# Brake Conundrum



## MaxAvidy (Jan 22, 2015)

1969 GTO. Discs up front, drums in the back.

My brakes lock up as they heat up. The front pads are rubbing so the wheels (both of the fronts) don't spin freely, but I can spin them by hand (with some effort) when they're cool.

I bled the brakes today all around, changing out the brake fluid.

The booster seems to work, as the brake pedal depresses more when I turn the car on. As I said, it does travel, though very little once I press the brakes a few times. And it's not as if the pedal stays at the floor, I just can't press the brake pedal down much at all as I'm pretty certain the brakes are locked up (too much pressure to move the brake pedal). When bleeding the brakes the pedal travels alright.

Everything seems to be working well enough individually, but together, somehow the bits aren't working properly.


Also, unrelated (or not) my emergency brake gets stuck on. The E Pedal comes back out, but it no longer makes the ratcheting sound when I press it to engage the brake, and the release handle moves freely as if it's not connected to anything. BUT sometimes it does work, like after I bled the brakes. 

I swear my car is haunted or damned or something along those lines.


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## PontiacJim (Dec 29, 2012)

Is it a factory disc/drum set-up or has it been added to the car?

Is the master cylinder original, replaced, or aftermarket?

The fluid level is not overfilled is it? You need some room to allow brake fluid to return to the master cyl when the brakes are released.

First thought is the pistons in the caliper are sticking. How old are the calipers? Have they ever been rebuilt? Last time you changed the pads? You should be able to turn them without too much drag.

Next thought is a possible problem with the proportioning valve.

Rear brakes may be adjusted incorrectly. Can you turn the drums without any dragging? They should spin easily. Sometimes the automatic adjusters can cause problems and over tighten the brake shoes. Last time you did a rear brake job?

Not trying to weenie out here, but sometimes it is easier and simpler to bring it to a brake shop and let them diagnose the problem. They might spot it right off the bat and save you time and grief in hit or miss attempts to find the problem. Let them find the problem and then make a decision whether you want to tackle the repair.:thumbsup:


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## Matthew (Feb 11, 2011)

The most common problem with front disc brakes not releasing is associated with the guide pins. I have seen brake calipers go bad, but not nearly as often as guide pins being bent. The pin is inserted into a sleeve (with rubber boot over it) that has two flat sides that must be positioned correctly when the guide pin is tightened. Improper installation can cause pins to be bent and calipers to bind. Guide pins are cheap and simple to replace. Just remember to check for that flat spot on the sleeve as you begin to tighten the guide pin. 

Not sure I understand your E-brake issue. When you have this problem, can you turn the rear wheels or are the brakes stuck? Or is this just a problem with the E-brake pedal assembly? Matt


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## 05GTO (Oct 6, 2004)

PontiacJim said:


> Is it a factory disc/drum set-up or has it been added to the car?
> Next thought is a possible problem with the proportioning valve.


:agree,

If the car was an original drum brake car and the disk brakes were added without changing the proportioning valve to a metered PV you could be having the problems that you are describing.


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## Pinion head (Jan 3, 2015)

05GTO said:


> :agree,
> 
> If the car was an original drum brake car and the disk brakes were added without changing the proportioning valve to a metered PV you could be having the problems that you are describing.


On the optional factory disc brakes for '67-70 Pontiac LeMans and GTO's, they use the same brass distribution block as same year drum systems, but added a metering valve hanging off the master cylinder to restrict brake fluid to the rear brakes. On '70 model GM Abodys with factory disc brakes, the metering valve changed designs (lost the big nut) and another piece located on the front of the crossmember where the rear axles brakes hose is attached to the crossmember. it is a residual pressure valve. In the early 90's I used to pull the '67-69 metering valves as specialty cores and occasionally sold them to a major national brake vendor who rebuilt them. Eventually, the early metering valves were getting so hard to find, just had them rebuilt and sold them with correct style disc changeovers. GM finally got it right for '71, went with an integral proporting valve mounted down on the frame. Have used a bunch of nice used '71+ disc proportioning valves in disc changeovers with next to no problems.


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