Leaky master cylinder

Ok I have finally decided to take a crack at rebuilding my master cylinder on my 78 KZ650. I have the trapazoid shaped master cylinder and I have located the rebuild kit on Z1. The only question I have is this. Does the kit fix the leaking between the reservoir and the body of the master cylinder?? Its always "wet" on the outside of the master cylinder so much that all the original black paint is all bubbled up and I can peel it off with my finger. Or can I be mistaken and its leaking from the top. I just cant tell exactly where its leaking from. Thanks!

Lou

Most rebuild kits cover the many and various seals/gaskets inside the master cylinder. Sounds like yours has a crack in the body letting the brake fluid out. You might have to see if the body can be repaired by welding(if possible) or start looking on E-Bay for a replacement.

It is possible the the diaphram or the top gasket has failed letting the fluid out too. Probably the best way is to remove all the parts,and paint and see if there is a crack in the body.

If it's the 1978 one-year only trapezoidal master cylinder 14mm bore used with single front disc (as 1978 KZ1000 with single front disc), and find it unavailable from Z1E, should check out Redline's listing, especially with regard to the 0-ring under the reservoir which hardens over time and starts leaking. The trapezoidal master cylinder went to 5/8" inch bore in 1979 KZ1000 with introduction of the dual front discs model. Am guessing the 0-ring fits both sizes trapezoidal master cylinders.

Also be careful if ordering the piston, as my dearership ordered the larger piston for the 5/8" trapezoidal master cylinder (which part number erroneously showed on the 1978 KZ1000 microfiche). The smaller 14mm piston assembly is part number 43020-1002.

Click here > Redline

In Stock at Redline Cycle

For all trapezoid master cylinders (1978 to 1980 1000A and 1000B models).... And for front round dual-disc masters (1977 KZ1000B/Ltd models)......
The o-ring that sits under the plastic reservoir on these master cylinders often leaks due to age......This part is not and never was available from Kawasaki.....

We stock a high-quality replacement o-ring to fix this problem......Exact diameter and width needed, and resistant to expansion from brake fluid.....

No, you can't get one of these for 15 cents at Home Depot....... $3.50 each

In Stock at Redline Cycle

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Good Luck!

You might want to replace the O-Ring under the reservoir housing. Atfer removing the top cover ( four 5 X 12 mm screws) remove the brake fluid and you will see two screws holding down a steel plate. Remove these two screws and steel plate and the reservoir will come loose of the metal housing. Replace the O-Ring found underneath the reservoir. You can purchase one for about $3.00 from Red-Line Cycle located in Ohio. This eliminated the same problem on my 1979 KZ650-B3.

KZ650 wrote:

You might want to replace the O-Ring under the reservoir housing...Replace the O-Ring found underneath the reservoir. You can purchase one for about $3.00 from Red-Line Cycle located in Ohio. This eliminated the same problem on my 1979 KZ650-B3.

Same with me on the smaller 14mm trapezoidal master cylinder fitted onto my Z1.

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Good Luck!

The o-ring from Redline fixed mine as well. I wanted to add that my reservoir was very hard to get off of the master cylinder. I ended up putting the master cylinder in a vise, putting the cap screws back into the reservoir, and pulling on them with pliers. I pulled as gently as I could and worked in a circle.

I didn't realize there were different trapezoid master cylinder. To be honest the master cylinder works fine except for the leak. I just thought I had to get the rebould kit to fix the leak. I'm going to order the I ring and see what happens. Thanks for the info guys.

leorider wrote:

Ok I have finally decided to take a crack at rebuilding my master cylinder on my 78 KZ650. I have the trapazoid shaped master cylinder and I have located the rebuild kit on Z1. The only question I have is this. Does the kit fix the leaking between the reservoir and the body of the master cylinder?? Its always "wet" on the outside of the master cylinder so much that all the original black paint is all bubbled up and I can peel it off with my finger. Or can I be mistaken and its leaking from the top. I just cant tell exactly where its leaking from. Thanks!

Lou

Could leak at top cover or 0-ring under reservoir or from bore or at banjo bolt connection to brake line.

If bore isn't too badly pitted, it may be restored to serviceable condition. A new piston assembly may be necessary to get the new rubber cups (primary cup may be separate part, but secondary cup comes already built into the piston.

Leaking secondary cup allows fluid seepage out the area where the brake lever pushes against it. The visible rubber piece on the assembled master cylinder is a dust cover which won't stop fluid.

To reitterate, the larger 5/8" bore piston assembly will NOT fit the smaller 14mm bore master cylinder.

Good Luck!