Topic: Master cylinder rebuild

[eldar]

I am looking at tearing apart my master cylinder to clean it and replace seals if needed. I have a 1978 cb750K   How do I pull the disassemble the master? I know all about the caliper but have not found anything about the master.

[Raul CB750K1]

I don't know the K model. I rebuilt my CB750K1 some time ago. There is a genuine Honda rebuild kit with all the pieces. The parts manual will help when showing how every tiny part goes. The biggest issue is a small snap ring that have to be removed. I had to file my snap ring pliers to get access to it.

Raul

[eldar]

Hey thanks a lot Bob. Something like that was just what I needed. I thought there was something with the C-clip but you know with these old bikes, it gets harder to find parts, I didn't want to break something. Thanks again. Any chance you might have a diagram of my 1978 k style carbs??? My accel pump is not working right!

[dpen]

an easy way to get the circlip out is to pry it out with an electrical tester (the type that look like a pointed screwdriver) or an engineers scribe. Worked a treat on every one I've done. To clean the cylinder once it's empty, use very fine (about 1000) wet & dry and metho. rinse everything in metho & blast with compressed air. Some people recommend using brake fluid to lubricate new seals & cups but I've never had any trouble using a very small smear of rubber grease.
Dave

[cben750f0]

any ideas from you guys on how to get a corroded circlip out?... have two master cylinders, and one has a stuck circlip.... have had WD40 soaking it for weeks but doesnt seem to want to budge?....peace

[Bob Wessner]

I had the same problem last year, soaked it for God knows how long. I finally tried putting it in a vise and used a fine nail set, not a center punch, and tapped around the exposed edge, which there is not much of, but the flat end of the nail set seemed to work. It freed up after that, but not sure it was the tapping around or the penetrating oil finally worked. Just an idea.

[scout18]

Hi there folks. I am the proud new owner of a 73 350f. I saw this post and it caught my eye because while I have read the stuff on the brake cylinder and have mine apart, I also have questions about the master . Now the brake cylinder was taken off the bike by the PO and left in a bucket. It is nice and dry in need of a good cleaning. The hose to it was left dangling. When I squeeze the brake handle nothing happens. There is fluid in the resevoir and with the cap off it shoots out like it should but none seems to be going to the brake line. Any suggestions?

[Terry in Australia]

any ideas from you guys on how to get a corroded circlip out?... have two master cylinders, and one has a stuck circlip.... have had WD40 soaking it for weeks but doesnt seem to want to budge?....peace

G'Day Ben, have you got access to a beadblaster? I have one of those cheap benchtop one, anyway, I just fire glass beads at the top of the piston area and it not only cleans the circlip like new, it loosens all the rust and crud. If you can't remove it, send it to me mate, and I'll pop it out for you. Cheers, Terry.

[dpen]

To scout 18. When the system has been completely dry you have to bleed the cylinder before fluid will go to the lines.
1-cap off & fluid in cylinder
2-squeeze brake lever very slowly & gently. When a small air bubble (or bubbles) appear-DON'T SQUEEZE FURTHER
3-let lever go, wait 10 seconds & repeat
it may take some time (half an hour or so) to purge the cylinder of air but it's worth it.
Dave

[scout18]

Thanks dpen. I will give that a try. I am not sure if it was dry. there was fluid in it when I got it. Is there any chance that the PO blew the master cylinder seal? I mean is it possible to do that?

[Wammied]

I found it much easier to remove the brake line to the caliper, remove the bleeder screw and fill caliper with b/f. Then, get a small hand pump and some clear vinyl hose (get some to fit the bleeder too while your at it) to fit the pump intake and the pump outlet to the flared fitting on the end of your brake line.

Turn the handlebars to the left to make master cylinder run 'uphill'. (end of brake lever should be highest point)
Then, fill a glass container with brake fluid. Put the intake of your pump in and slowly fill the system, from the bottom up. After it is full, with the pump still connected, work the brake lever slightly to help bubbles through the piston area. You shouldn't see many.

Now, hook up the brake line as efficiently as possible (cover it with your finger till it's on the caliper)
Bleed as usual.

I like to leave it parked with the bars turned left and come back the next day and wiggle the lever again.
What little air is left will be seen in the m/c.
Good luck/
Mike

[dpen]

 Scout-more than likely the PO pushed the piston past the port on the reservoir. You don't root around with brakes-best idea is to strip the cylinder & start from scratch, not a big job but very worthwhile. First things I do when I acquire a bike is overhaul brakes & front end. You don't know what the PO did.

[scout18]

Ok I got the piston out of the brake cylinder. Master seems to be okay. thanks all.