I need some help - I replace the front rotors, calipers, pad, flex line and m/c. Now when I went for a test drive after several hard stops the front brakes get hot and lock up.
After they cool they release.
What should look for?
Thanks
Tom
I would start by checking that the brake pedal is letting the master cylinder come all the way back. There needs to be a little clearance between the push rod on the pedal and the piston in the master cylinder. And make sure the brake pedal moves freely, not binding on the bushings.
Jim
Good call, Jim!
Experience is a teacher you remember!
Where'd ya get the crappy rebuilt calipers?
Tom, can we determine if a piston is sticking or not? Short drive, does one caliper get hotter than the other. Short stop, hands off the wheel, does it pull to one side?
It almost sounds like one of your knockback mechanisms' is not working properly causing excessive heat to the system, especially if you have new lines and MC.
Do you see any "blueing" on one of the rotors vs. the other?
Otherwise I'd double check that pedal free play again as it sounds tailor made to your problem.
One other thing to check is the bearing play on your new rotors etc. Double check the spindle nut for tightness and make sure there's no excessive runout causing the rotor to wobble and contact the pads causing heat.
Check the pad gap with the car cold... both inside and outside. Can you turn the rotor by hand (when cold) or do you feel a substantial amount of rubbing? If there is substantial rubbing, we may want to look at the bearings as a possible cause.
Let's dig in...
Thanks Eric - I don't think it is the person who rebuilt the calipers as much as the one who installed them
It does not pull to one side but the right does seem hotter than the left when it happens.
WQhen its cold I can turn the wheels buit there is some rubbing, a little more than I expect.
What should the pad gap be?
I will double check the spindle nut.
Thanks again!
Here's the file... the clearance number I spewed earlier is within spec.
Knockback_Description.pdf ( 228.28k )
Number of downloads: 120
OK - I have no clearance between either pad and the disc.
That can be normal for the first few miles on new pads. Pull the pads and check that the rotor is centered in the gap. If not we need to look at bearings. If so, I'll start prepping some new pistons.
cool,
So this knock back device....it rackets up as the pads wear so you would need to add fluid over time to fill the void behind the piston...
What and how do you reset them once you ahve new pads? Just push?
Rich
I loosend the spindle nut as you said and reinstalled the pads. While the pads were out everything appears centered. But the outside piston is sticking out further than the inside.
When I went for a test ride the same thing happend. Everthing is good for a feww low speed stops - then after a hard stop the free play on the pedal gradually disappears and the brakes lock (both sides)..
The bad part is you replaced a whole bunch of stuff, any one of which can cause problems . . . It sure sounds like you don't have pedal freeplay . . are all the calipers and the MC new? or did someone rebuild them ??
are you sure you're starting with known good units ?? If you're not sure, it's like shooting yourself in the foot. . .
Lets get to basics first for trouble shooting,
When the master cylinder is in the released or at rest position, you should be able to pry back each brake pads. . . the fluid you're compressing in the calipers goes back thru the uncovered inlet port in the master cylinder up to the fluid reservoir. . . If you can do this, then there is no mechanical reason why the pads when the pedal is released can't do it themselves. but your statement about only when hot or cold makes me think something is expanding when hot and binding. .
If you cant push the any of the pads in , my first guess is the master cylinder probably has the rod depressed and the piston is past the port hole for whatever reason.
When it's working correctly, as you step on the brake, the MC piston covers the inlet port, sealing off the reservoir, and forces fluid out to the calipers. . not back up to the reservoir, making it a one way system, but only if the piston port is covered.
If you can pry back any one, then the MC port is uncovered. . . . . Next, Make sure your can pry all pistons back. . . it should take only light force. . . you may have sticking pistons but I can't imagine all 4 sticking at once . .
Do all the pads fit in the calipers easily, do the move freely ? or do the rub and bind on the caliper ??
If you can move all the pistons, you might try putting your old pads back in a see if the problem changes. . that's easy. . . If that doesn't do anything and you're still puzzled, put the old MC back in. . that's a pain ion the butt, but there isn't anything else left to change. .
Just remember, you're going to solve the problem, it's just a matter of the steps you have to go through to get there. .
The MC was replaced about two months prior to the rest of the parts and was working well.
I have plenty of free play/ with the brake pedal until the brakes heat up the it goes away. Shouldn't the excess fluid go back to the reservoir?
I plan on changing the fluid again to see if any "crap" comes out since it does not appear the brakes were well maintained over the last 40 years.
Is the vent on the M/C reservoir plugged ? There is a vent and if plugged or capped would give symptoms like that
Problem resolved!!!
It was a combination of things:
1. Left front rotor had some play
2. Caliper bleed valve was cloged (probably from the over heating)
3. Brake pedal was not coming out far enough (my fault)
I first tried to push some brake fluid out the bleed valve on the left side and nothing would come out. Then I removed the caliper and saw the rotor was not centered in the caliper.
Then removed the caliper and remove and reinstalled the rotor.
Then removed the bleed valve cleaned it out and forced more brake fluid out of the caliper without the bleedvalve in place.
Reassembled and bled the brakes, then went for a test drive and still no luck. Then reread all of these post again and double checked everything. I could see no fluid was making its way back to the resivoir so it must be the brake pedal adjustment. I turned way more than it needed to and the car nearly rolled out of the driveway before i pulled the ebrake! Went for several hot laps around the block and everything working except for the idiot light (that is a problem for another day)
Thanks to everyone for their help. Especially Eric for the quality parts and toolguy for repeating the one thing I was sure not the problem!
Tom
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