1984 Brake Problem

[Thomas F.]

After I drive my car about 20 minutes until it reaches normal operating temperature where the fan comes on, my brakes tighten up to the point I cannot drive the car. After I let the car set to cool down I can then continue for another short period of time until it happens again. So far I have been able to get back home from short trips.

Here is some more information:

I have a new power brake booster which seemed to work ok when I first installed it.

When this happens I have put the car in neutral, made sure the emergency brake was off, and tried to push the car. I was unable to push the car.

When this happens I have jacked up the drivers side of the car, put it in neutral, made sure the emergency brake was off, and tried to turn the rear and front wheels by hand. I was unable to turn either wheel.

Before this problem started I had taken all the calipers apart, inspected, cleaned, reassembled, etc. I removed all the old brake fluid and blew out the lines before adding new brake fluid and bleeding the system. I had also taken the master cylinder apart, inspected, cleaned, reassembled, etc. and everything was working ok.

I have not replaced the Master Cylinder yet.

The problem only occurs when the engine is at normal operating temp. Everything works ok when the engine is cool.

I suspect the problem to be in the Power Brake Booster (even thou it is new) or the Master Cylinder.

I have inspected the rubber brake hoses and they seem to be ok.

If anyone can suggest any test I can perform or give me any suggestions I would appreciate it. Thanks in advance.

[Edward J.]

Re: 1984 Brake Problem

Tom, Did the problem start after the booster replacement? It almost sounds like the push rod adjustment is not correct. if the push rod is extended to far it will be pushing the pistons in on the master cylinder causing the brake to be applied. slightly.

[Michael W.]

Re: 1984 Brake Problem

Next time it does this, loosen the nuts that hold the master cylinder to the booster. If the brakes release, it's the booster/pushrod combo. If not, it's time to look at the master cylinder.

[Thomas F.]

Re: 1984 Brake Problem

Edward, thanks for your response. Yes the problem started after the booster replacement but not immediately? I had driven the car after the booster replacement without any problem. The problem started later. I understand what you are saying, but if this was the problem it seems it would do this all the time even when the engine was cold.

[Thomas F.]

Re: 1984 Brake Problem

Michael, this sounds like a great suggestion. Why didn't I think of that? Divide and conquer. I will give this a try, at least I will know which component is causing the problem and maybe I can get this old 84 back on the road again. Thanks for the reply.

[Jim T.]

Re: 1984 Brake Problem

When I replaced my brake booster on my 1985 I bought the replacement from Auto Zone and was happy to receive one identical including the manufacturer to the factory original booster for a lot less money than what GM wanted for one. My pedal was going to the floor when my problem occurred. I do not remember what I did in an attempt to rebuild the the master cylinder, however I installed a new one.

[Bill M.]

Re: 1984 Brake Problem

Next time it does this, loosen the nuts that hold the master cylinder to the booster. If the brakes release, it's the booster/pushrod combo. If not, it's time to look at the master cylinder.

I had the same problem on my '65. When I loosened the master from the booster, the brakes were still locked up. The small hole to the left in the picture was plugged. I cleared it and the brakes never locked again.

That small hole is for brake fluid to bleed back into the reservoir as it expands. If the hole is plugged when the fluid warms and expands, it applies the brakes, which heats and expands the fluid, which applies the brakes more. Completely locked up my brakes.

[John H.]

Re: 1984 Brake Problem

I had the same problem on my '65. When I loosened the master from the booster, the brakes were still locked up. The small hole to the left in the picture was plugged. I cleared it and the brakes never locked again.

That small hole is for brake fluid to bleed back into the reservoir as it expands. If the hole is plugged when the fluid warms and expands, it applies the brakes, which heats and expands the fluid, which applies the brakes more. Completely locked up my brakes.

Bill -

That little hole (the compensating port) is the hole through which we evacuated and filled the brake system in the plant, without ever touching the caliper bleeders.

[Bill M.]

Re: 1984 Brake Problem

Bill -

That little hole (the compensating port) is the hole through which we evacuated and filled the brake system in the plant, without ever touching the caliper bleeders.

Jonh:

A very clever innovation. When I was the new kid in brakes, another engineer described the process, and I figured he was kidding; just seeing if the new kid would buy it. I didn't believe him. I didn't fully accept it until I saw it being done in the assembly plant!

[Thomas F.]

Re: 1984 Brake Problem

Thanks to everyone who responded. I've temporarily set this brake problem aside to work on some other issues I am having. When I get the car back together I will take it back on the road to tackle this brake problem. All your comments were appreciated and very useful. When I solve my brake issue I will send another post to let you know what the problem was.

[Thomas F.]

Re: 1984 Brake Problem

I separated the Master Cylinder from the Brake Booster and the brakes were still locked up, so I decided the problem was in the Master Cylinder. I took the Master Cylinder off the car and took it apart for the second time. Everything really looked as if it was new on the inside. After talking to some of my car friends who told me to just go and buy a new one I did. The new Master Cylinder seems to be the answer to my problem, my brakes are not locking up now, however I now have a new problem....My brake warning light is on and will not go off. I have started a new thread on this issue on 3/28/13, Check it out.