Ok guys I need some help

I replaced and rebuilt my rear brake system, new lines, calipers and rotors. Front were also done along with new MC.

When driving the brake peddle is solid 5 out out of 6 times I apply the brakes. The 6th time, the peddle is soft. Then hardes up again.

I have read that when replacing the rear rotors you must check runout. I set up a dial indicator against the rotor and zero it out. I then rotate the rear wheels, I get a reading as high as 0.020. Bad right? I can smack the rotor with a rubber hammer and get that 0.020 down to about 0.015 if I can get it down to 0.002 as suggested without rivets what is my guarantee they will stay within tolerance?

How do I shimm the rotors if I can't get it down to 0.002?


One last thing, while in nuteral, when I rotate the rear wheels it spins freely but tightens up at one point per revolution, at that point is when I hit 0.020 on the dial indicator. Could something be bent? maybe half axle shafts are bad? u-joints?


Please help thanks for any and all input.

 

FWIW...new rotors aren't always "true" out of the box. Might have to turn them. I would try that first before pulling my hair out further.

 

The rotor runout can be due to the rotor not being true, or due to excess play in the trailing arm bearing setup.
Either way, the VB&P O ring kit should take care of the problem.

 

I did the VB&P oring upgrade on all callipers

 

Thanks Garys 68 & Nacho_Libre for the help.

Is there anymore, I think I may take it to local brake shop, maybe have a pro look at it.

 

If you are able to do the work then you're better off. I would check a few things first though.
You have to 100% sure the indicator is not moving on you. Rotating the rotor, on the workbench with new bearing can give you false readings, trying to do it on the car is even more tricky. If you are 100% sure you have .015-.020" runout then you have to correct it as it will lead to brake failure. Turning them or replacing them may not help much and may make them worse.. What I would do is to disconnect the 1/2 shafts and pull the caliper up out of the way. Now you're going to be rotating just the rotor and spindle. If the arms were hanging down before the 1/2 shafts might have been binding at the extreme angle- sound like it when you say it binds in one spot.
If the rotor rivets are out then you might be able to index the rotor on the spindle and get closer but I always looked at this a "Band-Aid" fix. Pull the rotor and check the spindle flange for runout and look for any burrs or rust that could be causing it to runout.
I've had new USA rotors runout .009 out of the box. Facing them will not solve this unless they are fixed to the spindle and concentric. I bolt the rotors on and have to shim them most times. I set them at .002 or under. I do this after I rebuild the spindles so there is no concern about bearing endplay contributing to the problem.

Here is a front rotor but the rear are done the same way, only harder if the spindle is out.
Good luck,


Gary

 

Thanks Gary This helps alot. I may try it myself but being a backyard machanic and not a very good one I would feel better if I took it someplace, since it is the breaks.

What type of screws did you use to attach the rotors to hub?

 

3/8-24 x 5/8 socket flat heads. Regardless of who does the job the runout has to be corrected. A good shop will do this, many never heard of an indicator.