Failed MOT, rear brake pulsing, ideas?

[millard]

It's a 2004 GS1200, bought from a former forum member (BigChris) up in Coventry about 5 months back. Factory service history up to when I bought it with 36k on the clock, it's now at 40k.
No other issues.
It failed because
"Rear Roller Test indicates excessive fluctuation of brake effort"

The tester reckons it'd iether be a warped disc or sticky caliper pistons.
Sounds more like the disc to me.

I'm planning to remove the wheel and get the disc on my surface plate or the lathe to check it's true, but was wondering if it'd show up if I put a DTI on it and turned the wheel?
Next step is to remove the wheel which will have to happen whatever the result anyway, and make sure the pistons ain't sticky.
I've rebuilt heapsa calipers on other bikes but is there anything to be wary of with the ABS system? Does it need any special tools? precedures? bleeding sequence?

cheers
millard

 

[shugie]

It's a 2004 GS1200, bought from a former forum member (BigChris) up in Coventry about 5 months back. Factory service history up to when I bought it with 36k on the clock, it's now at 40k.
No other issues.
It failed because
"Rear Roller Test indicates excessive fluctuation of brake effort"

The tester reckons it'd iether be a warped disc or sticky caliper pistons.
Sounds more like the disc to me.

I'm planning to remove the wheel and get the disc on my surface plate or the lathe to check it's true, but was wondering if it'd show up if I put a DTI on it and turned the wheel?
Next step is to remove the wheel which will have to happen whatever the result anyway, and make sure the pistons ain't sticky.
I've rebuilt heapsa calipers on other bikes but is there anything to be wary of with the ABS system? Does it need any special tools? precedures? bleeding sequence?

cheers
millard

Out of curiosity, and assuming as this is an ABS bike it will have the servos, did the tester have the engine/ignition on when he did the brake tests?

If he did, might the problem lie with the ABS getting upset with, presumably, a stationary front wheel?

 

[millard]

Hi Shuggie
Yup, apparently the engine was running when he did the test.
Thanks
millard

 

[Ali-bear]

I think a warped disk would be pretty obvious, by visual inspection. Seems unlikely.

 

[John Armstrong]

Yup, apparently the engine was running when he did the test.

And they'd got the ABS lights out by riding the bike over 10 mph (IIRC), I know it's sucking eggs time for you, but do they know

Not bled the brakes but IIRC the action of bleeding the brakes at the caliper doesn't cause the bar / frame mounted reservoir to empty, it's in the ABS control module. Think that dealers etc have a pump that can be replicated to replenish the ABS module reservoir and I also think it's been discussed in the last few months. Sorry can't be more exact

 

[Russ-AFC]

Another possibility might be damaged/bulged hoses. Check them out. You may see obvious damage or it might be a small bulge hidden by braiding. As its not so easy to check with braided hoses run your hand (wrapped in a cloth) along them while someone is operating the brake.
Just worth looking at.

 

[cusi]

I reckon the DTI will show if the disc is warped, quite possible at that mileage.

 

[EURTRAF]

Millard
Before condeming the rear disc worth giving a thorough clean with 'Brake Cleaner' as I have found that dirty discs will give a similar result as warped discs (pulsing on the MOT brake force meter)

Steve