brake queston...

[uudfourty]

First off, someone... I think one of my imperial British cousins... suggested just running a copious quantity of seafoam instead of cleaning out the carbs at season startup after improper winterizing.... for that, I would like to thank you sir. You've saved me worries and troubles beyond imagine. I just wish I could remember who you were and ship you a pint of Boddingtons or something...

Back to brakes--
81 GS550L. Last season, the rear brake was getting weak and it was to be repaired, but stuff came up as it always does, and now here I am.
In any event, I put on a new rear wheel (bought a wheel on ebay that came with a brand new dunlop tire... or tyre, as it were).

The calipers were squeezed down for the old disc, so the rear wheel wouldn't roll freely. Hmm.... Fixed that.... i guess...

I noticed that the calipers didn't squeeze when I applied pressure to the pedal and there was no backpressure either. I thought air leak, but when I attempted to bleed-- I ended up taking the bleed sert all of the way off--, no fluid squirted out at all when I pressed the lever.

I slapped it around and nothing came out at all.

What's going on here?

Plenty of fluid. It's dirty, though. Front and rear both.

In any event, the rear brake isn't working at all. There are no leaks, so it is pistons, or is it an obstruction somewhere along the way?
An obstruction would make me think that there would be backpressure, but there is none. But the lack of brake fluit coming out of the bleed port makes me think that there is none being delivered.

Something obvious? Something in-depth and contrived?
Something..... paranormal?


Thanks in advance.

[tkent02]

I'd say your brake broke.
By no back pressure do you mean no resistance to pushing the pedal down?
Could be clogged line from the reservoir to the master cylinder, clogged port somewhere in the master cylinder, rubber piston ring gone, not sure what else. If you take off the hose and step on the pedal, does any fluid come out?

[uudfourty]

its broke. im inclined to agree.

[Big T]

Sounds like it's time for a rebuild.
Get some Brakecleen (or similiar product) and take the major components off the bike.
Pull the caliper, pull the pads and see if you can pump out the piston by squeezing the brake lever. Have a container handy to catch the old fluid.

If the piston comes out, get a new O ring for the caliper. Check the inside of the caliper for corrosion. Scrub it with a Scotchbrite to remove any debris. Check the piston for corrosion. If it's pitted, replace it.

If the piston is stuck, pull the brake line and use compressed air to get the piston out. Wrap it in a rag before applying pressure to prevent damage

If the master cylinder doesn't pump fluid, the relief valve is probably plugged. Suck out the old fluid and look for the little hole. Use a piece of wire to see if you can degunk it.

Anything you take off should be sprayed with brakecleen, and kept clean prior to reassembly. Reassemble with clean brake fluid. Never, ever use any oil, WD40 or other lubricant on the brake components.

If your components need some work, now is a good time to upgrade your brake lines to stainless steel. Search for an article on how to make up your own lines.

Post some photos as you go and you'll get some moire advice

It's not paranormal, it's 27 years old and somewhat neglected.

[Nessism]

I concur with Big T. One caution to his post, Brake Cleaner will eat the paint off the caliper. If you use be careful and keep it off the paint if possible.

Brake systems build up gunk on the inside after a while. You should completely dissasemble the system and clean it out. The inside of the line will have scale on it so it should be replaced as well.

Good luck.

[uudfourty]

Awesome! More money!
I've got so much of it just laying around. I've been needing something to do with it.

[Steve]

Awesome! More money!
I've got so much of it just laying around. I've been needing something to do with it.

If that's the case, I'll send you my address, or at least some of my bills. 8-[


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[TheCafeKid]

Yeah no kidding :-D I myself have dumped more money into my 77 cafe project than i ever thought i would. Frankly, combining the price i paid for it, and what ive spent on it since, i could have bought something newer and in much better shape. Thats not the point to me however. The point is im building the bike *I* want. Not what i'll settle for just to be over the wheels. Its all worth it in the end

[robertob]

The inside of the line will have scale on it so it should be replaced as well.

Good luck.

Also, the shop manual suggests replacement of brake lines every two years regardless of miles. It's a very good idea. Not only do they get gunk inside, the liner tends to fall apart and can actually block off fluid movement in the line.

[TheCafeKid]

I had the same problem with my GS750B. Went a little nuts trying to figure out what was causing the problem, and untill talking to a few folks on here it really had never occurred to me the line was bad. I rebuilt everything, even swapped out the whole caliper, and still had a problem with it locking up. I went ahead and replaced the stock line with stainless line and so far (havent had it on the road yet, but seems to be working ok in tests) its seemingly done the trick.

[Nessism]

I had the same problem with my GS750B. Went a little nuts trying to figure out what was causing the problem, and untill talking to a few folks on here it really had never occurred to me the line was bad. I rebuilt everything, even swapped out the whole caliper, and still had a problem with it locking up. I went ahead and replaced the stock line with stainless line and so far (havent had it on the road yet, but seems to be working ok in tests) its seemingly done the trick.

I'd be very cautious about this; brake lines don't cause systems to lock up. If the caliper was swapped out that leaves the master. Pretty scary situation.

[tconroy]

Awesome! More money!
I've got so much of it just laying around. I've been needing something to do with it.

I'll give you my address and you can mail me some!!!!!

[Big T]

Awesome! More money!
I've got so much of it just laying around. I've been needing something to do with it.

After owing mine for 30 years, I can at least schedule when I spend the money. Buying an old bike is an adventure in repair. Ceaseless dweebery, is what my buddy calls it.

I don't think it'll cost you that much. Caliper kits are a glorified O ring. Master cylinder kits aren't much (check Z1, Bike Bandit or your dealer) and lines aren't that bad either. Around $100, I'd think. And imagine how well you'll stop.

[uudfourty]

found the problem... now what?

here's the problem:
inside the master cylinder, nothing moves. I pulled the bottom connector rod that actually pushes up when you press down on the lever off of the master cylinder. Shouldn't that little concave dome piece inside the cylinder move?

If so, that's the problem. It doesn't. It's frozen up in there.

All of the lines move air pretty well and have been thoroughly cleaned out. The caliper pistons look alright.

The cylinder isn't pumping because the pump isn't moving.

Any ideas?

[Steve]

Remove the master cylinder from the bike, soak the piston area with PB Blaster overnight or longer. If that does not free it up, get a new master cylinder. If it does free it up, you will definitely need a rebuild kit, and will also need to hone out the inside to get rid of the corrosion that caused it to stick in the first place. For honing a master cylinder bore, I have used sandpaper or emery cloth, held in a split dowel, turned by my cordless drill and found that it works quite well.


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