Brakes self engage

[don.piotrek]

Hi again, unfortunately again with an issue.

So after a rough engine start, as the engine heats up, it runs good. But then after some time or some distance driven, the brakes engage just by themselves. The brake ligth turns on and the car is harder to drive. When in drive gear and I release the brake pedal, it even doesn't start to roll. Once I noticed the rear wheels were quite hot - like from overheating of the drums, but the front ones were cool/ regular temp.
Initially I thought it may be something with the parking brake, but this doesn't light up the brake lights? The other day I drove the car for few miles, stopped it and turned the engine off. An hour or so later I started the engine, it was running in Parking gear and the brake lights lit up suddenly.

I assume this might be something with the vacuum system for the brakes? What do you think? The brakes were done by the previous owner few years back, maybe they just need some fine tuning? But on the other hand last year, and neither 2 years ago nothing like this happened.

Thanks

[paulr]

What model year?

[don.piotrek]

It's a 390cui cruise-o-matic 1964 Landau

[RAVEN]

Any mods like disc brake conversion?
Looks like a booster failure, but all 4 corners would engage, not just the rears. Also you state that engine runs rough, this is another indicator of booster failure and the vacuum is effected on the motor.
A good test is to pinch or remove vac hose to booster and plug it. Does motor smooth out and brakes release?

[paulr]

Any mods like disc brake conversion?
Looks like a booster failure, but all 4 corners would engage, not just the rears. Also you state that engine runs rough, this is another indicator of booster failure and the vacuum is effected on the motor.
A good test is to pinch or remove vac hose to booster and plug it. Does motor smooth out and brakes release?

@RAVEN, I like the vacuum and booster problems, Wally. But his pedal is not returning; I'd look at the return hardware. I've seen cars where that's frozen up from rust, hardened grease, paint and god-knows-what. Cases like that are mission creep. Wheel cylinders could be garbage, you know. At least there's no prop valve (uh, unless...mystery mods?)

@don.piotrek, how long have you had the '64?

[RAVEN]

Paul, we are talking of a MY64 car so Brake lites are signaled by brake fluid hydraulic pressure. It is stated that the brakes self apply, after a few miles of driving. This can only happen by booster self triggering, IMHO.
If the booster has an internal fault, it acts as if the brakes are being applied and pulls the internal diaphragm to actuate the booster/master cylinder.
One question is if a disc convert was installed, this would explain the separation of front to back brake action (prop valve)
Some gaps in information provided need to be filled in.

[don.piotrek]

Hi Raven, sorry for the missing details.
This is a factory 4x drums, no conversions.

[sseebart]

I'd start with testing the booster, too. It's possible that the self-adjusters in the front are worn or non-functional, causing the rears to engage (and heat up) first. Having the brakes "done" by the P.O. could be anything from new pads to a completely new system. Chances are, though, that the booster was not part of the job.

~Steve

[jtschug]

I bought a T-bird that had been in storage for 15 years and when I took it for a ride around the block, all the brakes locked up solid. What I found was brake fluid that looked more like butterscotch pudding. All the rear cylinders were replaced, and the front calipers and master cylinder were rebuilt and the booster was changed out, then I flushed the lines and filled with fresh fluid. Problem solved, but I don’t know what causes it. Maybe too much water dissolved in the fluid? I don’t know.

[Cliff Rankin]

Seen this before on a 64. The booster would brake the car. There are always some details that don’t make sense.
I was beginning to think the old owners spirit was haunting the car. Pull the vacuum see what happens.
Please post your results.
Cliff

[rzcrisis]

Hello All

I second Raven's diagnosis. I had the exact same problem when I purchased my 64 HT. All 4 drums locked and brake lights on. Pinched off vacuum at booster to release. Replaced booster and all back to normal. These boosters are a hit and miss even with rebuilds. Currently I have the third replacement booster on the car and cross my fingers it has been fine for the past 2 years.

Hope this helps.

Randy

[don.piotrek]

Ok, so the diagnosis was quite easy... the previous owner had put a two-circuit GM pump and booster on the car as he had the brake system 'redone'.
I don't know the reasons behind it, but that was making the car break in not very reliable way...

[Terry64HT]

Sounds like a not very good dual master cylinder conversion attempt.
Terry
64HT

[don.piotrek]

This is how this looks like

[paulr]

Risking redundancy here. The 64MY is capable of accommodating a dual chamber master with the OEM banded style booster (no doubt, either kind of OEM booster). I did it on mine with a '73 Mustang MC, but I also swapped out my left cowl brace with a 65/66 style curved brace giving the corner better elbow room. At the time of this picture, the car has 4 OEM drum brakes, and the setup stops more than satisfactory. Bend a couple of brake lines, and come up with some new fittings, but no other mods to the system. Just an encouragement if you're wanting to run with a dual.