Front brake has great pressure and feel and yet there is a small leak at the MC

Going through my recently acquired 78 KZ650 part by part.

I flushed what was left of the old brake fluid on the front MC and quickly enough had a nice firm front brake after a bit of bleeding.

My MC has peeling paint and evidence of previous leakage though I can not seem to find where. Would a rebuild kit always solve this issue or do I have a damaged MC as well?

Many thanks!

i would verify where the leak is first.
It could be a lid seal or the careless previous owner topping off.
I don't think a kit would cover an external leak.

The master cylinder has two seals. The front one holds the brake pressure. The rear one keeps the fluid from leaking out of the back of the piston.

Yes, a rebuild kit will replace both seals. Unless the cylinder bore is pitted, this should make it work like it's supposed to.

A we often say here, the first thing you should get is a copy of the genuine factory service manual for your bike. This manual had detailed diagrams for everything, including the master cylinder

Do you have a round cap or trapezoid... pictures would really help

Ninja1195 wrote: Going through my recently acquired 78 KZ650 part by part.

It would help a LOT if you stated which model 1978 KZ650 you own. Keep in mind that the KZ650-B models had single front disk brakes while the KZ650-C and D models had dual front disk brakes. The single front disk brake master cylinder is different than that of the dual front disk brake bikes. So without knowing which model you have there's no way of knowing which parts you may need. The easiest way to make sure this info is always included is to simply add it to your signature line. Ed

Single disk with 14x52mm (diameter/length) and round reservoir cap.





double disk with 15,8x62,7mm (diameter/length) and trapezoid reservoir cap.