Hot Rotors, What Do You Think???

[MGreer]

I replaced the pads on my truck last year and found a problem with the slide pins. The lower slide pins on all four calipers were frozen in place or very hard to move. I took the rubber boot out and rust was built up in the hole the boot fits in which squeezed the boot tightly against the pin.
I took a round file and cleaned the holes up until the pins slide like they should. If your pins are hard to slide, that could be one of your problems.
Also, this made the pads wear at an angle. The end that the pin wasn't frozen the pads were thicker than the other end of the pads.



View attachment 89604

 

[JohnHaggerty]

The question I now have is what parts to change? I'm leaning towards only the one caliper, both sets of pads and lots of fluid. I find it hard to believe that the rotor is damaged. That's a lot of steel at only 680 deg F for what was probably no more than 20 minutes. I see nothing on the rotor that makes me think it needs to be changed. What are your thoughts?

Thanks!

 

[jhenderson]

Calipers should be replaced in pairs.

 

[cerberusiam]

You will want to turn the rotor since it is probably glazed from the heat. Before turning it though check the runout to see if it is still pretty straight. These composite rotor are not hard fastened and they want to warp over tine and especially if they get hot. No use wasting time and money on turning a rotor that is already warped.

 

[jelag]

There is no reason to change the calipers in pairs unless both are damaged... if a caliper functions and retracts when the pressure is off there is no problem with it... within 100 miles of a rotor being turned... the surface will glaze (POLISH) from the action of the friction... after all the friction is an abrasive... often in the shop if a rotor needed to be turned and had a hot spot, we'd grind out that hot spot with a specific tool attached to the brake rotor lathe... The qualification of the rotor is based on heat spots (blue dots or raised metal) and/or out of tolerance using a dial indication, & groves in the surface from a rock, or metal to metal contact...... typically each manufacture might/could have their own specification for run out... we used +- .002" and have had lots of happy customers over the years... each rotor is stamped with a minimum thickness that is put on the rotor by the manufacturer... it is their intent for an equal amount of material to be removed from each side of the rotor until the minimum thickness is reached than it scrapped.... we used a s rule of thumb that once side shouldn't be more than .040 - .060" thinner than the other... since you can't actually measure this... we would look at the edge of the rotor and make the decision.... BTW this is on a rotor that ventilated.... its expected that as the rotor changes temperature that some material will slough off.... we'd run a wire brush through those ventilation slots with a wire bottle brush to keep the loose material out of those slots...

I've never seen a rotor fail for other than a mechanical failure... pads down to the metal, a rock stuck in the pad and it grinds through the rotor... heat checks and cracking from heat... all caused by heat...

 

[jhenderson]

I've never had a brake pull in a vehicle where calipers were replaced in pairs. I can't say that about vehicles that a customer would only authorize replacing one.