Front brakes dont disengage - Team Camaro Tech
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post #1 of 8 (permalink) Old Dec 1st, 13, 08:26 AM Thread Starter
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Front brakes dont disengage

I have a front and rear disc brake conversation on my 69. I have noticed there are times when doing normal driving that the front brakes don't disengage. The pedal becomes very hard. This only happens periodically. I can smell the brakes getting hot when I pull back in the garage.

My question is what do you think is causing this. Do you think the Prop Valve is bad?

????
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post #2 of 8 (permalink) Old Dec 1st, 13, 08:44 AM
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Re: Front brakes dont disengage

Usually it is due to the vacuum booster pushrod length where it engages the master cylinder. If too long, it won't allow the master cylinder to vent fluid. This is a common problem.

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post #3 of 8 (permalink) Old Dec 1st, 13, 08:48 AM
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Re: Front brakes dont disengage

Either you have seized pistons in your calipers or the caliper slides need servicing. With four wheel disc brakes I am pretty sure you shouldn't have a proportioning valve ?
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post #4 of 8 (permalink) Old Dec 1st, 13, 09:06 AM Thread Starter
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Re: Front brakes dont disengage

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Originally Posted by Ric67 View Post
Either you have seized pistons in your calipers or the caliper slides need servicing. With four wheel disc brakes I am pretty sure you shouldn't have a proportioning valve ?
On my 2nd gen Camaro I did not have a prop valve but there was one on the kit I bought for the 69 which I thought was unique as well.
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post #5 of 8 (permalink) Old Dec 1st, 13, 10:07 AM
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Re: Front brakes dont disengage

Without a doubt there are better qualified brake guys on here. But my understanding of the prop valve is that it is used on front disc and rear drum cars. Reason being the size difference between the rear brake cylinder and the front pistons. The rear cylinder taking less fluid to engage as opposed to the front pistons. The prop valve function is to equalise the flow of fluid to both front and rear systems so that the rear drums do not grab first. ( hope that is explained properly?)
David above brings up the booster push rod length. If you do a search here you will find lots of guys have had the same problem after a conversion.
So it is a possible booster rod, prop valve you don't need or sticky/seized calipers.
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post #6 of 8 (permalink) Old Jan 3rd, 14, 06:26 PM Thread Starter
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Re: Front brakes dont disengage

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Originally Posted by davidpozzi View Post
Usually it is due to the vacuum booster pushrod length where it engages the master cylinder. If too long, it won't allow the master cylinder to vent fluid. This is a common problem.
Thanks David
I decided to work on the car today and you were 100% correct with your diagnosis.

Took the car out for a quick drive. Came home and turned off car. Put car in neutral and tried pushing it. It would not move. Brakes were locked. I removed the two bolts on the MC/PB unit. Immediate the brakes came free. I ended up removing the adjustment screw and it the rod was still too long and brakes would lock up.

I covered up the engine compartment and grounded down the rod about 1/8 inch or so. Bingo... problem solved.

Now I am happy and will be working on the darn door latch as my driver door wont open. Grrr...always something.
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post #7 of 8 (permalink) Old Jan 4th, 14, 07:07 PM
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Re: Front brakes dont disengage

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Originally Posted by Ric67 View Post
With four wheel disc brakes I am pretty sure you shouldn't have a proportioning valve ?
I think this is an incorrect assumption. W/o a prop valve the rears would lock too often.

Front brakes do ~75% of the braking due to weight transfer. Thus, ~75% of pressure (and therefore clamping force) should go to the front since the same ratio of traction is given to the front tires.

If the front and rear tires are different widths and/or diameters, things change. I guess it really comes down to downforce, contact patch and tire composition all adding up to friction vs velocity (speed).

Finally, there's brake size and design. Rears are typically smaller, so the above may have already been resolved by the engineers...

How's that for BS!?
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post #8 of 8 (permalink) Old Jan 4th, 14, 09:50 PM
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Re: Front brakes dont disengage

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Originally Posted by 69&76 View Post
Thanks David
I decided to work on the car today and you were 100% correct with your diagnosis.

Took the car out for a quick drive. Came home and turned off car. Put car in neutral and tried pushing it. It would not move. Brakes were locked. I removed the two bolts on the MC/PB unit. Immediate the brakes came free. I ended up removing the adjustment screw and it the rod was still too long and brakes would lock up.

I covered up the engine compartment and grounded down the rod about 1/8 inch or so. Bingo... problem solved.

Now I am happy and will be working on the darn door latch as my driver door wont open. Grrr...always something.
A quick use of the search function above would have given u the answer maybe a 100+ times over and quicker without having to post.

My Spelling is not incorrect...it is creative

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