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Post by joneill4 on Aug 4, 2007 11:25:27 GMT -5
My rear disc brakes keep seizing up on me. This has been going on for months now. I don't even use them anymore, but almost every afternoon, I need to pull off the highway and bleed the pressure off. My first thought was that I had air in the system that was expanding in the afternoon heat. (90-100 degrees F)(~37C) However, I bled nearly half a bottle of brake fluid beyond the point of bubbles. I rebuilt the caliper, but did not change the piston. My hunch is that my piston is scored enough that it is sticking, and that the humongous brake pedal bounces downward every time I hit a bump. Sorry for writing a book, but I was trying to be clear.
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Post by chew652 on Aug 4, 2007 14:08:50 GMT -5
A heavier return spring might help the bounce phnenomenon.I have adjusted my rear brake so that it sits below my foot like it would on a dirt bike. I do not have to lift my foot off the peg to apply it.Because of this I have left a lot of play in the linkage so that it takes a definite downward movement to apply the brake. I can strill lock the rear wheel if necessary(I tried it about an hour ago).Also fresh fluid is imperative. Brake fluid will attract moisture so clean fluid from a previously opened can may still cause a problem.
I have had no problems with my rear disc but I may just be fortunate. A caliper rebuild may be in your future. Good Luck.
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Post by Bize on Aug 4, 2007 21:18:13 GMT -5
When you rebuilt the caliper, did you replace the piston oil seals? The seals are what pull the piston back when you back off the brake. Another common cause for brakes sticking is simply that they are dirty, but that, again, wouldn't be a factor if you've just rebuilt the caliper.
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Post by colinjay on Aug 5, 2007 17:34:11 GMT -5
I have had the same problem a few years ago. Stripping and cleaning both the caliper and master cylinder fixed the problem. From memory, the real problem was the return hole in the master cylinder being blocked up with gunk sttopping the brake fluid returning to the reseviour. I put the cause of the problem down to being slack and not having changed the brake fluid in about 10 years.
CJ
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Post by Bize on Aug 6, 2007 4:48:02 GMT -5
...down to being slack and not having changed the brake fluid in about 10 years. LOL, that is pretty slack  Brake fluid should be changed every 2 years. . . After 10 years it'd be mostly water. |
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Post by miker on Aug 6, 2007 8:21:22 GMT -5
First off, is the rear pedal linkage correctly adjusted? There's supposed to be some play. Mine was putting pressure on the MC at rest when I got it, and the brakes acted just as you describe - I think because the MC piston was probably covering the return hole.
New fluid - old fluid will act as you describe with heat.
Clean/rebuild MC.
Check for a warped rear disc BTW. Mine is a little; if I wasn't converting to spoke/drum I'd get an XS650 (thicker) rear disc for it.
miker
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Post by joneill4 on Aug 6, 2007 12:38:19 GMT -5
I never thought to look at the master cylinder. The bike sat for at least 3 years before I got it. The fluid in there now is definately fresh. Thanks guys. I might actually be able to use my rear brakes tomorrow!
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Post by wotavidone on Aug 6, 2007 19:11:58 GMT -5
"Brake fluid should be changed every 2 years. . . After 10 years it'd be mostly water. "
Love it. Have you seen the TV program called "Bush Mechanics"?
It's about the tricks and tips the outback Aborigines use to keep cars going long after city people would have had them towed to the wreckers.
Anyway one tip from the show "water mixed with a real good dose of laundry detergent powder, I think it was OMO or Drive, makes a very good substitute for brake fluid".
Same episode, they took the flat battery out of the car, heated it up in the camp fire, then sat it back in and it started the car.
I still reckon the best one was when the fuel pump carked it, so they put petrol in the windscreen washer bottle. Every time the car looked like stalling, he hit the washer button and pumped the carby full of juice again.
Mick
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RD
Full Member
Posts: 176
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Post by RD on Aug 6, 2007 19:35:51 GMT -5
Yeah I saw bush mechs while I was living in Alice Springs, the scary thing was that there were cars driving around Alice like that every day.
The favourites used to be XD,E,F falcons cause they still ran carbs and lots of family could fit in.
I did a a lot of 4x4 trips while I was there and was constantly amazed by the places those drivers could take one of those things, I suppose it helps to have a complete lack of respect or mechanical sympathy for the car.
Cheers
Rich
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Post by joneill4 on Aug 23, 2007 11:18:45 GMT -5
I finally got around to cleaning the master cylinder. I think it worked well. I took Chew562's advive and adjusted my pedal downward, but that led to a new problem. How does one remove melted shoe rubber from a chrome exhaust pipe? Thanks for the tip on the master cylinder. I assumed the problem was the caliper, so I may never have checked the master cylinder.
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Post by miker on Aug 23, 2007 12:19:37 GMT -5
If someone tightened the pedal/MC linkage enough to put pressure on the piston, the brakes sieze because the pressure relief hole in the MC is covered all the time.
You can adjust the pedal height independent of the linkage play... this is on page 37 of Clymer. First set the bolt and locknut under the rearmost end of the pedal 'arm' to the pedal height you want; then adjust the nut and locknut on the MC rod for correct free play, about .5-.6 inches.
miker
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