# Final shot at fixing my brakes. [before the car goes to the scrapper]



## Phreshnphunky (Dec 3, 2004)

Car, 1990 VW Turbo diesel Jetta.

Old set up..... stock 20mm master cylinder, front Vented rotors, and OEM pads. Rears drums that were spinning on shot bearings.

Solution, replaced master cylinder and upgrade to rear disc brakes. Seemed easy enough. I acquired a rear disc set up from a mk3 golf, and swapped over the stubs, the discs, and then I placed original mk2 GTI rear calipers on the carriers since they have a smaller piston than the MK3 rear calipers. 

So, 

new master cylinder, rear disc swap. 

Problem, brake pedal takes multiple pumps to attain pressure and firmness.

I've bench bled the master cylinder prior to installation, 22 mm brand new master cylinder.

I've opened up the proportioning valve prior to bleeding the rear brakes.

I've gone through each corner of the car 4 times to ensure no air bubbles.

I've used a pressure bleeder to ensure that there's always fluid going to the reservoir.

After a final attempt not 10 minutes ago, I go and test it out without vacuum assist. Brake pedal goes down 1/2/3/4/5 times and firms up. Thought that might be valid to try with the car on.

Turn on the car, pedal sinks to the floor. Press it 3 more times and it firms up. however it SLOWLY sinks.

I haven't driven the car in 3 weeks since the original master cyilnder went, and i've been losing my patience with the car.

anyone that's gone through this, can you please help out?


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## greyhare (Dec 24, 2003)

Phreshnphunky said:


> Car, 1990 VW Turbo diesel Jetta.
> 
> Old set up..... stock 20mm master cylinder, front Vented rotors, and OEM pads. Rears drums that were spinning on shot bearings.
> 
> ...


This screams faulty master. It is not common but, sometimes a new or rebuilt can be bad out of the box.


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## Phreshnphunky (Dec 3, 2004)

greyhare said:


> This screams faulty master. It is not common but, sometimes a new or rebuilt can be bad out of the box.


That makes no sense. But I do understand what you're saying.

I can't justify spending another set amount of money for new fluid and a new master just to have it fail on me again.

I'm going to have to give it one last final attempt tonight [after work, as I posted that originally in the mk2 section yesterday mid evening]

I'm just happy that work is easy to transit to. otherwise i'd be pissed off more so.


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## greyhare (Dec 24, 2003)

Put the original master back on and bleed with cheap DOT3 fluid. If the problem is solved the new master is bad and you can try to warrantee it.


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## Phreshnphunky (Dec 3, 2004)

greyhare said:


> Put the original master back on and bleed with cheap DOT3 fluid. If the problem is solved the new master is bad and you can try to warrantee it.


Aside from the boiling point differences, is there any true difference between dot 3 and dot 4 fluid?

And, I've been given a new master cylinder and tested and checked AGAIN.

I've come to a conclusion, or a theory.

When I replaced the rear drum cylinders with the rear discs, and when I split the hard lines to the soft......Then replaced them with the soft lines from the calipers to the car's hard line.....while I did tighten everything up, it could very well be possible that there is an airleak [albeit small enough to pull in air] as i pump and prime the brakes.

I'm going to check the unions at the master cylinder, and as well the rear lines, because those are the only places I've separated the system..

is there a means to ensure that the hard brake line unions and connections are air/liquid tight?


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## greyhare (Dec 24, 2003)

DOT 3 & 4 are compatible, use what the manual says.

The system will build pressure but not hold it? Air will give a spongy feel not a sinking. A sinking peddle is a master cylinder internal seal failure or a system leak. Hold pressure as much as possible and look for fluid leaks at all joints.


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## Phreshnphunky (Dec 3, 2004)

greyhare said:


> DOT 3 & 4 are compatible, use what the manual says.
> 
> The system will build pressure but not hold it? Air will give a spongy feel not a sinking. A sinking peddle is a master cylinder internal seal failure or a system leak. Hold pressure as much as possible and look for fluid leaks at all joints.


The system with the vacuum off will build "some" pressure, but as i release the pedal it will refresh back to zero. Starting over again.

one late night, i took it out thinking that it "worked" but when i drove it around my block, i quickly put the foot to the pedal, and only one wheel locked up.

I'm going to check and double check for any system leaks, but there isn't ANY fluid anywhere along any joints, or coming from the unions at the master


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## GTijoejoe (Oct 6, 2001)

Phreshnphunky said:


> Aside from the boiling point differences, is there any true difference between dot 3 and dot 4 fluid?


YES.... 

Its a common misconceptiong that all brake fluids are the same by the designation of DOT3/4, its not true. DOT3/4 is only a regulation, meaning if your fluid can meet all the qualifications set by the DOT than its compliant... but certainly doesn't mean its the same. The actual make up of the fluid can be different and its physical properties, for instance viscosity or lubricity.

Otherwise you can look up the DOT regulations if you truely want to understand the differencs.

back on point: A sinking pedal as stated hints at a leaking MC or also a leaking fluid system.... if you are stroking the pedal, the fluid displacement needs to go some where, or the MC seals are not creating necessary pressure.


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## Phreshnphunky (Dec 3, 2004)

GTijoejoe said:


> YES....
> 
> Its a common misconceptiong that all brake fluids are the same by the designation of DOT3/4, its not true. DOT3/4 is only a regulation, meaning if your fluid can meet all the qualifications set by the DOT than its compliant... but certainly doesn't mean its the same. The actual make up of the fluid can be different and its physical properties, for instance viscosity or lubricity.
> 
> ...


I understand the details behind the constant depression of the pedal, and displacement of fluids. [no frustration no sarcasm intended.

however, in order of progression....

Original 20mm mastercylinder went, pedal sank to the floor however it would be FIRM, to ultimately STOP the car, with all 4 wheels/brakes operable. Totally fine, replace master and redo the rear brakes [due to wheel bearings making noises anyways]

replace with. FREE 22 mm master cylinder from a mk3 GTI, and in the process replace rear brakes with disc counter parts. Rear calipers from a mk2 gti, both were tested prior to placement [from the guy i had picked them up from], full flush of the system with 2 liters of fresh DOT 4 fluid. TEST results were negative with a sinking pedal. Thought that it would be a master cylinder, since it was a used unite.

replace with, NEW 22 mm master cylinder...same results.

replace with yet another NEW 22 mm master cylinder, working it's way to progression. as mentioned, i had road tested the car to only find that the drivers side rear wheel is slowing the car down.



------


As mentioned, i will check on the lines AGAIN tonight, and see if there is any minor minor air leaks. or air suction.

As a note, when i was bleeding during the last attempt, I was using a tight sealed vacuum bleeder, and I had also teflon taped the bleeders to ensure a seal was made.

I set the vacuum to a very strong pull, and while watching the fluid SLOWLY rise, meaning NOT pulling into the catch can, it was sucking in constant air bubbles. Which had me thinking last night that there could very well be a suction leak in the lines. BUT as mentioned, there is no fluid leaking. 

No fluid absolutely anywhere along the braking system.


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## GTijoejoe (Oct 6, 2001)

ok, my last advice would be.... take the calipers off and point the bleeder directly up.... stick a block of wood (etc) in between the pads and bleed the calipers that way. It will guarantee 100% that it is impossible for any air to still be trapped in the cylinder area.. also tap the calipers slightly with a mallet. (you may laugh but I've experience this to happen before and this fixed the problem)

Of course you understand if there is a suction leak there would be a pressure leak post MC.
If this doesn't work i'm clueless :screwy:


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## Phreshnphunky (Dec 3, 2004)

GTijoejoe said:


> ok, my last advice would be.... take the calipers off and point the bleeder directly up.... stick a block of wood (etc) in between the pads and bleed the calipers that way. It will guarantee 100% that it is impossible for any air to still be trapped in the cylinder area.. also tap the calipers slightly with a mallet. (you may laugh but I've experience this to happen before and this fixed the problem)
> 
> Of course you understand if there is a suction leak there would be a pressure leak post MC.
> If this doesn't work i'm clueless :screwy:


Yesterday, I teflon taped the threads for the calipers, essentially all the joints i broke and reconnected.

Vacuum bled everything thoroughly. 

gf came over and I took a couple hours for a break.

she left and I took the car for a drive, as I tested the pressure unassisted. Seemed to work for the time being.....Took it for a drive and It worked for a good half hour. I stopped the car and found that there was a brake caliper [i think front drivers] that was dragging. 

started the car again only to find out that it didn't and the pedal sank. 

Going to try the removal of the calipers tonight and the block of wood and a large c clamp. However i was told by a friend to point the bleeders downwards. 

BUT i'll try both ways and see what I result with.


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## Elwood (Aug 10, 2001)

Phreshnphunky said:


> However i was told by a friend to point the bleeders downwards.


Air rises. Point the bleeder down and you trap air in the caliper.


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## Phreshnphunky (Dec 3, 2004)

Elwood said:


> Air rises. Point the bleeder down and you trap air in the caliper.


That too i know.

It's weird that he suggested that it point downwards?!

These are the messages he sent me. 



> remove caliper from the rears.
> install a c clamp witha piece of wood in between the caliper, as if the piece of wood was replacing the pads.
> then flip the caliper up side down. yes up side down. bleed like normal. see what happens. let me know!





> basically the idea here is to ensure the bleeding screw is at the lowest point possible while bleeding. minimizing air pocket space.


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## [email protected] (Aug 18, 2011)

when you change the rear to disk you need more fluid! did you replace the proportioning valve?


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## Phreshnphunky (Dec 3, 2004)

[email protected] said:


> when you change the rear to disk you need more fluid! did you replace the proportioning valve?


As far as I know the proportioning valve is the same for either disc or drum. of course I could be WAY off on that. I don't want to replace it because that involves cracking/opening all the connections to and from the proportioning valve

and I've tested both braking with the prop valve OPEN and CLOSED.

even played around with the pedal feel with it at various levels of being open/closed

still the same results.


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## GTijoejoe (Oct 6, 2001)

Elwood said:


> Air rises. Point the bleeder down and you trap air in the caliper.


.... ok, well if you want to try the downward position... at the very least try that one first and than finish with the bleeder in the up position :laugh::laugh::laugh:


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## Beetle.freak (Apr 16, 2009)

Dont mean to thread jack but this is my problem almost to the "T".......88' Cabriolet (original parts: front discs, rear drums, 20mm m-cyl....brakes worked "half decent" at best) ! Did the disc brake swap while i had it torn apart for fuel tank swap, the brake parts came from 94-95 (I think) Passat 16v automatic trans......stubs, rotors, hangers, calipers....changed everything over and started to bleed and could only get about 1/3 of pedal.....bled and bled and bled with no better results ( even lowered rear calipers to the ground with bleeders at the very top ) .....changed the factory 20mm m-cyl to 22mm G60 non abs m-cyl and can only get about 1/2 a pedal after bleeding all 4 corners !!!! After a few pumps its still the same pedal travel and hardness and dosent get any better. im running prop-valves that were given to me from afriend that said they came from a 88' 16v Scirocco.....im thinking it was really an 88' rear drum Scirocco ?!?!?! Is ther any way to find the correct prop-valves or something compatible from an Audi ????


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## gmullin (Sep 29, 2011)

have you questoned the vacume booster? ive had that same problem with a chevy and it was the same problems your talking about


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