Rear Brake Won't Bleed: Troubleshooting Help?

[grbl]

I'm going through the process of replacing all the fluids on a new-to-me 2004 with 30k miles, and I need some help fixing the rear brake. The rear brake was mushy (but functional I think) when I bought it. Here's what I've tried:

- I went to bleed with the basic method seen in this video https://youtu.be/qXHIlxfnLSI, and only got about 2" of hose filled.

- This being my first time bleeding brakes, I assumed I was screwing up and went and bought a vacuum bleeder kit. Pulling 8 psig vacuum and pumping the brake over and over for a couple of minutes, I just get bubbling from the bleed nipple. The nipple is definitely open and the reservoir cap is off.

- I was able to bleed the hose from the reservoir to the MC, so there's nothing wrong there. I pulled the bleed nipple and couldn't bleed it with an open port, it just makes a sucking sound like a straw in an empty drink when you pump the brakes.


Anyone know what problem this points to? Perhaps a blockage or a leak somewhere? Should I be rebuilding the caliper and MC and replacing the hoses anyway, and would this fix my problem? Should I just buy a complete used rear brake system off ebay?

Thanks for your responses!

 

[erburtt]

Did you try to pump out all the old fluid first without adding new? I watched a bit of the video, and they said it but I didn't see it, you have to make sure you never let the fluid in the master cylinder get low enough for it to suck any air. I would put the bleed nipple back in and start fresh, make sure the reservoir always has enough fluid in it and suck (or pump, if you've given up on the vacuum kit) away. It might take a little bit if you've introduced air to the caliper and lines.

I prefer to bleed with pressure on the pedal cracking open then closing the bleed nipple like they show in the video, might not hurt to tap around the caliper with a soft mallet to help any trapped air bubbles make their way out. Air in the lines, or water in the fluid from a bad maintenance cycle will definitely give a spongey feel

 

[TownsendsFJR1300]

Don't pump the brake lever AND use the vacuum tool at the same time... Do one procedure or the other at a time.

You should have the system topped off, pump your vacuum tool (with hose attached to the nipple) up to 25 (or the highest you can get it, then crack the nipple open watching the vacuum gauge. CLOSE the nipple BEFORE YOU HAVE 0 PSI.

As posted above, you may have some air in the line that loops up somewhat and then back down to the caliper. If you still have issues, possibly removing the rear caliper and bleeding with the brake line straight or lowered should help get any air out.


Some folks have done reverse bleeding... Pumping brake fluid thru the caliper up to the master cylinder. I've never done it but do a search here if needed...

 

[grbl]

The reservoir hasn't emptied -- I can't get fluid to flow through to empty it. It's definitely got some air in it now if it didn't already, after disconnecting the MC to try bleeding the inlet hose and after removing the nipple to see if it was clogged. But air alone wouldn't cause it to just not flow, right? I figured something's plugged up, or else it would bleed with vacuum even if it had an air leak.

 

[TownsendsFJR1300]

Its highly un-likely something clogged it up... You don't want it fully empty (which it sounds like it is right now).

If air is trapped in a section of the MC, you may try removing it (still hooked up), put it in some different positions, tap it slightly and vacuum bled again, same as the line. If fluid is in the reservoir and your pulling fluid with a vacuum without allowing air back into the system, that should work...

 

[grbl]

D
As posted above, you may have some air in the line that loops up somewhat and then back down to the caliper. If you still have issues, possibly removing the rear caliper and bleeding with the brake line straight or lowered should help get any air out.

So, it's unlikely to have an actual blockage? I'll give it a go pulling the caliper. Would I expect this sort of trouble installing a new, completely-full-of-air system?

Thanks for the suggestions.

 

[TownsendsFJR1300]

To buy all new parts, even if the MC has failed/clogged, is a waste.

All the parts, even if you did, would come separately.

If I had a complete set up, for sale, all bleed out already, by the time it got there, it'd been flipped up side down/ right side up and air surly introduced into the system...

IMO, absolutely worse case scenario, bring it to the dealer, or someone you know, and get it done correctly... It shouldn't take long at all (maybe 1/2 hour un-less somethings failed). I've NEVER, on here, read of a rear MC failing in 7 years...



I did have back in the 80's a VT1100 with the "over the fender" front brake line I could NOT get the air out. It went to the dealer and I never found out what their secret was.


Just as a side note, I replaced my line with SS several years ago, no issues with bleeding but the MC wasn't dry, or run dry either. And full lock on the rear brake is maybe 1", tops...

 

[greg]

when i changed the seals on my rear brake I hung it up overnight so the air could rise to the top by the bleed nipple

 

[grbl]

Well, I made an appointment to bring it in tomorrow. I hope I just have no idea what I'm doing and they can get it bled :don'tknow:

 

[TownsendsFJR1300]

Well, I made an appointment to bring it in tomorrow. I hope I just have no idea what I'm doing and they can get it bled :don'tknow:

They'll get it bled or find the issue (bad MC-not likely).

You'll really appreciate at nice tight rear brake that applies as it should W/O mush.


Its MUCH simpler to bled than the fronts(with the over the fender loop).

If they'll answer, ask where the air likely was at or what specifically the issue was and post back..

 

[FinalImpact]

MC refill concept:
When a brake lever is at rest, the port from the reservoir to the MC piston cup and brake line are OPEN and connected. The system can be vacuum bled.
However, If the lever(s) or pedal is adjusted wrong; as in actions that have DEPRESSED the piston cup into the MC, this SEALS THE PORT CLOSED and the reservoir is now isolated from the brake line and can NOT be bled. This is when the system can begin to build pressure if the piston is depressed further.

Nutshell; if adjusted wrong and the MC piston is depressed, it can not access the reservoir to refill the line set and will not bleed (partial closure is possible too). Verify the piston can fully retract and that there is some amount of free play such that the levers movement has a tiny gap at the MC piston...

 

[grbl]

Update!

Took the bike in today, and it turns out everything from the MC to the caliper is full of lumpy brown sludge. So, looks like a water/corrosion issue at heart and something's plugged up in the MC. They told me I could probably get away with pulling it apart, blasting it out with contact cleaner and cleaning the seals, then trying it out. It doesn't appear to have a leak, so with fresh fluid it should be protected from further corrosion. At least the front brakes are in great shape.

FinalImpact, thanks for the explanation of how the cylinder works, I'd been wondering how it was plumbed. Makes sense. I did try detaching the brake lever from the piston so it could travel freely, earlier. Once I get everything working I'll have to look up how to achieve proper adjustment.

 

[FinalImpact]

Re: Update!

With so many of these bikes being parted out, I'd opt for replacement unless tear down inspection reveals NO PITS in the walls of the aluminum pistons bore on BOTH the MC and Caliper Piston. Pits tear up seals and you loose brakes...

Thats not to say an ebay purchase is the way to go, but a local member here may be able to offer some history and comfort.

 

[TownsendsFJR1300]

Re: Update!

+1 ^^^^.

Bikes are parted out all the time here and I'd buy from a "regular member" here before I went to E-bay.

Someone didn't maintain the brakes obviously for you issues to have occurred.

I'd be suspect on the front brakes (service them if you haven't already) as they didn't maintain the rear, they likely didn't maintain the fronts either..

 

[grbl]

Re: Update!

Thanks again for all the advice, folks. I pulled everything apart and blasted it all out. The cylinders looked pristine afterward, without pits. I do wonder where all that crud came from, it was even upstream of the MC and the reservoir fluid was brown too. Once it was cleaned out it bled like normal and a choir of angels started singing. Test drive shows prompt engagement and good solid feel, and usable but poor stopping power. I suppose I got brake fluid on the pads, will that bake out/wear away?

The mechanic said there were no problems with the front brakes, fluid was old but no signs of sludge or chunks and they bled nice and easy, so I'm content to leave them alone (I did have them bled).

Good call that I should avoid the total rando ebay parts. Time to go see if anyone on here is selling their luggage rack...

 

[TownsendsFJR1300]

Re: Update!

Thanks again for all the advice, folks. I pulled everything apart and blasted it all out. The cylinders looked pristine afterward, without pits. I do wonder where all that crud came from, it was even upstream of the MC and the reservoir fluid was brown too. Once it was cleaned out it bled like normal and a choir of angels started singing. Test drive shows prompt engagement and good solid feel, and usable but poor stopping power. I suppose I got brake fluid on the pads, will that bake out/wear away?

Congrates!!!


Re brake fluid on the pads:

You can pull the pads out of the caliper and spray them down good with brake cleaner. You should do the same with the caliper itself as well..Brake dust, fluids, etc tends to gather up in there and get nasty.

A scruff on a flat surface to the pads with with either sandpaper, or nice a nice flat concrete sidewalk will help knock off any glaze ( after cleaning with brake fluid / soap and water)

And lastly, the rear brake caliper "floats" and centers itself on the rotor. The two bolts and sleeve (and you'll see two rubber "accordion" covers) should be nice and clean a lubed with brake SPECIFIC GREASE.

Parts 7 and 9:Yamaha Motorcycle Parts 2004 FZ6 - FZ600SS REAR BRAKE CALIPER Diagram