Motorcycle Clutch Master Cylinder Rebuild

This is a clutch master cylinder rebuild for an early 1980's Honda motorcycle. The hydraulic clutch system has three major components, the clutch master with the clutch lever on the handlebars, the clutch slave which actuates the clutch pack in the transmission and the clutch pack itself. When the clutch pack wears out, the engine will have trouble transmitting power to the rear wheel and when bad enough, the engine will spin without driving the rear wheel at all. When the master or slave no longer function correctly, the opposite is true as the clutch never seems to actuate fully and changing gears becomes difficult and rough. The clutch slave will usually fail first as all of the debris in the system will fall to the bottom where the slave is and gum it up causing it not to function correctly. When the slave is rebuilt, the master should also be rebuilt as it is usually the source for much of the debris that fouled the slave cylinder.
This rebuild is also applicable for the brake master cylinder as the arrangement is very similar. The only special tools needed for this job is a Japanese Industrial Standard (JIS) screwdriver which looks very similar to a Phillips screwdriver, but the star profile is different enough that a Phillips screwdriver will likely strip a JIS screw head, and the other special tool is long nose right angle snap ring pliers. The master cylinder piston assembly is held in place with a snap ring, but due to the recess it is located in, the special snap ring pliers are needed.
Tour Max - Master Cylinder repair kit (clutch) MSC-101
Tour Max - Master Cylinder repair kit (brake) MSB-102
A motorcycle will likely have either a cable clutch or a hydraulic clutch which operates on the same principle as motorcycle front hydraulic brakes. Using an Archimedes principle that stipulates a liquid can be used to transfer equal force over a distance since liquid can not be compressed. As equal volumes are displaced at each end of the system, the force can be amplified as a long stroke small bore piston can be translated into a short stroke large bore which is what motorcycle hydraulic clutch and brakes use increase force at the actuating end.

[@davidlafranchise4782]

Still a good video

[@psychedelicbdsm7301]

awesome vid, awesome description what products did you use to clean the master?

[@andrew_ball]

Thank you so much! I used regular brake cleaner in a spray can and made sure it was completely dry before reassembly. I'm never shy with the brake clean and always use more than I need as I really try to get everything as clean as possible. Best of luck!

[@dc-wp8oc]

Andrew...you must have the patience of Job. The JIS tip was worth the watch. I was wondering if some other component or condition in the clutch system, could cause a premature failure of the master clutch cylinder?

[@andrew_ball]

Thank you so much for watching! A premature failure of the master cylinder would always make me suspicious of how the rubber components were inserted into the bore, or the condition of the bore itself. If the rubber components hang up or catch on the lip of the bore when they are inserted, the skirt or edge of the rubber cup may get damaged and it would be difficult to tell until it fails and tears. If the bore/inside of the master cylinder has corroded it is problematic as it will accelerate the rubber cup skirt wear through a "sanding" abrasive effect. The installed replacement components are important too as there are a bunch of low priced and sadly some counterfeit overseas components where the rubber is less forgiving and in some cases dimensionally inaccurate causing it to never really work properly. I wish you the best of luck on your next rebuild and hopefully the bore is clean and shiny after a hefty dose of brake clean as that is the only part that is truly expensive!

[@dc-wp8oc]

@@andrew_ball Andrew who is your go to source for parts?

[@andrew_ball]

@@dc-wp8oc Hello, I use the cmsnl website to confirm part numbers and pricing, then I search either Amazon or Ebay for good pricing. Failing that, there is a local motorcycle shop with a good parts guy who can get his hands on most regular parts. My last resort is taking a trip into town to visit the various motorcycle dealers and pay full price for factory parts over the counter. Best of luck!

[@cBake0]

Definitely a great tip, wish I'd learned it the easy way. Stripped my originals and replaced them with 10x22 Phillips

[@davidlafranchise4782]

So no taking it apart????

[@davidlafranchise4782]

I guess it started halfway. Oopps

[@andrew_ball]

You had me scratching my head as I worried I missed some important steps! Best wishes!@@davidlafranchise4782

[@davidlafranchise4782]

You should have gloves on

[@andrew_ball]

You are right about that! I have always been a cleaning hands with Comet and gasoline kinda guy, but that will likely catch up with me...