Rear Brake thumping

[Imp558]

Obviously this sound is associated with a warped rotor, usually due to a hung caliper.

Before the June meet I did a rotor and pads, the caliper was moving freely.

After a couple weeks the sound returned so I took it apart, rotor doesn't appear to be warped when on a flat surface so I put it back together and no noise for a couple days.

Last weekend I did pads again, a new rotor, honed and rebuilt the caliper (which is still moving freely) and a couple days later my familier thumping returned.

Today I got new slides and hardware to put in, (one of the old clips is less than perfect). Anybody have a suggestion as to what else may cause this?

[LumiLTZ]

A couple of years ago I had a left rear caliper hanging up on my Lumina. It'd killed the pads/rotor so I replaced them, but still had the problem after a couple of days. Took it all apart again, the caliper seemed to move freely on its slides. I decided to bleed it, and that's when I discovered I had a bad/clogged brake hose. Had very little flow even with the bleeder wide open. Replaced the line and I was good to go.

[Imp558]

Oh,that's a good one, after the hardware and slides I'll do that. Trying not to buy a caliper since I really want to upgrade everything in the rear.

[Imp558]

Bought an effing caliper! The seals from the rebuild kit were not a problem, it's the stupid integrated E-Brake self tightening and getting too tight so the rebuild kit doesn't have parts to rebuild that part of it.

Honestly, I'll rebuild the fronts, and would encourage others to do so too, all it is to do is a couple seals and hone the cylinder. I got a small hone and rebuild kit for a quarter of what a caliper cost. Stupid E-Brake!

[Schurkey]

Bought an effing caliper! The seals from the rebuild kit were not a problem, it's the stupid integrated E-Brake self tightening and getting too tight so the rebuild kit doesn't have parts to rebuild that part of it.

How does a too-tight E-brake cause thumping? How does the E-brake self-tighten?

[Imp558]

E-brakes are self tightening, every time you brake in reverse they snug up a bit. With drum brakes that's the purpose of the star shaped wheel with the little dogleg against it.

In the rear disk brakes that have E-brakes incorporated into them there is a shreaded stud internal that the E-brake portion has an internal mechanism to spin the piston on and tighten it against the pads as they wear.

The caliper is getting too tight and warped the rotor.

[Schurkey]

E-brakes are self tightening, every time you brake in reverse they snug up a bit. With drum brakes that's the purpose of the star shaped wheel with the little dogleg against it.

Somewhat true. The mechanism that turns the star wheel requires a certain amount of travel to engage the next tooth on the star wheel. If the shoes don't have excess clearance, the mechanism doesn't have enough travel to grab the next tooth. Therefore it cannot over-adjust.

 

 

In the rear disk brakes that have E-brakes incorporated into them there is a shreaded stud internal that the E-brake portion has an internal mechanism to spin the piston on and tighten it against the pads as they wear.

Again, somewhat true. WHAT TURNS THE THREADED STUD? Hint: It is NOT activated by backing up.

 

 

The caliper is getting too tight and warped the rotor.

My point is that you aren't accurate in what is making the caliper too tight. In fact, I'm concerned that you haven't found the real problem yet. You also haven't confirmed that you've trued the rotor after installing the fresh caliper. Did you cut it, or replace it?

[Imp558]

I replaced it, it works fine now

[Imp558]

Yeah, it took a lot longer this time but the damn thing did it again. With the new SSEI occupying my workspace my options are limited so I fed it another brand new rotor and pads the other day. Once the Regal can come in I plan on reversing the rear lines at the Master cylinder/ABS conglomeration and watching to see if the problem followes it to the other side. That should tell me if it's in the line or before it.

At this point I don't think it's in the line since it flows so well, unless perhaps the liner inside the rubber line is broken and flapping like a reed valve or something.

[Schurkey]

In fact, I'm concerned that you haven't found the real problem yet.

 

Yeah, it took a lot longer this time but the damn thing did it again. With the new SSEI occupying my workspace my options are limited so I fed it another brand new rotor and pads the other day. Once the Regal can come in I plan on reversing the rear lines at the Master cylinder/ABS conglomeration and watching to see if the problem followes it to the other side. That should tell me if it's in the line or before it.

At this point I don't think it's in the line since it flows so well, unless perhaps the liner inside the rubber line is broken and flapping like a reed valve or something.

If the caliper is sticking because of a defective hose or other hydraulic system problem, you could jack up the rear end, have a helper step on the brake, release the brake...and see if the rear wheels turn freely.

[Imp558]

If the caliper is sticking because of a defective hose or other hydraulic system problem, you could jack up the rear end, have a helper step on the brake, release the brake...and see if the rear wheels turn freely.

 

It's like an intermittant dragging caliper, but once it does it one time the rotor is warped and headed for the steel scrap bin. It can spin free 100 pedal presses and then drag once or twice. I really have to get it in where I can swap the lines and bleed them, my guess is that it followes to the other side and probably pisses my ABS module off too. Probably looking at doing the underhood assembly.