ABS issue rear only

[GSX_Rich]

Hi guys, first post here as my latest bike has me stumped. I recently picked up a GSX S1000, private sale and no warranty. I discovered on the ride home that the rear brake is completely locking up despite it having ABS. I have since nervously tested the traction control and ABS on the front wheel and both are working. There is also no ABS warning light, it comes on and goes off as you'd expect. There is a sensation through the rear pedal that's almost like a click when the brake locks up and the brake only releases when the bike comes to a stop even if I lift off the pedal.
Any help is much appreciated.

[Easy-X]

Just for more information are you saying the rear brake locks up with even light pressure or only when you give it some boot?

Sounds like the ABS unit is buggered.
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[GSX_Rich]

So it's only when I really boot it. The odd thing is that the front works fine and the bike has only done 3k. I also find it odd that it completely locks, only releasing when the bike has come to a complete stop.

[MCN]

[Easy-X]

I always like to understand these systems when problems crop up, correct me if I'm wrong here...

If you really boot the rear brake the wheel might lose traction and lock up so Step 1 is sensing the wheel has suddenly stopped rotating. Something is happening to your system given the brake won't unlock till you've stopped so I'd guess the sensor and ECU are working in the sense the ECU is saying "do ABS!"

Step 2 the ABS isolates the braking system from the master.

Step 3 is to remove pressure from the system until the wheel starts rotating again (usually a passive reservoir in the ABS unit)

Step 4 is to add pressure back in via an electric pump until the wheel locks again

The whole thing cycles between 3 & 4 until the ECU decides the traction loss event is over.

Step 5 restore master cylinder control over braking system

Thinking on the OP's situation Steps 2 & 5 are definitely happening but brake pressure isn't being relieved in Step 3. Could be the brake piston(s) sticking a bit and relieving some pressure is having little effect or, once isolated, pressure isn't being siphoned from the braking system. This could just be a bit of crap blocking a channel in the ABS... no idea what you'd do about it though

BTW the front and rear systems are parallel so one won't affect the other.
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[colink98]

rear ABS sensor / ring is not registering the rear wheel locking up.
Hence ABS pump is not kicking in.
which is by design.
____________________
PCX125 (stolen) - CBF600 (current)
Ride it like you stole it.
ride sensible and not like an idiot and you wont get 6 points in one week.

[Easy-X]

Yes, but why would the rear wheel lock up and not unlock until the bike has stopped?
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Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[stevo123]

Sensor ring for each wheel

[Robby]

This could be that the whole area is filthy and needs a good clean - abs not working because the whole area is caked in shit, and the caliper sticking because the whole area is caked in shit.

[colink98]

[steve the grease]

Does the system do a self test when you start up ? If it does and it's checking out Ok then it sounds like the caliper is sticking, or possibly the hose collapsed internally.
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All the above is my personal opinion, you can see my lips move, but I'm talking out of my arse.
I've been riding, and fixing , bikes for 50 years, in that time the more I learn, the less I am absolutely sure of.....

[GSX_Rich]

Firstly thanks for all the replies guys.
Today I removed the rear brake from the caliper to take a look at the piston and clean it up, It was very clean and the piston moves correctly. Also the whole unit seems to float in the correct manner so I have ruled that out too. In terms of the speed sensor I believe if there was an issue with this the traction control would be affected but this functions correctly.
Another potential I thought of was the lines for the ABS being the wrong way round hence when the abs tries to release the pressure it just applies more force. Happy to hear people's thoughts on this theory though. Also on initial inspection they seem to be laid out correctly.
A mechanic mentioned that as it has aftermarket braided lines sometimes they have gunk in them when they leave the factory and if they are just fitted and not checked it can cause blockages. Has anybody else heard of this being an issue?

[MCN]

When was the fluid last changed.
Bleed all the air out.
That may need some tech knowledge to activate the system. Is it a pumped system?
I had a Brake Modulation Valve fail on one of my BMW R1200GS.
Pumped system.
Never a problem with brake sticking.
Only the yellow warning would flash now and then but clear after a bit until it stayed on and I could hear the pump running on with brake not active.
BMW mech at dealer saw 1300psi on the test bench.
Brake pressure was not being modulated.
It was a common issue with BMW ABS.
Bastirt Muff Waffen refused to kelp with remedy.

New module costs £1100 ex VAT and fitting.
I bought a second hand unit and the dealer fitted it for me for a good price.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[GSX_Rich]

Tbh I'm not too sure if it is a pumped system. Is there a way to check? The warning light only flashed when I first locked it up and accidentally did a very long skid. Since it's been coming on at start up then going off as soon as I start riding. Not even flashing when skidding.
I've changed the fluid recently as I completely bled the system to try to remove any air incase this was the issue.
I think you might be right and it might be a case of replacing the abs module over the winter months.
I have also just seen they do an abs delete cable so going to check it doesn't have one of them installed that isn't working correctly. I've also attempted to contact the previous owner to see if he has changed anything that might have caused the issue.
Thanks for your responses.

[MarJay]

I have a 24,000 mile GSX-S1000F. When you lock up the rear you can feel pulsing through the pedal. I still went a little bit squirrely when I did it by accident, but the bike was a touch more controlled than if I had just locked the rear on a non ABS bike. Could it be that your bike is doing the same?

It's not cornering ABS so it is a touch on the crude side compared to 6 axis IMU equipped bikes and the like.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[GSX_Rich]

Unfortunately not it's definitely a case of something not working correctly as the brake locks on until the bike stops and there is a definite flat spot on the tyre afterwards.
I have spoken to the previous owner and he didn't notice any issue however the sprockets were changed so maybe the sensor isnt close enough to the ring to pick up the speed correctly.
Mar Jay would you mind measuring the gap between the rear speed sensor the the ring for comparison?

[davebike]

Is the ABS setting i.e. the abs light comes on when you start the bike and goes off when you first reach 5/10mph ??

If not I say the rear sensor or ring have problems
If it setting I suspect teh rear ABS modulator (ther is two one for each wheel ) Two channel ABS
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Dave
NC750Xdct + others at work !
davebike1@gmail.com

[PotatoHead202...]

Get it plugged into a code reader. They can be had for around £40 on ebay plus the licence.

I had issues on my BMW's several times. Once the ABS module became stuck (ABS light stayed on solid). Few knocks and regular activation and no longer an issue.

New front tyre caused ABS/T/C lights to stay on. The metal ring sensor was damaged (you couldn't really tell from the naked eye).

Third the ABS/T/C light just continued to flash after riding on. Plugged in the code reader, front wheel speed was either zero or only occasionally registering whereas the rear was fine. Sensor wasn't seated properly.

Most of these issues required the ABS to be rebooted - with the code reader. It's strange that the light doesn't stay on but it could well be air in the line or something. Most people don't realise that on an ABS equipped bike you need to bleed the ABS module/pump as well so old fluid stays in there or even an air lock (as happened on a BMW).

In my experience if one wheel is knackered then the other will be as well though. This is why I don't think it's a sensor issue. The unit must be registering wheel speed for the front to not lock up. Must be an issue with the pump/module feed to the rear brake.
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Suzuki V Strom 1050XT, Honda CBF500 ABS,

[GSX_Rich]

Thanks for the suggestions guys. I had a better look at the abs today. The rear pipes leading from the model appear to have been removed at some point maybe when upgrading the brake lines. Anyway it seems that the "MC" connection goes to the rear brake caliper where as on the front it goes to the reservoir. This would explain why the brake locks on till the bike comes to a stop and then releases as the abs is effectively working against itself then releases when the bike stops. Going to change them over tomorrow and hopefully all will be good.