[Don-mak]

I recently purchased a 2006 FJR1300 for what I thought was a very good price. It has a weak front brake that I thought would be an easy fix. Just rebuild the master cylinder.
I was quite incorrect on my estimation.
For a quick check, I swapped the master cylinder off a 2007 FJR that I have also. The brakes on that bike work well.
That master cylinder swap gve me the same results. I bled the front brakes several times with no improvement, before learning of the ABS test/flush procedure required to do a proper system bleed.
I bled/flushed the system sevaral times using over a quart of fluid. During the test, the front brake pressure increased dramatically pushing the lever all the way out to the stop against my force. After the test cycled through each time, the front brake lever looses all pressure rapidly and pulls right back to the handle bar. Pumping it several times it gains pressure, then as I hold it, it slowly creeps back to the bar.
Reviewing the brake system schematic, I see that there is a check valve between the front brake mastercylinder and the ABS hydraulic pump. I suspect that check valve has failed.
These units are apparently not rebuildable and cost over $1,600 new. I found a used one on ebay, and am hoping that one works.

My ABS test jumper. #12-10 wire gauge female terminal end.
It required some slight reshaping and squeezing, but works perfectly.

 

[RaYzerman]

To my knowledge, there is no check valve, nor would you want one. When you release the brakes, fluid needs to flow freely back to the reservoir to relieve pressure at the calipers. Take a look at the Gen2 ABS flow diagram below.

Also, with ABS not activated, the fluid is in by-pass of the ABS valves for normal braking. Only when ABS is activated that is shut off and fluid directed into the ABS fluid circuit within the ABS hydraulic unit, which pulses the pressure/relief sensing wheel lock-up. There is fluid in all the lines to and from the reservoir to ABS unit to the calipers, should be no air. Rear circuit separate from front, of course.

The master should be intaking fluid into the piston which then pushes it to the calipers..... then there is a return hole also beside the intake hole in the reservoir. Since everything is immersed in fluid, it would seem the master is not pushing fluid, thus lever going to the bar. I'm not seeing why there would be any other reason.

I am not sure why you had the same symptom with the '07 master, other than air trapped in the master.... to fix that, crack open the banjo bolt at the master and lightly press the lever, air will escape past the banjo washer and you should then have the master bled and working. Snug up the banjo bolt. Of course, put an alcohol soaked rag to catch the fluid, and clean up with isopropanol. If you have pressure and the lever creeps back to the bar, that would suggest you need to rebuild the master with fresh rubber parts.....

The ABS test procedure just flushes out the ABS fluid circuit by pushing a small amount of newer fluid in.... after activating, I'd recommend a quick squirt bleed, then repeat the test.... and repeat this perhaps 3 times.. this will ensure no stale fluid in the ABS fluid circuit, a common issue with this generation and prior of ABS systems on FJR's. Although again, I've not heard of a front ABS pump issue, more likely happens on the rear. I don't think you have an ABS pump issue on the front at least.

 

[RaYzerman]

There is a service who rebuilds the ABS hydraulic units, FYI. Thankfully. But you're not there yet.

 

[Linton West]

Sounds like air in the system.

 

[Don-mak]

To my knowledge, there is no check valve, nor would you want one. When you release the brakes, fluid needs to flow freely back to the reservoir to relieve pressure at the calipers. Take a look at the Gen2 ABS flow diagram below.

Also, with ABS not activated, the fluid is in by-pass of the ABS valves for normal braking. Only when ABS is activated that is shut off and fluid directed into the ABS fluid circuit within the ABS hydraulic unit, which pulses the pressure/relief sensing wheel lock-up. There is fluid in all the lines to and from the reservoir to ABS unit to the calipers, should be no air. Rear circuit separate from front, of course.

The master should be intaking fluid into the piston which then pushes it to the calipers..... then there is a return hole also beside the intake hole in the reservoir. Since everything is immersed in fluid, it would seem the master is not pushing fluid, thus lever going to the bar. I'm not seeing why there would be any other reason.

I am not sure why you had the same symptom with the '07 master, other than air trapped in the master.... to fix that, crack open the banjo bolt at the master and lightly press the lever, air will escape past the banjo washer and you should then have the master bled and working. Snug up the banjo bolt. Of course, put an alcohol soaked rag to catch the fluid, and clean up with isopropanol. If you have pressure and the lever creeps back to the bar, that would suggest you need to rebuild the master with fresh rubber parts.....

The ABS test procedure just flushes out the ABS fluid circuit by pushing a small amount of newer fluid in.... after activating, I'd recommend a quick squirt bleed, then repeat the test.... and repeat this perhaps 3 times.. this will ensure no stale fluid in the ABS fluid circuit, a common issue with this generation and prior of ABS systems on FJR's. Although again, I've not heard of a front ABS pump issue, more likely happens on the rear. I don't think you have an ABS pump issue on the front at least.


View attachment 109510

That is the exact schematic I have.
What is that item with the spring in it next to the hydraulic pump (5), on the front brake circuit?
That is what I am guessing is a check valve.

Air trapped in the system would give a spongy feel. There is no spongy feel, the lever bleeds down and looses pressure as if the master cylinder seal is bad. Pumping the lever several times builds pressure but it does not hold, bleeding down slowly.

During the ABS test, the front brake lever does not just pulse, as does my '07, it actually pressurises and goes to the full forward position, pushing my hand out. Then when the pump stops running, the lever quickly goes all the way back to the handle bar.
I doubt air in the system would do that.

Everything I did to the '06, I also did to the '07, with a totally different result.
After swapping the master cylinders, it took no time and only a few ounces to bleed the '07, but with the '06 I used over a quart of fluid bleeding and repeatedly running the ABS test, and still had the same response.
The original fluid was discolored, so I flushed the rear brake system also.

Trust me, there is no air in the system.

Just to give some background, I worked as a motorcycle mechanic back in the early '80s. I have bled "a few" brakes and clutches, but this is my first experience with motorcycle with ABS.

 

[FlatTop]

Not a brake or hydraulic guy, so this is a long shot...
Could a weak but not fully failed brake line bulge when the lever is pulled, but with the ABS pump on it generates enough constant pressure to force the lever out?

 

[Don-mak]

Not a brake or hydraulic guy, so this is a long shot...
Could a weak but not fully failed brake line bulge when the lever is pulled, but with the ABS pump on it generates enough constant pressure to force the lever out?

I cannot imagine that. A weak/bulging line would probably have a similar but lesser symptom as air in the line, a spongy feel.

 

[alnbama]

Trying to help. Item 5 in the schematic is labeled hydraulic pump, item 6 it's labeled buffer chamber that might function as a relief valve to control pressure. These are all within the 2 box, which is the Hydraulic unit. My manual has two test of the unit. Test 1, test the function of the Hydraulic Unit after servicing, test 2 checks the function of the unit operationaly. My manual is for 2016 up. The system has no function on normal breaking.

You switched the master cylinders so that should have eliminated the '06 part. You might try removing the brake caliper and rotating them around, like tipping, still connected to the hose, to remove the possibility of trapped air, then re-bleed . Note: old BMW rear calipers needed this.

Good luck

Ride Solo

 

[RaYzerman]

In the flow diagram, Item 5 only opens to let fluid into the ABS fluid circuit (5,6,7) when ABS activated, then likely it acts as a check valve to not let it flow back out unless electronically it opens as ABS pulses. Doesn't make sense to me, given the master is providing constant pressure. The fluid would flow to the solenoid valve item 7... bottom line, all fluid circuits are full no matter what, and if bled, there should be no air in there. When ABS is not activated, it bypasses 5,6, and 7 for normal braking. When you are bleeding or using your brakes and get a spongy master cylinder, my opinion is it has nothing to do with the ABS hydraulic unit. I'm back to the master cylinder somehow and ensuring it is primed with fluid..... however, how to test that. If you were somehow to plug the banjo fitting at the master, can you build pressure... then try the same thing on one of the front calipers..... if OK, then try the opposite one.... if all that was OK, then there's no issue with the ABS hydraulic unit since all fluid passed through there first.......

So the next question is.... do we have a stuck piston in one of the calipers which is trying to deploy and being delayed (lever losing pressure), and retracting more than normal (potentially due to bad caliper seal?).
Another test you could do is plug the outgoing line on the hydraulic unit leading back to the front, but that should have been ruled out already if the above was successful.

It is possible to have air trapped in the hydraulic unit, so when you bleed, open whatever bleeder up front and squeeze the lever quick and hard to the bar, then quickly release it. Repeat a couple of times..... not fixed, then I suppose the only way to get the air out is to loosen the fittings at the hydraulic unit and let air escape .... that gets a bit messy, so have lots of rags and isopropanol to clean up....

 

[jasonm.]

Brake lines internally fail...the brake line has layers and the layers can separate where the fluid gets in between the layers.....where it does not belong and into a "soft area of the hose". Examine all hoses , especially where they bend. EX:The problem is common on the clutch hose due to its bend bye steering and handlebar

 

[Don-mak]

Item 5 is labled as Hydraulic Pump. There is a unit adjacent to item 5, with a spring and 2 triangles on this unit. That may actually be a part of the hydraulic pump, but it is certainly a check valve of some sort. I am surmising that that check valve should be closed when the master cylinder is operated. If that is not closed when the master cylinder is operated, there will be fluid/pressure loss through that valve to the Buffer Chamber.
This is my assumption, having not seen a system operation description telling what does what and when.

Item 7, Hydraulic Control Valve, could also be the culprit.
Either one of these items could possibly be bleeding fluid and pressure into the Buffer Chamber.
Either way, I am satisfied that the system is not operating as it should, so I have a used replacement on order, hoping that one solves the issue. If the replacement unit doesn't work, I will delete the ABS system and go to standard brakes.

Brake lines internally fail...the brake line has layers and the layers can separate where the fluid gets in between the layers.....where it does not belong and into a "soft area of the hose". Examine all hoses , especially where they bend. EX:The problem is common on the clutch hose due to its bend bye steering and handlebar

 

[alnbama]

Good luck on your repair, I guess it is possible the unit could fail in the manner you propose. Did you try the operational test 1 from the service manual? I wondering if a electrical connection could cause the failure..

Anyway, keep at it.

Ride Sane

 

[Don-mak]

I replaced the ABS hydraulic module, bled the system, and the brakes now work properly.
I appreciate all the suggestions that were offered to help solve the problem.

The link below is to a video I made of how the front brake lever behaved during the test.

Used ABS hydraulic module.

 

[SkooterG]

How much of a pain in the ass was it replacing the ABS hydraulic module?

 

[Don-mak]

It was a pain!! Pull side panels, lift the tank, pull thebox under the seat, pull the rear fender part way out, loosen the rear fairing to get the rear fender loose.......... Oh it was fun (he says tongue in cheek).

I get it all back together, feeling really good that the brakes work, then an electrical problem pops up!
I'll start a new thread on that.

 

[ChrGrVoy]

Good to know you fixed it.
Mine 2005 have similar problem.
Is it possible to check the valves inside ABS module if they are somehow stucked? And perhaps come up with some pictures if you dive into it?

 

[Don-mak]

Good to know you fixed it.
Mine 2005 have similar problem.
Is it possible to check the valves inside ABS module if they are somehow stucked? And perhaps come up with some pictures if you dive into it?

Yes, I plan to attempt to get inside the unit in a little while and post my findings, but right now I am chasing grounding issues that just came up.

 

[Don-mak]

Well, I tried exploring the hydraulic module that failed.
I pulled 2 large and 4 small allen head "grub" screws, and one 2" long pin fell out of one of the small holes. There are a couple of internal snap rings holding caps in place, that I cannot get out.
There are what seem to be pressed in rivets or pins at various locations.
Entering this unit without destroying it, is outside of my scope of skill or patience.
Sorry.

 

[SkooterG]

Well, I tried exploring the hydraulic module that failed.
I pulled 2 large and 4 small allen head "grub" screws, and one 2" long pin fell out of one of the small holes. There are a couple of internal snap rings holding caps in place, that I cannot get out.
There are what seem to be pressed in rivets or pins at various locations.
Entering this unit without destroying it, is outside of my scope of skill or patience.
Sorry.

Conventional wisdom had always been that it was unserviceable. But not too long ago on one of the forums (FJRForum.com I think), somebody posted a video on hot to repair one. Though I can' remember if it was Gen I, or Gen II+. I didn't actually watch the video.

 

[RaYzerman]

I swapped one out on a '07 at a tech day, took it home.... yeah, those "rivets" are a special thing (one can get replacements for), but screw it, leave it to the professionals....
Rebuilder here:

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