Bonneville America Forums Forums Technical Forums General Tech Rear Brake Master Cylinder

Well the story goes like this. I decided it was time to improve the braking system on my TBA. Installed new stainless front and rear brake lines. Installed new front and rear pads (SBC's from Brent) and currently waiting for the front EBC disc from Brent. Everything went fine with the front brake. But... the rear just doesn't seem the wanna bleed correctly. I bled the guts out of it and can't seem to get barely any pedal on the rear brake. I mean that pedal goes almost to bottom before it really takes ahold. Before that the pedal would start taking ahold about 1/3 of the way. I followed the service manual step by step and used a brake vacum bleeder also and can't seem to make any headway. I finally concluded the piston in the master cylinder must be going bad, so I ordered a new piston and spring for the master cylinder. Anyone ever experienced this problem? Any input would be greatly appreciated.

Kerby

I've only ever bled the rears once and had the same problem.
I have a theory, which I'm sure others will be along soon to shoot holes in, but it worked for me.

If you look at your rear caliper, the highest point is an arc in the brake line. I tried the speed bleeder and the Mity-Vac, but the only way I got all the air out was to remove the caliper, remove the brake line guide, fish the caliper out between the rear wheel and the front of the shock, and hold the caliper so the bleed screw was the highest point.
But then, I do funny things like that......

Grump, That makes alot of sense. I used a clear line on the bleeder valve so I could moniter the brake fluid being pushed out. In the arc of the clear line there was always a little air pocket. So I tryed putting the catch can and bleeder line as low as possible, but still couldn't get that little air pocket out of the line. I still think the piston in the master cylinder is part of my problem, but will try your theory.
Thanks, Kerby

That is a very interesting theory! I wonder if the reverse would be true, lowering the caliper so it would force the bubbles the other way, like the old "zip tie the lever down" trick.

Probably.
It's in the same category as the "tappy tap tap" method....

Why, yes it was...

I considered the brake bleeding limbo trick, but with my back, I pictured myself lying crippled on the garage floor with a 500 lb motorcycle on top of me....
Sometimes you just have to find alternative methods.

hey Kerby.. you can try this way to bleed your Brake's and it's the way i do it.. was showing this way when i was a kid and so far has worked every time..it's called back bleeding.. first get your self a hand pump oil can.. and put about 2 foot of clear hose on it
then fill the can with Brake fluid then put the clear line back in the bottle and pump the can till the line is full of fluid then take it over to you bike and hook it all up to your back bleeder
then go to the front of the bike take the lid off your Brake reservoir and suck out most of the fluid...then go to the rear and losen the bleeder vale and start pumping but watch as you pump so that you do not over fill your brake reservoir..once up to the max line stop close your bleeder vale and but your lid back on your reservoir.. and pump up your brake pedal and then bleed it back the other way once this should get rid of all the air and you should have a good hard pedal..

BIKER

Grump you are right, air bubbles tend to rise to the highest point in the line. I have used a method like this and always come out with a solid brake pedal.....Angelis

Quote:

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Grump you are right, air bubbles tend to rise to the highest point in the line. I have used a method like this and always come out with a solid brake pedal.....Angelis

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hi angelis745 you talk to grump but replyed to me so just asking what method do you use the one grumped talked about or the one i show

thanks BIKER

What would I do without you guys. I'm having a moment right now. OK I finished. Gonna give it a whirl. I sometimes tend to overlook the simple details when I'm troubleshooting.
Thanks a million!

Biker, I tryed your back bleeding method and I still cannot get any pedal. I know for fact the more I bled that thing, it slowly but progressivly got worse. That leads me to believe I have a problem elsewhere. Mosy likely the master cyclinder. I tryed Grumps method also and same results. So now it's a waiting game for my parts.
Thanks again, I'll keep everyone posted so if anyone else stumbles across this problem they'll have some kinda idea

Grump, Got it! Hooray! I got tired of waiting for parts so I thought, what the heck, I'll go ahead and tear the master cylinder apart and see if anything is obvious. Needless to say everything looked fine. So I cleaned everything out and blew out the brakelines and reassembled. I back bled the brakes and proceeded to bleed them with the caliper hanging down as far as possible(bike on stand) and pumped the brakes a few times. Bled it. And pumped a few more times and wham-oo. I have what I consider a great pedal now. Before when i tryed your method I didn't have the caliper as low and I believe that very well could have been a big part of the problem. Thanks. Hey if you ever get over towards the Breezewood area look me up.

Kerby, did you use speed bleeders or a vacuum pump?

I'm ready to bleed the brakes, but I need the diameter of the clear plastic tubing for the bleeder. Anyone?

5/16 I think. As I recall, the 1/4 stuff I brought home from work was too tight.

Maybe I'm thinking of 3/16...

OK you guys lets make up your minds! I'll just buy both. I'm a big spender you know.

Matt, I used a vacum pump and back bled my brakes. Which helped, but.... I believe the trick to it is removing the caliper and putting it at the lowest(and I mean lowest) point possible. If you have a MC lift, jack you bike up until the caliper dangles on the brake line then start to bleed. That was the only thing I had success with. Every bike is a different beast, so I'm telling what worked for me. After you get a good pedal, then ensure your resevoir isn't full and carefully depress then brake shoes back to the retract position and reinstall the caliper. Once you've gotten this far then pump your brakes again until your pedal feels good. That's about all I can tell ya, I spent a couple nights tinkering with it until I finally figured out what worked (with alot of advice from this site)
Kerby

It's 5/16.

Or you could just let the fluid spew. It adds a nice sheen to concrete....

benny i have been useing 3/16 I.D ... for this job.. it's goes on tight.. but does the job

matt that set up i have in the pic's cost me all of 2 buck's

BIKER

I think I'll try Pat's suggestion first, then if that doesn't work I will try Grumps. Hopefully I won't have to go as far as back bleeding the rear. Any suggestions on doing the front?

The front is pretty simple, and not as much a pain because the line flows downhill all the way. I did (gently!) pump the lever a couple times while doing it to make sure no bubbles were in the master cylinder. Then I did Pat's trick of zip tying the lever to the bar overnight, then gently tippy-tap-tapping the line from the caliper all the way up. Then a while later releasing the zip tie. Nice solid feel now.

One thing that hasn't been mentioned... Back when I dropped my bike (first day I had it, WAY before I discovered this site, maybe even before it existed), I had the old no feel in the pedal problem. The guy from the dealer suggested a trick which worked for me. I cracked the banjo bolt on the master cylinder loose, pumped the pedal, tightened it, released the pedal, rinse/repeat.

you pumped the lever with the top off the master cylinder? or with the bleeder open?After you tie the lever back overnight did you rebleed?

I GENTLY moved the lever with the top off and the fluid level pretty low. I saw some bubbles come up. I did not re-bleed ater the lever tie trick.

I'm going to give it a try this week. I don't need any problems. I hope the Brake gods look down on me favorably!

I have to say thanks to you guys. I tried Pat's technique first on the rear brakes and it worked like a charm. I was ready to use Grumps way as a back up. The fronts went off without a hitch, too. Not much fluid comes out at a time on the fronts. The only problem I had was almost stripping one of the screws on the from master reservoir. I will have to get to the dealer for a replacement. Thanks again to all.
Matt