Rear Master Cylinder Rebuild

[Mike T]

Hello! I've removed my rear master cylinder for a rebuild. Is it safe to remove what appears to be a bolt with 2 leads for the rear brake light? I want to thoroughly clean the master cylinder and do not want to ruin the leads. Thanks!

[m in sc]

yes. use a box end wrench or a socket. those switches are pretty easy to find as well. i know mikes xs carries them.

This Yamaha 341-83980-30-00 STOP SWITCH ASSEMBLY fits the following models and components:

Yamaha Motorcycle 1977 RD400D Brake Pedal - Master Cylinder

Yamaha Motorcycle 1976 RD400C Brake Pedal - Master Cylinder

Yamaha Motorcycle 1975 XS650B FRONT MASTER CYLINDER - BRAKE HOSE TXS650A - XS650

Yamaha Motorcycle 1974 TX650A FRONT MASTER CYLINDER - BRAKE HOSE TXS650A - XS650

Yamaha Motorcycle 1976 XS650C FRONT MASTER CYLINDER - BRAKE HOSE TXS650A - XS650

Yamaha Motorcycle 1975 XS650B FRONT MASTER CYLINDER BRAKE HOSE TXS650A - XS650B

Yamaha Motorcycle 1976 XS650C FRONT MASTER CYLINDER - BRAKE HOSE XS650C

Yamaha Motorcycle 1975 RD250B MASTER CYLINDER BRAKE HOSE RD250B

Yamaha Motorcycle 1973 RD250 MASTER CYLINDER BRAKE HOSE RD250B

Yamaha Motorcycle 1975 XS500B Master Cylinder - Brake Hose

Yamaha Motorcycle 1975 RD350B Master Cylinder - Brake Hose

Yamaha Motorcycle 1973 TX500 Master Cylinder - Brake Hose

Yamaha Motorcycle 1973 RD350 Master Cylinder - Brake Hose

Yamaha Motorcycle 1974 RD350A Master Cylinder - Brake Hose

Yamaha Motorcycle 1974 TX500A Master Cylinder - Brake Hose

Yamaha Motorcycle 1973 TX750 Master Cylinder - Brake Hose

Yamaha Motorcycle 1974 TX750A Master Cylinder - Brake Hose

[Mike T]

Perfect! Thanks so much!!

[SoCal250]

Also be sure to remove the reservoir fitting and clean the two small ports inside. There's a really small one and a slightly larger supply port underneath. Under the fitting is a copper crush washer, which is a 17mm IIRC but it can be reused if you anneal it.

[Mike T]

Just want to say thanks for the help! This is my first time rebuilding a rear master cylinder. I used the recommended Mikes XS switch and used the HVC Cycle rebuild kit. I bought a Harbor Freight ultrasonic cleaner and ran all the parts through it a few times. It took 3 tries to get it done; the initial rebuild, but wouldn't build pressure; disassembled and cleaned the "little hole," that even the ultrasonic cleaner didn't get, still wouldn't build pressure; disassembled, re-cleaned the hole and reassembled adding fluid on the bench and ensuring the clips were in correctly - starting building pressure immediately. It was a learning process and well worth it. Everyone should get a ride on one of these motorcycles in their lifetime