Brakes locking - Team Camaro Tech
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post #1 of 26 (permalink) Old Oct 25th, 11, 05:08 AM Thread Starter
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Brakes locking

Hi!

I have an original power brake disc front / drum rear set up on my 68 camaro, with 1 piston calipers. New brake lines and flexibles, new master cylinder, rebuilt calipers, new pads.

And the brakes are locking when they heat up. My brake pedal gets firm and the short.

When the car is hot I can't hardly push it as the brakes are locking.

It is an anoying problem did you ever experience something similar? Where can I start to look for?
I already changed and checked for the correct master cylinder....


Regards

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post #2 of 26 (permalink) Old Oct 25th, 11, 05:56 AM
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Re: Brakes locking

When this is happening, is the car still braking straight or is it pulling to either side? Is there more brake dust on one front wheel than the other? If you stop when this is occurring is any wheel much hotter than the others?

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post #3 of 26 (permalink) Old Oct 25th, 11, 06:22 AM
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Re: Brakes locking

Incorrect intermediate rod or rod length, or incorrect MC. MC has either shallow or deep piston. Improper rod freeplay exerts pressure on MC piston, thus causing fluid pressure.
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post #4 of 26 (permalink) Old Oct 25th, 11, 06:35 AM
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Re: Brakes locking

Did it always do this?
If not I would look at the last thing that was done to the car, brake related.

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post #5 of 26 (permalink) Old Oct 25th, 11, 11:47 AM
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Wink Re: Brakes locking

1968 Camaro's didn't use "1 Piston" calipers - so it's not "original"

Make sure there is no residual pressure building on the front system as you drive ...

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post #6 of 26 (permalink) Old Oct 25th, 11, 11:48 AM
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Re: Brakes locking

Scott hits thw nail on the head.....All may need is a bit fround off the end of your pin and how to set the activation pin length/ check is covered many times in other posts....very common issue
A quick check ...check if the MC depth to piston is the same as your old one...

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post #7 of 26 (permalink) Old Oct 25th, 11, 02:38 PM
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Re: Brakes locking

A good check to start for the suggestions given of residual pressure on the front brakes if the MC rod is too long, open a bleeder to relieve the pressure to unlock the brakes.

Car should move easier, as by hand, if pressure is relieved.

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post #8 of 26 (permalink) Old Oct 25th, 11, 05:19 PM
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Re: Brakes locking

Quote:
Originally Posted by Sauron67MM View Post
Incorrect intermediate rod or rod length, or incorrect MC. MC has either shallow or deep piston. Improper rod freeplay exerts pressure on MC piston, thus causing fluid pressure.
x2

If the piston in the master cylinder does not completely release when the pedal is released, it will trap fluid in between the master cyl and caliper(s). This makes the calipers drag a little, which then makes the fluid heat up and expand. Since the expanding fluid has no place to go, the brakes apply even more until the wheels will lock.

To check this, you can drive the car a little until the brakes start to drag/lock, then loosen the bolts that hold the master cylinder to the booster. If loosening the bolts makes the brakes release, then for sure it is a problem with the rod adjustment or size (rod too long).
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post #9 of 26 (permalink) Old Oct 25th, 11, 09:46 PM
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Re: Brakes locking

Quote:
New brake lines and flexibles, new master cylinder, rebuilt calipers, new pads.
Now if that actuator pin is the correct length....
Who rebuilt the calipers...
A very common mistake is installing the 'O' ring seal on the caliper pistion....without looking real close at it it...
It is NOT square, more a rombus cross section....the high edge goes to the outside and to the pad side.
Unlike slave cylinder in shoe brakes there is no spring return, the piston moves stuff all, and the O ring sort of rolles, when the hydrolic pressure is released the O ring rolls back and in doing so the piston reslease it grip....
Sry I had just headed out for the day and rememberrs this...I havementioned in other threads.....

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post #10 of 26 (permalink) Old Oct 26th, 11, 02:40 AM Thread Starter
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Re: Brakes locking

Thank you Guys!
I think the first thing to do is make the test as described and tell you.


Quote:
Originally Posted by TMessick View Post
x2

If the piston in the master cylinder does not completely release when the pedal is released, it will trap fluid in between the master cyl and caliper(s). This makes the calipers drag a little, which then makes the fluid heat up and expand. Since the expanding fluid has no place to go, the brakes apply even more until the wheels will lock.

To check this, you can drive the car a little until the brakes start to drag/lock, then loosen the bolts that hold the master cylinder to the booster. If loosening the bolts makes the brakes release, then for sure it is a problem with the rod adjustment or size (rod too long).

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post #11 of 26 (permalink) Old Oct 26th, 11, 02:47 AM Thread Starter
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Re: Brakes locking

About residual pressure, if I remove it by bleeding when the brakes are hot, yes it will help by unlocking the brakes but I guess right after if I start driving around again the locking will happen again.

Actualy it is not really 'locking' it is that the brakes apply and they shouldn't. I can still push the car by hand but very difficult. I can't turn the front wheel by hand though. When cold it is free and runs easely the brakes don't apply.

Yes it does occur always. The more I drive hard the more it heats up the more it happens. The pedal lenght gets shorter this is clear. The pedal gets as a brick.

Marc

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post #12 of 26 (permalink) Old Oct 26th, 11, 03:22 AM
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Re: Brakes locking

First thing I would do is check the free play of the pedal to the booster, it only needs about 2-3 mm. Adjust accordingly. Free play is needed for preventing the valve from staying open allowing engine vacuum coming in and applying the brakes ever so slightly.

Since you changed the master cylinder and not the booster, you should do as previously suggested, loosen the master cylinder mounting nuts allowing the master cylinder piston to retract reducing the line pressure you found previously.

If loosening the master cylinder reduces line pressure, the next step would be to remove the master cylinder from the studs, brake lines can remain attached, and measure the depth of the piston hole from the mounting surface and compare the length of rod sticking out from the wall. If rod is too long, cut some off and match the same contour as original end. Install the master cylinder.

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post #13 of 26 (permalink) Old Oct 26th, 11, 01:16 PM
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Re: Brakes locking

Quote:
About residual pressure, if I remove it by bleeding when the brakes are hot, yes it will help by unlocking the brakes but I guess right after if I start driving around again the locking will happen again.
That is clasic actualtion pin too long
Follow Evertetts instructins above....when i measured my orgial MC and booster there was 1.5 to 2 mm clearance....and that is what I have set all mine to over the years what the factory spec is Im not sure.
I would grind off the 1.5 /2mm and try, if not OK go out to the 2mm+ it is easy to take metal off harder to put back on.

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post #14 of 26 (permalink) Old Oct 28th, 11, 02:10 AM Thread Starter
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Re: Brakes locking

Hi!

I made the test.
I went for a ride, stopped back home with brakes hot and locking, detached the mastercylinder from flange on booster braket and let it for a while waiting the pressure to release.... It didn't help release the pressure on the brakes.

So there is enough free play at the rod.
I can say it is locked both front and rear.

New master cylinder was installed by a professional so it sounds normal to me that he checked this.

Now I attach a picture of the 'thiever' maybe that part is the problem??

Regards

Camaro 1968, propane 327ci, Big Brake, Hotchkis, T56

Last edited by Marc; Mar 21st, 12 at 01:13 AM.
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post #15 of 26 (permalink) Old Oct 28th, 11, 03:23 AM
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Re: Brakes locking

Maybe, maybe not. This is the distribution block.

It's function is to cutoff the leaking axle so the other axle can still be used for braking. The BRAKE light would come on if the block were forced to one side - the tip on the left side would either be extended or retracted depending upon faulty axle.

So, you dismounted the master cylinder and pressure did not relieve.
Was the piston in the cylinder touching the retaining ring? This defines a fully retracted master cylinder piston.

You can bleed off the residual pressure with the bleeder screw(s) and mc rod is not too long.
If brakes are locked, can you use a large C-clamp to squeeze the piston back into the caliper, do you see the fluid returning/bubbling in the mc reservior?

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