800 degrees brake temp! - Diesel Forum

dannyleo · 06-19-2009, 09:34 PM

I smelled some brakes the other day just doing some normal driving. Got out and checked the right front and it was 700 degrees at the disc. Waited for it to cool down and then went out and tried to 'loosen' it up, everything appeared fine. Drove a ways more and both fronts were at 350. (I was trying to dislodge anything that might be stuck by forward and backward with hard, ABS engaging stops. Drove to work, 65 miles, all okay. Got half way home, smelled something, 800 degrees!

I replaced the calipers and it appears that they were so rusty around the clips it was just riding against the rotor.

QUESTION: What else might have been screwed up? The rotors and engagement all feel fine, so it doesn't appear they were warped. I thought brake fluid had a boiling point of 350-550, depending on the type you got. As long as there is sufficient quantity, am I still okay?

chuckster57 · 06-19-2009, 10:28 PM

Understanding Brake Fluid - RPMnet.com tech articles - by AFCO racing

If your reading 800 degrees at the rotor, that doesn't mean the fluid is the same temp. The point of friction will be hotter than the surounding metal. Some heat will dissipate through the caliper and the built in venting of the rotor. Any way thats way too hot for comfort, I am suprised that a rotor wasn't warped.

Quote:

I replaced the calipers and it appears that they were so rusty around the clips it was just riding against the rotor

Did you use a good lubricant when you put it back together? I use a light coating of disc brake rated wheel bearing grease, others use a silicone based lube found in the little "condiment" packs on the parts counter.

dannyleo · 06-20-2009, 07:06 PM

I cleaned the caliper mount and the slots for the clips with a small steel brush to get all the rust off and used brake cleaner. I did use the grease, but only on the back of the pads and on the pins. I didn't put any where the clips are.

chuckster57 · 06-20-2009, 08:11 PM

Shoudn't use any grease on the backs of the pads. I use "disc brake quiet" or something like it. It is an adhesive that helps hold the pads to the caliper so they retract off the rotor when you take your foot off the pedal. The surface that the calipers slide on to stay centered on the rotors is where the grease should be.

FMTRVT · 06-20-2009, 09:34 PM

800°F really isn't all that high. Since you haven't mentioned anything about what vehicle this is it's hard to reply with any advice. But I'd be checking the piston boots and any slide boots if present.

As mentioned, there is a temperature differential from the friction to other parts of the brake system. If the rotors were at 800°F, then the pads were probably at 600°F or thereabouts. Theoretically, the temperature at the friction interface between the friction material and rotor gets up into the thousands, but it's at the molecular thin level.

I'd be more worried about "disc brake quiet" then I would having silicone based grease on the backs of the pads. Honda and Toyota for decades has used silicone grease with moly on the backs as a very effect brake noise suppressant.

Two graphs showing what these trucks go through during the FMVSS procedures for public release. One is a disc / drum and the other disc / disc.