Bleeding clutch

Bill Seward · Nov 16, 2020

I recently rebuilt the clutch slave cylinder on my '85. I filled the reservoir with fluid, and bungee corded the lever to the grip. Came back the next morning, the fluid level was down. I refilled it, put the cover back on, and everything worked fine. I've used this method a number of times when the leaky slave cylinder dropped the level down in the reservoir and air got in. Worked every time.

LazyLiberty · Nov 17, 2020

I made pictures of how it all came out, so it's in correctly. The investor (father - in-law) feels it most important to keep the bike as original as possible. So reman or new Yamaha pump (expensive) or try the rebuild... I'll try cleaning the bore more, and otherwise run you guys' info past him! Thanks people (y)

desert_max · Nov 17, 2020

I must have had better luck with rebuilding - only one failure and have done many master and slave cylinders. If the bore is decent there should be no problem. The clutch slave that failed on me came from a 1200 Goldwing Standard and looked like it had been on the bottom of the ocean. Didn't surprise me.

Fire-medic · Nov 17, 2020

Here's one of the nastiest and oldest I was able to-save. This was a bike I bought as a donor for another project, and all I really needed to accomplish was a front brake so I could safely move the bike, including transporting it. The bike was a early 1970's SOHC Honda 750-4.

The last tag and inspection sticker was from late 1970's, and I've had the bike for a long time, so the master cyl piston was stuck in the bore. No amount of air pressure was going to remove it. I rigged-up an alignment tool for a drive-pin to force-out the piston from the master cylinder bore. Yes, the body got lots of PB Blaster, before I resorted to the drive-pin method of piston removal. I'm always wary about the use of heat for these alloys, and those in carburetor bodies, because I've seen a bit too-much heat turn a body into useless slag. That's why I was in-favor of the 'brute-force' method.

Here are some pics of that procedure (not in-order).

The front brake master cylinder, the drive-pin, and the PVC pieces I chose to make an alignment tool to hold the drive-pin. The drive pin was sized to be the largest diameter which would fit into the threaded-fitting hole for the master cylinder banjo bolt. This method of piston removal is possible because the banjo bolt threaded hole is in-longitudinal, concentric alignment with the master cylinder bore, and piston. The male threaded plug with the hole drilled in it was to provide a larger striking surface for a ball-pein hammer.

The VMax has the banjo bolt tapped hole at 90 degrees to the travel of the master cylinder piston, so this isn't feasible for us. Those of you with the bike collections, try this where it's suitable.

A pic of the grody brake master cylinder piston, once-removed, showing what multiple decades of crystallized brake fluid and galvanic corrosion can do to an assembly.

A pic of using a cordless drill, a 3/8" drive adapter, and some fine sandpaper taped/wrapped-around the long 3/8" socket extension, to rapidly-hone the master cylinder bore.

Also, a shot of using a hydraulic grease gun to extract a caliper piston, by use of the bleeder valve nipple. Works every-time. If your air compressor won't work, this will.

Once reassembled with a quality rebuild kit, the master cylinder was quickly-bled using my favorite method, the 'reverse-bleed,' and has functioned perfectly since.