Rear ABS brake pedal won't move

[jjjmbailey]

I have a 2007 650 ABS model V-Strom. I have owned since new but have only had limited use. Just getting back onto it recently and notice rear brake pedal intermittently locked solid and no rear braking. Seemed to sort it self out a couple of times then stuck permanently. A bit of poking around  showed me that brake piston and pads were free to move and if I loosened pipe above master cylinder pedal freed up and fluid came out. If I loosened pipe before brake caliper nothing came out. My guess then is that the ABS unit is blocking the brake fluid. So before I take it in for what I suspect will be a very expensive exercise does anybody have any ideas or suggestions?

[Andy M]

Pull the fuse on the ABS. The fail safe on all non-integral ABS units is a reversion to standard braking. In ten years of dealing with warranty and other complaints I never saw one "stick". If it did the self test would fail as there would be no current cycle as the solenoid moved, the red light would be on.

If the dealer tells tales of witchcraft and expensive black boxes run away, he's a bull****er who's out of his depth. You plug in the diagnostics and it tells you which bit to change.This sounds more seal related to me.

Andy

[edwardatherton]

Try undoing the lever from the masyer cylinder rod and see if the lever still feels 'sticky'.
I have had to clean and regrease on both my 2010 and wife's 2005 bikes. It made a tremendous difference.

[Mr Nick]

It might even be a failed hose: I had a similar experience years back on a car I suspected had knackered brakes but it turned out that one of the hoses was effectively blocked.

[Fatbelly]

Ditto for the brake lever. Check it is not sticking due to road grime at the pivot.

[Locky]

yes check the brake lever pivot incase its ceased ..

[mr_diver]

The lever on mine was sticking and if I ever gave it chance to sit for a few days would require a little oil to get it moving again. Took the lever off, cleaned and greased the pivot and all was well again.
You'd be suprised how manky it can get.

[jjjmbailey]

Hi everybody. Thanks for the replies but I need to clarify the issue. While the brake pedal appears to be locked solid, if I release pressure by opening line nut above the master cylinder the pedal and Master cylinder work fine and fluid oozes out. I now have some air in the line and the pedal moves a bit but has no effect on brake and no fluid is even getting to the caliper end. The blockage is either in the lines or the ABS unit, and it is no different with ignition off or on or the bike being driven, have tried taking ABS fuses out and this makes no difference. Does anyone know what goes on inside the ABS unit and could it block off the brake fluid. If so could it just need cleaning/flushing or is it likely to be too complicated. My thought is that it has corroded/seized in someway possibly as a result of the brake fluid not being changed even thought the bike has only done 11,000km and the fluid reservoir has never been opened. Any more ideas. Cheers

[Andy M]

The ABS unit is a pair of solenoids. When the wheel leaves the predicted slip curve it fires the hold solenoid which stops more fluid going to the caliper. If this does not return deceleration to the curve it fires the second solenoid that by various routes depending on system design lets the fluid come back so the brake releases. Depending on the system there will be a pump or nitrogen accumulator to give it the mechanical means of getting any returned fluid back into the pressurised line before the hold solenoid, without the pedal dropping when it tries again for a higher decal a tenth of a second later.

The solenoids are cycled at system start up. As the core moves the current draw changes. If the current draw does not change because the solenoid is stuck the red light comes on. The solenoids are pressure/spring return so in the event of a failure they just become open galleries and the system reverts to pull function non-ABS.

Letting air in will make the pedal spongy, so if you have a blockage you will see the pedal go soft, all it is doing is compressing the air before the blockage.

That happens if you crack the bleed nipple at the caliper? Do you own a vacuum bleeder (or even a large syringe)? Can you get fluid to flow through an open system?

Andy

[Firestorm]

This is really quite difficult without seeing the Bike. Here is what I would try given AndyM says default on ABS is normal brakes.

Remove the pin that connects the master cylinder rod to the brake pedal and disconnect. Does the pedal move really freely?
If yes, reconnect the rod and remove the rear caliper and pads. Pump the pedal GENTLY. Do the pistons in the caliper move easily. You should see them 'pulse' a little.?
If no, put the caliper back on the bike and undo the bleed nipple, depress the lever to the bottom of its stroke and hold down. Tighten the nipple. Did fluid come out of the nipple? If no, repeat several times. Hopefully it will after a few tries. If it does come out, keep repeating and topping up the reservoir until the fluid coming out of the nipple is clear. This will have changed the old fluid. Remove the caliper and pads again and check the pistons are moving. Look for the 'pulsing in and out slightly. Do this GENTLY. If there is now fluid at the nipple and the pistons don't move they are seized and the caliper will need to be stripped.
If you now have fluid at the rear and the pistons in the caliper are moving freely pump the pedal several times and check whether the brakes still lock on. If they do then the following is worth a try as I've come across the following 3 times(although it means letting all the fluid out again - I hate brake issues!).
Remove the rear master cylinder and reservoir. Remove the master cylinder piston. Where the hose from the reservoir goes into the master cylinder there is a circular plastic 'bung'. Carefully prise this out and underneath you will see 2 holes. One is perhaps 2mm dia and the other is a pin hole. The pinhole is what releases the pressure once you take your foot off the brake. If the fluid hasn't been changed in the life of the bike this can become blocked and does not allow pressure release resulting in a build up which then locks the brake on. This MAY be your problem as you say when you crack the banjo bolt on top of the master cylinder the brake lever then moves. I have VERY CAREFULLY pushed a sewing needle through this hole (using it like a drill) until you can see the end of the needle in the bore of the master cylinder. Reassemble, re bleed (I know this is easier to type than to do on a Dry system) and it should be fine. It will at least have eliminated everything other than the ABS and will only have cost you time and a bit of fluid.

I don't think I've missed a stage but if I have, someone cleverer than me wll be along to put us both right!
Good Luck with it.

[jjjmbailey]

Thanks again for the rapid responses but I may still not have explained my problem clearly enough. I have no rear brake operation at all. The brake pads and caliper piston seem to work fine, I can push the piston in. There is however no fluid getting to the caliper at all. At the other end the rear brake master cylinder, break lever etc work fine, if the top banjo nut is loosened to release the pressure, and brake fluid, but as soon as this is tightened the brake pedal won't move (it does a bit now there is a bit of air in the line). Because of this I have no way of pumping brake fluid through the lines. My guess is that either there's a blockage in the lines or more likely in the ABS unit. And my main question is whether anyone has any knowledge of the ABS unit and possibly any links on the internet as to what it looks like and how to work on it? I seem to be having problems finding any information on the ABS system. Cheers

[Firestorm]

Sorry if I misunderstood - more likely to be me than your description. The only thing I can think of is to start at the master cylinder where you have fluid, then take off each brake line connection in order from the cylinder and see if you can push fluid through. This must surely isolate which line or component is blocked. It'll be messy I suspect but should at least isolate the fault. Good luck with it and I'll be really interested in what you find.

[jjjmbailey]

Thanks for all your help and tips. I managed to find a workshop manual with at least some ABS info. I worked out the blockage was in the ABS unit and not the brake lines. I have removed the ABS unit and discovered that the rear brake side is working like a one way valve, I can blow air back through it but not forward. The front brake side works in both directions. Does anybody know if the ABS unit is serviceable or if it is a replacement job, or if anyone has any ideas what might be happening in the ABS unit that is only allowing fluid movement in one direction? Cheers

[Andy M]

Car and truck ABS modulators are not serviceable.

A blockage will be just that, debris or dirt. Try  soaking the hydraulic bit in brake cleaner .

Andy

[phraedrus]

Hi, you may see this. I have the same problem. If you fixed it, what did you do?

[Ianmc]

    It simply seems to me that the hydraulic hose on the rear caliper has collapsed,loosen the pipe before the flex and press the brake lever,if it works then it is simply the hose has collapsed internally.It has happened to me 3 times over the last 60 yrs.once on a Ford Escort and twice on separate BMW bikes.