Hot rear rotor.

[Epping]

Have done a search without luck so here goes.
The rear disc is always too hot to touch. There is no real drag when on the rear stand. I don't use the rear brake at all, just relying on the linked system. I have tried touching the rear brake pedal first to disable the rear brakes but after some distance, the disc still very hot. I understand there is only a single disc at the rear but this seems to be too much emphasis on the rear brake under normal use.
Could anyone verify similar temperature? BTW this is not related to my other post about the vibration as the disc had this issue before the tyre change.

 

[HoebSTer]

Re: Rear disc heat

One thing that comes to mind is making sure the slider boots and pins move freely. If not, some times one side of a caliper can cause slight drag causing excess heat build-up. Other than that, it had been noted on some of the Honda ST's with linked brakes where the rear would be worn out first where the fronts were still fine.

 

[EricV]

Re: Rear disc heat

I'm not sure what it is that you are concerned about? Are you worried something is wrong, or just commenting that the rear brake gets used?

If the rotor is not discolored, it's most likely a normal condition. The rear brake is part of the effective braking process. The linked system, as you point out, is going to use the rear, even if you don't activate it with the brake pedal, and heat will be generated.

 

[Poohbear]

Re: Rear disc heat

I am led to believe that on most BMWs with a linked brake system it is quite normal for the rear pads to need replacement before the front so that would confirm that the rear gets used alot more than on a conventional braking system. I would guess that the fact that it get's hot is normal as the heat has to go somewhere :-\

 

[markjenn]

Re: Rear disc heat

I think the litmus test for whether you have a real problem would be to ride the bike at speed on open roads for 10-min or so without using the brakes. Then pull over but let the bike coast to a stop with very little or no braking. If the rear rotor is hot (and presumably the fronts would be stone cold), then you probably have a drag issue.

I don't think the LBS works that you can "touch" the rear brake and then disable the LBS for some set period of time. My understanding is that the linking is disabled as long as you are using the rear by itself or the rear braking force is more than the front. But as soon as the start braking normally with the front, it resumes feeding some proportion of the force to the rear. At least that's how I read the service manual.

- Mark

 

[Tremor38]

Re: Rear disc heat

I don't think the LBS works that you can "touch" the rear brake and then disable the LBS for some set period of time. My understanding is that the linking is disabled as long as you are using the rear by itself or the rear braking force is more than the front. But as soon as the start braking normally with the front, it resumes feeding some proportion of the force to the rear. At least that's how I read the service manual.

- Mark

Exactamundo!

 

[tomatocity]

Re: Rear disc heat

I think the litmus test for whether you have a real problem would be to ride the bike at speed on open roads for 10-min or so without using the brakes. Then pull over but let the bike coast to a stop with very little or no braking. If the rear rotor is hot (and presumably the fronts would be stone cold), then you probably have a drag issue.

I don't think the LBS works that you can "touch" the rear brake and then disable the LBS for some set period of time. My understanding is that the linking is disabled as long as you are using the rear by itself or the rear braking force is more than the front. But as soon as the start braking normally with the front, it resumes feeding some proportion of the force to the rear. At least that's how I read the service manual.

- Mark

What happens if you use both brakes equally at the same time?

 

[mcbrien]

Re: Rear disc heat

I checked my rear rotor after a 30 min ride home from work , half interstate , half 2 lane twisty
50ish temp outside and it was pretty warm . I could touch it but wasn't going to try to hold on.
Also rear drive housing was pretty warm but not as warm as the rotor . May just be normal ... I hope .

 

[markjenn]

Re: Rear disc heat

What happens if you use both brakes equally at the same time?

Yamaha's documents on this are cryptic to the extreme, but as I read it, if the amount of force you apply to the rear brake pedal is less than the amount the LBS would normally apply rearward with no application of the rear brake pedal, then applying the rear brake pedal does nothing. But if you exceed this threshold, then the rear brake pedal governs the rear braking pressure. Basically, you can "override" the LBS by applying enough pressure to the rear brake. Of course, ABS is working too, so you may get intervention from the ABS system if you stomp down hard enough.

- Mark

 

[GrahamD]

Re: Rear disc heat

I don't think Mark is out of the ballpark on that one.

Look the bike has allegedly almost 50/50 weight distribution, so under fairly normal braking could probably contribute a fair bit of the effort.

Obviously as the brake forces increase the force will have to shift to the front otherwise the ABS will be kicking in all the time. So I expect that with reasonable braking effort the rear will be working a little less than the front but with only one disc to dissipate the heat, so just like on BMW's / Honda's I would expect to get heat back there.

Do what Mark suggested and coast to a stop somewhere and see what the results are.

 

[roy]

Re: Rear disc heat

Mine was warm after a ride today and I never touched the rear brake. I'm certain it's due to the shaft generating heat. I say "normal". ride on...

 

[Combo]

Re: Rear disc heat

Mine was warm after a ride today and I never touched the rear brake. I'm certain it's due to the shaft generating heat. I say "normal". ride on...

I say normal also. ::026:: If you use the front it will apply the rear so you will generate heat also on the rear.

::021:: ::022::

 

[stevepsd]

Re: Rear disc heat

I'll take my temp gun out on my afternoon ride in a few minutes, and take some temps in various conditions (front only, rear only, both, and no brakes).

-steve

 

[stevepsd]

Re: Rear disc heat

Here are my brake rotor temp(s) listed Front/Rear in degrees F

F R
Starting: 79 / 79
No Braking #1: 83 / 87
No Braking #2: 86 / 90
Max Braking #1: 103 / 127
Max Braking #2: 105 / 145
Front Only 124 / 106
Rear Only 86 / 247
No Braking #3: 83 / 85



Final Drive temp: 155

Ambient temp: 78

 

[stevepsd]

Re: Rear disc heat

Here are the specifics:

Starting rotor temp: 79F/79F - ambient 78F

Rode 7 miles@65mph, stopped without braking. Rotor temps 83/87
Rode a additional 13 miles@65mph, stopped without braking. Rotor temps 86/90

Rode a additional 2.6 miles and did a max performance stop from 65mph (ABS did engage), Rotor temps: 103/127

I then let the rotors cool to 90F (about 5 minutes) then

Rode a additional 2.4 miles and did another max performance stop from 65mph (ABS did engage), Rotor temps: 105/145

Let the rotors cool to 90F (about 10 minutes this time) then

Rode a additional 2.3 miles and did a front brake only max stop from 65mph (ABS did engage), Rotor temps: 124/106. Note that the rear brake is being applied even though I only used the front brake lever.

I let the rotors cool to 90F then

Rode a additional 7.5 miles and did a max performance rear brake only stop from 65mph (ABS did engage), rear brakes got hot and really stunk. Rotor temps: 86/247 It appears that the front brake is not applied to rear-braking only.

Waited until the rear rotor cooled down to 90F. (about 20 minutes)

As a control, to replicate the start of the test, I rode an additional 7.4 miles @ 65mph (just about the same distance as the first test) and coasted to a stop. Rotor temps were: 83 / 85. By this time the ambient temp had dropped to 73F (temps drop fast in the desert as it approaches dusk) and the wind started to pick up.

Notes:
It should be noted that the actual braking temps were higher than I recorded as the rotor temps dropped very quickly after I started taking measurements.

It took me about 15 seconds after stopping to take the first measurements. For example the rear brake only rotor temp of 247 was down to 215 in 20 more seconds.

I tried to be as consistent as possible in the time to take the temp readings, and the locations where I measured the rotor temps.

Also, the final drive housing temps stayed at a consistent 155F.

 

[Combo]

Re: Rear disc heat

Thats good stuff Steve and about what I expected. Its good to know also about the drive temp stays around the same with different running conditions.

Thanks. ::008::

 

[Combo]

Re: Rear disc heat

I feel with this topic I should share this story.

Back, way back in 1986 I had a Yamaha Fazer 700 (I loved that bike) and showed up to a friends party. My friend wanted to ride my bike and I said OK before the drinking started. My friend Pete is a good rider so I had no problems with him riding it. He was gone for about 10 min. on a hot run. Pulled it back into the shop & A guys girlfriend noticed the red and blue front disc's, said how pretty and went to touch them. Thats when everybody in the shop at the same time said NO!

She did it anyway. : She left her fingerprints smoking on the disc and her boyfriend could not catch her running down the road screaming.

I guess what I am trying to say is they get very hot (and pretty) when used.

 

[markjenn]

Re: Rear disc heat

Nice data collecting! All sounds very consistent with what you'd expect from the system.

- Mark

 

[Epping]

Re: Rear disc heat

stevepsd, thank you so much for the time you have spent on this, and to others also who have contributed. I may have created a bit of a red herring stating "there seems too much emphasis on the rear brake under normal use." I don't believe the heat is due to normal use. I was racing at Eastern Creek on the weekend so have not ridden for a few days but will try markjenn's suggestion and ride a distance with no brakes at all. I was really asking if others had same issue and it seems no one does so will check pad retraction. As I mentioned, there seems to be no real drag when parked on the rear stand. I understand there will be heat transfer from the diff but the disc temp will not exceed the diff if the rear brake is not used. I will also re read the manual on the linked system. I seem to have miss-understood, believing I could disable the link for the duration of the application by activating the rear first. Anyway, more investigation required. I will do so & report. Thanks again all for your help.

 

[stevepsd]

Re: Rear disc heat

As you can see from my data, go for a 7-10 mile stint and coast to a stop without using your brakes.

The rear brake will just be slightly warm, the front less so. I put my hand on them to see how the rotors felt as well (no brake stops only). If it is hot to the touch then you have a issue.

Even after 40+ miles the the rear diff did not seem to impart any temperature rise to the rear rotor (see the rotor temps for my first & last no-brake stop). The rear diff takes considerably more time to cool-down than do the rotors.