Super irritating brake issues

[Guest]

Okay so I have had a 1980 gs550e parts bike for about two years now, but never really had motivation to do anything with it because it had no title and I couldn't ride it on the road. However, I found a clean title 1981 gs550L over thanksgiving for a good price and jumped on it because I would basically have two bikes for any parts I would need. The bike had a very obvious air leak and upon tearing it all down, I found that every single carb intake boot holes in the back of the motor were stripped and not sealing. So I bought a helacoil kit and repaired that bit, got everything else buttoned up and got it running like a top. NOW is where I find the problem. As I took the bike for a spin to make sure everything was mechanically sound, as I would come to a stop, I would slow down extremely fast before I even got on the brake. I leaned over and looked at my front caliper and there was steam rising from it. The brake was stuck and the bike wouldn't move. I was a few miles from my house so I had to get it unstuck. I put the bike on the center stand and heel kicked the **** out of the caliper. The brake released and I was able to get home just using the rear brake for stopping, I didn't use the front brake again. When I got home, I let the bike cool off before I began wrenching on it and when I came back out to investigate, the rear brake was now stuck and the front brake was stuck again as well. I then took the front caliper off my parts bike and blew out the brake line with compressed air and re-bled the system. Front brakes worked again. Took the rear caliper and master cylinder apart and ordered rebuild kits for them. Parts come in, I rebuild the rear and reinstall it, works like a dream. Go for another ride, and everything performs phenomenally. Get home, put it on the center stand and come inside for a bit to warm up. I come back out about an hour later to out the bike in the garage and when I take it off the center stand, **** me sideways if the front brake is not completely locked up and I can't move the bike at all. So I again heel kick the caliper and get it unstuck enough to move the bike, get in the garage and begin tearing it down. So, I concluded that the problem must be in the master cylinder. I take that off and tear it down. It is full of rust and god knows what else. I then ordered a rebuild kit for it off of amazon only to find that when I searched for "1981 gs550L front master cylinder kit" it showed me a 1983-1986 gs550L kit. Now I know the pistons are going to be a bit different, but is it close enough to make it work?

[tkent02]

It sounds like the return port or compessation port in the master cylinder is blocked. Tiny hole. You should also use new brake lines, yours are full of thirty year old crap.

[prometheus45]

Any idea on how to remove the reservoir from the master cylinder. There looks to be a large O-ring at the base, but I don't know if it is threaded on or if it is a press fit. I want to let the master cylinder bathe in a carb cleaner bath for a few days to clean the passages, but plastic is not safe in the bath.

[tkent02]

There are a few different type reservoirs. Are there screws down at the bottom of the reservoir?

[prometheus45]

It is the cylindrical type reservoir. And yes there were screws that secured a circular plate to the bottom the reservoir and I removed them, but after that, I have no clue.

[prometheus45]

It is the front master cylinder model X if that helps at all.

[tkent02]

A picture would help more.

[prometheus45]

[Nessism]

Better replace the old brake lines and tear down the calipers while you are going through the system. Bet you a six pack the calipers are full of brown crud.

[prometheus45]

I rebuilt the rear caliper and rear master cylinder, but the front caliper off my parts bike is perfect. That front master cylinder is torn apart and awaiting the rebuild kit. And I'm gonna use my current brake lines. Just flushed them out an blasted the hell out of them with compressed air.

[Nessism]

Do what you want man, but Darwinism won't be denied.

[prometheus45]

I believe that is actually Murphy's Law, though I do agree with you. And having something catastrophic occur with the brakes is probably one of the most dangerous things that could happen. While it's colder than Frosty the Snowman's nipples, I should get all of this stuff taken care of anyway. Thanks mate for the advice. NOW, if I can just figure out how to remove the reservoir, I will be golden.

[Nessism]

I believe it just pulls out after removing the screws. The O-ring is likely petrified which is making the task more difficult.

[prometheus45]

I need to remove it, but I don't really want to ruin it in the process like I did the rubber boot for the piston. If anyone knows any tips on how to remove it, it would be much appreciated. Completely irrelevant to the subject, but I put the "GS550E" side cover emblem on my GS550L and when my dad saw it, he said "that's blasphemy." I would really like to figure out how to put the E's seat and tail section on my L, but modifying the frame just seems wrong right now. Eventually, I'm gonna make a flat tracker/ brat seat. I initially wanted to go cafe racer with the bike, but I am 6'4" and rear sets are super uncomfortable. I rode my buddies cb750 cafe around a little bit and my knees felt like playdo when I got off of it.

[eil]

The reservoir will come out if the screws are removed, but it does take some persuasion. I don't advise hitting it with anything. Just get a good grip on it and wriggle like crazy.