Rear disc brake issue- need advise

[OR VietVet]

Likely that they machined too thin and then the warp shows up when enough heat is transferred to the rotor surface.

Like I have said before: These rotors are "BIC" rotors.

 

[Rocket Man]

But he mentioned it was reputable machine shop. Curious about how they ******* up machining the rotors and the condition of brake lathe used

Understood but the rotors were the issue. Like others I no longer have standard rotors machined. That was done back when they were designed to be surfaced. These days very few are with the exception of some like Brembo or Wilwood that have enough material to be removed without compromising them.

 

[blueinkd]

Understood but the rotors were the issue. Like others I no longer have standard rotors machined. That was done back when they were designed to be surfaced. These days very few are with the exception of some like Brembo or Wilwood that have enough material to be removed without compromising them.

I was agreeing with you. Was trying to understand how they jacked that one up. But someone made a good point that rotors may have not had enough meat to even machine in the first place. Warped on initial use after reinstalling.

 

[badtothe bone]

A man goes to school, pays $50,000 to get an education to learn how to work on automobiles.. Then some shade tree mechanic comes along with his box full of Harbor Freight and Salvage tools and wants to be like him. Only then he finds out that just because he owns a wrench and a socket and a hammer and a c clamp, doesn't make him a mechanic.
So why is the brakes thumping?
Well, first there is cast into the rotor - a minimum thickness.
Only the shade tree mechanic doesn't own a micrometer.
Then there is the physical inspection - when the rotor was cut, it removed all traces of the cracks in the rotor.
Out of sight, out of mind.
Only the cracks are still there..

Unlike the Honda or Toyota or Hyundai car your wife drives 100,000 miles with the original brakes, the darn Chivie can't go 40,000 miles on one set of rotors and pads - unless its all highway miles, which doesn't count in my book anyways.

So there is lot's of things most good mechanics learns how to read the signs - like a hunter in the woods..

I know guys that will throw away the brake calipers and caliper brackets and the old rotors and start with all new, along with occasionally even replacing the brake lines which can and do go bad.

Along with all of that, flushing all the brake lines and putting in new brake fluid. Cleaning the inside of the rim of the wheel and the axle flange and applying liberal amounts of antiseize to everything.

Lets' just say I've been down this road and got burned multiple times doing a brake job where all I thought it needed was new pads or resurface the rotors.

Them junk Chevies and GM junk brakes caused many a sleepless night and skinned knuckles and multiple trips to Advance Auto Parts for extra parts.

Not to mention how many times I had to machine out the bolts from the flange that holds the backing plate to the axle.

Brake job today is a lot more then just changing out the pads and hoping that it will work. How many times I needed the Tech II to pulse the anti lock brakes to bleed the brakes properly so I had full pedal when I was done - don't ask!

Time to buy some new rotors son and maybe even some of the other stuff I mentioned - throw money at it till the problem goes away! No Crystal ball here, so no guarantee's that any one solution by itself will work for you!

 

[bladenbullet]

i'm glad you found a solution and at the same time sorry you had to endure some of the responses...

the machine shop didnt "jack" anything as the op's runout measurements indicated...and rotors do not "warp" when hot then return to next to no runout cold...

a likely possibility is the rotors had hot spots in the metal...when rotors are machined and cut with a tool bit the bit will skip over hard spots and leave them in the surface of the rotor as an irregularity...temperature can effect the areas with hot spots differently and cause problems with pad noise...the cast material used today is poor at best due to raw materials not being what they once were, including reclaimed material missing trace elements...this is the reason so many shops are giving up on machining rotors and playing it safe with replacement...i would be willing to bet that if you checked runout on the new rotors it would be more than the very small but within specification numbers you got with the machined ones...

for the record...on car machining is much more accurate and leaves a superior finish with a rotor matched to hub runout...but still wont eliminate hard spots if they exist....

**** happens...nice job isolating the concern and correcting it...chalk it up to experience...

 

[OR VietVet]

Your statement: "and rotors do not "warp" when hot then return to next to no runout cold..."

My statement: "The warpage happens after they get hot and then dissipates a bit when cooled."

Where in my statement does it say what you insinuated? FAKE NEWS! Or am I mistaken about what you are implying?

 

[bladenbullet]

Your statement: "and rotors do not "warp" when hot then return to next to no runout cold..."

My statement: "The warpage happens after they get hot and then dissipates a bit when cooled."

Where in my statement does it say what you insinuated? FAKE NEWS! Or am I mistaken about what you are implying?

you cant be serious...that's exactly what your statement says...lol...

 

[OR VietVet]

I said it dissipates a bit when cooled and did not say returns to next to no runout cold. I never insinuated it goes back to no runout or even close to that. I said it cools and diminishes a bit till heated again and then will be more noticeable. I think everyone else can see that but you can't.

Not going to argue the point with you. Your mind is made up and you know way more than I do. I give up to the all knowing of your prose.

I am not worthy.

 

[Xsbank]

My information is that rotors do not “warp.” They definitely have runout built in as this is necessary to get the pads to retract so they don’t drag. The pulsing you get through the pedal etc, which is commonly called warp, is a result of pad material being laid down on the hot rotor and causing areas that have different coefficients of friction than other areas, causing “warp.”
Turning rotors is a have, it does remove the friction anomalies but it removes material that is needed to absorb heat and messes with runout. If you have “warp,” replace the rotors. The only correct solution.

Keeping bad rotors for long will damage your tires too, so don‘t mess with it, get ‘er done!

 

[OR VietVet]

In a properly functioning disc brake system that has properly functioning hardware and lubed slide areas, the caliper piston settles back a bit after you release pressure with your foot on the brake pedal. That is caused by the square cut seal in the caliper bore that twists back after pressure is released. The pad is then in limbo with no pressure against it forcing a very minimal rub of the pad on the rotor surface. That ever so slight rub is not going to build enough heat to override the air flow thru there that carries the heat away. I have machined literally gobs of rotors in my days at the shops. I have machined where there is maybe a hair's width of runout on that rotor surface. The runout that would then be there is from mounting to a hub and that will contribute to the runout you speak of to help push pad back a very tiny amount. I say warp but a better description is "high spots" and that, when bad enough, will cause brake pedal pulsation.

If this is wrong, I truly hope to hear what I am missing.