How hot do brake discs get?

I had my tires replaced today and had to replace the rear brake pads. I just had this done last time I changed tires and thought it was a bit quick. Anyway on the way home I thought I felt the brakes hanging up and when I got home I touched the discs and one of the fronts was too hot to keep a finger on and the other side was cool. The rear was also hot, hotter than the front one. Is this the norm? Thanks

Race cars with steel discs tend to prefer operation in the 700 to 1100 degree F range. Automotive up to 600....800 if you do a bunch of quick stops and want to start lighting firecrackers on them. So, I would think just about any use whatsover is going to beyond the finger burn threshold.

When's the last time you took apart and cleaned your rear brake actuator near the foot? They're prone to gumming up.

rockmurf said:

I had my tires replaced today and had to replace the rear brake pads. I just had this done last time I changed tires and thought it was a bit quick. Anyway on the way home I thought I felt the brakes hanging up and when I got home I touched the discs and one of the fronts was too hot to keep a finger on and the other side was cool. The rear was also hot, hotter than the front one. Is this the norm? Thanks

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Your rear brake pedal actuates the rear brake and also one piston on the front right caliper. Do you remember which front one felt hot? I'll bet it was the right one and I'll also bet that Iggy is right on the money with suggesting a sticking rear brake pedal. Clean and lube that puppy and I'll bet you're good to go! :yahoo:

ITS NOT NORMAL!!! THEY ALL GET HOT!!!

What's a brake?

Oh, those...

Hi rockmurf,

If you had just been using the brakes, you would not be able to hold your hand against them for any length of time. The temp will be high enough to hurt so be careful (couple hundred degrees without trying hard). Your statement of one front disk hot & the other one cool isn't the way it should be working. I'd expect them both to be sharing the workload and be roughly the same temp. The temp diff between front and rear depends on your riding style. I use the front much more than the rear so my fronts run hotter to the touch. I wear out front pads quicker too.

Start looking into the right vs. left temp difference on the front brakes. That's odd. That means one side is grabbing more than the other in a balanced system. That side could also be binding like you mention.

W2

BTW, F1 carbon-carbon brake disks can peak at about 2,200 deg F (1,200 deg C) when used in anger...FYI.

Thanks WW.

QUOTE (Wee Willy @ May 7 2010, 01:47 AM) <{POST_SNAPBACK}>

Hi rockmurf,

... I'd expect them both to be sharing the workload and be roughly the same temp. ...

Start looking into the right vs. left temp difference on the front brakes. That's odd. That means one side is grabbing more than the other in a balanced system. W2

...

Not quite. Remember the left side has two sets of brake pads used from the front brake lever, the right only one set (the other set being linked from the rear).

Illustrated by the wear on my pads (click on image for larger view).

Left side:



Right side:



So I'd expect the left side to be warmer after normal braking. Unless the rear brake lever is stuck on (as mine has been in the past), then it'll be the other way round (and the rear brake disk will be hot).

mcatrophy said:

Not quite. Remember the left side has two sets of brake pads used from the front brake lever, the right only one set (the other set being linked from the rear).
Illustrated by the wear on my pads [SIZE=8pt](click on image for larger view)[/SIZE].

So I'd expect the left side to be warmer after normal braking. Unless the rear brake lever is stuck on (as mine has been in the past), then it'll be the other way round (and the rear brake disk will be hot).

Click to expand...

Does this mean that all the pots on the front brake system are NOT tied/plumbed together with a common reservoir? That one pot on the front side talks only to the rear hydro system? Curious minds want to know.

If the pots on the front have a common reservoir then all would want to actuate together for balance unless there are check valves at strategic locations. And THAT sounds a bit too sophisticated for this bike. ($...not engineering know-how).

What you've pointed out would be a low cost solution to an interesting balancing problem once you decided to have the back system talk to the front. I ought to get a service manual one of these days.

Thanks Mcatrophy. Good catch.

W2

Harald said:

Clean and lube that puppy and I'll bet you're good to go! :yahoo:

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Thanks Harald,

Ig wants the "actuator" cleaned and you mentioned the "pedal." What part on the rear brake system is prone to the sticking problem?

Curious,

W2

Wee Willy said:

Does this mean that all the pots on the front brake system are NOT tied/plumbed together with a common reservoir? That one pot on the front side talks only to the rear hydro system? Curious minds want to know.

Click to expand...

That's right. So on a Gen II, when you grab a hand full of brakes, you've only got 3 of the 4 pistons working for you.

A hotter Gen II right-front disc hints at one of two things to me.....a sticking rear pedal.....or misuse/overuse of the rear brake. Or rather, under use of the front brakes.

Wee Willy said:

Ig wants the "actuator" cleaned and you mentioned the "pedal." What part on the rear brake system is prone to the sticking problem?

Click to expand...

The brake pedal on its pivot. It's pure metal-on-metal, gets NO lubrication except for what the owner puts in their, and gets very filthy from collected road spooge when you DO lubricate it.

RadioHowie said:

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Gorgeous...carbon ceramics at operating temp...~ 2,000 deg F. That's one hell of a machine.

Thanks.

Wee Willy said:

That's one hell of a machine.

Click to expand...

"A Fiat by another other name stills rusts as quickly." -- overheard at the Globe Theater, circa 1580

RadioHowie said:

Wee Willy said:

That's one hell of a machine.

Click to expand...

"A Fiat by another other name stills rusts as quickly." -- overheard at the Globe Theater, circa 1580

Click to expand...

Does carbon fiber rust? And it WOULD look better in red.

QUOTE (Wee Willy @ May 7 2010, 02:23 PM) <{POST_SNAPBACK}>

Does this mean that all the pots on the front brake system are NOT tied/plumbed together with a common reservoir? That one pot on the front side talks only to the rear hydro system? Curious minds want to know.

Correct. This photo shows the smaller pot for the back-linked brake, the larger for the front (click on image for larger view).



QUOTE (Wee Willy @ May 7 2010, 02:23 PM) <{POST_SNAPBACK}>

Thanks Mcatrophy. Good catch.

W2

That's what I'm here for.