Brakes not releasing pressure (locking on).

[Quint]

Still having fun with my brakes, only thing holding me back from the WOF.
background:
viewtopic.php?t=80970&highlight=

Honed and replaced the seals in the master. Got pedal and brakes. But now after using the brakes heavily they'll stick on, they'll get heavier and heavier until the car is really dragging and I have to pull over and release the pressure off the callipers.

I've put a spacer(gasket) between the master and the booster hoping it'd fix the problem. Nope. Do I need a thicker gasket?

Running out of ideas (and time!) Need to fix them to get a WOF next week for MM. Anyone know what's causing this?

edit: proportioning valve may be the culprit. Anyway to check them?

[CAMB01]

What did you use to lube up the new seals in the master when you put it back together?

[Quint]

I used brake fluid.

[allencr]

...the car is really dragging and I have to pull over and release the pressure off the callipers. I've put a spacer(gasket) between the master and the booster hoping it'd fix the problem. Nope. Do I need a thicker gasket?

Yeah, an extra gasket might do it but you'd be better off if you just adjust the booster's rod back a bit.
You could use a very fine wire VERY softly to figure out when the seals start to cover the ports, or you can measure the difference between where the piston sits & how far the rod sticks out of the booster.
They can usually use a little pre-load so you aren't spending too much pedal travel pushing fluid back into the reservoir. Your problem is too much.

[MAGN1T]

Flexible rubber hoses get blocked from time to time. Will give those symptoms.

Have you lifted the car to see if all the brakes are stuck , or just one?

Modifications don't work if it's broken.

Steve

[whynot]

just to clarify. Is it all 4 brakes binding?

when they are playing up have you released the pressure at the brake or at the master cylinder?

[matt dunn]

I have to pull over and release the pressure off the callipers.

How are you doing that? Opening a bleeder?
Does fluid squirt out under pressure?
When it does it next crack the line at the master cyl instead of the bleeder,
that will tell you if it the M/C holding the pressure or something in the lines/bias valve/hoses etc etc

[Quint]

Was bleeding it at the calliper.

Found the problem, The primary return port on the master cylinder was blocked by the return seal. The seal I was sold was ~1.5mm too long so was covering the port not allowing the fluid to return. So only one set of brakes were binding up (front right and rear left) but the secondary would balance the other two to lock up the same.

Lesson: when rebuilding the master, once you've rebuilt it, blow through the line fittings on the side of the cylinder when it is at rest and see if you can hear air coming out of your return ports (pin hole sized). If you can't they are blocked (dirty) or the seal is wrong.

Side note: Weighed the ga70 in, 1410kg. aw11 came to 980.

Cheers for the help guys.

[whynot]

we had issues with the return port on the old mans bike brakes. it had never been drilled out at the factory! took a while to figure that one out