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1981 GS850G rear brake master cylinder (I need help)

S

Slowride

Forum Newbie
It's been a while since I was a member of this forum but I'm back because, as in the past, I needed help and I always received great advice and assistance from members here.

I'm pretty sure I need to rebuild (or buy new) my rear brake master cylinder. I have a 1981 GS850G. Can anyone tell me a good place to either buy a rebuild kit or a new master cylinder? I live in NE Ohio if that is any help. My local Suzuki dealer told me last year (when I needed something) that they can't help me because I bike is too old.
 
Ok, start by describing the problem
Then, when was the last time you flushed your brake fluid?
Have you replaced the brake line?
 
I can't remember the last time I flushed the brake lines. I started by pumping the brake pedal, as if I was going to bleed my lines and nothing came out from the calipers, so I worked backwards to the master cylinder. I opened the connection where the brake line meets the master cylinder and again, pumped the brake pedal, again, nothing came through. I took the master cylinder off the bike and started to take it apart. I removed the push rod but the insides of the master cylinder did not come out. As of now, I have it sitting in some penetrating oil with hopes I can remove the inside to rebuild it. I ended up seeing there is a parts section on the forum and ended up ordering the rebuild (inside parts) from Z1Enterprises. I hope I'm on the right track.
 
You should be able to rebuild it as long as the bore is not too corroded.. Did you order a new piston? That's usually the bit that corrodes worst. I fitted on from an EX300 on my skunk but was a bit of messing around. Did a thread on it somewhere. I think one from a V Strom could be made to fit as well... :)
 
Yes, I did order a new piston. Hopefully tomorrow I'll see if the penetrating oil freed up the pieces inside, piston and all.
 
You could also try boiling the master cylinder in a pot of water to dissolve the gunk and hopefully the piston, etc will come out.
 
Luckily most Suzuki rear masters are straight thru, remove the banjo bolt from the top & use a punch to push the piston & innards out the bottom. I've not heard of the boiling thing, but will keep it in mind in the future.
 
I pushed the piston out this morning and the inside of the master cylinder looks pretty clean (I think I got lucky). While I'm waiting for the new parts to arrive, I figure I better flush out my front brakes and maybe try to clean my rear calipers. Any trick to getting the pistons out of the calipers?

I haven't ridden the bike in over a year so if the weather ever improves here, I'll be able to get out for a ride.
 
For the rear you have to split the caliper. There is an O ring in the middle. You can use air pressure or grease pump to move the pistons... :)
 
Thanks. Great info. I'll have to attack it tomorrow. The weather here was nice today so the yard work took priority.
 
The piston and spring arrived this evening. I purchased the KL kit from Z1 and I saw it is also for several other bikes. There seems to be an extra rubber seal with the kit. Since my bike is a GS850G, am I to assume it is for another bike? If not, where does it fit within the assembly?
 

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The photo in the previous post is the original piston and spring. This photo is the new kit. The rubber seal in question is the one to the right. Any idea if it is an extra part for another rebuild or what do I do with it? There is no center hole in it.

image.jpg
 
Please read my previous three posts. Where does the "cup" (rubber seal) fit in with my rebuild? I have looked at diagrams but they are not clear. In the diagrams, it looks like it might fit on top of the piston and the base of the spring fits inside of it. When I took my master cylinder apart, there was not a rubber cup in it. Maybe I'm assembling it wrong. I thought when I took apart my master cylinder, the fatter part of the spring came out first. Does the tapered end of the spring go into the cylinder first or is it just the opposite?
 
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OEM is always, always, always, always best if it's available. And in this case, it is available. K&L parts are very often problematic, and their application charts are often off base.

That said, these imitation parts are what you have in hand and they might even work. Just be aware that they also might not.

Hard to tell -- the piston and seal are definitely visibly different, but I don't know whether they differ in a way that matters.

Here's the OEM parts diagram:
https://www.onlinecycleparts.com/oemparts/a/suz/50d40183f8700230d8b4e4f8/rear-master-cylinder

In your photo, no one can really tell for sure what that added blob is.

It may be a boot, #6 in the diagram.

It may also be a different seal, and you're intended to change it depending on the application -- note how the seal in the imitation part seems shorter than the seal in the original. The blob seems like it might possibly be a taller version of the seal? Hard to tell.

This is a better-lit photo from K&L's website showing a completely different master cylinder kit. The thingy on the left is the boot that keeps muck out of the MC. The blob in your photo is differently proportioned, but if it looks like it performs a vaguely similar function, then that might explain it too.
32-1118_l.jpg
 
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So, does the tapered part of the spring go in first or does the larger diameter end go in first? I put the wider end in first, then the smaller diameter end seemed to fit into "cup" with the bottom of the cup coming in contact with the piston. It seems to move ok but I'll have to see what happens when I put it back onto the bike and connect the brake line. I may just end up buying the OEM parts.
 
Oh, by the way, years ago when I was working on my bike you (bwringer) helped me a lot. Thanks, I appreciate your time and expertise.
 
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