84 MK1 GTi brake problem

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mjkeenan1
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84 MK1 GTi brake problem

Postby mjkeenan1 » Thu Sep 07, 2017 9:02 pm

So about a month and a half ago, my brake pressure suddenly went out. Got a new MC, still nothing...got a new booster, had some pressure. Not much, but enough to drive. Weird thing is if I pulled the handbrake a bit before braking, I got increased pressure at the pedal. Had no $ for a bit so I dealt with it. Figured I'd just replace hardware all around, so I bought new cylinders, hardware & drums for the rear & new calipers for front. Output rear hardware on tonight... (they sent me the wrong drums, but my old ones are fine, so still using them. Drivers side rear first, no issues. Took a test drive & had better pressure. Not great, but better than before. Did passenger side, no apparent issues, but now have ZERO pressure at the pedal. If the car is off, pressure will build up, but as soon as its turned on, every bit disappears. Seems like a vacuum leak, but all my lines are snug & look good. Any thoughts? I'm out of ideas.
1984 GTi
1986 Cabriolet

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masterbeavis
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Re: 84 MK1 GTi brake problem

Postby masterbeavis » Fri Sep 08, 2017 6:16 am

I've had the worst luck with replacing a master cylinder on a mk1, seemingly impossible to properly bench bleed. The fluid will dribble out before I can get the lines hooked up. The only way I've been successful is by using a power bleeder.
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Re: 84 MK1 GTi brake problem

Postby 8v fury » Fri Sep 08, 2017 5:28 pm

How is the the brake booster and the brake booster hose.
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Re: 84 MK1 GTi brake problem

Postby xspeedracer » Fri Sep 08, 2017 5:52 pm

So if you replaced both the master and the booster was there a gasket between the master and the booster sealing vacuum from escaping some are sealed and some are not. so if the car is shut off and you pump up the brakes and hold them when you start the car you should get a slight drop in pedal but no more, also it could be they sold you a master for rear disc brakes instead of rear drums as well check part numbers. As far as bench bleeding all you need to do is put the master on the car and run a hose from the front and rear ports to the reservoir and pump the pedal till you don't get any more air. I don't know if these cars had a rear proptioning valve attached the the rear suspension that could go bad as well.
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Re: 84 MK1 GTi brake problem

Postby masterbeavis » Fri Sep 08, 2017 7:26 pm

These master cylinders have ports on the bottom. Fluid leaks out when you try to install the lines.
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Re: 84 MK1 GTi brake problem

Postby mjkeenan1 » Sun Sep 10, 2017 11:41 am

8v fury wrote:How is the the brake booster and the brake booster hose.

Booster is new, hose isn't new, but in good shape
1984 GTi
1986 Cabriolet

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masterbeavis
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Re: 84 MK1 GTi brake problem

Postby masterbeavis » Mon Sep 11, 2017 7:26 am

Re-bleed your brakes. If it build pressure when the car is off and you loose it once it's on, you've got air in your system. Try parking your car in a way that the MC is level, and use a pressure bleeder to try to get more air out.
Red Green: All it takes is a little imagination, some mechanical ability, and neighbors who mind their own business.

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Re: 84 MK1 GTi brake problem

Postby mjkeenan1 » Mon Sep 25, 2017 12:07 pm

Ended up being a bad caliper on the front... Once replaced, full pressure. Now I have a bad ball joint & wheel bearing.
1984 GTi
1986 Cabriolet

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Re: 84 MK1 GTi brake problem

Postby masterbeavis » Tue Sep 26, 2017 7:09 pm

Was it leaking?
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