Disc brakes temperatures

MrWizard wrote:

JRscooby wrote:
I can't say what temps to expect but unlike drum shoes, the disc pads rub all the time not just when brakes are applied.

I did a Google check on that very topic because a friend of mine thinks like you do, and I think differently, I think there is suppose to be an air gap
Pads that touch mean friction and drag, they will wear more, wear it faster, and get hotter,

What I found was the statement and drawings, that when brake pressure is removed the bellows style piston cover retracts the piston and disc/rotor "run out" forces the pads away from the surface allowing for an air gap between pad and rotor, no value was given for the size of the gap

They do not touch when wheels are turning aka driving down the road

Think about this
A tire with a 4ft circumference will spin 1300 times in one mile, if you are driving 60mph that tire is spinning at 1300 rpm , if a brake pad is touching the disc rotor, it and the rotor are going to get hot, that is what friction does, brake pads have lots of friction capability or your vehicle would not stop

Go to a car race at night and it might make you rethink or every car out there is not set up right. I also think there is a gap " very small" but seeing them glow is another story. I have pulled brake pad off right after driving and you must have good gloves on to take them off. But I agree with you on the gap. I try to get runout to .002 or zero if I can. You will know it when they go out of round. Vehicles with a good brake job will not build up of rust or other stuff on the rotor due to the very low runout. They shine. Remember they are floating calipers.

JRscooby wrote:
I can't say what temps to expect but unlike drum shoes, the disc pads rub all the time not just when brakes are applied.

I did a Google check on that very topic because a friend of mine thinks like you do, and I think differently, I think there is suppose to be an air gap
Pads that touch mean friction and drag, they will wear more, wear it faster, and get hotter,

What I found was the statement and drawings, that when brake pressure is removed the bellows style piston cover retracts the piston and disc/rotor "run out" forces the pads away from the surface allowing for an air gap between pad and rotor, no value was given for the size of the gap

They do not touch when wheels are turning aka driving down the road

Think about this
A tire with a 4ft circumference will spin 1300 times in one mile, if you are driving 60mph that tire is spinning at 1300 rpm , if a brake pad is touching the disc rotor, it and the rotor are going to get hot, that is what friction does, brake pads have lots of friction capability or your vehicle would not stop

Whenever I do brakes on cars (which is often) the biggest thing I look for is equal temps on both sides. As long as they're about the same I call it good to go.

If something isn't right the gun will let you know it.

As someone that has been doing this for years, I can tell you that the results can be confusing until you understand what you are looking at in very complete terms.

The walk around did tell me that a rear wheel bearing was just a little too tight. The red numbers were right and I got that fixed before it became an expensive issue.

Our classic (boarding on antique) coach is a disk and drum set. I am also paranoid because it is old (so am I) and I really like to head off problems before they are expensive. We did have a caliper hang up and the routine temperature walk around told me about it early on and it was an easy fix.

What did puzzle me most was that when I did the walk at a mid-day stop, all the brakes on one side were hotter than those on the other.... We had been going west and the left side was hotter. When I was the reverse when we were home bound....

We now have an IR gun dedicated to the coach.

Matt

Think you are going to have a hard time. Brake pad are made from different material and each will have they own temp readout. Disc will be one temp, and drums will be another. You might find the info from whom made your brake. On my sport car my pad are cooler than on the AWD 4 runner. They both have Disc and both are very good brakes. Have fun with your new toy.

Just went out and check the sport car and it show in history that the pads run right at 185 average. All 4 are different and the 185 was the middle range. They are 5+ degrees different with the fronts the highest. My front pads are one brand and the rear another. On braking hard it shows 250 plus.

Never seen those numbers. Average your temps for a couple of weeks? “Shoot” other RVers’ wheel temps?

I can't say what temps to expect but unlike drum shoes, the disc pads rub all the time not just when brakes are applied.