Rear Brakes - Another what would you do question

[JScro]

So I rebuilt my brake system about a month ago, and it's really be working well. I was feeling pretty good about it, especially since it's the first time I've ever attempted anything brake related besides changing pads.

Early this week, my rear pedal feel to floor. I tried bleeding, adjusting the pedal, and while doing this I noticed brake fluid was actually coming out of the caliper. I figured the new seal I put in must have got some crap behind it or something.

Last night I pulled it all apart, and it's still spotless inside. No problems with the seal at all. Wierd. I decided to put it all back together and bleed it. Nothing happens, at all.

Fast forward to two hours later, and I've disassembled everything, cleaned it all out again (didn't need it, everything was still spotless inside), bled the master cylinder before I put it back in, filled the caliper and line with fluid, started the bleeding process and...

Nothing. I can get air bubbles from the bleed valve, and fluid is pumping through, but I never get any real pressure built up. I pumped it for another couple of hours, and the fluid in the reservoir went down ever so slightly.

I'm sort of at a loss what to do next. I could take it somewhere, but I bought this thing with the intention of learning this stuff myself. This however, I don't know how to troubleshoot. Is my rear caliper bad? Is my master cylinder shot? I have no idea.

[CatatonicBug]

What is the condition of your piston? Did you make sure to really clean out the groove that the seal sits in, inside the caliper? That is where most of the "gunk" collects. When you are bleeding it, and you say that you can't get pressure to build up behind it, are you seeing any fluid leaking?

[JScro]

The piston is brand new. It was replaced when I rebuilt the caliper. When I pulled it apart, I looked for any evidence of pitting, but there is none. The caliper is also spotless inside.

I'm not seeing any fluid leaking.

[Danny Crawdad]

Are you bleeding at the caliper and master cylinder banjo bolts also? I've had the rear brakes apart more times than I'd care to talk about (I took them fully down and disassembled caliper in the parking deck at work last week), and every single time I've bled the rears, the trick to getting a good bleed has been

a) Starting with a bench bleed on the caliper. I use my hands, cover hole with thumb, pump cylinder with hand, until I get fluid shooting from the master cylinder.

b) Reassembling, and then bleeding at the master cylinder banjo bolt once or twice until it's clear fluid.

c) Then, bleeding at caliper banjo bolt until there's no air popping or hissing out.

d) THEN, touching the bleeder on the caliper.

[natemoen]

I don't know the size difference between piston but could you have the wrong sized piston?

[CatatonicBug]

The piston is brand new. It was replaced when I rebuilt the caliper. When I pulled it apart, I looked for any evidence of pitting, but there is none. The caliper is also spotless inside.

I'm not seeing any fluid leaking.

If there is no fluid leaking, your problem is all about air in the system. Be sure to bench bleed the MC, connect the hose to the MC and bench bleed the hose. Fill the Caliper with fluid and connect the hose to it, THEN bleed the caliper. Large pockets of air in the MC can make it so it never pumps the air out.

[bikerphil]

I tried bleeding, adjusting the pedal

If the rear brake pedal is misadjusted (plunger too far in) it will be impossible to bleed the system. Make sure the pedal is adjusted according to the FSM, page 2-15, 2-16.

[BA80]

If the rear brake pedal is misadjusted (plunger too far in) it will be impossible to bleed the system. Make sure the pedal is adjusted according to the FSM, page 2-15, 2-16.

I agree, that's what it sounds like. The pushrod should just about touch the plunger with everything at rest. If you have it too tight the plunger can't return far enough to draw fluid from the reservoir.

The caliper leaking is not a good thing. It sounds like you did it right with a new piston and I assume kit. Did you get all the crud out of the groove in the caliper where the square cut seal sits? The fluid has to be getting past that seal somehow.

[ESJr1642]

Master Cylinder

Ok, since we are on the subject, I just picked up a kit for the rear master cylinder of the G. It came from Yamaha with one seal installed. ( I know, I know, much cheaper elsewhere, I don't have the time to wait).

So, my question is, the "top" cup goes in which way, big end to the top or small end to the top.

The parts drawing don't seem to be clear. Rear brakes did not work when I picked it up so I am not sure the master cylinder was put together correctly when I got it.

Ernie

[bikerphil]

The center one goes as follows...

http://www.xs11.com/xs11-info/tech-tips/repairs/38/83-master-cylinder-rebuild-plunger-rubber-installation.html

The end one goes with the cup facing the banjo bolt.

[BA80]

big end to the top or small end to the top

Big............

[ESJr1642]

Thanks guys, I will be working on that Saturday, bleeding the rear seems to be painful. I will make sure to use the process outlined above.

Ernie

[WSL91]

So I rebuilt my brake system about a month ago, and it's really be working well. I was feeling pretty good about it, especially since it's the first time I've ever attempted anything brake related besides changing pads.

Early this week, my rear pedal feel to floor. I tried bleeding, adjusting the pedal, and while doing this I noticed brake fluid was actually coming out of the caliper. I figured the new seal I put in must have got some crap behind it or something.

Last night I pulled it all apart, and it's still spotless inside. No problems with the seal at all. Wierd. I decided to put it all back together and bleed it. Nothing happens, at all.

Fast forward to two hours later, and I've disassembled everything, cleaned it all out again (didn't need it, everything was still spotless inside), bled the master cylinder before I put it back in, filled the caliper and line with fluid, started the bleeding process and...

Nothing. I can get air bubbles from the bleed valve, and fluid is pumping through, but I never get any real pressure built up. I pumped it for another couple of hours, and the fluid in the reservoir went down ever so slightly.

I'm sort of at a loss what to do next. I could take it somewhere, but I bought this thing with the intention of learning this stuff myself. This however, I don't know how to troubleshoot. Is my rear caliper bad? Is my master cylinder shot? I have no idea.

On my bike the proportioning valve had failed and no amount of bleeding would get fluid to the rear caliper. I own a vacuum bleeder and no dice with it either. I ended up disabling the linked brakes and doing away with the proportioning valve

[JScro]

Thanks for the suggestion Danny. I bleed the system this way and was finally able to get the rear caliber to bite again. My pedal still is going to the floor but it's definitely pressurizing now. I bet I have the pedal adjusted incorrectly as others have stated. More bleeding to do but I think I'm on the right track now.

[JScro]

Once I adjusted the pedal to the specs in the manual, everything starting working again. I'm still really unsure how or why the rear caliper sprung a leak like that, but I guess I'll just keep an eye on it for now.