1980 KZ750H leaking front right brake caliper

Hello all, haven’t posted here in a few years, but I did manage to get the old KZ roadworthy (well, it was anyway) since the last time I posted.

Anyways, I installed new SS front brake lines along with a new master cylinder (from a ZX6R, iirc) yesterday, and was having trouble getting the lines bled as I ended up calling it a night after it had gotten dark out. What I had failed to notice in the dark was that I appear to be having brake fluid leak out from around the threads of the bleeder nipple on the right front caliper, which is likely why I was having trouble getting the lines bled. 

To clarify:
1) I put aftermarket handlebars on because I couldn’t stand the stock bars. As such, the bend of the lever on the stock MC didn’t match up with the new bars, so I went with the ZX6R MC. 

2) The bleeder nipple didn’t leak before, but while I had the lines off, I noticed the rubber cover for the bleeder nipple was installed backwards, so I removed the nipple, flipped the cover over and reinstalled. From what I can tell, I didn’t damage the threads of the nipple or the MC when reinstalling. 

3) The front brakes worked before yesterday, but the feel in the lever was never really all that great. It always stopped the bike though.

Is there any kind of o-ring in there that might have been damaged? Would a new bleeder nipple solve this issue? If not, am I looking at finding a caliper? I’ve never run into any vehicle leaking fluid from the bleeder nipple, so this one has me stumped. 

Thanks in advance!

 

A new bleeder screw would be a cheap gamble and might solve the problem, but I bet there is either some junk in the threads preventing the screw from seating, or the threads in the caliper are toast.

I would take the screw out and take a careful look at the hole. A flashlight might help.

I’ll try to check that out tomorrow after work. I’m inclined to think that there isn’t anything gunking up the threads since I noticed no unusual resistance when threading the bleeder screw back in, but it’s worth checking it out. I suppose I’ll order the bleeder screw and hope for the best.

The bleed nipples rely on the taper seating in the hole to seal so the slightest debris will cause a leak if the taper isn't seating

Would it hurt anything to take the caliper off and run it through an ultrasonic cleaner? I happened to get on the harbor freight website and turns out they are less than what I thought they would be so I’m going to go pick one up since I’m sure I can find uses for it. 

Haven’t messed with the bike today, but I did manage to find a caliper on eBay so I ordered that just in case I can’t get the one I have in working order. I’m wondering if maybe I didn’t overtighten the bleeder screw and maybe messed up the seat in the caliper? I did pull the bleeder screw out the other day and I didn’t notice any damage to it. I’m not sure if the caliper seat would be made of softer metal than the bleeder screw?

TooMuchJunk wrote:

Would it hurt anything to take the caliper off and run it through an ultrasonic cleaner? I happened to get on the harbor freight website and turns out they are less than what I thought they would be so I’m going to go pick one up since I’m sure I can find uses for it. 

Haven’t messed with the bike today, but I did manage to find a caliper on eBay so I ordered that just in case I can’t get the one I have in working order. I’m wondering if maybe I didn’t overtighten the bleeder screw and maybe messed up the seat in the caliper? I did pull the bleeder screw out the other day and I didn’t notice any damage to it. I’m not sure if the caliper seat would be made of softer metal than the bleeder screw?

First thing I'd do with that caliper is pop out the piston and perform a full tear down.  Brake calipers are not "sealed for life" components. They need maintenance.  Inspect the piston for pitting, clean out all the corrosion, which is sure to be present after 44 years, etc.  An ultrasonic is useless for this sort of work.  Bleeder nipples are cheap, so I'd order one straight away too.  I'd also get new OEM seals and dust caps.  Start fresh with a properly rebuild caliper, and go from there...

Hey TooMuchJunk - ultrasonic won't do any good for your caliper, but if you're thinking of getting one for carb cleaning, etc I would stay away from the harba frate ones. Some of their stuff is good but their ultrasonic cleaners not so much.  I ended up on amazon and got a reasonably priced Creworks brand 6.5 liter one that will fit 3 disassembled carbs (you are planning on breaking the rack apart, right? ) then the 4th one and a few extra parts. Cleans them up nicely.  They're all chinese made but some are a little better than others.    But Nessism is right, rebuild your caliper(s) the right way as he described.

I was thinking an ultrasonic cleaner because Wookie mentioned debris in the bleeder screw hole and I’m really not sure what would work to ensure there’s no trash left in there besides tearing it apart and spraying the hell out of it with brake cleaner. I’m open to ideas for cleaning it out. Anyone have a preference on the bleeder screws? Found OEM ones on eBay for $15ish. Saw Z1 had speed bleeders for about the same price for two. Are the K&L rebuild kits ok?

Also, no plans to mess with the other calipers (assuming they don’t give me any trouble) as the shop I had work on the bike last year rebuilt pretty much the whole brake system, among a ton of other things a bike that was sitting for 30+ years needed. I would have had them put new lines on at the time, but I didn’t know I was going to change the handlebars out til I started riding it. Carbs I will likely bring back to the shop to do as they need to be jetted since I put a 4-1 Ripple Rock Racers/Hindle exhaust, mostly because I’m terrified of 1) managing to actually get them on/off the bike and 2) screwing up the sync to the point I have to bring it back to the shop anyway. Would be nice to save the money to DIY, but it intimidates me. 

After you've owned an old motorcycle for a while, you'll start to overcome the intimidation of DIY.  
As you gain more confidence the guys here can help you a lot.