Rear brakes locking

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MZ107
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Rear brakes locking

Post by MZ107 » Fri May 18, 2012 5:22 am

I just picked up this 1982 GTV6 Balocco and found your group as well and look forward to picking your brains as I rebuild this car. The brakes were a known problem from the day I first test drove the car. I had a hard time getting the rear wheels off since the car had been sitting for a while and the lugs were seized, thankfully after breaking my T-bar I brought the car over to my buddies shop in Brooklyn and he hit it with his impact gun. I spent the better part of a day under the rear of the car cleaning up the disk which appear to have no wear on them as well as the calipers which even with the surface rust seem to be replacement units. I bleed out the rear calipers (air came out) until the fluid came out and I figured since I didn't find any wet connection I correct the problem. Wrong! I did feel the brakes engage but I also felt like they did fully disengage. I read through some of the other post and will be looking for blockages now going backwards through the system.
However any tips are greatly appreciated.
Michael
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Murray
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Re: Rear brakes locking

Post by Murray » Fri May 18, 2012 1:46 pm

MZ107 First thing I would consider is replacement of the two flexible hoses which connect to the calipers.Over time these hoses can degrade internaly and act like a one-way valve- letting hydraulic pressure get to the caliper but preventing it from returning.They're relatively cheap and should be replaced even if they're not the cause of your problem.In the process of replacing them you'll be flushing your brake fluid which is always good practice.If that process doesn't improve matters you need to look at the brake proportioning valve which on your era GTV6 is probably under the car near the connection for the flex lines.Later cars have this valve located next to the master cylinder in the engine compartment.If all this fails it's also possible that the problem originates in the master cylinder itself.There that should keep you busy for a while. :)
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Re: Rear brakes locking

Post by Giuliettaevo2 » Fri May 18, 2012 11:03 pm

Take the rear callipers off the car and rebuild them...

There is an adjusting mechanism inside the callipers, that needs to work properly to set the brakepad clearance. If this clearance is not good you either get a very low pedal or dragging brakes.

New hose ( only one in the rear) is definetely a good idea. But be prepared to replace the brake pipe also, they tend to shear off when you try to disconnect the hose. :( It has M10x1 threads in case you need new couplings. :wink:

Replacing the brake fluid is always a good idea.

And if your doing the rear you might aswell do the front. replace hoses and bleed all the old fluid out. Also check if all the pistons can move freely in the callipers.
Drive it like you stole it...
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Re: Rear brakes locking

Post by kevin » Sat May 19, 2012 1:08 pm

Sometimes the handbrake causes the problem . Check when handbrake is down that the levers on the calipers have returned back . On old calipers normally the right one does not so you have to tap it back . It's happened a few times . As said above you have tobclean and rebuild .
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Re: Rear brakes locking

Post by MZ107 » Sun May 20, 2012 4:08 am

Going back under today and I am going to go back through the hoses and tubes. I will check the hand brake release and see if this is contributing. I have to swap out the headers and down pipes today, old ones are done! They must have been a poor style replace since they cracked at the flange and the pervious owner tried to fix it with some kind of patch goo. Also bottom it out and destroyed the pipes at the bend.
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Re: Rear brakes locking

Post by MZ107 » Wed May 23, 2012 6:08 pm

Well that didn't go as expected! Not only did I not get the brakes or exhuast done, I found the flex joint on the rear of the drive shaft is bad! So I have to go through all of the connection on the shaft, and what the h**l is the center flex joint do! ($189 from IAP!) Would I be crazy to skip this while I'm doing all this?
The reason I didn't finish the exhuast was the fit of the new performance headers from IAP wouldn't allow me to use the original starter heat shield. The guys at International auto said I can use the starter wrap fron JEGS, but I am a bit concerned. Has anyone else used these headers and this wrap? I am setting up for a all out push this weekend,
Finish exhuast
Change flex joints on drive shaft
Fix rear brakes proper!
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Re: Rear brakes locking

Post by MZ107 » Thu May 31, 2012 5:53 am

What is the story on the brake booster, can they be purchased somewhere? Rebuilt? I believe I have created a new problem while trying to fix the rear brake issue. The paddle went hard and I did some testing which leads me to believe the booster is bad. This car was seriously neglected!
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Re: Rear brakes locking

Post by Murray » Thu May 31, 2012 2:23 pm

MZ107 Typically boosters "go bad" in one of two ways.Either they cannot hold vacuum or the seal at the rear of the master fails and brake fluid leaks into the booster.My experience has been that the most common problem is a sticking check valve that prevents vacuum from building and makes the pedal hard.The valve is in the vacuum line that runs to the booster from the plenum.Take it out and clean it.Next run the engine for a minute and remove the hose at the booster.You should hear the hiss of vacuum.if you don't then your booster could in fact require replacement.If you have vacuum ,unbolt the master cylinder and check to see if there is brake fluid present in the booster.Good luck
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2014 Audi Q5 3.0l TDI - torque MONSTER
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Re: Rear brakes locking

Post by MZ107 » Thu May 31, 2012 6:19 pm

Thank you, I will be going throug it more tomorrow. I will update the page what I find.
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Re: Rear brakes locking

Post by MZ107 » Fri Jun 01, 2012 11:34 am

Pulled the brake booster valve and it was dirty, but after cleaning and testing vacuum (Which the vacuum was good) the brake peddle still feels hard. I went through a test procedure for the booster,
1) Engine off start engine while pressing peddle and should see 1/2 to 1 inch of peddle drop. (It didn't!)
2) Run engine, turn off, press peddle, first push soft, second harder, third still firmer. (Just stayed hard)
3) Start engine, press brake and hold shut off engine, it should hold position! It did go slowing down (Most likely master cylinder)
So I am going to change out the master cylinder and try and find a replacement booster just in case.
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Re: Rear brakes locking

Post by MR2 Zig » Fri Jun 01, 2012 5:00 pm

You might first change out the vacum hose from booster to manifold....it could be collapseing internally. Cheap and worth a shot.

HTH,
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Re: Rear brakes locking

Post by MZ107 » Sat Jun 02, 2012 3:23 am

I should have put that in the text somewhere, but the hose was eliminated. I have a spare booster and master on its way, so I will just get all connection loose and await the part. I still have a lot of other things to address.
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Re: Rear brakes locking

Post by MZ107 » Sat Jun 02, 2012 3:28 pm

Why does it seem that you order parts from International Auto Parts and they send things that don't fit! They sent me the bleeders for the front Brambo calipers and they are too small for the bore. Does anyone know what the actual size of this bleeder is? This is a new one for me, the pad material separated from the back plate on the front brakes! And yes it does look like we are going to rebuild the front caliper at this point. The only good thing that came out of this was that I was able to separate all the connections on the front end brake lines with out shearing off any of the lines.
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