Do I need a new master cylinder?

[Guest Anonymous]

Brakes won't release. Both fronts are locked, rear are tight enough to be difficult to turn. I rebuilt the front calipers recently, installed new rotors, pads and flexiblie lines. This evening I cracked a bleed valve enough to relieve some pressure, and worked the pads out on the drivers side. I was able to press the pistons back in with little effort, but of course one goes out when another goes in. Putting a pad in I can't get the pistons to return as a unit - in other words the brake fluid won't go back up the line.

My tentative diagnosis is I need a new master cylinder. But I've never seen a master cylinder fail this way.

Alternate opinions? Is this something you've seen before?

I tried to save kittens, and the archive did give me some hits, but in those cases it was binding calipers and working the pistons in and out a few times freed them up. I think my calipers are ok.

[Guest Anonymous]

not in an 02, this car was involved in a front end hit and the

master cylinder moved inwards into the booster, so the

plunger that actuated the hydraulic lost some of the travel and

would not release the pressure on the way back, solution was

to put some washers to reestablish the geometric relationship

(not ideal, but it worked for this particular pos car). I still don't

understand it well, hope this helps.

[Guest Anonymous]

how old are your brake lines? Original 02 rubber brake lines are known to swell up internally over the years, and eventually start closing up. What happens then is that the fluid pressure builds up at the wheel cylinders, but will not release. It does seems strange, however, that this would happen to you with all four lines...

Chris B.

'73 ex-Malaga

[Guest Anonymous]

If you can reproduce the problem, try unbolting the master from the booster. The booster depends on some funny little valve and a diaphragm that pushes hard on the master when the linkage opens the valve. If it gums up, the master can't relax. Another diagnostic is to disconnect the booster vacuum and see if the problem recurs. Be careful, you have to stomp extra-hard on the pedal if there's no vacuum.

Mike

[Guest Anonymous]

- rubber brake lines in front were acting like a one way valve.

P.O. had spent $600.00 on new front brakes but did't replace the hoses. I thought the car was a dog until I replaced the hoses and drove it w/out the front brakes being on constantly.

[Guest Anonymous]

That may have confused the situation a bit, since I don't know if it was the M/C or the booster that didn't release.

But I know it wasn't flexible lines, because they are new.

So, if the booster valve is "gummed up" can I clean it and get it to release? Or is this "the end?"

[Guest Anonymous]

No vacuum on booster. Pumped brakes, locked. Had to loosen M/C on booster to release. Tightened M/C mounting nuts back up, brakes locked again. Loosened, brakes released. Obviously the actuator rod from the booster is extended and won't release.

The brake pedal itself is coming back up all the way, and the linkage is contacting the brake light switch, so I think it is not a case of gummed up linkage.

Anyone got a spare booster?

[Guest Anonymous]

I might have a booster I can part with. I'll have to looksee. I'm in Santa Rosa, CA, north of San Francisco.

Mike

[Guest Anonymous]

But as of 10 minutes ago I am the successful (and only) bidder on a Tii booster on eBay. So this problem should be solved. And when I install that Manx sidedraft and DCOE 40, I'm set :-)