[Rob Eh?]

Hey Folks, I am working on a '78 CB 400 T II and am currently stumped on the master cylinder restoration. The original piston was removed with all parts in tact except the boot which ripped coming out, of course. Lots of gunk build up which cleaned away well with brake cleaner and steel wool. The two openings in the well leading to the cylinder were cleared. Installed a new Honda master cylinder piston kit (part # 45530-404-315). Everything is moving when wet with brake fluid BUT very little fluid will come out at the threaded brake line connection point and none seems to be moving as if under pressure from the piston assembly. Fluid is not leaving the mc to fill the new line down to the caliper. Caliper bleed valve is open.

What am I missing? Any suggestions?

Thanks, Rob A

 

[ancientdad]

Rob, old Honda master cylinders can be a PITA to get properly rebuilt when they are allowed to deteriorate badly by many POs, we see it often. Most here just buy a modern master cylinder of proper piston size for their bikes to avoid fighting with the old one. LDR and others will be along to offer suggestions, 76Twin has used an aftermarket master on his 500T as well. They'll weigh in with some advice, there are plenty to choose from on eBay at reasonable prices

 

[Rob Eh?]

Rob, old Honda master cylinders can be a PITA to get properly rebuilt when they are allowed to deteriorate badly by many POs, we see it often. Most here just buy a modern master cylinder of proper piston size for their bikes to avoid fighting with the old one. LDR and others will be along to offer suggestions, 76Twin has used an aftermarket master on his 500T as well. They'll weigh in with some advice, there are plenty to choose from on eBay at reasonable prices

Thank you Tom. In case it makes a difference, I did not hone the cylinder as it appeared healthy and the testing I ran was without the dust boot installed. Thinking now maybe the boot is required for more than just dust protection, perhaps to seal out air also. (?) - Rob

 

[longdistancerider]

There are 2 holes in the top of the master. One large one for fluid to flow into and the second tiny hole in front of that for pressure release. Both have to be open for the master to work, Look for a divot like someone started to drill and stopped. That's the second hole. You can try clearing it with a sewing needle, small drill bits tend to break off unless you're doing it by hand.

 

[Rob Eh?]

The holes have been cleared. All new piston parts in the cylinder. Is the exterior rubber weather boot doing double duty to also keep air out? Thanks, Rob. '78 CB400T II lite resto/mod

 

[longdistancerider]

That's just a dust/debris cover, no mechanical function.

 

[Rob Eh?]

Thought so. Thank you. R