spewing rear brake

[LAWMAN]

I am slowly but surely getting my '07 300E set up for the enduro season, with the help of the members of this board & my friendly local GG dealer. my latest issue is this:

my rear brake gets hot & fades. I flushed & refilled it, no help. my dealer put a rebuild kit in the M/C & that helped, but I noticed yesterday a little fading & there was fluid spewed out of the slave cylinder, & the cap on the refill nipple had blown off. I'll check into rebuilding that, too, just to remove another variable.

I'm going to lower the pedal as far as it will go to keep my foot off it as much as possible, & try to remember to stay off, etc. etc., but I've never had this problem on another bike.

beyond that, is this a common problem? has anyone tried any fixes for it?what about 1 of those cooler/radiator things made for the slave cylinder on the Honda CRF?

 

[PEB]

It is notr that hard to boil a rear brake, but it should never pop the cap off the bleed nipple and drool all over. I would guess it didn't get tightened enough after replacing the fluid. Perhaps to keep things cooler you could swap out the master for an older one with a remote resevoir, I think they stay cooler. I also find that the pedal on my 02 rides pretty high with my pegs in the low postion.

Paul B

 

[GMP]

Mine had air in it when new and was a PIA to bleed. I like a low pedal and always set my bikes up that way. Cut a few mm off the MC piston stud to allow adjusting the pedal lower without it hitting the pedal in the clevis.

 

[stay_upright]

I would check the brake is not dragging when you are riding or are you just !!! fast?

Only time my brake gets anywhere near hot is when my KTM dragged the brake 'cos I had it adjusted the pedal couldn't move up enough to let expending fluid back into the reservior when teh brake was not in use.

Also a vented (or more vented) disk will stay cooler (at the expense of brake pads)

 

[LAWMAN]

thanks for the advice.

the nipple is tight; I can't tell where the fluid got out, but it definitely did.

I think the key is to get the pedal lower, & since that's free, I think I'll try that next. I've put on the low pegs & that I am sure has made it worse. I think I'll also take GMP's advice & grind off a few mm of the piston stud & try that--I'm always looking for a good excuse to fire up the grinder anyway. I'll post back as things develop.

 

[iancp5]

Only time my brake gets anywhere near hot is when my KTM dragged the brake 'cos I had it adjusted the pedal couldn't move up enough to let expending fluid back into the reservior when teh brake was not in use.

You too - I've been there.

 

[LAWMAN]

OK, here's the latest: I took off the pedal & caliper to remove the piston stud & grind a little off the top so that I would not have to mess with cleaning up the threads, as I would if grinding on the bottom. problem: I couldn't figure out how to remove the stud! I'm used to KTMs, where the stud just falls out. what's the secret?

 

[GMP]

Just run a nut up the stud, cut about 5mm off, and run it back off. The boot is a tight fit in the MC.

 

[LAWMAN]

thanks, Glenn, I will do that. sure would be easier if they'd put a height adjuster on the pedal. if you Gofasters guys see this, you might mention it to them in Spain....

 

[GMP]

The pre '04 frames had an adjuster. It got in the way of the newer frame guards so they eliminated it. Actually it is not needed as the bottom of the clevis pulls the pedal down as it is adjusted up the MC rod. You just have to shorten the rod, but you had to do the same thing on the older bikes anyway.

 

[Steve@Motowest]

If the bleeder fitting in the caliper is leaking remove it and check it closely. They can be easily crushed if overtightened - look at the passage hole in the side of the bleeder, is it round or oval. It should be round, they turn oval as they are being crushed or it might be smashed flat. Either way replace it.

Those finned coolers that mount on the master cylinder are near worthless, they are mounted too far away from the heat generated in the caliper to do any real good. There are some heat-sink type coolers available that attach to the caliper, that could help a little. And use the Motul 600 brake fluid, it has a very high boiling point.

We are working on a fluid circulation system (like they use on race cars) that will circulate the fluid through a cooler and back to the reservoir each time the pedal is pumped. This is the only real way to deal with overheating fluid.

 

[gasgasman]

Try the Ford Motorcraft brake fluid.
It is DOT 3 with a minimum dry boiling point of 500 °F (260 °C)

There was a company that would machine your caliper piston and install a Teflon button where the pads ride to reduce heat transfer to the caliper.

 

[LAWMAN]

thanks for the advice! I have cut off the bottom of the stud but did not get to finish adjusting the pedal. if I have time by Sunday, I'll try to find the exact source of the spew, but I may just have to ride it as is on Sunday. I think it will help a lot to have the pedal lower, we will see.

thanks again for all the help.

 

[iancp5]

Try the Ford Motorcraft brake fluid.
It is DOT 3 with a minimum dry boiling point of 500 °F (260 °C)

There was a company that would machine your caliper piston and install a Teflon button where the pads ride to reduce heat transfer to the caliper.

On my KTM they have a piece that pushes into the piston on the rear - wondered why, now I know.

 

[LAWMAN]

status report: cutting the stud & raising the pedal seems to have solved the problem.

for the benefit of future generations of GG newbies, here's how I did it: I cut 5-6mm off the stud with a Dremel tool & cut-off wheel. I forgot to leave a nut above the cut, so I cleaned up the threads a bit with a die, nothing to it. then I adjusted the pedal as low as it would go & went riding at a gnarly place in the Ozarks, & no problems (so far). I'd get it a little lower if I could, but I think it will do.

thanks to all for the help!

 

[LAWMAN]

Well, here's the late final:

I thought I had this fixed, but no joy--it would still get hot after a while & boil, altho it was better w/the pedal lowered--it took me longer to boil it. I knew that something mechanical had to be wrong w/it, but I could not tell what it could be & did not have the time to use trial & error replacing everything 1 part at a time.

so I eliminated all the variables at once--I replaced everything behind the master cylinder (since I'd already had it rebuilt) where fluid could be leaking. this entailed the hose, slave cylinder & bleeder valve.

& that fixed it, now it works great. thanks to all for the advice!

John

 

[GMP]

Yes, I cut the studs for a lower pedal as well. Organic pads(less heat transfer) and a solid rotor(less wear on the pads) help as well.