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turbofoot1
09-26-2009, 05:35 AM
Ok, my 86 powermaster is slamming the master cylinder when the key is turned on. As soon as I turn the ignition on the powermaster comes on and the brake pedal starts moving to the floor and goes almost all the way to the floor and after the powermaster shuts off, the pedal is slammed down and the brakes are LOCKED up and the pressure has to be released mechanically. I tried another 87 master cylinder and 3 different pressure switches, 1 was brand new. NO change. Master cylinder works normal with the powermaster disconnected, just no assist of course. Any ideas out there?

Keller
09-26-2009, 10:35 AM
Never heard of this 'slamming' behavior.

Is the first unit one that had been OK and used before?

Did you replace the entire unit (i.e. unbolted the old one from the firewall and pulled it off the pin on the pedal, then replaced with another one) when you changed it out? Were both from TRs and not from wagons? Were they known good working units? Are either of these junk ones picked up from swap meets or from the internet?

Are the brakes on the car known to be in good working order? What about the proportioning valve? How old is the accumulator(s)?

Have you gone through the test trees and information presented on this website?

turbofoot1
09-26-2009, 11:00 AM
All parts are off my 86 and 87 T-Types. Powermasters are working good, but as soon as I turn the key on, pedal goes to the floor and brakes are applied and locked up, then the powermaster shuts off automatically. It's odd. Worked fine before but the pedal was sticking at the top so I swapped out the master cylinders. The sticking master cylinder did NOT stick when bench testing after I removed it so I'm thinking that was not the problem. The accumulator is 6-7 years old but only has 2-3k miles on it. I've had bad accumulators before but they didn't act this way. Now, if I return the entire system back to the way it was (just a sticky pedal at the top but worked fine) with all the same components, it still powers the pedal to the floor and locks the brakes up before shutting off the powermaster. Go figure

Keller
09-26-2009, 02:54 PM
Now, if I return the entire system back to the way it was (just a sticky pedal at the top but worked fine)
I must not be understanding this well. What is "sticky" about the pedal at the top of the stroke? It will not move? It is hard to push? It has gum on the surface? :loll:
with all the same components, it still powers the pedal to the floor and locks the brakes up before shutting off the powermaster. Go figure
I've never heard of a Powermaster system that caused full apply of the brakes. Nor one that could do something like that and stop the motor normally, as if in cyclical use. (As opposed to a motor being stuck on, and eventually popping the fuse or overheating the circuit breaker.)

Perhaps I don't understand what parts are being swapped between the units. Could you clarify?

The issue sound like it could be an internal leak. But it seems odd that it would occur in this way.

turbofoot1
09-26-2009, 04:55 PM
As soon as you turn the ignition on, you can hear the powermaster run and the brake pedal slowly moves towards the floor all by itself and stops near the floorboard when the powermaster stops. At this point, the brakes are fully applied and car won't budge. I have swapped out 2 powermasters, 2 mastercylinders, 3 used accumulaters, 3 pressure switches (1 was brand new), all parts off of 86-87 T-types. I have 3 t-types. Bench tested both master cylinders=OK. OHM'd all 3 pressure switches in open and closed positions= ok. Same result, ignition on, pedal goes to floor(obviously by Powermaster pressure) and brakes are fully applied with no foot assist. I'm stumped.

Keller
09-26-2009, 06:08 PM
Um...wow. :shock:

I'd like to hear what someone like Richard Clark would say about this. He's the good friend of Dennis Kirban who has demonstrated the repair of PM units at the GS Nats every so often. Have his card somewhere. He also hangs out on turbobuick.com sometimes....

Short of this, I believe Karps Brake Service does rebuild the PM units. http://www.resleeve.com/ And several mainstream parts retailers still sell units rebuilt by Cardone.

I'm sure some will suggest moving to vacuum. I have seen a conversion to Hydroboost as well.