Rear disc is hot

[dntemp_ca]

I thought I had a dragging rear brake pad, but cleaned that up and the rear disc is still hot to touch when I stop. Rear wheel rotates fine, when on centre stand...no binding, grinding or dragging. Is a hot rear disc normal perhaps since it's out of any airflow for cooling?

[prometheus578]

Carefully take a screwdriver and pry apart the rear pads. Try to put it on the metal part, and not the actual pad surface. (Don't need to break a chunk off)
Good, now with the pads loose and not touching the rotor, go for a good ride.
DO NOT USE THE REAR BRAKE!
Stop somewhere, and carefully feel the rotor. With the pads slack... they shouldn't have been touching at all. Is it still hot?
If not hot, then the pads were rubbing... stuck or grungy caliper piston, and needs to be taken apart and cleaned.
If still hot.... you may have bearing troubles.... bad bearings heating up... heat transfers to the hub and rotor. How's the hub feel?
The final drive unit may be suspect, as well, but these are known to build up some heat due to the friction of the gear meshing and the oil.

[TopCatGr58]

Well,

Dennis, mine also gets hot, too hot to touch comfortably, but not seizing hot! And I've got the piston lever set fairly loose as well, so that I have to press a moderate amount before I can lock up the rear brake. However, I haven't lubed the rear brake lever shaft, and it's been suggested that it can be slghtly inducing drag on the action of the lever, keeping more pressure on the MC, and therefore the calipers than what is wanted. But there is supposed to be a slight amount of drag of the pads against the disc!
T.C.

[prometheus578]

True, TC. I just jumped to the conclusion that his hot was HOT! Could be just the normal temperature.

[Ken Talbot]

The rear rotor on SWMBO's 'H also tends to run a bit on the warm side. In her case, I'm pretty sure the problem comes from a very slight warping - not enough to put it out of spec, but it seems to be enough to cause just a bit of friction and a very, very slight pulsation in the pedal.

We were out for a spin a couple of weeks back and were oving along a bit faster than normal. I surprised SWMBO when I pulled up short at a turn-around spot where she had been expecting to keep on going. She got on both brakes hard enough with her stainless lines to get stopped without incident. I checked her rotors like I do just ebout every time we stop, and I $%% near burned the skin off my fingertip on the rear rotor. I thought I was in for a system cleaning when we got home, but we pulled over for another check about half way home, still travelling a bit oon the fast side. She made a point this time of not using the rear brake. Thankfully, the rotor was back to its mildly warm condition.

I gues the message is don't get too excited about having a hot rotor unless you have been very careful not to use that particular brake at all. Even just a single, hard application from speed will warm them up considerably.

[dntemp_ca]

Not red HOT, but too hot to grab onto. I can touch and hold the front discs no problem...and they are moderately warm. If I wipe a wetted finger across the rear disc, it evaporates quickly. I went for a ride and stopped without using the rear ....the disc is still as hot. Looks like I'll have to take the rear master cylinder apart and check for spooge poop. How do you get the rear m.c. out of there anyhow?! That looks like a real tight spot!

[Ken Talbot]

It is a bit of a tight spot, but it will come out. You'll have to push in a bit on the lower end of the plastic inner fender. It will pop loose from its anchor so you can twist it forward to get enough room to get the MC out. By then, the plunger should have dropped from the piston in the MC too. If you loosen off the brakeline retainers all the way back, and unbolt the caliper, you can get the entire assembly off without opening it up and spilling brake fluid everywehre. The reverse of this means you can also prime and bench-bleed the system before reinstalling it.

[dntemp_ca]

Thanks for the great tips, Ken!
That's going to save a world o' hurt on my brain cells (and knuckles)!
Man, is there a nut or bolt you HAVEN"T taken off these machines?!

[Ken Talbot]

There's a few, but not many...

[dntemp_ca]

You da man, Ken!