Looks like My RSV needs a new or rebuilt rear Master Cylinder

[BlueSky]

My RSV's rear brake was barely working. Today, I finally got around to trying to repair it. I bled the rear brake using the old pump the pedal and release the pressure at the caliper and it appeared to be working well but I kept bleeding it hoping to get all the old fluid out of the system and it quit pumping fluid. Now, I have no rear brake at all. Soo, I suppose I need a new MC or I have to rebuild it. Partzilla has a rebuild kit in stock but a long delivery on the compete MC. Have any of you RSV owners had to rebuild your rear MC and how did it turn out?

 

I wanted to use my mity vac to see if I could pull more fluid through the system but could not find it in the garage!!!

Thanks!

[Marcarl]

I would start with pulling it all apart first, and then decide. You might find something that is causing the issue.

[BlueSky]

Well, I removed the rear brake master cylinder and it looks okay with no corrosion pits that I could see. There wasn't anything that was blocking the fluid flow. So, I ordered a rebuild kit from partzilla. They hit me for sales tax even though their business is in another state! It's a really simple device and it appears that the only parts really needed are those two rubber cups that push the fluid. But, you can't order just those.

 

The manual states in order to get it off, to remove the brake pedal and disconnect the brake line. Looks to me like the foot peg/pad has to come off too so I took it off. That made it a lot easier to remove the brake pedal with the master cylinder attached. Now, I have to wait for parts. Even with the bike on the stand that Sylvester was kind enough to sell to me, it still requires a lot of lying on the floor. Ain't as much fun as it used to be at 76 yrs old!

[Semi-retired]

You might find something that is causing the issue.

 

Love the way you think, Carl.

 

I KNOW I'm part Scott-ish......but I've suspected that most bikers come with a Dutch chromosome, as well! (IF you know what I mean. And I know you do! :-)

[Marcarl]

Keep in mind that the MC won't pump air very well without some fluid to help out. So if you pumped the reservoir dry and then added more fluid, it could take a bit to get things flowing again.

[BlueSky]

Keep in mind that the MC won't pump air very well without some fluid to help out. So if you pumped the reservoir dry and then added more fluid, it could take a bit to get things flowing again.

 

I made sure the reservoir didn't go dry. It's weird in that it started out with very little pedal and very little brake and plenty of fluid in the reservoir. After bleeding it a few pumps, it had a full pedal and the brake was working. Then after bleeding some more it quit pumping any fluid and there was no pedal and no brake. I found my mityvac and used it to pull a vacuum on the caliper and pumped the heck out of the pedal and no fluid came out. It does sound like I pumped the reservoir dry, but that didn't happen. A MC rebuild kit is on the way. I'll let you know how it turns out. If there was an obstruction in the line to the caliper there would have been full pedal. When I disconnected the reservoir tube at the MC, the remainder of the fluid in the line gushed out, so I don't think there was an obstruction in that line. Has to be the master cylinder bad seals. Famous last words! Ha!

 

OR, the tiny orifice in the MC that feeds the fluid from the reservoir to the MC could have been plugged??. The supply line is large but the orifice is small. When I disconnected and removed the MC the fluid in it came out all of its orifices and that could have flushed the crud out that could have been blocking the feed orifice? I wonder if I put it back together if it would work?

Edited June 19, 2020 by BlueSky

[Marcarl]

Something that you might not be aware of, is that the reservoir is more rubber bellows than it holds fluid. I'm not sure how much fluid it holds but my guess is that 3/4 of it is bellows.

[BlueSky]

Something that you might not be aware of, is that the reservoir is more rubber bellows than it holds fluid. I'm not sure how much fluid it holds but my guess is that 3/4 of it is bellows.

 

BINGO! I think you just solved the problem! The rubber bellows was on the bottom of the reservoir. I think it was blocking any fluid from draining down to the master cylinder! Thanks! Now I sorta feel dumb! I've been doing brake jobs for 60 years on my autos and am quite familiar with the master cylinder on those but went dumb on the bike.

[BlueSky]

I reassembled the master cylinder, installed it, and bled the system using my mityvac and pumping. The rear brake works great now. It was indeed the bellows on the bottom of the reservoir blocking flow. Evidently, it doesn't take much to pull it from its location under the cover of the reservoir.

 

I had ordered a master cylinder rebuild kit from partzilla.com two days ago. According to their web site it had not shipped so I called and asked that the order be cancelled. They said it had been shipped but would refund the money I paid and not to worry about returning it. I was speechless and could only say "okay". Never heard of an online vendor doing that. So, if anybody needs a rear brake master cylinder rebuild kit for their RSV they can have it for shipping cost.