Rear brake frozen

[Guest]

First of all thanks to all the help everyone has already given me in getting my 1980 GS550L running. I bought it when I got out of college in 82 and put 15k miles on it in two years before I moved from Virginia to Chicago. Anyway it's been sitting since 92 in my garage and I finally got around to getting it running. Cleaned the carbs and gas tank and it it runs pretty darn good. Finally took it out on the road today and after about a mile the rear brake froze up solid. I didn't think I would make it home but pretty much just put it in first gear and rode at 5k rpm thinking the brake pads would have to wear down sooner or later.

Obviously I'll have to clean out the master cylinder, but the front brake works fine so should I assume it's the rear caliper that's stuck? Can you just take them apart and clean everything or is a kit necessary?

Thanks and I'll post pictures some day.

Steve

[Speedo]

Steve - welcome to a great site! I'm sure you will be getting the super duper welcome package email from BikeCliff soon!

As my dad always said: "check the simple things first". Do NOT assume it's something complicated like a frozen caliper and/or master cylinder problem (although of course, it could be).

I had the same problem when I bought my bike 20 years ago. Know what the problem was? The previous owner apparently never used the rear brake, so the shaft that sticks through the round opening for it in the frame and that the brake pedal assembly bolts to and that rotates when you push down on the pedal were so rusted to each other that when I pressed on the pedal, it stayed put - ie the brake stayed on and the pedal return spring was not strong enough to return the pedal and disengage the brake pads. A few squirts of PBblaster, a little pounding with a hammer to set up a vibration, and bingo, it works to this day.

So check that out first. Also see if the return spring is there and works right.

If that checks out, next take the caliper off and look at the brake pads. If they are very worn, then the caliper pistons have to extend a lot (do a lot of work) and can get stuck (this happens a lot on car brakes too). Put on new pads and test again.

If problem persists, next suspect is the caliper. Probably easier and cheaper to buy a used one than to fix, but there are a lot of smarter guys than me on this site, so keep checking for advice.

Last suspect is master cylinder. You can hone the cylinder and put in a new piston which is not hard to do if you can find a kit (again, smarter guys than me will probably chime in).

Just remember: brake fluid is evil and quirky. Do NOT let it get on anything painted as it will strip paint almost instantly (the "evil" part); brake fluid and water are like vinegar and oil and don't mix (the "quirky" part)! To make matters worse, brake fluid is "hygroscopic", which means it absorbs water. And worse, the more water mixed in with brake fluid, the worse it works for your brakes and can actually cause your brakes to fail (boiling points, etc, etc, don't want to get too technical).

So if you don't know when the fluid was bled/changed last, do that regardless. FIRST. And always get the little cans of brake fluid because you should always use FRESH fluid (not opened and exposed to air, which contains moisture, and which the brake fluid hungrily, quickly, hygroscopically absorbs). So after you open a bottle of fluid, whatever you don't use that day, is pretty much useless and should be tossed.

Hope this helps and keep us posted!

[Speedo]

but the front brake works fine
Steve

One more thing: the front and rear brake systems on your (and pretty much every) bike are 100% independent of each other (unlike cars), so that has absolutely nothing to do with your problem.

[Steve314159]

Thanks for you quick replies. I see now that there is a master cylinder for each brake. I am going to take everything apart over the next few days and try cleaning and replacing the fluid and looking for stuck or rusted parts. I have never seen brake fluid in a car that looked it had amphibians living in it. Should take a few days but I'll get back to you.

[Steve314159]

I took the caliper off and the pads and boots looked good. Squished the pads back in with a C-clamp and they moved pretty easily. So I did as you suggested and changed the brake fluid, bled the brakes, and could see that the master cylinder was sticking. I'd press the pedal, and fluid would come out, but I'd have to wait 20 seconds before I could press it again. After half a pint of fluid everything started moving smoothly. Rode it today with no brake problems. Other problems, sure...

[Nessism]

I took the caliper off and the pads and boots looked good. Squished the pads back in with a C-clamp and they moved pretty easily. So I did as you suggested and changed the brake fluid, bled the brakes, and could see that the master cylinder was sticking. I'd press the pedal, and fluid would come out, but I'd have to wait 20 seconds before I could press it again. After half a pint of fluid everything started moving smoothly. Rode it today with no brake problems. Other problems, sure...

Bleeding the brakes doesn't get all the crud out of the system, you have to take the calipers and master apart to properly clean them. Bleeding is better than nothing but you still have work to do if you want to fix the bike properly.

Check these photos to see what the calipers look like after the fluid turns brown. You think all that crap will come out by bleeding? The brake lines also have that same crap inside which is why it's important to change them while you are there.

[Steve]

Contrary to Speedo's suggestion that the master cylinder would be the last suspect, I would suspect it first.

Especially since it has very old fluid in it, in spite of your claimed fluid flush.

Remove the rear master cylinder from the bike. Remove the large fitting on the side, where the reservoir feeds in. In there, you will see a small hole. Chances are, that hole is plugged. Clean that hole, flush the entire master cylinder with fresh brake fluid, re-assemble.

One other thing to be aware of, even though it's too late for this time: don't simply press the caliper pistons back into the caliper. Especially after sitting for so long, there is a good chance there is a LOT of crud built up on the outside of the pistons. By pressing the pistons back into the caliper, you are forcing that crud (could also be physical damage due to rust) past the seals. If this damages the seals, your braking could be seriously compromised. It is better to use some compressed air to pop the pistons out for inspection of the pistons and the seals. Besides, it will give you the opportunity to make sure your calipers don't look like Nessism's.

.

[Steve314159]

Thanks for the suggestions guys.

[Speedo]

Mr Pi (I just got that one...I'm a little slow...good one) - just so we're all clear here, so does it all work properly now? (I think you said that)

Even so, it would be wise to listen to guys like Steve and Nessism, thoroughly clean out the works so you cross that totally off your list of worries/to do's and move on.

Did you check the shaft and return spring? Remove/Lube shaft (or at least WD40 the heck out of it)?

[Steve314159]

Speedo,

I'm an electrical engineer and pi is one of those numbers that I see all the time. Mostly w=2pif, converting between radians and Hertz, but just now I was testing gluing some 600 grit sandpaper strips into a cylinder to use with my dremel tool and darned it that number didn't come up.

Yes I checked the shaft and that may have been part of the original crisis, and a funny thing about getting stuck a mile away from home thinking I had to jog home to get some tools is I completely forgot about the tool kit under the seat. The brakes worked fine on the last ride. I'm pretty sure the master cylinder was the problem because when I bled the brakes I would press down on the pedal and fluid would come out but I'd have to wait 30 seconds before I could press and more come out. After a while everything started pressing and returning like it should... I'm not done with that by any means but I'm on to adjusting the valves and trying to get the idle screws right so don't be offended it I don't reply to posts til April.

Steve