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Component -Brake Temps


motocat12

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I'm frustrated at how hot my rear rotor gets even unused, pads seem to wear pretty fast. Spinning the tire by hand on a stand has no drag. Maybe I'll let it idle for 10 min and see if it heats up still.

Just popped a new rotor and sintered pads on today and cleaned the pistons, bled er. wrapped exhaust packing and loom between the horizontal master/ brake line and motor. I've always been able to skid the rear, today it chirped.

Grabbed the IR temp gun tonight after 10 highway miles.

front rotors 90f 

rear rotor 135f  with little use (feels hot as fck.Do polished surfaces read accurate?

rear caliper 130f

master 125f

clutch cover 165f

swinger 150f

Header/crossover/link pipes range  311f(rear cyl) -175f front.

I'm tempted to mount a duct on the swinger to see if it's just due to being faired behind all the hot stuff or friction. 

 

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Most rear brake set-ups require some free-play in the brake pedal before it starts to pull on/actuate the master cylinder piston.  That'd be one of the first places I'd check.  Pretty easy adjustment.  Sounds like you've disassembled the caliper and done the proper maintenance and care, but I'd also check that your caliper pins are clean and rust-free to allow easy movement of the the caliper as the pads wear in.  The only other explanation I can offer is to make sure your rear brake pedal is positioned so that your foot isn't resting on it and inadvertently activating the brake.

 

To be fair, 135*F is too hot to touch, but nowhere near max operating temp.  Brake fluid boils at over 400*F.  So, your rotor isn't really that hot.

Edited by Bubba
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went from goldfren s33 hh to tufstops.

I just can't get around the fronts used hard are about the same temp as they are from being parked in the sun. 

I checked the plunger and there's slack at rest. I also put on a shorter return spring last week as the old one had no tension at rest. I generally cruise with toes on the pegs.

 

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10 hours ago, motocat12 said:

I just can't get around the fronts used hard are about the same temp as they are from being parked in the sun.

 

Think about the swept area, though.  Figure you've got twin front rotors that are +/- 320 mm diameter, vs a single rear that's about 245 mm.  That's about 3 - 3.5 times the swept area front vs rear, which means lots more mass and surface area to both absorb and shed heat.  Given, you prolly use your fronts more, but that difference coupled with your observation about the rear cylinder/exhaust header temps and I'd bet that would account for the difference.

Edited by Bubba
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Think about the swept area, though.  Figure you've got twin front rotors that are +/- 320 mm diameter, vs a single rear that's about 245 mm.  That's about 3 - 3.5 times the swept area front vs rear, which means lots more mass and surface area to both absorb and shed heat.  Given, you prolly use your fronts more, but that difference coupled with your observation about the rear cylinder/exhaust header temps and I'd bet that would account for the difference.


Also think about air flow over the disc, the front is out in a fairly open area, rear is block by the whole bike basically.

Sent from my SAMSUNG-SM-G890A using Tapatalk

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had some issues similar to this in duc, is this a brembo rear system on the ape? preface: I am a complete noob when it comes to mechanical skillset, but hopefully this helps since I had similar problem to this and know how frustrating it can be

 

I am pretty sure you did this, but just in case to be systematic / assuming all the more common scenarios like wrapped rotors, non aligned wheel / faulty calipers/components etc are ruled out

1 start cold > both front rear cold > check play for the rear brake before it engages / spin rear wheel see how smooth / mark lvl of fluid in rear reservoir / check temp in cylinder and reservoir

2. go for a ride over 15 to 30 mins, slow around the block not using any rear brake at all and front as minimal needed

3. Come back check temps > for sure the back will be higher I guess which is why we have this discussion

4. Spin rear wheel again / check rear brake pedal free play again  right after stopping

5. both front and rear is supposed to heat up since the rotor and pad touches every so slightly plus various other reason stated above > but the brake reservoir system should negate the pressure build up from heated up fluid.

6. But If there is more bite and more resistance to spin in rear compared to before > more pressure in the rear system >  then this means fluid is not backing up to the reservoir as its supposed to > and in turn it ends up similar to you dragging your feet on pedal with mild force

7. If free play is reduced significant compared to before that means you probably can get away with giving it still more free play and try again

8. If reservoir lvl stays the same this means there is problem with fluid back up as in the minor pores in cylinder getting clogged etc /

 

9. At times in some bikes due to location of the rear cylinder closer to exhaust/ engine component etc   it can get heated up pretty fast and cause more pressure build up. In this case the cylinder will be much higher temp than the rear rotor

10. some times its just a cylinder which needs revamped or changed. ( this is why I asked about brembo as the duc monster 1200 had some recalled rear cylinders )

 

excuse me if the whole wall of txt is a bunch of malarkey > that's the way I understood after reading some threads about it. there are tons of better guys to take advice from in this forum and mine should be the last to consider.  Again my mechanical know how is at best close to a toddler working on tricycle. But if this kinda helped give you a new thought process so be it and come to epic ride and shake my hands.

 

Edited by NinjaDoc
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23 minutes ago, motocat12 said:

After a 5 mile ride today in much cooler air temp

front disc 81f

rear disc 125f

disc side hub 125

chain side hub 95f

chain /sprocket 98f

 

It does look like i'm losing freeplay in the pedal/rod when it's hot.

Give it max free play and try again to see if it still heats up. 

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Get ass end in the air and check lateral play in wheel....if your wheel bearing is shot out, it will not be able to sustain a right angle between the axle and the wheel, causing your disk to rub the brake pads on the inside of the caliper when you turn one way and the outside when you turn another.....I know it's a stretch but it's possible. Put a dial indicator up against the rim and see if there's slop in it. 

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I do not believe that you have an issue. Your temp numbers in the first post really have no meaning because you had no base numbers to refer to for comparison. Google your situation and you will find that you are not alone in your wonderment. Hotter rear rotors are a fact of life. Your swing arm was actually warmer than your rotor. 

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wheel may spin even better hot. One side of the rotor was 10 deg hotter but it was the bottom so it may have just been conducted from the pads.

Hub was hotter near the rotor than bearing so it seems ok

The seat was 130f, my hot ass causing the problems again.

Would the chain torque cause enough swingarm flex for the rotor to rub on acceleration?

The tire was 140f and just felt warm I guess that's part of it, how denser materials feel hotter and you can walk on red hot coal.

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Something else, the pistons have plastic "center cups" that stick out past the piston edges(air pressure?), but not overlapped, but do make it harder to press the metal to get them back in.

reason for those? 

Last set of pads with Ti shims was impossible to fit pads over the rotors with the shims in...

maxresdefault.jpg

Edited by motocat12
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https://www.google.com/patents/US6729445
sounds like maybe an insulator to reduce rotor/pad to caliper/fluid heat transfer?  how has that turned out for me.

Quote

The piston has a composite cap that is formed of a cap piece made of strong material, such as steel, and an insulator, made of polyimide resin material, for example. The insulator is preferably in the form of a ring clamped between the cap piece and the piston to create a thermal break and minimize heat transfer from the brake pad to the piston and caliper assembly.

actually this patent was after my bike was produced.. (Italy vs US file dates?)

Another heat factor would be that my front rotors are semi floating and the rear rotor and caliper are fixed.

Edited by motocat12
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took a dremel bit to the caliper where the pads make indents. It was some of the mildest i've seen(one side more than other), and I'd think the old pads and new pads would hit different spots anyway..? I usually inspect that on pad slaps but this bike has the speed sensor connected to the caliper mount giving less movement

Yesterday and today after a long ride rotor was 111F huge difference, swiinger still at 150f as before.

*not actual photo

DSC08370.JPG?resize=320,254

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