ABS activating in error during slow speed braking

[finbarr]

Hi there,
My 1150GS has developed an odd fault a few days ago.
When pulling up to a set of lights (nothing extravagent - just slowing down from legal speeds) as I'm going slow enough in first to pull in the clutch and coast the last few metres under brakes, the brakes suddenly let go and I go surging forward!

It's definitely a fault with the ABS and has all the hallmarks of the ABS erroneously thinking there's a lockup and so releasing the brakes. This only happens at slow speeds - less than 20MPH. I cannot reproduce the problem at speeds greater than this.

Starting the bike with the ABS switched off makes the problem go away and the bike behaves normally.

I've blown out the area around the two sensors with an air line in case some dirt/debris was lodged in there - but it didn't make any difference.

Any suggestions or help is greatly appreciated.

Kind regards,
John.

 

[blues n twos]

Hi there and welcome,

I recently had the same problem and the sensor gap was to much.

In your toolbox there should be a feeler gauge with max / min on it.
If the max fits to easily between the surface of the sensor and the abs ring you need to remove some shims to get the gap right.

Undo the two alan key bolts that hold the sensor on to the fork leg. you may need to tap it to loosen or in my case gently pry out with a hammer and thin blade screwdriver. Once out you will see various shims that vary from wafer thin to about 1/2 mm. Remove whats needed and reasemble.

Then check your abs again.

Hope this helps,

Jon

 

[finbarr]

Cheers, Jim - I'll give this a whirl this arvo and let you know how I get on.

Kind regards,
John.

 

[finbarr]

Jon,
Sorry for the typo (who's Jim?)!

On closer inspection by someone who knows what they're doing - it turns out that the front wheel ABS ring is slightly damaged.

A small section of the "bars" on the ring are dented inwards (away from the sensor) and the effect is that at very slow speed the ABS sensor cannot see these bars as they are another mm or two away from the sensor, so the ABS unit thinks the front wheel has locked and lets go.

I'm going to attempt to straighten them out tomorrow and see if this fixes the problem. I'll take some pics and post before & after shots if these seem useful.

Cheers,
John.

 

[Bananaman]

It's wonderful what you learn looking through the technical bits.
Forewarned is Forearmed as they say.
Look forward to seeing pics

 

[finbarr]

My pics are a bit cr@p so I won't bother posting - you really can't tell what's going on.

Good news is though, tapping out the dented bar from the other side with an old blade screwdriver until it was all flush again has solved the problem!

So all fixed.

 

[Taff]

.. Good news is though, tapping out the dented bar from the other side with an old blade screwdriver until it was all flush again has solved the problem!

Any idea what dented them in the first place?

 

[finbarr]

Taff,
I guess it was a stone that flicked up or some twat bashed into it parking her scooter where I park in central Londonistan.

Hard to say really. It was only two bars that were dented and one not seriously.

Cheers,
John.