Hot rear rotor.

[howie ronic]

Re: Rear disc heat

stevepsd I'm moving from Seattle to Southern Oregon. You stated that the ambient temp was 78. I don't think our high temperature ever got over 78 for the summer last year . We wuz robbed!

 

[stevepsd]

Re: Rear disc heat

stevepsd I'm moving from Seattle to Southern Oregon. You stated that the ambient temp was 78. I don't think our high temperature ever got over 78 for the summer last year . We wuz robbed!

Well...the 78 was at my CA home in the Mojave Desert. It's a fair bit cooler on the Southern Oregon Coast, the high last year was only 74F !

 

[Dogdaze]

Firstly, if the mods want to merge or eliminate this thread I'm good with that. I did do a search and none of the answers were to my question. So, got going early today in a small 450km ride from Zurich to Davos and through the pass's (several), got home about 6 1/2 hours later. Smelt either clutch burning or brake smell. Figured it's not the clutch so touched the rotors, front warm but not hot, rear, HOT. WTF? Last hour was highway, a few turns off the highway and I'm home with very little braking, I almost never use the rear brake because of the UBS. The wheel spins, a little grinding, not unusual to say the least, so changed out the pads with EBC organic, yes they wear quicker but cheaper than rotors. The caliper piston moved back with hand pressure, not binding at all, bolts were all greased several weeks ago and not 'sticky' free mpovement. So, any ideas or is this normal? I mean hot, not warm.

 

[tomatocity]

Have you tried bleeding the rear caliper? My 2012 had this problem early on and the dealer bled the rear caliper. Other than changing pads one time, never had a concern.

 

[Dogdaze]

Yep, did that. And the clutch while I had the tubes out....

 

[Don in Lodi]

I've always been concerned about a boot toe resting on the lever. I lowered the lever. ::008::

 

[Dogdaze]

Could be the boots, I wore 'proper' MC boots today, but I rest the balls of my feet on the peg, hardly ever on the arch, and when on the arch the toes are below the pedals...... another run this week me thinks???

 

[xtadvrider]

Rear Discs Overheating

• Hi All!
  
  I hope I'm posting in the right section. I have a 2013 S10 which I bought new from the dealer last year.
  
  I also got these disc locks to serve as a deterrent from theft. Using these disc locks after riding is when I noticed that my rear discs were super hot to touch compared to the front discs. When I say super hot, it is really really hot. I don't think the discs should heat up so much under normal usage.
  
  Anyway, since it was new, I took it to the dealer. The first thing they told me was I had a lazy foot and I was probably doing it accidentally. But I had the dealer's technician take it for a ride and he experienced the same phenomenon. They even measured the temperature using a temperature gun to be sure. After some back and forth with Yamaha, they replaced the rear disc for free.
  
  Fast forward a year after winter, I'm riding my bike again and I'm noticing the same overheating. It is definitely not me.
  
  So my questions are:
  
  • Is this normal? I don't want to keep taking this back to the dealer if it is.
  • If not, what are my options? I've already had the disc replaced. Could the ABS have an issue? I'm concerned about going on longer trips with such critical issues.
  
  I may probably be out of the factory warranty period now but I do have the YES warranty and I want to get this problem fixed once and for all before that runs out. I love my bike and I want to to keep it for a long time.
  
  Your thoughts are appreciated.
  

 

[Nikolajsen]

Re: Rear Discs Overheating

Hmm...no I don't think it should be that hot.
I think you may have a piston in the caliber, that is not "moving free" (meaning that it will brake a little all the time). That is the normal issus when brakes gets hot.
I really don't think the ABS have anything to do with this.

When on central stand, and you turn back wheel, can it turn easily?
And when turning 1 turn, is the 1 (or more) places on a turn, where the turning get harder? If so, the disc might not be completly level.

 

[hobdayd]

Re: Rear Discs Overheating

I was in the business of developing disc brakes and braking systems for many years for major OEM's working for a tier 1 brake supplier.

I might be able to help but there could be many things driving your "hot" disc issue.

First, I need empirical data.

Can you turn the wheel by hand easily when everything is cold? (There will be some residual drag but you should be able to rotate the wheel without too much effort).

If you ride the bike for 2 miles at 50 MPH what is the rear disc temperature if you do not touch the brakes (front or rear as they are linked) starting from cold to touch rear disc?

All disc brakes generate heat off brake due to the friction material being in contact with the disc but if the brake is not applied I would suggest under 50 deg. C to be OK if ambient starting temperature is beliw 25 deg. C.

Let me know what you find...

Don

 

[Checkswrecks]

xtadvrider -


First off, welcome to the group.
::004::


Merged your thread with this existing one so you can see that you're not the first to bring up how hot the rear disc can get. Like hobdayd wrote, if the disc isn't warped and you can turn the wheel by hand, that's a good start. Two other big clues are if the bike is eating brake pads and getting bad gas mileage. If you pull in the clutch when riding does the bike coast or seriously slow right away?


Obviously, gas mileage and pad life are related to how hard you ride, but if you aren't going through both then I wouldn't worry too much.

 

[xtadvrider]

Nikolajsen, hobdayd & Checkswrecks

Thanks for taking the time to respond. I don't have a temperature gun with me. I will buy one tomorrow and respond to each of your suggestions. More to follow. Please standby.

 

[Nikolajsen]

::008::
(It seems we all respond almos the same to you, never did figure out why this offen happen )

 

[tallpaul]

First, I need empirical data.

If you ride the bike for 2 miles at 50 MPH what is the rear disc temperature if you do not touch the brakes

Whilst I don't doubt the validity of the test, finding anywhere to perform that test safely would be very difficult for most people, certainly here in the UK. Maybe with the long straight roads you have in the US it may be do-able, but coasting to a stop after a 2 minute spell at 50mph with no braking requires a lot of road, even using engine braking.

 

[hobdayd]

This test is easily done. Its important to have data!

A disc brake that has no pressure applied from the hydraulic system can still cause "parasitic drag". In fact, the system is designed to run with minimal pad to rotor to piston clearance so that lever travel is kept to a minimum. Mc hydraulic actuation only displaces small volumes of brake fluid for each application.

The brake piston has a seal that sits in a shaped groove that is "designed" to retract the piston from the pad backplate a fraction of a mm to ensure clamp is not generated on the friction couple...(pads and disc)...this is called piston seal rollback. Rollback can change throughout the life of the friction couple and is influenced by pad wear, temperature, disc run out, friction couple expansion etc...it is a very complex system before you even start to discuss hydraulic actuation.

The seal alone can generate enough force in normal operation to drive off brake temperatures up to 65degC.

This is "normal" but worrying to the average user. 65degC is too hot to touch but not much for a brake friction couple that can hit 500degC easily. (1,100degC on a truck disc brake doing an alpine descent...go YouTube it).

A dragging brake will generate much higher temperatures than 65degC so it is important to find out if this is "normal" friction couple off brake heat generation or dragging brake heat generation.

If the latter there can also be many reasons ..before we move on to considering the hydraulic system. Any remedy will start with cleaning the brake up making parts move freely. Don't use just any old grease as brake rubber components need special grease to avoid contamination and swelling. Only use grease where specified. At this point you can also push back the piston and cycle out then recheck. This will "reset" the piston seal rollback and affect the clearance between the friction couple and the piston.

Don



Even

 

[Checkswrecks]

The Doctor and his glowing ceramic discs.

 

[Squibb]

With a single piston caliper, it could be that it's just not sliding on the pins freely; not uncommon on GSs, which was mentioned earlier. Usually throws up wear on the pad being addressed directly by the piston, Slipping out the pads, which should have a similar residual thickness, & checking the pins slide freely is a pretty straightforward double check if this still troubles the OP.

 

[DaveTDM]

Whilst I don't doubt the validity of the test, finding anywhere to perform that test safely would be very difficult for most people, certainly here in the UK. Maybe with the long straight roads you have in the US it may be do-able, but coasting to a stop after a 2 minute spell at 50mph with no braking requires a lot of road, even using engine braking.

finding a straight road in Whitworth is the first impossible part

 

[xtadvrider]

All!

Thanks for your patience. It's been raining over the weekend and I couldn't go out for a ride. I was finally able to head out last night and do all the mentioned tests. Here are the responses:

-----

@Nikolajsen

On the central stand, I'm able to turn the wheel. There is some resistance (which is to be expected I guess) but I don't think there was any place where it was getting "caught". I believe the disc is level.

@hobdayd

Yes, I was able to turn the wheel when cold with the expected residual drag.

It was hard to not use the brake but I did manage to do between 2~3 miles at 50-55 MPH. Here are the temperatures as requested:

Pre-Ride Cold Temperatures:

Front: 17 deg. C
Rear: 21 deg. C

Post-Ride No Break Temperatures:

Front: 20 deg. C
Rear: 28 deg. C

I also went to ride some more after the "no brake test" with using the brakes and here are the temperatures:

Front: 21 deg. C
Rear: 26 deg. C

It was a constant speed ride with minimal braking and I believe the temperature with the brakes is lower than the temperature without brakes because the ambient temperature dropped pretty quickly after sunset. It was about 72 deg. F when I started the ride and by the time I got back it was 66 deg. F. That or the temperature gun I brought from Harbor Freight is useless.

@Checkswrecks

When I pull in the clutch during the ride, the bike begins to slow down but it is not a quick slow down when the brake drags.

-----

Performing focussed tests like this leads me to believe the issue may have been me all along. If that is the case, while a little embarrasing, it is still great news. Yesterday, I relied heavily on the front brakes and didn't use the foot brake for the rear at all. Next time I ride, I will try to only use the rear brake and see if the behavior is different.

I did have a question though: I normally use both front and rear brakes together but seeing as how the brakes are linked, using both together may be applying excess force on the rear rotor. Could that be the cause of overheating?

 

[hobdayd]

Define overheating...the ST has such massive engine braking I would be surprised if you ever see over 150degC to 200degC on the rear unless you are dragging or have a dragging brake or have many roundabouts back to back or live in a mountainous area. These temperatures are fine for a disc brake measured at the disc.

If you are regularly seeing these temperatures without using the brakes much I would suspect a dragging brake but from the info you have supplied you are looking OK.