rear disk heating excessively

[NZDeano]

I noticed my rear disk/rotor was excessively hot after a good ride the other day. It has even tinged the disks colour. It was after a sprited ride on local twisty roads on a very hot day. After allowing it to cool down over night I raised the rear and checked that the wheel could turn freely and it did without any rubbing. Pressed and released the pedal whilst turning it, no problems, pistons were letting go and returning.
Am I correct that the likely causes of disk heating might be one of the following: Warped rotor? Sticking pistons not releasing properly (for whatever reason)? Excessively worn pads (causing over extension)? Unitentionally riding with foot resting on pedal and/or overuse of rear brake? Wheel alignment issues?
Any further suggestions of possible reasons?
If disk has heated to the point of discolouration (bluish tinge) will it be OK or need to be replaced?

[Tiger-G]

Hi,

The first thing that springs to mind is just resting your foot on the lever as your riding. When your riding and not using the rear brake, it's quite an effort to keep your foot up and hovering above the lever, and sometimes it can drop and just start to put pressure on the lever. I just let mine dangle to the side.

If it's not that, then the only thing I would expect it to be is binding brake pads due to either the calipers not releasing or some grit / dirt on the sliders ??  When did you last change the caliper seals or do some maintenance on your brakes ????

Take it out again, make a concious effort not to use the rear brake. Find out if it's heating up, and if it isn't, then it may have been your foot resting on the lever. If it does heat up, then have a good look at the caliper.

I would say it would be ok to still use the bike, but if you feel any pulsing through your foot when braking, then the disc may be warped and need replacing.

Keep us posted and let us know how your get on  :-)

[blacktiger]

Hi,

The first thing that springs to mind is just resting your foot on the lever as your riding. When you're riding and not using the rear brake, it's quite an effort to keep your foot up and hovering above the lever, and sometimes it can drop and just start to put pressure on the lever. I just let mine dangle to the side.

Then you need to adjust the height of your pedal. Undo locknut on pushrod going into the master cylinder and twiddle so that the pedal is just below where you rest your foot.

I agree with everything else. The calliper catches a lot of crap from the rear wheel so it needs a good clean more often than you'd realise.

[NZDeano]

Thanks for your answers guys.
I did what you have suggested and triple checked I wasn't resting my foot on the pedal. Today I will thoroughly clean and inspect everything.
I have had a rear wheel alignment issue lately and was wondering if it could be to do with this. Heres my reasoning: The rotor/disk is attached to the wheel. The calliper is attached to the frame. If the alignment had been out for a significant period of time the pads would wear in a certain fashion/angle. Then when I re-aligned it all the pads are re-wearing so to speak.
What do you think?

[blacktiger]

I have had a rear wheel alignment issue lately and was wondering if it could be to do with this. Heres my reasoning: The rotor/disk is attached to the wheel. The calliper is attached to the frame. If the alignment had been out for a significant period of time the pads would wear in a certain fashion/angle. Then when I re-aligned it all the pads are re-wearing so to speak.
What do you think?

Not really because the pads should get knocked back when they contact the disc without pressure in the system. The only way pads remain in contact with the discs enough to do that is when the sliders a crudded up or the pistons are sticking which is probably what the problem is in the first place.
Time to take the calliper off its mount and attack it with a tooth brush and a can of brake cleaner.

[Mustang]

 

[Chris Canning]

Time to take the calliper off its mount and attack it with a tooth brush and a can of brake cleaner.

Non of my bikes have ever seen a winters day in their lives,but I strip pads out of all the bikes and clean the calipers and the pads at least twice a year,hence why I can do it with just a cloth and some WD,the more often you do it the easier and faster it is.

[NZDeano]

Thanks for all help.
So to report back about this:
Yesterday did as suggested and removed the calliper and cleaned everything thoroughly. Polished the pistons which were gungy. Pads are on wear limit so will replace this week.
At the same time finally worked out procedure to correct my rear wheel alignment issue by slackening the spindle nut and turning the eccentrics opposite to each other until both front & rear wheel were aligned with a straight edge, tightened pinch bolts, retorqued spindle nut, then loosened pinch bolts off again, adjusted chain, tighten pinch bolts.
Very happy with alignment at this point, turn back wheel. Shit somethings still rubbing on disk. Turns out to be the alloy part of the caliper. Had to slightly readjust wheel alignment to stop it happening.
So wheel alignment can effect the way the disk lines up through the calliper, but I am guessing that because mine does this with the alignment supposedly correct and with an ever so slight tweak to the left it dosen't that either my calliper or mounts are slightly out or possibly tires?
Are there any tips for bleeding all the air out of the system once it's been fully pulled down. My pedal is staying spungy no matter how many times I repeat the procedure. Thinking of trying to pull it through with a big arse syringe maybe? Any suggestions?

[blacktiger]

So wheel alignment can effect the way the disk lines up through the calliper, but I am guessing that because mine does this with the alignment supposedly correct and with an ever so slight tweak to the left it dosen't that either my calliper or mounts are slightly out or possibly tires?
Are there any tips for bleeding all the air out of the system once it's been fully pulled down. My pedal is staying spungy no matter how many times I repeat the procedure. Thinking of trying to pull it through with a big arse syringe maybe? Any suggestions?

Check that the bolt into the swing arm on the calliper torque arm is tight. If loose that could allow the calliper to wander.

Bleeding the rear brake is easier if you take the calliper off its mounting and hold it/suspend it in the air so that any bubbles can migrate upwards towards the bleed nipple easier.

[NZDeano]

Cheers BT,

So wheel alignment can effect the way the disk lines up through the calliper, but I am guessing that because mine does this with the alignment supposedly correct and with an ever so slight tweak to the left it dosen't that either my calliper or mounts are slightly out or possibly tires?
Are there any tips for bleeding all the air out of the system once it's been fully pulled down. My pedal is staying spungy no matter how many times I repeat the procedure. Thinking of trying to pull it through with a big arse syringe maybe? Any suggestions?

Check that the bolt into the swing arm on the calliper torque arm is tight. If loose that could allow the calliper to wander.

Bleeding the rear brake is easier if you take the calliper off its mounting and hold it/suspend it in the air so that any bubbles can migrate upwards towards the bleed nipple easier.

sure enough it was slightly loose.
If you take the calliper off to bleed do you need to place something between the pads to stop them over extending????

[cosmo]

Yes. Bit of wood will do nicely.

Cosmo

[blacktiger]

Yes. Bit of wood will do nicely.

Cosmo

Or a spanner.