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Hello All,
I have searched through lots of threads and can’t seem to find one similar to what I’ve been experiencing with my brakes. At this point any advice will help.
I have a 90 2wd 1/2 ton pickup on which I’ve recently (less than 200 miles ago) replaced the brake pads and rotors. The caliper casting is F18Q. It was a tight fit.
At first the brakes worked great. Then recently they both started getting stuck in the front. The last time they got stuck, I traveled about 1/4 downhill and the rotors and pads started smoking up before it was safe enough to pull over.
I have since inspected my brakes and found that the pistons do not return flush in the caliper. After compressing the pistons and attempting to bleed the brakes, I found that there was no fluid bleeding from either of the rear wheels.
This is where I think I may have found the problem. Could the brake lines to the rear wheels have gone dry, causing the caliper pistons to stay out?
While bleeding, I opened the brake line connection above the passenger rear wheel and got pure fluid. So I suspect the problem is isolated to where the lines split to the two brake cylinders.
I will inspect the brake cylinders tomorrow and post an update.
It isn't likely that both calipers "stuck" at the same time, it is far more likely that you have issues with your master cylinder or the pushrod length to it and there is still hydraulic pressure being applied to the front brakes.
As to the rear brakes not bleeding, again maybe a master cylinder issue, but you say you got fluid before the tee, so probably the bleeder screws are plugged.
Also, the front brake calipers to not retract back to flush when you let off the brakes, the square cut seals around the piston help draw it back ever so slightly and just relieve the clamping force.
The next time your front brakes are stuck, especially if you can duplicate this in your garage or driveway, jack up the front end and verify that you can't rotate either wheel by hand. Then crack the brake line loose for the front brakes at the master cylinder and try rotating the wheels again. If they spin you have just verified that there is residual pressure on your front brakes being trapped by the master cylinder.
akwheeler, Thanks for the advice. I used your method to verify that my calipers indeed weren't stuck. And sorry for the super late response. I failed to fix this problem for a few months and by then I completely forgot to update this thread. But I did figure out what caused it.
I pulled my brake booster off and found that it had a blackish fluid inside. Then I inspected the master cylinder and I determined that fluid had been seeping around the piston and into the booster for quite some time. I then ordered and replaced both.
On another note, upon further inspection of my rear brakes, I discovered that my Load Sensing Proportioning Valve was shot and had so much dust and grime build-up clogging the lines which is why I wasn't getting any fluid at either wheel cylinder so I bypassed it with a spare T-fitting and refilled and bled the entire system. With a new master cylinder and brake booster and clean fluid all the way to my wheel cylinders, my calipers functioned properly again, returning every time.
In short, my theory is that my LSPV failed, fluid leaked out from there until the booster was forced to manually depress the piston in the master cylinder which eventually caused it to leak back into the booster which ruined it. And with air filling the lines, there was no way that the rubber in the caliper could return the piston to the open position.
Feel free to school me on any part of my theory though. And sorry for only reviving this thread now.
These pics don't tell much but hell, it's progress. Old booster Replacement
07-26-2018, 04:23 AM
