Rear brake calipers staying engaged.

[FlaD90]

I changed the master cylinder, rear brake calipers and flushed the whole system with new castrol fluid.

I can drive for a short distance depending how many times I brake and after a few minutes the rear calipers and staying closed to the point I have to pull over.

after changing the master cylinder I used a one man bleeding tank were you connect an air hose to the unit and connect the hose to the caliper bleed screw. I started with the drivers rear and then after both rears were done I did the front calipers. It seemed all fine and braking was fantastic.

Once the rear calipers engage you have to open the bleed screw to let out the pressure and then it goes back to normal. untill it all happens all over again.

Anyone have any suggestions on what can be wrong?...the master cylinder was leaking so thats why I changed it.

[evilfij]

Did you put the brake pipes back in the right places on the MC?

Failing that I would not be surprised if the calipers are seized.

[FlaD90]

The brake lines went back in the same spots on the new master cylinder, is it possibel there is some sort of air still in the lines?
Is there some sort of valve on the D90 for the brakes besides the MC?
I'm out of ideas and thought this was going to be straight forward, maybe this one man bleeding system caused a problem.

[Roadsiderob]

You might check the brake pressure reducing valve (PRV) located below the heater box. I have occasionally seen problems with these. I would map the layout of the lines and then test drive the vehicle to the point that the rear brakes lock up. Next, loosen the line at the MC that feeds the rear brakes via the pressure reducing valve. If there is pressure at the MC, you may have a misadjusted pushrod or something wrong at the MC. If there is no pressure at the MC, loosen the output line at the PRV that feeds to the rear brakes. If there is pressure here, you probably have a stuck PRV. If there is no pressure here and the rear brakes are still stuck, work your way back inspecting all steel and rubber lines for kinks and damage and loosen every fitting until you locate the point which pressure is present. This should help narrow things down to find the restriction.

[FlaD90]

Great advice Rob, I will give this a try.....