# brakes locking up when its hot outside. 96 golf



## mk3slutted (Apr 27, 2008)

ok i have a 96 golf and the brakes have been locking up after about 20 mins of driving and the brake pedal gets rock hard. it gets worse the hotter it is out. if i let the car sit for an hr the brakes release but then the prob repeats. i replaced the mc and the 2 rubber lines to the front calipers and bled the entire system w brand new brake fluid. also put new front rotors and pads on i was told its a vac leak but checked the line going from intake to booster and when i take the line out of the booster it hisses. could this be a proportioning valve prob (is leaking slightly). any help would be greatly appriciated bc my tech is stumpt im stumpt and the local shop is just having me blindly dump money into parts tht i dont need.:screwy:


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## greyhare (Dec 24, 2003)

Something is preventing fluid from returning to the reservoir.

Pinched or blocked line, bad flex line, or bad master cylinder.

Is it one wheel or all wheels?


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## mk3slutted (Apr 27, 2008)

im pretty sure its the 2 front but the burning smell is coming from pass front....


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## GTijoejoe (Oct 6, 2001)

greyhare said:


> Something is preventing fluid from returning to the reservoir.
> 
> Pinched or blocked line, bad flex line, or bad master cylinder.
> 
> Is it one wheel or all wheels?


This is normally correct.... perhaps you have some pedal stroke/adjustment issue? Sometimes, if the pedal is slightly stroked it will close the passages in the MC from fluid entering back into the res...becasue the pedal is slightly stroked you get minor brake drag which heats up and expands the fluid which can't go back into the res. and just applies the brakes even more.


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## greyhare (Dec 24, 2003)

GTijoejoe said:


> This is normally correct.... perhaps you have some pedal stroke/adjustment issue? Sometimes, if the pedal is slightly stroked it will close the passages in the MC from fluid entering back into the res...becasue the pedal is slightly stroked you get minor brake drag which heats up and expands the fluid which can't go back into the res. and just applies the brakes even more.


I have been through this on my old Rabbit. I can not find any peddle adjustments for a MkIII on the Bentley manual.


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## mk3slutted (Apr 27, 2008)

now if this is the issue and there is no adjustment just replacing the pedal assembly should work correct in which case im gonna have to deal with that clip with the ball in it right?


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## cuppie (May 4, 2005)

I'm not sure how the mention of an adjustment issue led you straight to "should replace the pedal cluster," as there's nothing in the pedal cluster to restrict the rearward travel of the brake pedal - it freely swings in there; its motion is restrained only by what it's attached to (the brake booster, and thru that the master cylinder and the rest of the brake system.)

Do this:
drive the car until the brakes start to lock up (from the sounds of things, it shoudn't take too long), and you're unable to push the car by yourself (it's a MkIII - it's not heavy.)
Shut the engine down. Disconnect the vacuum hose on the brake booster (never mind the hissing - you're releasing a large vacuum reservior.) Are you suddenly able to move the vehicle yourself yes/no? 
If yes, control valve in booster has failed (and booster needs new.) 
If no, unbolt the master cylinder from the booster, and try moving the car again. If now OK, booster is hanging up internally (and needs new); if brakes are still stuck, issue is with the hydraulics.


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## GTijoejoe (Oct 6, 2001)

cuppie said:


> I'm not sure how the mention of an adjustment issue led you straight to "should replace the pedal cluster," as there's nothing in the pedal cluster to restrict the rearward travel of the brake pedal - it freely swings in there; its motion is restrained only by what it's attached to (the brake booster, and thru that the master cylinder and the rest of the brake system.)
> 
> Do this:
> drive the car until the brakes start to lock up (from the sounds of things, it shoudn't take too long), and you're unable to push the car by yourself (it's a MkIII - it's not heavy.)
> ...


This is sound advice :thumbup:


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## mk3slutted (Apr 27, 2008)

thank you very much for the advice. we have spent the last 3 days diag the prob. we replaced mc and proportioning valve and attempted to bleed the brakes and it bleed from the pf and dr no prob but the the others wouldnt bleed at all. so we put ANOTHER mc in it and same problem again so we hooked a vac pump to the pr (which wouldnt bleed ) and pushed air through the lines into a cup of fluid and it made bubbles so we bled the brakes again and everything was fine??? well after driving it tonight it seemed to lock up again so as i was trying to find a place to pull over the brakes released.... the pedal was hard but then just released. as for the advice it started locking up one day and so i yanked vac line out of booster and the pedal softened up. im begining to think the booster is going.


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## germancarnut51 (Mar 23, 2008)

mk3slutted said:


> thank you very much for the advice. we have spent the last 3 days diag the prob. we replaced mc and proportioning valve and attempted to bleed the brakes and it bleed from the pf and dr no prob but the the others wouldnt bleed at all. so we put ANOTHER mc in it and same problem again so we hooked a vac pump to the pr (which wouldnt bleed ) and pushed air through the lines into a cup of fluid and it made bubbles so we bled the brakes again and everything was fine??? well after driving it tonight it seemed to lock up again so as i was trying to find a place to pull over the brakes released.... the pedal was hard but then just released. as for the advice it started locking up one day and so i yanked vac line out of booster and the pedal softened up. im begining to think the booster is going.


After reading your thread, I was going to suggest that the brake booster is goign bad, but it looks like you're going that way anyway.

The master cylinder and the proportioing valve would not cause symptoms like you are describing, but a faulty brake booster would.


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