Brake calipers locking - Team Camaro Tech
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post #1 of 13 (permalink) Old Mar 8th, 09, 07:58 AM Thread Starter
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Robert
 
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Brake calipers locking

On my 76 camaro the front calipers lock down after pressing on the brake pedal. I can remove them and manually push the piston in but as soon as the brake pedal is used they lock up again. Any ideas on why this is happening? Thanks
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post #2 of 13 (permalink) Old Mar 8th, 09, 10:11 AM
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Re: Brake calipers locking

In my case it was the master cylinder. It was new along with alot of new parts so took me awhile to figure it out. Just because somethings new doesn't mean it works. Good luck.

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post #3 of 13 (permalink) Old Mar 8th, 09, 10:43 AM
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Re: Brake calipers locking

I hope this helps.

Ken
These are classic symptoms of a master cyl that is not returning fully. Some boosters have a pushrod that is a bit too long preventing master cyl piston return, which prevents fluid from being vented back to the reservoir. The first thing to check is that nothing is preventing full pedal return, check the brake light switch adjustment and any rubber bump stops. Power brakes do not use a rubber bumper for the pedal, the booster pushrod stops the pedal and controls pedal height. The clevis on the brake pedal has a small amount of adjustment available. Next pull the master cyl slightly off the booster, if the booster pushrod to master cyl is a bit too long you should be able to feel it when pressing the MC into position. If you drive the car and the brakes drag, undo the two nuts and pull the master cyl forward a bit and see if this helps. I had to grind the rod a bit on the last booster install I did. .010" is the proper clearance here.

There are two lengths of MC rear holes a deep one and a shallow one, and two booster pushrod lengths to match them. A cross match of them usually prevents rear brake bleeding and you can't get much pedal at all. So I dont' think your problem is a complete mis-match. Probably a length issue.

Another problem might be a bad brake hose or pinched brake line, it would act like a check valve, but it would do it all the time, not just hot.

Sometimes the caliper can be miss aligned to the rotor and if a brand new outer pad is put on, the caliper cannot move outboard any more to get enough running clearance. Pickup truck pads are slightly thicker than car pads but use the same identical shape, so this easy mixup can cause pad drag.
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post #4 of 13 (permalink) Old Mar 12th, 09, 01:08 PM Thread Starter
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Re: Brake calipers locking

The car had been sitting for over a year. It has a new master cylinder and brand new pads on the front and rusty rotors. When I move the car today the front wheels turn , but its hard to make the car move. When I use the brake pedal the car stops and when it is let up the car will move again but with alot of drag. The brake pedal itself feels good. Do you think this may wear in? It seems like too much drag to be something that will work itself out.

Last edited by tyrob; Mar 12th, 09 at 01:43 PM.
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post #5 of 13 (permalink) Old Mar 15th, 09, 12:29 PM Thread Starter
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Re: Brake calipers locking

I have check the pedal and it is not being restricted by anything. I have loosened the master cylinder and pulled it forward and the front brakes still drag. I have bleed them 5 times and nothing seems to help. Is there anything else I need to check? Oh yea, I also replaced the master cylinder. If it was on just one side I,d think maybe a caliper ,but it is both fronts that drag. With the front jacked up I can not turn the wheel at all. Anymore ideas would be appreciated.
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post #6 of 13 (permalink) Old Mar 15th, 09, 01:16 PM
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Re: Brake calipers locking

As mentioned above.. length of push rod
Where the rears adjusted with the cable (big nono) or with the adjusters inside?
Or the seals in the calipers installed correct? these also act as the 'return spring' for the pistons.

My Spelling is not incorrect...it is creative

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post #7 of 13 (permalink) Old Mar 15th, 09, 04:32 PM Thread Starter
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Re: Brake calipers locking

If it were the legnth of the rod wouldn,t it have released them when I loosened the master cylinder? I have no emergancy brake cable so it cannot be that. The caliper seals look good. I am thinking it is the calipers. I bought the car last may with no engine or transmission off ebay. There is no telling how long the car sat before I bought it. It just seems weird that both of them would be bad. When I open the bleeder valves fluid oozes out, so it must have constant pressure on them. The only thing I know to try is new calipers. Thanks
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post #8 of 13 (permalink) Old Mar 15th, 09, 08:52 PM
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Re: Brake calipers locking

When u release the pressure do the calipers release?
If so then it is the master cylinder
If not something else is holding them in...and the only thing is calipers are not moving on the slides and the pistions are not returning...it is the seals correctly installed that pull the piston back.

My Spelling is not incorrect...it is creative

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post #9 of 13 (permalink) Old Mar 15th, 09, 09:07 PM
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Re: Brake calipers locking

Quote:
Originally Posted by Steptoe View Post
As mentioned above.. length of push rod
Where the rears adjusted with the cable (big nono) or with the adjusters inside?
Or the seals in the calipers installed correct? these also act as the 'return spring' for the pistons.
Seals in the first gens are square cut... not possible to install wrong. These are not "low drag calipers" like later models that retract pistons slightly.

Quote:
Originally Posted by tyrob View Post
If it were the legnth of the rod wouldn,t it have released them when I loosened the master cylinder?
Correct
Quote:
I have no emergancy brake cable so it cannot be that. The caliper seals look good. I am thinking it is the calipers.
not much else there that can go bad besides seals and piston.
Quote:
When I open the bleeder valves fluid oozes out, so it must have constant pressure on them. The only thing I know to try is new calipers. Thanks
Quote:
Originally Posted by Steptoe View Post
When u release the pressure do the calipers release?
If so then it is the master cylinder
I'll vote for that!
Quote:
If not something else is holding them in...and the only thing is calipers are not moving on the slides and the pistons are not returning...it is the seals correctly installed that pull the piston back.
It sure sounds like a hydraulic problem to me.

Jeff
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post #10 of 13 (permalink) Old Mar 15th, 09, 09:14 PM
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Re: Brake calipers locking

Quote:
It sure sounds like a hydraulic problem to me.
yep

Quote:
Seals in the first gens are square cut... not possible to install wrong.
they have a slight taper, which I did not know the 1st time on one caliper, and it is not hard to catch one when installing ....also found out the hard way . didnt use the copper lube stuff.

My Spelling is not incorrect...it is creative

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post #11 of 13 (permalink) Old Mar 16th, 09, 03:46 AM Thread Starter
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Re: Brake calipers locking

With the bleeder valve open the pistons do not retract by themselves. I had to use a C clamp to push them back in. I will check the caliper seals again today. Thanks
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post #12 of 13 (permalink) Old Apr 20th, 09, 03:45 AM Thread Starter
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Re: Brake calipers locking

I am happy to say that I replaced the calipers and the brakes now work great. I beleive the old piston were froze in the position they were in. Once I removed the calipers the pistons would not move under the pressure of a large C-clamp. It is strange though they were both froze up. Thanks for all the help everyone gave me.
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post #13 of 13 (permalink) Old Apr 20th, 09, 12:09 PM
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Re: Brake calipers locking

Quote:
Originally Posted by tyrob View Post
I am happy to say that I replaced the calipers and the brakes now work great. I beleive the old piston were froze in the position they were in. Once I removed the calipers the pistons would not move under the pressure of a large C-clamp. It is strange though they were both froze up. Thanks for all the help everyone gave me.

Glad you got it fixed!

Ken
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