Thought the brakes were finished, then rear master!!!

[mild83]

So my front brakes had zero stopping power and a friend of mine helped rebuild the master. MUch much better feel.

I had previously attempted to bleed the rear brakes (even though they were in fine working condition, would almost stop the bike, even without the front brake), but after they were drained, could not get pressure built back up.

My friend that rebuilt the front master, tried bleeding with a speed bleeder, no luck. He said he's 99.9% sure the rear master is bad as well. I'd like to just replace it instead of a rebuild (time is of the essence and he's going to replace it, so I want to make it easy as possible), and I was trying to find a reasonable repalcement. I'm not looking to upgrade, or even keep it OEM, just replace it.

Any suggestions on reasonable sources?

 

[CaptainKyle]

I have some good working used ones. If you have not found one email me at [email protected]

 

[MaxMidnight]

Have you tried stripping the unit and confirming it's junk?

The reason I ask this because I have had an issue recently with my rear M/C.
I had checked that the calliper was functioning and the brake light working before I took it in for its annual MoT.

It failed as the rear brake wasn't working, the pedal didn't apply pressure and it was assumed that the fluid had somehow escaped.

There was fluid in the reservoir but it wouldn't bleed.

When I stripped the M/C the piston had stuck at the top of its travel and wasn't returning. Closer inspection showed it was a build up of crud causing the issue.

It was 'persuaded' to come out of the housing, cleaned up and re-lubricated and now functions perfectly.

As I said, if not already done may be worth checking and the fix may only cost some of your time.

 

[naughtyG]

When I just replaced the front lines with SS ones, I had to drain the M/C too (I resprayed it) and then once all in place it seemed to take ages to build any pressure to bleed.

I found that in the long run, I had to close the nipple completely, apply the brake all the way to the bars (almost no resistance) and only then open the nipple very slightly, and then a tiny bit of fluid and lots of bubbles would come out. Then close the nipple completely again before releasing brake and repeat.

Eventually that did it, pressure built back up and I was able to bleed properly. Took a good half-hour of pumping though!

 

[mild83]

I guess my question would be, would it get gunked up after having no issues just 2 weeks prior? There was constantly fluid in it, then closed off. I'm tired of dealing with it and would rather replace it, know that it's ready to roll and be able to try to squeeze a few more weeks out of it.

 

[naughtyG]

Anything's possible, the holes are tiny!

 

[Miles Long]

I had a similar problem last time that I worked on the rear brake - I couldn't get any pressure to build up, after numerous attempts at conventional bleeding, and then with a Mityvac. NO WAY could I get it to work properly!
The problem, and the solution, was simple - the diaphragm in the reservoir was out of place, and I hadn't noticed this during the frequent top-ups required during the bleeding attempts.
Always look for the easy fixes first!
Cheers!

 

[[email protected]]

I had a similar problem last time that I lworked on the rear brake - I couldn't get any pressure to build up, after numerous attempts at conventional bleeding, and then with a Mityvac. NO WAY could I get it to work properly!
The problem, and the solution, was simple - the diaphragm in the reservoir was out of place, and I hadn't noticed this during the frequent top-ups required during the bleeding attempts.
Always look for the easy fixes first!
Cheers!

I don't understand how that would have an affect? The reservoir cap and diaphragm is totally removed when you bleed and it still builds pressure.

 

[jfeagins]

I don't understand how that would have an affect? The reservoir cap and diaphragm is totally removed when you bleed and it still builds pressure.

+1 Would have no affect IMO.

Usually, when a m/c gives grief during a bleed, you can get it to start back up by 'bench bleeding' it, or in other words, take the banjo bolt off where the line attaches. Put finger pressure there while pumping the brake lever. Once you have fluid to that location, re-attach the line and bleed all the way throughout. This has always worked for me, but then, I've only encountered this problem with the brake and clutch reservoirs up on the handlebars, and never had it happen with the rear master cylinder.

Parts for these master cylinders and/or wheel cylinders are relatively dirt cheap, and so simple to do. Unless there's been water in one and it has begun pitting, I'd see no reason to buy different ones - unless it was to be upgrading the system from stock.

 

[[email protected]]

If the system was totally drained it is highly possible that there is air in the master. When replacing my rear caliper and brake line I had to loosen the banjo bolt at the master to bleed it there before I could get any feel at the pedal. Then I moved down to the caliper and finished up.

I would try ths first. If you still can't get a pedal then I would open it up. As noted, it may just need cleaned up.

 

[Fire-medic]

When I just replaced the front lines with SS ones, I had to drain the M/C too (I resprayed it) and then once all in place it seemed to take ages to build any pressure to bleed.

I found that in the long run, I had to close the nipple completely, apply the brake all the way to the bars (almost no resistance) and only then open the nipple very slightly, and then a tiny bit of fluid and lots of bubbles would come out. Then close the nipple completely again before releasing brake and repeat.

Eventually that did it, pressure built back up and I was able to bleed properly. Took a good half-hour of pumping though!

I have used a Mityvac for 30 years, but after trying the reverse-flush using a 60 ml syringe, the hydraulic bleed is faster this way. I may still use the Mityvac for front brakes because it seems to work OK, but doing the rear brake of the clutch at the slave cyl, the reverse-method w/a syringe works better for me, and it was the reports from that technique that I read-about on here that made me try it again. I had done it before, years-ago but I hadn't had to on my VMax, until I was having a difficult time getting the bleed on my clutch ass'y.

BTW, if you disassemble and clean your syringe of all brake fluid after using it, it will last a lot longer. I use a medical one instead of a mechanic's one.

 

[PATMAX]

I think you could buy a completely operational rear brake set up on fleabay cheap. You don't even have to crack the system to take it off do you? I think thats how my Rattlecan project went. In fact I have it and the front both draped over a sawhorse sealed/ intact. I'd still change out the fluid but hoe easy is it hanging straight up and down!
I always preferred bleeding by wiping out the resevior with a rag, fill with fresh fluid and draining but I got quicker results pushing up from bleeder but hated having a reservior of dirty fluid then to drain and clean out.

 

[PATMAX]

I think you could buy a completely operational rear brake set up on fleabay cheap. You don't even have to crack the system to take it off do you? I think thats how my Rattlecan project went. In fact I have it and the front both draped over a sawhorse sealed/ intact. I'd still change out the fluid but hoe easy is it hanging straight up and down!
I always preferred bleeding by wiping out the resevior with a rag, fill with fresh fluid and draining but I got quicker results pushing up from bleeder but hated having a reservior of dirty fluid then to drain and clean out.

 

[Fire-medic]

Double-post!