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Discussion Starter #1
This is a long shot, but I am hoping someone knows where I can get a 14mm diameter brake piston with the pressure seal at a distance of 32mm from the pusher end of the piston (see attached picture). The piston does not have to look anything like the drawing as long as those two key dimensions are met. The master cylinder and parts for the master cylinder are no longer available anywhere and I don't want to trust buying used parts that are 36 years old. The 32mm distance can be a couple of mm shorter but not longer.

FYI this is for a 1984 ZN1100 LTD Shaft.
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If you can't find the correct piston, you might be able to get a different one & swap the rubber seals. There are two pistons listed for the 1000J models & one of them is the same as the ZN1100 (part #43020-1035, NLA). The other piston assy is still available: 43020-1019. Partzilla has a pic of it. It may be that the J1 had the -1019 piston, then Kawasaki made a change for the J2 or J3. Just guessing here.

edited: to correct the -1035 part number.
 

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Discussion Starter #4
This business shows the master cylinder as if it is available. Might want to call if you can handle a complete MC.
Unfortunately the ZN700 and ZN1100 do not share the same master cylinder, but thanks for checking.
 

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Discussion Starter #5
There are two pistons listed for the 1000J models & one of them is the same as the ZN1100 (part #43030-1036, NLA). The other piston assy is still available: 43020-1019.
Martin I think you nailed it. The piston does not look identical but since it is effectively a cross reference and since scaling the drawing makes it look like the critical dimensions are there I think it will work. So I have gone ahead and ordered one with fingers crossed. Just for reference for others that may have to follow the same path, here is a picture of my piston. And for the record, I think you made a typo on one of the part numbers. The ZN1100 part number is 43020-1035. The cross reference piston that I hope will work is 43020-1019. I will post back here when the piston arrives.
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Good luck. I corrected that part number. sorry about that. I got the idea for swapping the seals from another forum in regards to another model.

Kind of related, someone else found that a K&L Fr brake piston kit from a different model will work on the Z1R Fr mc. He noticed that the K&L part looked similar to the Kawasaki part & took the chance. He measured the heck out of both w a digital caliper & found that any differences were inconsequential to the function. I saved a pic comparing the two.
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Discussion Starter #7
Thanks Martin. Shared knowledge like this helps us keep our vintage bikes rolling and underscores the value of forums like this. On the note of shared knowledge, I called Brakecrafters and spoke with a very helpful, knowledgeable lady there. She researched the issue and reported back to me that in that era, Kawasaki was experimenting with a lot of different configurations of pistons and master cylinders. It seems that the design used on the ZN's fell out of favour and thus have become no longer available. To try to find something that would work, she even measured several pistons for me and I ordered one that was close (BC265M). Upon arrival however, I found it was a few mm too long. I was preparing to machine it so it would work, but figured I would try one last time by posting on this forum.

I am hoping the -1019 piston will be a direct fit, but in the alternative hope the seals can be swapped.

Another interesting thing: The OEM piston is made of steel whereas most third party pistons are made of aluminum or white metal. I was not too happy about running aluminum on aluminum since the MC is also aluminum.
 

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Thanks. As for the material, I read somewhere that some of the aluminum pistons have a steel insert where it contacts the brake rod plunger or whatever it's called. I don't think I've ever seen that. or maybe just didn't notice.

Also related, I think an earlier 650B Fr brake piston will work on my 81 KZ650-CSR Fr mc. They look pretty much the same. I haven't tried it, because I went with a modern Honda mc after swapping handlebars.
 

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Discussion Starter #9
The BC265M piston does not have any inserts. Looking closely it appears to be die cast and then machined. A magnet won't stick to it anywhere so my guess is it is aluminum or white metal. It is an interesting design though. The spiral groove allows for brake fluid to pass freely to both seals while also providing lubrication for the sliding contact of the piston and its bore. It also provides a greater surface area of contact with the MC bore because the top of the spiral groove is sized to fit the bore. Here is a picture.
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Discussion Starter #10
Ok, the new piston 43020-1019 arrived. It is also too long, but the seals might fit the old piston. However, the old piston is badly pitted at the pushrod end. Sigh. I have posted a picture of my old one next to the two new ones.
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Even though it's different, could it still be used?
Or are there differences in the other master cylinder parts?
 

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Discussion Starter #12
The reason the 32mm dimension is so critical is because if it is longer, then that puts the lip of the pressure seal past the brake fluid supply hole. This means that fluid from the reservoir can never reach the pressure side of the master cylinder. So while I could tolerate perhaps a 30mm distance, a 34mm distance will not work. I looked at drilling a new supply hole, but I don't have enough room to do that. It looks like I will have to machine a new piston or try to repair the old one.

What I did learn from all of this is that Canada (and I think California) use a different master cylinder/piston than the rest of the USA. The Canadian ones are no longer available and as I now know, the Canadian ones use the shorter piston and presumably a shorter master cylinder.

What I also learned is that it is incredibly difficult to remove these seals and damage to the seal is very likely. So I will be returning the pistons that don't fit and I have ordered two new seals and when those arrive, I will machine a piston to suit.
 

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Discussion Starter #13
While waiting for my brake seals to arrive I decided to try my hand at shortening the BC265M piston from Brakecrafters.

This piston is a popular design on many Kawis but was about 2 mm too long. I am pleased with the results and I think I will try this out. I may still build a brand new steel piston from scratch when the seals arrive, but for now will put this one to the test. It has the advantage of the new, free-floating pressure seal design along with greater support offered by the square threads. See pix below.
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Discussion Starter #14
I forgot to provide an update to this "project" so here it is:

To finish I still had to source a seal to fit the groove shown in the above photo. I considered pulling a seal off a brand new but different Kawasaki piston, but figured I would destroy the seal in the process and since the piston cost $60 that would be one heck of an expensive seal.

So I sourced a nearly identical 14 mm seal that is used in brake cylinders of racing go-karts for $8.50. I got mine from Brake Seals :: Brakes :: Comet Kart Sales it was the two lip seal that is needed since it has to seal on the bore of the cylinder and on the piston itself at the bottom of the groove, therefore two lips are needed.

Now the problem is, how does one stretch a rugged oil seal like this to nearly twice its diameter without destroying it?
I used a very gradually tapered wooden dowel, covered in greased electrical tape and slid the seal up the taper until it was big enough to fit over the head of the piston, It worked, but it took so much force that I may have damaged the seal.

In any event, the end result was that the seal wept brake fluid. After all that work I wept too.:cry:
So what now? It will work for my first test ride so that is the current focus. The brakes will function, but a tiny amount of brake fluid will leak with each hard application of the rear brake. So with good front brakes I will get it out for a test run and then figure things out.

To be determined:
Did I damage the seal or is the leaking due to me honing the cylinder?
Should I abandon this master cylinder and instead focus on adapting a new one to this bike?
Do I dare try one of the cheap, Chinese master cylinders???
Does anyone know of a better way to install these seals?
 

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Is it really that hard to put the seals on the plunger? I have done so in the past and had very little problems doing so.
Also if you have the dimensions of the piston you can get a machine shop to make you a new one.

What happened to your old piston if you don't mind me asking? If you still have it but it is now damaged I would think you could take it to just about any machine shop and they could duplicate it.

I have not read this entire thread so if that has been mentioned already they disregard this comment.
 

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Discussion Starter #16
It absolutely was a tremendous struggle to fit the seal over the head of the piston in my case. Perhaps it was due to the seal design or seal material. I think there might be a special tool available.

I am a retired machinist and I fully agree that any competent machine shop can make a new one. The issue is cost.
To make only one of anything gets expensive really fast and I estimate the cost to make one new piston would be $150-$200 CDN. At that price I can buy a whole new master cylinder from a newer bike and adapt it to fit. That is likely the route I will take.

I do have the old one which was made of steel. I can only assume that the previous owners through years of neglect did not change the brake fluid. Brake fluid as most of us know is hydroscopic so it absorbs moisture. Moisture = rust and rust = a corroded piston which if I continued to use it, would have permanently damaged the bore of the master cylinder.
 
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