Rear Master Cylinder - Piston Seal

[Langbolt]

My Laeger363R was leaking brake fluid at the Master Cylinder at the end of riding season last year....I thought I'd just rebuild it in the winter.....well Winter is here....Ordered a Rebuild kit and tore into it.

I removed the boot and there as quite a bit of fluid.....removed the circlip and out came the push rod and then the piston....to my surprise! The piston did NOT have a seal on it ?

WTF! Are these rebuild kits using a rubber that isn't compatible with DOT3 or DOT4 brake fluid ?

The one on the Left is the one I removed....the one on the right is a spare for comparison as it has the seal.



John

[All250R]

There is a seal that goes over the end of a plunger. It's been a year since I rebuilt one, but the plunger I don't think looks like the one I'm familiar with.
This is a pic of the Shindy kit that I think is for all years: https://i.pinimg.com/originals/a0/0f/bc/a00fbc00234a3beb09725357ceaf9232.jpg

By the way, if you have had mild water related corrosion in the MC, a ball hone isn't very expensive insurance against leaks. I can look up the size if you think you need it.

[broken1]

Another option for honing your mc is to cut a notch in a piece of 1/4" bar stock with a hacksaw than tear off a piece of fine emery cloth, fold in half & slip it into the notch you cut in the bar stock. Chuck it up in your favorite drill & you have a home made small cylinder hone.