Rear Brake disc heating.

[Kazz]

Hi, I find that the rear brake disc on my GS is very hot( too hot to touch) even with a short ride and moderate braking. Is this normal. There is also slight blueing on the disc.
The fronts remain cool. I did an experiment , rode 1.4 miles with TC and ABS off, used only front brake, both the front and rear discs were too hot to touch.
Any feedback welcome.

 

[abraxas]

Doesn't sound normal. Usually a result of riding with back brake on. Most commonly as a result of touching the pedal with your foot or brake binding.
When you put it on the mainstand does the wheel spin freely?

 

[Kazz]

Doesn't sound normal. Usually a result of riding with back brake on. Most commonly as a result of touching the pedal with your foot or brake binding.
When you put it on the mainstand does the wheel spin freely?

Hi Abraxas, it's hard to tell due to the final drive resistance, but I would say that it spins freely. I can get half a turn freely when I take off the pressure.

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[abraxas]

Fair point... When you press and release does it go back to same "resistance" immediately?
Also, check for a warped disc, does it do full revolution unimpeded?

Just trying to help you eliminate the obvious... By the time we do that, someone more experienced / knowledgeable may help us take it to the next level.
If you put a bit of info about your bike may help people help you diagnose.

Welcome to the forum mate.

 

[Santa-2512]

What year is the bike

ABS or non ABS

 

[TLSgazza]

Check the caliper is moving freely on the floating pins as well. They need cleaning and re greasing every now and then. How are the pads. Plenty of life and worn evenly.
Prise the pads apart a little and see if the wheel spins better. Then apply the brake again and how different it feels

 

[Kazz]

ABS 13 reg but 12 manufactured

 

[Kazz]

Hi,Thanks, yes on releasing the brake wheel goes back to the same resistance.

 

[Kazz]

Hi, if i twist the caliper to free the pads the wheel spins more freely. Then apply the brake and the Resistance is more.

 

[Kazz]

Does your rear disc get too hot to touch after about 2 miles and moderate braking.

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[abraxas]

Hi, if i twist the caliper to free the pads the wheel spins more freely. Then apply the brake and the Resistance is more.

I think that is a clue. Any resistance from the brake pads means constant friction = heat. There should be no resistance. Callipers should slide freely and discontinue contact with the disc. Maybe time to get intimate with some brake cleaner and grease... at least in the first instance. Good luck.

 

[Slipperyeel]

I think gazza12adv made the most likely suggestion. The pin that retains the pads gets corroded and notched - its easier to buy a new one. Motorworks sell a small kit with the tensioner spring and a pad rest (opposite side of the pin for the pads).

And the other thing is, the pistons could easily be gummed up with crud. Take the pads out, eek them out 7-8mm using the fit pedal, then clean.

I doubt a warped disc is the cause, though it's not impossible it's is now warped as a consequence, but I'd even hold out on that... There's not really much going on in the rear caliper.

Obviously if the reservoir is over filled it could feasibly cause the brake to lose its ability to back off.

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[Kazz]

I think gazza12adv made the most likely suggestion. The pin that retains the pads gets corroded and notched - its easier to buy a new one. Motorworks sell a small kit with the tensioner spring and a pad rest (opposite side of the pin for the pads).

And the other thing is, the pistons could easily be gummed up with crud. Take the pads out, eek them out 7-8mm using the fit pedal, then clean.

I doubt a warped disc is the cause, though it's not impossible it's is now warped as a consequence, but I'd even hold out on that... There's not really much going on in the rear caliper.

Obviously if the reservoir is over filled it could feasibly cause the brake to lose its ability to back off.

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Hi, Thanks for that, I have taken this issue to the dealer, who did a caliper service and changed the slider pin. But, the issue has not gone away, the disc is not warped, checked by spinning the wheel. Basically if i use the rear brake twice to come to 30 from 60, the disc is so hot that I cannot touch it for longer than a millisecond.

 

[Slipperyeel]

Hi, Thanks for that, I have taken this issue to the dealer, who did a caliper service and changed the slider pin. But, the issue has not gone away, the disc is not warped, checked by spinning the wheel. Basically if i use the rear brake twice to come to 30 from 60, the disc is so hot that I cannot touch it for longer than a millisecond.

How soon after braking are you feeling it? They get flippin hot, I mean impossible to touch soon after breaking. But they should dissipate heat pretty quickly, hence I ask how soon after stopping are you checking. Rear is always going to be hotter than the front.

Noted service was done with new pin fitted... the other parts? Did they say?

Just to get it off the list, is the foot pedal adjusted correctly? Just wondering if it doesn't have enough play? It should have some.

It sounds like it's either not backing off or it's being activated during riding. And if the disc is changing colour, you've got a real issue (I know you know that ).

Are you able to post a pic of the colour change?

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[Kazz]

How soon after braking are you feeling it? They get flippin hot, I mean impossible to touch soon after breaking. But they should dissipate heat pretty quickly, hence I ask how soon after dropping are you checking. Rear is always going to be hotter than the fron.

Noted service was fine with new pin fitted... the other parts? Did they say?

Just to get it off the list, is the foot pedal adjusted correctly? Just wondering if it doesn't have enough play? It should have some.

It sounds like it's either not backing off or it's being activated during riding. And if the disc is changing colour, you've got a real issue (I know you know that ).

Are you able to post a pic of the colour change?

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Hi, Pic attached, not the best but the blueing is visible.

https://paste.pics/b1977254f4eadfa9fe3935d432c9d6f2

 

[TLSgazza]

Hi, Thanks for that, I have taken this issue to the dealer, who did a caliper service and changed the slider pin. But, the issue has not gone away, the disc is not warped, checked by spinning the wheel. Basically if i use the rear brake twice to come to 30 from 60, the disc is so hot that I cannot touch it for longer than a millisecond.

I wouldn't be too happy with the dealer if they looked at it and sent you away with a faulty brake still.
So they replaced the pads retaining pin, yes?
Did they drop the pads out. Remove the caliper and check the piston is moving freely?
Did they remove the caliper from the sliding pins and make sure they are clean and well greased as I said in an earlier post.? I know you said the replaced one but there are 2.
If the caliper doesn't move on the pins it will most likely make the rear pad stay in contact with the disc. Hense the heating up.
You said the front discs are getting hot too. Does the front wheel spin freely.
The hand guard isn't touching the front brake lever is it. Not likely though because I think the bike would show a fault if it is. Brake lights are going on and off when they should do?
I still think it's something to do with the rear caliper either the sliding pins or sticking piston.
One other thing are the pads moving freely in the caliper? I should think so if the dealer looked at them.

 

[Steptoe]

Stand at the right rear of your bike facing the brake caliper. Grab and hold the rear subframe, place your foot on the outside of caliper, where it says BMW, hold the subframe and push the caliper with your foot. This should cause the caliper to slide on its two sliding pins and spread open. Operate the rear brake a few times to close up the caliper, then repeat the procedure. Do this a few times and your problem should be cured. If the caliper doesn’t spread when you push with your foot then it’s totally seized. It’s a good idea for everyone to do this at least once a month anyway, as it stops the rear caliper from seizing.

 

[Kazz]

Update, did the step on the caliper. Also I noticed that brake fluid was seeping out of the front brake fluid reservoir. No leak just fron under the cap. Used a paper towel and reduced the level. Checked the rear its below the max mark.
Rode the bike without applying any brakes front or rear. Checked after 2 miles disc was slightly warm. Did it again and again with slight braking, the disc is not heating up.
The wheel also moves a lot more freely.
So hopefully problem solved.
Thank you everyone for their advice.
Guess the disc heats up very quickly when used.

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[botus]

perfectly normal

if you have linked brakes the rear does a lot of the work. Its one reason these bikes stop well.... Mine almost glows red when I'm giving it some... I guess if still running tractor tyres, stoppies from 130 may not be part of the game you play but the bikes perfectly happy doing it.... but the rear does get exceptionally hot in a very short time.

There was a post of exactly the same concern middle of last year

 

[TLSgazza]

Update, did the step on the caliper. Also I noticed that brake fluid was seeping out of the front brake fluid reservoir. No leak just fron under the cap. Used a paper towel and reduced the level. Checked the rear its below the max mark.
Rode the bike without applying any brakes front or rear. Checked after 2 miles disc was slightly warm. Did it again and again with slight braking, the disc is not heating up.
The wheel also moves a lot more freely.
So hopefully problem solved.
Thank you everyone for their advice.
Guess the disc heats up very quickly when used.

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That makes sense. Too much fluid might be pressurising the system and applying the brakes I suppose.
On one occasion when I pushed the front pistons on both calipers in to fit new brake pads fluid leaked out of the overflow pile at the rear of the engine. Made me wonder what was happening. Mine is a servo abs model though.