up for 3 yrs before I sold the 2.0


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## germancarnut51 (Mar 23, 2008)

*Re: brake proportioning valve (ricardo)*

If your rear brakes are locking before the fronts, I would say that your brakes are not working fine.
Sounds to me like you were lucky not to need to do any panic stops.
Installing the correct rear disc brake proportioning valve would have corrected your INCORRECT PREMATURE REAR BRAKE LOCKUP.


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## ChinkyVdub (Jul 18, 2003)

*Re: brake proportioning valve (germancarnut51)*

also remember that the rear proportion valve is a load sensing valve. So if you have more weight in the car the greater the rear lock you will feel.


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## izcorrado18 (Aug 21, 2005)

i went from abs to non abs. do you have to adjust the valve? i can hear the back ones whenever i do hard stops.


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## ChinkyVdub (Jul 18, 2003)

*Re: (dri0514)*

how i understand the rear proportional valve is weight dependant. so the more your car sags the more pressure is applied to help stop your car. The abs just helps pulse the breaks under slippage. if you had drums then you would need adjust for discs. hope this helps.


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## Heesay (Jan 28, 2010)

*Re: brake proportioning valve (bobsright)*

So... How does the proportioning valve work? When should I consider buying a replacement?
*It depends on weight to distribute fluid quantity... but how should I really bleed the rear system? With weight on it, or with it lifted?



_Modified by Heesay at 5:44 AM 2-23-2010_


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## ChinkyVdub (Jul 18, 2003)

*Re: brake proportioning valve (Heesay)*

To bleed stock setup you can do it the traditional way. in the air is fine.
Proportional valve on a VW is load dependant so the more weight you have in the car the more braking the rear will have or when you stop hard with extra weight typically the rear will come up and cause a fish tall effect. The valve adjust for this therefore (technically) applies more fluid to the front. Think of it this way the proportional valve proportion how much hydraulic fluid is sent between the front and rear brakes. In this case for vw it is weight sensitive.(this may not be so for other manufacture)
Now if you going from rear drum to disc setup the proportional valving is different. I know this because I plan to do this. however some people do it with out swapping or adjusting the proportional valve after the conversion. This could cause unwanted fishtailing or essessive rear brake wear. 
The proportional valve is adjustable however you will need a hydraulic line pressure gauge to do this. And the specs are in alldata, maybe bently I have to double check.
Also a side note cars with a abs the valving is done by the computer via abs unit.


_Modified by ChinkyVdub at 12:48 PM 2-24-2010_


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## germancarnut51 (Mar 23, 2008)

*Re: brake proportioning valve (Heesay)*

When do you need a replacement?
When your exisiting proportioning valve is leaking, OR when you change from rear disc brakes to rear drums brakes OR when you change from rear drum brakes to rear disc brakes.


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## PeOpLeG60T (Jul 5, 2004)

i must add that a slammed car would throw more power to the rear brakes since the rear prop is adjusting with the height and not the weight .... weight is indirectly calculated with a normal ride height and the loading of the car , making the car go lower. 
so a 2inch drop would be interpreted as an approx of probably 250-300 lbs and will put more pressure on the rear. 
i personally installed non ajustable prop valves at the master cyl


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## ChinkyVdub (Jul 18, 2003)

*Re: (PeOpLeG60T)*


_Quote, originally posted by *PeOpLeG60T* »_i must add that a slammed car would throw more power to the rear brakes since the rear prop is adjusting with the height and not the weight .... weight is indirectly calculated with a normal ride height and the loading of the car , making the car go lower. 
so a 2inch drop would be interpreted as an approx of probably 250-300 lbs and will put more pressure on the rear. 
i personally installed non ajustable prop valves at the master cyl

please elborate on the non adjustable prop valves at the master cyl? how does this work?


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## PeOpLeG60T (Jul 5, 2004)

*Re: (ChinkyVdub)*

its just a non adjustable valve that bolts in-line with the rear brake hoses , usually bolted directly on the master cylinder. 
you can find em on sciroccos or a few sellers do sell them new 
i dunno exactly if some other models had them but i'd check to be sure they were rear disc brake system


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## vdubobsession (Apr 26, 2006)

*Re: (PeOpLeG60T)*

anybody ever install an aftermarket proportioning valve such as a wilwood that uses a knob to adjust rear pressure?


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## 6thGearGLIGuy (Jul 25, 2005)

Good discussion,
I got a car im building pretty much for auto cross only and Im gonna run all new brake hard lines and I bought a new/used prop. valve in great shape, but I was wondering if I even need to run a prop. valve. Can I just run in-line ones off the master cylinder for the rear lines? It would be easier to run the hardlines then. Thanks for the info


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## ChinkyVdub (Jul 18, 2003)

*Re: (6thGearGLIGuy)*

same here. interested to see how this would work.


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## PeOpLeG60T (Jul 5, 2004)

yes they work without the rear valve


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## 6thGearGLIGuy (Jul 25, 2005)

*Re: (PeOpLeG60T)*

works with no rear vavle, and just run non-adjustable inline vavles? Any idea where to get a couple of those. Thanks











_Modified by 6thGearGLIGuy at 10:24 AM 3-16-2010_


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## PeOpLeG60T (Jul 5, 2004)

there was a guy selling a pair on the vortex here , just search proportioning valve


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