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Why would a rebuilt caliper still leak?

cowboyup3371

cowboyup3371

Forum Guru
Past Site Supporter
As I mentioned in my project thread, I have had problems getting firm pressure on the front brakes since rebuilding them again this year. I have calipers from a '89 Kawasaki Ninja 600R while the MC is from a 08 Kawasaki Ninja 650R with year old stainless steel lines.

Well, I think I found my problem - the right hand caliper is still leaking even after receiving new pistons and seals. I was at the garage tonight to finish installing the rear turn signals, tie back the front brake handle, and begin tightening bolts when I saw fluid on the right side of the tire. I placed a paper towel down and within a few minutes noticed a drip fall to the towel. After straightening the wheel and tying the handle back again, I found a small droplet forming on the bottom of the right hand caliper. I didn't time it but I believe it's on the scale of a drip every five or ten minutes maybe? :confused:

I'm leaving the handle tied back for the night and will go by there tomorrow to check it but I think something is wrong with that caliper. I'm just not positive as to why it would still be leaking. Any suggestions?
 
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cowboyup3371 said:
As I mentioned in my project thread, I have had problems getting firm pressure on the front brakes since rebuilding them again this year. I have calipers from a '89 Kawasaki Ninja 600R while the MC is from a 08 Kawasaki Ninja 650R with year old stainless steel lines.

Well, I think I found my problem - the right hand caliper is still leaking even after receiving new pistons and seals. I was at the garage tonight to finish installing the rear turn signals, tie back the front brake handle, and begin tightening bolts when I saw fluid on the right side of the tire. I placed a paper towel down and within a few minutes noticed a drip fall to the towel. After straightening the wheel and tying the handle back again, I found a small droplet forming on the bottom of the right hand caliper. I didn't time it but I believe it's on the scale of a drip every five or ten minutes maybe? :confused:

I'm leaving the handle tied back for the night and will go by there tomorrow to check it but I think something is wrong with that caliper. I'm just not positive as to why it would still be leaking. Any suggestions?
Click to expand...

Damage to the caliper body around a seal so not getting a good seal.
 
After market or OEM seals?? Some have troubles with them..some too tight and the piston wont retract and some that leak. Did the piston go in real easy..almost seeming TOO easy??
 
Second rebuild still leaking. I would call it wear and be looking for a replacement caliper. In an ideal world you could arm yourself with mikes and such but you are chasing numbers around 0.003" so unless you are really good with good gear and know how that translates to real world and not just the manual, you will get meaningless results.
Might be worth opening it up again to see if you haven't flipped or nicked a seal.
 
If the groove where the seal sits is scratched or dirty that will cause a leak. Some rubbing with some wet and dry will fix the problem.
 
Are you sure none of the seals are in backwards? They go in so that the pressure spreads the rubber pieces to make a tighter seal, for instance on a cup shaped seal the open side of the cup goes towards the pressure side so the pressure spreads the cup. if that makes sense. if one is backwards it leaks.
 
So the friend whose garage I'm using and I took the caliper apart and found some small paint chips inside of the piston area. It's possible it got there when I reassembled it but we aren't positive about that. Verified everything was still in good shape, put it back together and bled it. It seems to have a bit better pressure but we'll see if there's any leaks in the AM. The only other things we found was that some teflon tape managed to find its way down around the holes of the bleeder valve but that could have happened while bleeding. I think I might even have a bad line, albeit new, so we'll keep an eye on that too. I put new crush washers on the banjo bolt for it though.

Fingers are crossed....
 
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So far so good; I went by the garage this morning and no leaks that I could see for sure. I took a picture of the garage floor after seeing the paper towel was dry but I'm still keeping an eye on it.



I was able to take a drive tonight (more on that in my project thread) and did some brake tests in a parking lot. It didn't feel like a lockup type of braking but was enough to stop me - especially since I hadn't rode for the last year and it was dark.
 
Whenever you pull apart a main or slave cylinder it is a good idea to clean it up with a 400 wet/dry paper, and use it wet.

This is because over time there will be small pits and/or grooves in the wall. They may not be deep, but they can allow a tiny amount of fluid to pass, and that will decrease brake line pressure, and decrease braking ability.

There are hones for this, as well, but they strip metal away faster than paper, and their overuse can enlarge the cylinder. If you do not have a micrometer, there is no way to know if a PO has done it, so the wet/dry paper is often best.

Work slowly and carefully, so you get even cleaning.
 
tkent02 said:
Are you sure none of the seals are in backwards? They go in so that the pressure spreads the rubber pieces to make a tighter seal, for instance on a cup shaped seal the open side of the cup goes towards the pressure side so the pressure spreads the cup. if that makes sense. if one is backwards it leaks.
Click to expand...


I was going to suggest the same thing, sometimes the seal will roll a little un-noticeably also.
 
jwhelan65 said:
I was going to suggest the same thing, sometimes the seal will roll a little un-noticeably also.
Click to expand...

After we took it apart and put everything back together again, I think this is probably what the problem was. It's been sitting in the garage now for ten days since my one and only ride without leaking. So I'm confident we fixed it.

Thanks for the advice Argonsagas. I'll keep that in mind for my daughter's brakes when we start on those this weekend.
 
Do the tie back the lever trick...youll be amazed at the levers feel after an all night sit.
 
argonsagas said:
Whenever you pull apart a main or slave cylinder it is a good idea to clean it up with a 400 wet/dry paper, and use it wet.

This is because over time there will be small pits and/or grooves in the wall. They may not be deep, but they can allow a tiny amount of fluid to pass, and that will decrease brake line pressure, and decrease braking ability.

There are hones for this, as well, but they strip metal away faster than paper, and their overuse can enlarge the cylinder. If you do not have a micrometer, there is no way to know if a PO has done it, so the wet/dry paper is often best.

Work slowly and carefully, so you get even cleaning.
Click to expand...
I'm not sure I agree with this:confused:
The surface that must be unmarked is the surface of the piston not the cylinder.
The piston moves against the seal but is only guided by the cylinder.
Many times a small pit of rust develops on the surface of the pistons and the leak will start:eek:
Having a nice and smooth cylinder is of course a good thing but if the piston's surface is not perfectly smooth you might aswell throw it away...
 
As John said, if it's not a copper washer, then it would be the piston's surface or the area within the tangential groove that the square seal fit's into. The caliper bore per say does not seal anything.
 
John Kat said:
I'm not sure I agree with this:confused:
The surface that must be unmarked is the surface of the piston not the cylinder.
The piston moves against the seal but is only guided by the cylinder.
Many times a small pit of rust develops on the surface of the pistons and the leak will start:eek:
Having a nice and smooth cylinder is of course a good thing but if the piston's surface is not perfectly smooth you might aswell throw it away...
Click to expand...

Good insight. But the rubber cup on the piston seals against the cylinder wall, so any grooves or pits in the cylinder will prevent the cup from sealing, correct?

S.
 
Try using some red rubber grease, had a similar problem with a 4x4 caliper fitted new seals and pistons (aftermarket) but started leaking past the seal! stripped it again using a smear of red rubber grease on the pistons and seals never been a problem since.
 
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