Brake Overhaul - Rear Master Cylinder Leak question

[scott]

Spray some more in tomorrow and try to spin it. Don't even try to pull until you can get it to spin. Once it twists a little, spray some more PB Buster in there until it comes free. Be careful with compressed air. You've got a potential bullet there.

No luck with the PB Blaster or my small air compressor.

The push rod spins fine - it just doesn't pull out. If the front is similar to the back and there is a push rod with a "cap", maybe the cap part is rusted to the master cylinder body?

 

[hampshirehog]

You're going to have to resort to heat. PITA as you have to take the plastic bits off and repaint the thing but sometimes it's the only way.

 

[chuck hahn]

Shouldnt be a cap per say..maybe a washer is rusted in place. Take a small flat tip and see if you can hook it just under the edge of any lip and try to gently pry it up.Maybe take a wire bent at a 90 and feel around to see if it " slips under " any rim just below the leading edge.

 

[scott]

Success! I was able to hook the end of the ripped boot with a pick and put it out some before it snapped. Then I used needle nose pliers to keep pulling at the pieces of rubber until I got most of it out. Then it all pretty much fell out! Thanks for helping with all the ideas.

Of course, now that I can inspect the bore and it doesn't look as good as the rear master cylinder. It seems to be rusted near where the oring was. Is this shot? I may need to get a better pic.

 

[chuck hahn]

bore brush and some hoppes number 9 is my go to soultion for removing that crap..get it scrubbed out real ggod and then youll be able to see what going on better..so there was a bit of boot rubber holding it back then?? I hadnt thought of that possibility, but i will remember it.

 

[scott]

bore brush and some hoppes number 9 is my go to soultion for removing that crap..get it scrubbed out real ggod and then youll be able to see what going on better..

I'll see if I can get my hands on that. I thought MAYBE it could be that it's only the groove holding the snap ring / circlip that rusted rather than the o-ring groove.

so there was a bit of boot rubber holding it back then?? I hadnt thought of that possibility, but i will remember it.

Apparently. When I tried to remove the boot, it ripped off and left the bottom part. I didn't think it would be an issue. Should the boot wrap around the washer? It seemed like it was in my case.

 

[scott]

I picked up some Hoppes Number 9 and a gun cleaning kit that includes various bore brushes. I applied the solvent with q-tips and scrubbed with the brass bore brushes. It definitely seemed to help.

I'm having a hell of a time photographing the bore - this isn't really what it looks like to my eyes but:

It seems like the rust/pitting stops at the grooves. Deeper in, everything seems smooth.

 

[chuck hahn]

Youll probably be alright..heck throw it back together and bleed the system well and see how the lever feels. Look for any leaks. Worst case scenario is you gotta replace it

 

[chuck hahn]

Hoppes is designed to disolve the powder and copper fouling from gun barrels and is equally as good at disolving the scale and crust in the bores. may swab some more on the worst looking spots and let it sit for a half hour or so to get good action.

 

[scott]

Hoppes is designed to disolve the powder and copper fouling from gun barrels and is equally as good at disolving the scale and crust in the bores. may swab some more on the worst looking spots and let it sit for a half hour or so to get good action.

It definitely helped - I used it to clean out other parts of the master cylinder, not just the rusted parts. The fumes started to get to me though - I should have used it in a better ventilated area.

Youll probably be alright..heck throw it back together and bleed the system well and see how the lever feels. Look for any leaks. Worst case scenario is you gotta replace it

I assume I should order a new piston/cup set, right? Or do you mean I should try it with the existing one?

I've been waiting to place an order for all the brake parts which includes a piston/cup set for the rear in addition to the various seals, o-rings, etc. I was guessing I'd need either a new piston/cup set for the front or a whole new front master cylinder (which don't seem to be available).

 

[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?