Rear Brake Problem - blockage?

[Greabr]

Hello All! Here is my first post for my "new to me" fjr. Previously a member of the Honda ST Clan. I am having a problem with my rear brake. Most urgently, I seem to be unable to bleed the line. A little history: had a problem with heat and lost the rear all together on a ride, I think from the brakes dragging. Anyway the rear master seemed unusually hard to pump fluid thru to bleed so I began to check the hoses one at a time starting from the master. master pumps fluid easily, hose from the master to the ABS pumps fluid easily, but after that I get nothing. more specifically: when I disconnect the hose that feeds the ABS (at the ABS) and seal it off with my fingers, I can feel the pressure in the line when I press the pedal, also if I release the seal and press the pedal down then seal and release the pedal, I get a good draw from the reservoir (just like bleeding). but then I reconnect that hose and disconnect the hose leaving the ABS, I would expect the same results by sealing off the exit with my finger, but nothing. No pressure when I press or pump the pedal. Cannot get any draw from the reservoir at or past that point. same results at the caliper. also cannot bleed with a vacuum pump at the caliper. Any Ideas? (04 FJR with ABS)

Greabr

 

[Queensland Ken]

The service manual has a large section on the ABS system, could also pay to get the abs test coupler adapter.

The test coupler allows access into the ABS ecu.

Don't know if this helps, BUT, have worked on a few different bikes & brakes.

Sometimes if the master cylinder sucks air, or you replace a in line pressure sensor / switch, you have to bleed out the banjos.

Maybe you have to bleed out each joint starting at the master cylinder working your way through to the slave in turn..

 

[Fred W]

Sounds from your description like the valve for the rear brake circuit in the ABS hydraulic block is stuck in the closed position. I vaguely recall this happening to one other 1st gen owner a couple of years ago. These valves get stuck pretty often, but usually they are in the "open" position where it is just a fluid pass-through, so the brakes still work fine but the ABS no longer cycles pressure.

The stuck valve was probably also responsible for overheating the brake as it wouldn't release back pressure to allow the pads to retract. I think that was the other guy's situation too.

The hydraulic block is not repairable as far as anyone has been able to determine. I don't think anyone has ever even been able to figure out a way to disassemble it non-destructively. And it is quite expensive. You could bypass the ABS block by connecting the in and out hoses with a banjo bolt and nut (and appropriate washers). At the very least that would confirm that the rest of your braking system is OK before shopping for a used block.

 

[Greabr]

Well, I am suspect of the ABS Block being the problem. The caliper and rear master seem to operate perfectly if I bypass the ABS block (using the hose that feeds the ABS, and connecting it directly to the caliper), the piston engages with the brake lever and retracts slightly when I release the brake lever. But back to the ABS Unit - the way I understand it, when the ABS is activate, the ABS only release pressure on the piston by allowing fluid back into a reservoir inside the ABS Block (lets call this State A). Then alternates back to "complete the circuit" (so to speak) from the pedal to the caliper (lets call this state B) . I am under the impression that the ABS Block can only be in one of these 2 states - state B normal brakes, or modulating state A and B for anti lock. Still not sure how state A or state B can cause dragging. This does not sound to me like a solenoid failure or a stuck valve of sorts, but more like blockage from debris, or something of that nature that would prevent the fluid from returning to the rear master. Any Ideas?

 

[RaYzerman19]

A safe flush might work with isopropanol and try to vacuum out the ports......??

 

[Donal]

A safe flush might work with isopropanol and try to vacuum out the ports......??

If I got to the stage where I felt the only option was to replace the ABS metering block I would try soaking/flushing the block with Park Tools Chainbrite Cleaner. It is water based so should be safe to use (what have you got to lose anyway). I always have some in the garage for bicycle maintenance and it works miracles on all gunked-up parts.

I would cycle it through the block using the ABS testing procedure detailed by Ionbeam here. If it gets things moving then a normal flush with brake fluid should get you back to normal (whatever that is)!

 

[RossKean]

If the innards are gummed with old hydraulic fluid, I think Ray's suggestion of using pure isopropyl alcohol might have some merit. As a solvent, it is water miscible (like brake fluid) and is pretty good at dissolving goo. Methyl alcohol might work but could be too aggressive toward any rubber/plastic parts it might encounter. I think something like acetone might be a little too damaging, depending upon what's inside. In addition to pumping it through under pressure while "exercising" the moveable parts, a dunk in an ultrasonic tank during the process would be helpful to loosen the stuff. It would be an interesting experiment. If someone had the wherewithal to carry out the procedure, there would be nothing to lose since a FUBAR ABS block doesn't seem to be repairable by conventional methods.

 

[Greabr]

Here is what I ended up with - an ABS Bypass for the Rear Brake - see pic below. I'll be keeping my eye open for a replacement ABS Block and replace later. I did make some progress with the blockage by pushing fluid backwards through the ABS by vacuum and also pumping with the rear master - alternating forward and backwards through the block by reversing the hoses, and also running the abs hydraulic test to activate the valves. This got me from total blockage - where no fluid was passing through the ABS Block to the caliper, to fluid flowing but with resistance. Anyway, not sure I can trust it even if I got It working again - so for now, front ABS only. Below: Stainless Nuts to seal ABS Block, and a double banjo bold with a cap to couple the brake lines.

 

[Fred W]

Nice work. And for what it's worth, I think that you may have the hot setup for ABS right there. There have been occasions (mostly on unpaved roads) where I wanted to drag the back end around to slow me down, but the ABS would sense slippage and the braking was essentially non-existent.

Having a front wheel lock on a street bike at a bad time can result in a quick tuck (and subsequent crash). A back end sliding is no big deal, especially of you ever spent any time on a dirt bike.

Now to take this bluebird dreaming one step further, I'd really like to have a linked braking system that applied the rear a little when braking the front, but not the front when braking the rear. Combine that with front only ABS and I think you have a winner.

 

[Harald]

Now to take this bluebird dreaming one step further, I'd really like to have a linked braking system that applied the rear a little when braking the front, but not the front when braking the rear. Combine that with front only ABS and I think you have a winner.

Unless you like to hold the front brake and light up the rear tire while walking the bike in a circle doing a smokey burnout.

 

[RugbyCanada]

Here is what I ended up with - an ABS Bypass for the Rear Brake - see pic below. I'll be keeping my eye open for a replacement ABS Block and replace later. I did make some progress with the blockage by pushing fluid backwards through the ABS by vacuum and also pumping with the rear master - alternating forward and backwards through the block by reversing the hoses, and also running the abs hydraulic test to activate the valves. This got me from total blockage - where no fluid was passing through the ABS Block to the caliper, to fluid flowing but with resistance. Anyway, not sure I can trust it even if I got It working again - so for now, front ABS only. Below: Stainless Nuts to seal ABS Block, and a double banjo bold with a cap to couple the brake lines.

the photo is a dead link, any chance you still have it. I'm looking to see how you attached the 2 lines to the double banjo. Thanks

 

[RossKean]

the photo is a dead link, any chance you still have it. I'm looking to see how you attached the 2 lines to the double banjo. Thanks

Greabr hasn't been on the forum in 9 years and three of his total of four posts were in this thread! Wouldn't hold my breath waiting for a response.

 

[RugbyCanada]

Greabr hasn't been on the forum in 9 years and three of his total of four posts were in this thread! Wouldn't hold my breath waiting for a response.

I saw the date and wasn't confident there would be any reply by anyone. Thanks for the added info. If anyone knows the procedure I would appreciate it. I'm guessing he put the double banjo into the ABS "in" feed and plugged the "out" line but wanted to verify. Thanks again.