Rear Brakes

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Sep 17, 2007 | 07:42 AM

Timboto

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Rear Brakes

I'm having an issue with my rear brakes and wondered if anybody else has experienced this....

When I first start my bike the rear brakes work fine but after about 30 or so minutes my rear brakes seem to lock up... there is no play in the pedal and the rear caliper has constant pressure on it. The exhaust pipe does run pretty close to the master cylinder, could it be that the brake fluid is getting too hot?? I am running DOT 5 in it....

Thanks..

Tim

Sep 17, 2007 | 02:22 PM

crampfan

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RE: Rear Brakes

There could be a few causes for this. first you will have to isolate the problem. when the brakes are locked up crack the brake line fittingat the master cyl. if the brake releases. the problem is in the master cyl. (it could also be the push rod adjustment) if the brake does not release try opening the bleed valve on the caliper. if the brake releases your problem is in the brake hose, if not the caliper will most likely be the problem. Make sure that there is free play in the pushrod, and that the master cyl.is notoverfull. I hope this helps, let me know.

Sep 17, 2007 | 02:54 PM

Timboto

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RE: Rear Brakes

My brakes are fine when the bike is cold or after sitting for a bit after a ride... there is plenty of play in the pedal. Once the bike has been ridden for a bit the pedal looses all of it's play and the caliper starts dragging...

Sep 17, 2007 | 03:51 PM

crampfan

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RE: Rear Brakes

Yeah, thats the way it works. as the fluid gets hot it will expand. There is a bypass port in the master cyl. that will bleed off the pressure as the fluid heats up. If the master cyl. push rod is too tightthe bypass port will be covered by the plunger. or the bypass port is just plugged.(it could also be that themaster cyl. is overfilled, when its locked up loosen the top)I have had problems with calipers, brake lines, and master cyls. check it the way I told you, and you should be able to narrow it down.

Sep 17, 2007 | 08:41 PM

Shovels4ever

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RE: Rear Brakes

What kind of rear caliper are you using. If you're running a banana caliper, make sure the heat insulator biscuit (it lookslike a mini hockey puck)is in place between the piston and the outboard brake pad.How old is the master cylinder? crampfan has a point. You need to check to see if there some room left inside the master cylinderforheat expansion,or the mcmight need a rebuild.If it's new, itcould be defective - wouldn't be the first time. Another thing to check is to make sure the caliper is aligned properly, andnot cockeyed which might cause a small portion of the pad to ride on your disc. You wouldn't feel the drag (as much) when the pads and disc is cold, but couldcausethe problem you're describing when the pad and the discheat up and expand.

Sep 18, 2007 | 07:52 AM

Logger

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RE: Rear Brakes

One other possibility... moisture in the fluid.

Sep 18, 2007 | 09:43 AM

Timboto

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RE: Rear Brakes

I'm not sure what brand calipes they are, they are custom chrome ones that were on there when I got it. I flushed the MC when I got the bike because it has been sitting for a while. I don't feel any drag when the bike is cold, if it sits for 10 - 15 minutes it tends to free up pretty good and there is again play in the pedal, but is like a rock after a bit of riding. When I flushed the system fluid went to the caliper pretty easily so it doesn't really seem like there is an issue with the caliper or MC functionality.. maybe there is too much fluid!??! I'll have to check that bypass port that was mentioned earlier also..
thanks for the info!

Tim

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Sep 18, 2007 | 10:42 AM

Shovels4ever

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RE: Rear Brakes

You'd mentioned that you're running DOT 5 brake fluid. Do you know ifyour systemhas always hadDOT 5, or did you changed it from DOT 4 (or DOT 3) to DOT 5? You CANNOT mix DOT 5 with any other type fluid. And you can't just flush your system onceand put DOT 5 in sinceDOT 5 is silly-cone based, and others are glycol based - it's like mixing oil and water, it will never mix.Flushing your system oncewill notget all of the old fluid out of your system because the old stuff canhide in places such as the brake light switch. You'll end up withsomething thatlooks like the stuff found insidea lava lamp. You will need to flush it a few times more, but that DOT 5 purple stuff is pretty pricey! To do it right, you mighthave to take everything apart, clean everybit with brake cleaning fluid, let it dry out completely, and thenputnewfluid in. Also, some of the older rubber components might not be compatible with DOT 5 fluid. Personally, I would use DOT 4, but only if you've completelypurged all of the DOT 5 from your system.IMHO,DOT 5 is not all that much better than the other stuff, but I digress.