Brake Overhaul - Rear Master Cylinder Leak question

[chuck hahn]

Try the existing one and do the lever tie back thing..what they heck, if its all good and you now know everything inside is cleaned then why waste the cash on a part you dont really need? If it doesnt work or leaks..then order the piston..You can have it back apart in 10 minutes now that you know the procedures. Then again if you just want that new part piece of mind then yeah order another one.

[chuck hahn]

I would, at the least, replace the oring before giving it a whirl though.

[scott]

Then again if you just want that new part piece of mind then yeah order another one.

I think I'll just add a new front piston/cup set to the list - I'm compiling quite the list of parts for this. My biggest concern was that I'd get a new piston/cup set and the bore was in too bad of shape that it would leak.

Just when I think I'm ready to place a parts order, I remember something else to check. My front caliper piston looks fine but the 2 rear caliper pistons have some pitting. I've seen pictures of really bad pistons on here and mine aren't like that. Are things like this anything to be concerned about:



The small pits on the side feel smooth but the bottom edges are a little rough.

[hampshirehog]

Those pits on the side will be enough to make the thing leak. If they are on the outside of the seal then then you are ok though - you'll have to take a look to check.

If you want to play safe fit stainless - job done forever then./

[scott]

Those pits on the side will be enough to make the thing leak. If they are on the outside of the seal then then you are ok though - you'll have to take a look to check.

How do I check that? Measure how deep the o-ring ridge is from the bottom of the caliper bore and compare to the height of the rust spot?

Maybe I'm getting ahead of myself, I assumed my rear caliper was fine but there is some corrosion. I didn't think it was a big deal but ...

Here is the main side of the rear caliper:


And here is the other side:

[oldrookie]

I can tell you to be VERY careful when putting the rubber boot back in (the one you had such trouble getting out.)

Accidentally punched a hole in my new one and had to order another entire piston and cup set to get a new rubber boot.

[scott]

I can tell you to be VERY careful when putting the rubber boot back in (the one you had such trouble getting out.)

Accidentally punched a hole in my new one and had to order another entire piston and cup set to get a new rubber boot.

Ouch! That's the most expensive piece too.

From what I can tell, the open end of the boot was over the washer / circlip which is why I had so much trouble. I have no idea how it was installed like that though. I was planning to just push the boot on until the small opening got over the push rod end and not push it REALLY in to get around the washer, if that's even possible. It's not like the boot can slide out once it's installed on the bike (I don't think) so I don't see why it would need to be "locked" in there.

[oldrookie]

Circlip goes on first, boot sits on top.

Planning to try a Q-tip soaked in brake fluid to push the rim into the appropriate groove. I know for sure that the, "Hey, this set of needle-nose pliers doesn't look real sharp" method is a recipe for disaster.

[scott]

Circlip goes on first, boot sits on top.

Planning to try a Q-tip soaked in brake fluid to push the rim into the appropriate groove. I know for sure that the, "Hey, this set of needle-nose pliers doesn't look real sharp" method is a recipe for disaster.

Okay, so the inner groove, inside of the breather hole, is for the circlip and and the outer groove (on the other side of the breather hole) is for the dust boot rim. Makes sense.

[scott]

I measured the piston's rust pits and the caliper bore.

All of the rust pits seem to be around 14mm or higher from the bottom of the piston:


The groove for the o-ring in the caliper bore seems to be about 11.5 mm to 16.5 mm from the bottom of the caliper bore.


Does this mean that any pits below 16.5 mm could cause leaks and that I should be looking at new pistons?

[hampshirehog]

I wouldn't risk it. A pair of stainless rears is only about £20 and it's job done forever then. And no need to buy the rubber boots either.

[scott]

I wouldn't risk it. A pair of stainless rears is only about £20 and it's job done forever then. And no need to buy the rubber boots either.

I think that would be roughly $32 USD which doesn't sound bad. My rear caliper pistons are roughly 38mm outer diameter by 22 mm high. I tried doing some searching but haven't found any stainless pistons in that size. Is there a UK site that the GS people use to get the appropriate pistons?

It looks like I can get the OEM piston set for around $42 which I think includes the o-rings, boots and the seal between the caliper halves. I would hope even the non-stainless OEM pistons wouldn't start rusting THAT quickly (or would they).

[hampshirehog]

Best place to buy them is from this guy:

http://www.ebay.co.uk/itm/Suzuki-gsxr-rear-caliper-pistons-Booted-/390367523674?pt=UK_Motorcycle_Parts&hash=item5ae3b7b35a

(yes, those pistons are identical to the ones you have, just in stainless).

He does them without the groove for the dust boot and they are fine as well (no need to fit that boot when you go stainless).

[TooManyToys]

......He does them without the groove for the dust boot and they are fine as well (no need to fit that boot when you go stainless).

That's really a bad idea.

[1_v8_merc]

I've sanded down pistons worse than those...never had a leak.
But i'm dirt cheap, I'll take the chances with my Rear Brakes....never my fronts!

I'm not telling you what to do, if you have any doubts, get new ones, or get some cheap calipers off ebay.