Supra Forums banner

1 - 16 of 16 Posts

·
Registered
Joined
·
1,343 Posts
Discussion Starter #1
94 TT 6spd, stock calipers, stock lines, stock master, stock reservoir, Project mu pads, slotted rotors.
ABS is removed.
Brakes bled fine all corners, pedal feels great, no sinking, firm, etc.
All 4 calipers are rebuilt with new pistons, seals and O-rings

PROBLEM:
Drive the car for 20 minutes or so through city driving and BOTH rear calipers bind up (as if you were driving with your foot on the brake). JUST THE REARS.

Crack the bleeders, or the main line for the rears at the master cylinder and they release.

I took the reservoir out and checked for debris, I cleaned the master out, and I made sure there was no foreign material in the fluid or anwhere in the master (as far as I could see).


My guess?
Bad Master?!?

Figured I'd get a few other oppinions on the matter before I bought anything.


Thanks,
 

·
Registered
Joined
·
3,236 Posts
Were the rear calipers binding before the work was done?

The rear is holding pressure, that is why when you crack the bleeder the rear brakes release. If it were a stuck piston they usually will not disengage when you crack the system open.

Have you taken the master cyl off the vehicle before?

Lawrence
 

·
Registered
Joined
·
408 Posts
Sounds like a proportioning valve problem. I don't know where it is located, but it is the only thing common to both rears and not the fronts. Whatever it is there is surely pressure being held to the rears.

Good luck,
 

·
Registered
Joined
·
1,602 Posts
That is weird Alex. IS there a kink on any of the lines? Is there a SS line somewhere that is being bent for some reason?

I'd say it's the proportioning valve, and not the MC.
 

·
Registered
Joined
·
1,343 Posts
Discussion Starter #5
The prop valve is in the master. It does not have an external one like some other cars. There are sepperate lines coming off the master for the front and rear. The line closer to the firewall is for the front brakes, the other one is the rears. All stock lines, steel and rubber.
Both rear calipers are binding the same and it appears that its the inner and outer that are locking, just like if you were braking.
The rear brakes never worked the way they were supposed to anyway, and when I did take them apart I found each caliper was missing an O-ring. So they were taken apart before, like I said though, they are completely rebuilt now.
I took the master apart and found nothing VISIBLY wrong with it.
 

·
Registered
Joined
·
3,236 Posts
A master cyl that is bad generally wont hold pressure to the brake system. When it is bad it will usually by pass past the seals which leads to a sinking pedal. I am not saying that the master cyl is not the cause of your problem because it is possible but not likely. I would check the pushrod from the booster to make sure it is not pushing on the master and causing the brake system to be pressureized.
Lift the rear wheels to verify that when you depress the pedal and let off, that the rear brakes are dragging or locked up. Then unbolt the master cyl from the booster and let it poke out about 1/2". Do not loosen the lines comming off the master. See it the rear brakes release.

Lawrence
 

·
Registered
Joined
·
1,343 Posts
Discussion Starter #7
I'll try that next time it does it. I was out for an hour or so last night cruising around, and it did not bind at all. I'm sure with my luck they will again though. Sticky pushrod makes sense.
 

·
Registered
Joined
·
1,343 Posts
Discussion Starter #8
It did it twice again. I could basically remove the master with the lines still connected with no results.
Wouldn't you think a stuck pushrod would bind the fronts as well as the rears?
I can feel the pedal get harder as they start to bind.
Could it be a collapsed rubber line? Although I would assume opening the line at the master wouldn't work then.
Still at a loss.
 

·
Registered
Joined
·
3,236 Posts
IF it was a pushrod out of adjustment it would bind the fronts as well. Well that pretty much rules out the master cyl. You are right a rubber colapsed line would hold pressure as well. But its very unlikely that both lines are colapsed. Unless you clamped the line or streatched it pretty badly. I guess the next step would be to replace both rear lines.

Lawrence
 

·
Registered
Joined
·
7 Posts
this has happend to me on other cars thou only to one caliper. the problem was the rubber line that hooks to the caliper collapsed in side the line. if you take the other side of the rubber line off and its still stuck then you have your answer.
 

·
Registered
Joined
·
358 Posts
Wait... you said the pressure releases when you remove the line at the master. Does the pressure release easily? If it does then your problem has to be in the master cylinder. As you said the proportioning valve is in the master cylinder, so that may be your problem. I would suggest borrowing a master or buying a new one, because that seems like the only part that could be causing the problem from what you said. It couldn't be a line if the pressure holds all the way up to the master cylinder.
 

·
Registered
Joined
·
1,343 Posts
Discussion Starter #12
I'd blame the rubber line, but both calipers are binding EXACTLY the same. One is not more than the other, so the odds of BOTH rear lines being colapsed the same are sim to none. PLUS, the pressure is making it all the way back to the master.
If the lines were colapsed or pinched the only way to relieve the pressure would be to open the bleeder at the calipers, or open the lines at the caliper. Anything between the pinch and the master would not hold pressure.
The calipers are basically brand new and they release the way they should once pressure is relieved. Fluid moves back and forth in all the lines from the master to the calipers....EXCEPT when they start binding, then pressure only goes TO the calipers, and does not return into the master causing the binding.

The more we diagnose this, and the more I type this the more I think the prop valve (which is part of the master) is bad, requiring a new master.
 

·
Real Girl Thread FTW!
Joined
·
4,627 Posts
I'm having the same problem with a Nissan Sentra ! lol
It has new calipers, lines, fluid and master cylinder, and after driving for about 10 min. all 4 brakes lock. Im going :nuts:
I have checked for a prop valve, but it does not have one!!!!!!!!!!!
is all built in inside the master.....
Im going to check for Booster Rod runout.
Good luck to myself.
 

·
Real Girl Thread FTW!
Joined
·
4,627 Posts
Update.

It was the booster rod, somehow it over extended,
and with no budget from the customer, I installed shims in between the booster and the master and fixed the problem!
 

·
Registered
Joined
·
1,343 Posts
Discussion Starter #15
I ordered the master last week. should be here Monday. We'll see then if that's my problem.

Wish mine was as cost effective as your fix :)
 

·
Registered
Joined
·
1,343 Posts
Discussion Starter #16
UPDATE:::::::::

installed the new master cylinder today, bled the brakes, took it for a drive and NO BINDING!!!

The master was the problem. I got the 98 master aswell, so no more trac nipples :).

Thanks all for the help.
 
1 - 16 of 16 Posts
Top