Gang, We need some help.
1995 16v 4dr Sidekick
(had rear ABS, not using diff sensor anymore, haven't disconnected anything except the rear sensor, haven't unplugged any fuses or any connections under the hood)
We are using Toyota Land Cruiser FJ80 axles
4 piston fronts, single piston rear disc brakes.
We've been experiencing a problem with our brakes, that we need some help with.
Brake fade after bumps;
When driving over washboards or other rough surfaces the brake system seems to have a bunch of air in it. IE needs pumping to bring up to pressure to be able to brake effectively. Meaning the front brakes don't appear to be working at all and the rears are weak. They can almost be locked up after mashing the pedal on the floor hard, but still nothing from the fronts. Unless of course I pump the crap out of them, then normal brakes.
(rear brakes seem to work better than front)
Brake fade after water crossing;
Just after having driven through a creek crossing, (could be related to sympton number 1) the brakes need pumping to bring up to pressure. (again, like air in the lines) The rears work better then the fronts.
Brake pedal modulation when going over bumps (percieved when only going downhill);
I've noticed that when going over washboards, or other rough surfaces while going down hill. Slightly applying pressure to the brake pedal (riding the brakes), I can 'feel' the brake pedal modulate under my foot with the bumps. AND it feels like the brakes work 'better' when they are modulating. (actually getting 'brake-like' action) Kinda feels like a modern ABS system on the pedal, where the pedal pushes back against your foot. However, I think that its because the rear tires bounce off of the ground and lock up slightly. (very strange feeling)
Unpredictable pedal behavior.
Sometimes the brake pedal feels perfectly like it should, firm and solid. All wheels can be nearly locked up. Other times the pedal seems to hit the floor and needs to be pumped to get pressure. Most often the rears can be locked up and feel like only they are doing the braking.
We've replaced the booster and master cylinder
And have bled the system THOROUGHLY.
Several quarts with the 3 pump then bleed method, starting with the farthest away brake and moving closer to the master cylinder finishing up with the wierd device next to the master cylinder. (4 doors are different than 2 doors and have some secondary device inline with the brake system with a bleeder cock on it.) Maybe related to ABS system?
Not ever having serviced quad pistion calipers, is there anything special that anybody can think of?
Maybe the elusive proportioning valve isn't working properly, or maybe it is? Maybe it needs to be removed/replaced/re-engineered?
(don't know where/what the proportioning valve might be, nor how it may affect my issue.)
Overall, it feels like at times there is air in the system. The symptoms requiring the pumping seems to be totally random.
Sometimes the brakes are tight, just fine, right there, even after long periods of no braking, no pumping was needed. Just like normal.
Sometimes, the brakes need to be pumped between 1 and 6 times to get good braking power. Then let off the pedal, drive 2 seconds and then they may need to be pumped again to get the brakes working.
Overall the rears seem to be working MUCH better than the fronts. They can almost ALWAYS be locked up, even though the pedal is RIGHT near the floorboards.
The fronts however won't lock until I pump the every loving heck out of it a bunch of times and then REALLY lay into the pedal, then, only then may I get a squeak of the tires from the front.
Anybody got any ideas ?
Maybe there is still some air in the lines? (unbelieveably?)
We are not experiencing any leaks. No additional fluid has been needed. All of the pads and rotors are in good shape. (I haven't rebuilt the calipers yet, but getting close)
Any help, advice, comments you can provide would be greatly appreciated.
~Nate & Heather