Brakes completely locking up and boiling?

[shuggy]

Hi got a bit of trouble. Bought Andrews 76 coupe yesterday, it's awesome, but the brakes are screwed. They Lock up after pressing a few times and when I pull up coz they are locked on, the wheel arches are smoking.

So I released the bleed valve, the calipers released, an drive home with handbrake only.

So last night I bled the front brakes completely, put new fluid in, removed the master cyl from the booster and as I did the master cylinder sounded like it releived. I put the master back on after checking the booster and the master were both free, and pumped the brakes with engine off and the calipers were closing and opening with ease.

So i took it for a drive and after 2km and a few hard brakibgs, the calipers locked up again and by the time i got home the face of the disks weren't looking too good! Bled the brakes to releived pressure and the dot4 fluid boiled out everywhere again.

The rear rh wheel cal has blown a seal from the pressure, but both sides are still free moving. The front struts are gh struts with gh brakes. The master cyl and booster is stock galant. The engine is 2.6 with cam.

My current theories, the master cyl could be jammed, but why would it work after reproving bleed valves?
The booster might be getting way too much vacuum and staying errected, therefor holding the compression on the brakes?
Both front calipers might be scored, but why would they work normally after pressure released again?
There is no proportioning valve on the car, only the thing on passenger side with one inlet and outlet going to rear so can't be that.
Or the rear cyls could be buggered and not releiving pressure in the first Half of the master therefor holding the second piston (front brakes) compressed... Help!

[C_Fernance]

The calipers generally either work or they don't. If they don't then they are generally seized in the one spot but yours obviously aren't.

I had the exact same problem years ago on a Scorpion, which use a very similar master cylinder (larger bore). Not sure exactly what part of the master cylinder was causing it, but after putting a new seal kit through it, it worked great again.

[astronturbo77]

master cylinder.

[75wagon]

From what I read, tango hasn't owned it for 8 years, and I don't think it's been driven in that time.
Brake fluid absorbs water. Water rusts the insides of things like master cylinders and slave cylinders.

I'd say it will be fine with a brake re build. Or replacing with new parts.

Dave...

[sigmaralliart]

If the rod from the booster to the master cyl in adjustable it might have been played with and pushed out to far??

[Decrepit]

Had the exact same problem a couple of years ago.

It was the master cylinder sticking and not releasing (the car would stop by itself and not go till I released the pressure build up by cracking the bleeder).
Either put a kit through it or swap it for a known good one from another car.

Randolph

[Superscan811]

If the rod from the booster to the master cyl in adjustable it might have been played with and pushed out to far??

In the Master Cylinder there is a bleed hole. If the adjustment rod (off the back of the brake pedal) is out too far, the hole is blocked and won't release the pressure when the brake fluid is heated up by braking.
This, of course, just gets worse and worse until the brakes completely lock up.

Cheers.

[shuggy]

I'm liking the last comment. I took off the master cylinder again today, and I took off the rubber boot on the master. I came to the conclusion that the booster rod is extended too far, and was either locking on the shoulder of the master bore or on the booster piston shoulder. But then I measured the pin vs master and yea, I'm thinking the master ais compressed all the time thus causing pressure lock.

Going for a drive tonight, wish me luck!

[Smithy]

Andrew if you need a hand give me a yell.

[shuggy]

thanks rod

I took off the master and put a washer on the studs behind it, thus protruding the master cyl out an extra 1.5mm out awaw from the master vac.

Works perfect, took it for a 100k round trip last night on the permit, cant beleive i didnt get pulled over, the car is 4 colors, has wires hanging out, sounds like a dinosaur and has no plates haha

Cheers guys.