Master cylinder questions

[Guest]

If it ain't one thing it's another is right! This thing's going to have me broke before I get a thousand miles on it! It's not being very appreciative of my attempts to save it.

Get the motor running smooth as silk (going to wait until off-season to try to fix the weeping head gasket), get about 30 miles on it, and now the front brake is staring to lock up when it's hot outside OK, it's parked until fixed, again. So now I know I must clean out the master cylinder and un-block the little holes under the reservoir. That's all well and fine, but...

The front master cylinder on my bike does not match the parts fiche. An 82 GS550LZ should have one of the square master cylinders, but mine has a round reservoir with the fake wood-grained lid. A LOT of the parts on this bike look more like 80 or 81 parts. And the 81s at least had a round reservoir. But mine is a straight cylinder; the parts fiche looks like the reservoir should have some tilt to it.

OK my question really is, how interchangeable are the master cylinder parts on the GS series? If I take it apart and find parts need to be replaced, how do I know what to order? Were they all the same? Should I just buy a used master cylinder of known origin so I can be sure what parts I would need? (If so, got one for sale cheap?) What other bikes might I be able to transplant a MC from?

Thanks in advance.

[Nessism]

Are the parts numbers the same for the different piston kits?

[mike_of_bbg]

OOh, fast. And that's a good question! Thanks.

Looks like the pistons are compatible between 80, 81, and 82 model GS550Ls; square or round reservoirs. That's good but, if I look at say a GS750L, it's different. Would that be a possible swap? I didn't really see one, but should there be a part number stamped somewhere? Fact is, I really can't be sure this MC is from a GS550L at all. What would make an acceptable switch? Would it have to be another single-caliper bike?

[Nessism]

Single disc masters have a 14mm piston and dual disc masters are 5/8". The master typically has engraving that states which type it is.

[duaneage]

There are significant differences between the master cylinder internals over the years. I ordered a kit for the 650 and what came was for a 750, Both were dual disk but completely different.

You can replace the entire unit just be sure to do dual master cylinder on duals and vice versa, I would not play around with brakes, do it right and don't take any shortcuts.