KZ900 Front Brakes

Hello everyone. So, I salvaged a KZ900 in really bad shape (paid $200). I've done a lot of work on the bike (see pictures), and I've opted not to restore it to original condition just to save some time and money. Anyway, I am now getting to the brakes. My bike has dual front caliper brakes. I'm far from a brake expert, so I'd rather just have new front brakes than rebuild the ones I have, but I couldn't find anything online. So, instead, I took them apart and cleaned them up. The old pistons were pretty pitted and beat up and all the rubber/plastic parts were in poor shape. I purchased two rebuild kits and rebuilt the brakes. I have all new brake lines, master cylinder, splitter, etc. I am in the process of adding brake fluid and bleeding my lines, but I have discovered that both brakes are leaking at the piston. Is there something obvious that I am missing here? The seals on the pistons are new along with the pistons. The only thing I'm not certain about is installation of the dust seal. There were no directions with the kit, and I really couldn't figure out the correct orientation for this thing. Could this be the issue i'm having? I'll try and get some pics added so you guys can help me better. Thanks for the help.

Nice project.
 I fixed your pictures. Next time click the insert all tab.
Did you have problems with the piston ring rubber seals fitting 
Nice polish job on the wheels . what did you use on them
Dave

Will do. Thanks for the heads up. I didn't really have any issues with the rubber seals fitting. Everything seemed to be going very well. 

I used Bar Keepers Friend. The stuff is magic. 

There is a seal that fits inside the cylinder, in a groove.  It's critical to ensure this groove is clean of any build-up.  I normally go in with a sharp pic to clean everything out.  

The only brake parts I trust are Brake Crafters. That being said I agree with HRM. The caliper bore must be 100% clean and clear of all corrosion and debris. Red rubber grease or brake fluid is needed to assemble the caliper. The piston seal is installed into the grove in the caliper bore. Then apply lube to the bottom radius edge of the piston, and a very, very light smear on the sides of the piston. Two methods of installing the piston work. 1) tip the piston slightly as you insert it into the bore, square it to the bore as you feel the piston start to slip past the seal. 2) insert the piston into the bore square and slightly twist to get the seal to slip onto the piston. Either way push the piston all the way to the bottom of bore once it passes the seal. It should be hard if not impossible to pull up. That’s resistance is what helps retract the piston when brake pressure is removed. 

The dust seal sits under a thin metal ring the needs to be gently pressed into the caliper. It sits around the piston. The dust seal is slid over the piston. I usually slide it on past it’s receiving grove on the piston to give you a little more material to work with. Again lube here is your friend. Use your thumb and finger to pinch and pull the dust seal over and under the retaining ring. It’s easier if you start at the top of the caliper (as installed) get it under the retaining ring and work it around. Verify it is a consistent shape. If it’s not under the ring correctly it will not be symmetrical. Once your sure it’s under the ring and symmetrical then pull the dust seal toward the open end of the piston and into its grove. 

Regardless of the dust seals installation it has no effect on retaining fluid. That is 100% the job of the piston seal. Either the seal rolled, came out of the grove, it’s the wrong seal or the wrong piston size, or the grove is contaminated. But it’s not the dust seal leaking. 

Guys, I appreciate the information. It sounds like I'm going to try a rebuild again. FYI, the rebuild kit came from Brake Crafters. The piston was brand new and clean, and I installed the seal into the groove, but maybe the cylinder was not so clean. The piston did fit snuggly, which I would assume is a good sign here. I will try the technique you are suggesting Mikaw. 

Couple Questions:

1. I don't have a metal ring, which is probably why I was confused about the dust seal and what it was actually doing. Any suggestions on where to get one? I imagine brake craters sells that also?
2. Do I even need a dust seal?

Thanks!

wrote:

Guys, I appreciate the information. It sounds like I'm going to try a rebuild again. FYI, the rebuild kit came from Brake Crafters. The piston was brand new and clean, and I installed the seal into the groove, but maybe the cylinder was not so clean. The piston did fit snuggly, which I would assume is a good sign here. I will try the technique you are suggesting Mikaw. 

Couple Questions:

1. I don't have a metal ring, which is probably why I was confused about the dust seal and what it was actually doing. Any suggestions on where to get one? I imagine brake craters sells that also?
2. Do I even need a dust seal?

Thanks!

Here you will get the metal ring part# 43049-002

z-fever.de/shop/en/?cat=c662_CALIPER---B...-DISC-FRONT-662.html

 

Yes you need the dust seal. I’m sure the piston seal would fail relatively quick without it

Just a heads up, I'm not sure i'd use those old invader wheels on a Z900, apart from being heavy, they were prone to crack where the spokes meet the rim.....

wrote:

wrote:

Guys, I appreciate the information. It sounds like I'm going to try a rebuild again. FYI, the rebuild kit came from Brake Crafters. The piston was brand new and clean, and I installed the seal into the groove, but maybe the cylinder was not so clean. The piston did fit snuggly, which I would assume is a good sign here. I will try the technique you are suggesting Mikaw. 

Couple Questions:

1. I don't have a metal ring, which is probably why I was confused about the dust seal and what it was actually doing. Any suggestions on where to get one? I imagine brake craters sells that also?
2. Do I even need a dust seal?

Thanks!

Here you will get the metal ring part# 43049-002

z-fever.de/shop/en/?cat=c662_CALIPER---B...-DISC-FRONT-662.html

 

Just a little tought about the parts diagram, where is the piston seal? Looks like KHI miss it in the diagram or the ring comes only with the caliper body!!!

It’s number 15. I always took care not to lose mine. I wasn’t sure they were available alacart. Scirocco always finds the coolest best quality parts. 


EDIT. Never mind you were talking about the seal. But you do find the best stuff!!!

Thanks Scirocco. German website is the only option for these rings? Expensive as hell!

Is there a preference on whether the brakes should be front or rear mounted on the front wheel? I've seen both. I have the forks arranged for a front mount, which looks better to me.