P30 Brake Lockup - Solved
I have a 1988 Pace Arrow on a P30 chassis with 4-wheel disk brakes. Recently, the brakes have been getting pretty mushy and brake fluid has been disappearing regularly with no external signs of leaks....
Forum Discussion
okhmbldr,
Thanks for the interest. I've been trying to approach this in a somewhat scientific manner instead of just replacing things willy-nilly because someone said to try it. My approach is to develop a theory about what could be going on and perform a test to verify it.
My original theory was that an overfill of the MC fluid reservoir was causing a constant pressure charge on all the wheel cylinders when the fluid heated and had no place to expand. I tested for this by modifying the old MC cover to have vent/pressure relief holes with straws that extend down into the fluid. If the fluid was truly expanding in the MC reservoir, the pressure relief tubes would prevent a pressure build-up. I put this rig on a few days ago, but the brakes still lock up after just a few miles of local driving.
Reminding myself that this condition only appeared immediately after installing the new MC, I'm pursuing a new theory, that the plunger on the Hydroboost booster that actuates the MC piston doesn't have any clearance and is keeping the brake system constantly pressurized, causing brake drag and heating. This condition has been noted on the racing forums. I'm going to perform a test this weekend to investigate this. I plan to loosen the 2 bolts that hold the MC to the booster and insert some shims to keep them a little farther apart. If this cures it or improves things, I'll know I'm on the right track.
I'll keep you informed.
Joe
Thanks for the interest. I've been trying to approach this in a somewhat scientific manner instead of just replacing things willy-nilly because someone said to try it. My approach is to develop a theory about what could be going on and perform a test to verify it.
My original theory was that an overfill of the MC fluid reservoir was causing a constant pressure charge on all the wheel cylinders when the fluid heated and had no place to expand. I tested for this by modifying the old MC cover to have vent/pressure relief holes with straws that extend down into the fluid. If the fluid was truly expanding in the MC reservoir, the pressure relief tubes would prevent a pressure build-up. I put this rig on a few days ago, but the brakes still lock up after just a few miles of local driving.
Reminding myself that this condition only appeared immediately after installing the new MC, I'm pursuing a new theory, that the plunger on the Hydroboost booster that actuates the MC piston doesn't have any clearance and is keeping the brake system constantly pressurized, causing brake drag and heating. This condition has been noted on the racing forums. I'm going to perform a test this weekend to investigate this. I plan to loosen the 2 bolts that hold the MC to the booster and insert some shims to keep them a little farther apart. If this cures it or improves things, I'll know I'm on the right track.
I'll keep you informed.
Joe
