MOT Advisory - Front brake fluctuation ?

[roddy]

Folks a little advice please,

took the 1150GSA (with servo) for it's MOT today and it passed with an advisory of
" Front roller brake test indicates slight fluctuation of brake effort"

what does this actually mean, is it my brakes are pulsing slightly ? as I can't feel anything through the lever, the bike feels like it's stopping smoothly, I even tried it with the servo off and still couldn't feel anything on the lever.

I have done a visual check of the disc's and they appear to be running true and straight

I recently replaced the brake fluid, would a small air lock cause this ?
I haven't cleaned the calipers yet but it's on the list to do this weekend anything else I should look out for ?

cheers for any help

 

[robc]

Hi Roddy,
I got exactly the same thing last week.

Story: A few months ago my front brakes developed what felt like warped disks. I bought a new set and a couple of months later the problem returned. It was bad enough for me to see the front brake lever pulsing when braking.

Fix: Remove the brake disks and give the mounting points on the disks and the wheels a good clean. I used a wire brush but I need to do it again with emery paper to get all of the crap off.
It appears that over time the mounting points corrode slightly and collect a load of road crap. Cleaning it all off solves the problem - unless your disks are actually warped of course.

Regards

Rob C

 

[Fanum]

Did the muppet tester just yank on the lever and not realise that the ABS was kicking in (might be hard to hear over the roller noise)? that would do it, but it'd be pulsing rather than 'fluctuating', but I guess that could just be down to wording

 

[Greg Masters]

I have done a visual check of the disc's and they appear to be running true and straight

The discs may well be straight, but are they of consistent thickness. Use a micrometer and check the discs thickness at several points around the discs.

The readings should all be the same give or take thou or two.

If the discs do have varied thickness, this may manifest itself with long lever travel due to 'pad knock-off'.

Either buy new discs or learn to live with it and find another MoT station for next year.

Greg

 

[ktmmark]

just picked up on test if you can't feel it on the road don't worry about it won't be abs as wheel would not have spun fast enough for it to kick in

 

[Fanum]

just picked up on test if you can't feel it on the road don't worry about it won't be abs as wheel would not have spun fast enough for it to kick in

How fast does a wheel have to be going before the ABS kicks in?

It 'sets' itself in a few revolutions, so it would be active, and you can trigger the ABS at around walking speed on gravel

 

[roddy]

Fix: Remove the brake disks and give the mounting points on the disks and the wheels a good clean. I used a wire brush but I need to do it again with emery paper to get all of the crap off.
It appears that over time the mounting points corrode slightly and collect a load of road crap. Cleaning it all off solves the problem - unless your disks are actually warped of course.

On this list to do this weekend

Did the muppet tester just yank on the lever and not realise that the ABS was kicking in

This did cross my mind but I'd be surprised if the tester got fooled by the ABS, he's done the tests for a while at Motorad Central so would be aware of such things

The discs may well be straight, but are they of consistent thickness. Use a micrometer and check the discs thickness at several points around the discs.

The readings should all be the same give or take thou or two.

I check this out while the calipers are off I didn't realise a thou or two would make such a difference

cheers folks

 

[ebbo]

My experience is, if you can read any difference in thickness of the disc with a micrometer, you’ll feel it at the lever. The more the difference the worse it is.

I once took a pair of cast discs to be re ground flat at an engineering place in Bradford, one was done perfect, the other wasn’t ground perfectly flat
Result = pulsing brake

 

[Wrigsby1]

MOT advisories can be a little bit "overly". If you can't feel it at the lever and the bike is smooth on the brakes then you may not even know what you have fixed unless you get another MOT done at the same place.

Mine got an advisory on the back coming off the numberplate!

G

 

[ktmmark]

How fast does a wheel have to be going before the ABS kicks in?

I have tested all abs (passave and active) car' and bike's always lock, the rollers run around 3 mph + only running one wheel

 

[t'other dave]

Did the muppet tester just yank on the lever and not realise that the ABS was kicking in (might be hard to hear over the roller noise)? that would do it, but it'd be pulsing rather than 'fluctuating', but I guess that could just be down to wording

If you just yank the lever on it just stops/locks out (pass)and gives a reading. To roller test brakes, you lock out, mental note the reading say 100 then you start the roller again and gradually pull the lever to say 85/90 and hold it to see if the machine reading (needle/lcd) fluctuates (goes up n down) then lock out again for final read figure which is entered.
Sometimes oddly worn duel porpose tyres give a slight fluctuation.

 

[D6]

newer brake testing rollers are v sensitive, mine picks up fluctuations regular, but on the road you cant feel anything, wouldnt worry too much

 

[D6]

fluctuation is not at locking point, its done on low pressure at the lever

 

[roddy]

the general idea I'm getting is, it's nothing to be overly worried about, I haven't put a air lock in the system, an give the calipers a bit of a clean an I'll be cool

chheeers

 

[johnnyboy]

The majority of ABS systems don't operate until atleast 5MPH has been exceeded. Although I'm sure someone will come along shortly to tell me otherwise

 

[ktmmark]

The majority of ABS systems don't operate until atleast 5MPH has been exceeded. Although I'm sure someone will come along shortly to tell me otherwise

Thats about right

 

[John Armstrong]

Thats about right

Most don't operate below about 5 mph.

 

[*DAVE*]

anything else I should look out for ?

Insurance Company should you need to make a claim your fault or not
This info will be logged with VOSA / DVLA .

You just Know it's a way out for them to pay if not resolved correctly

I might be talking out of my arse hear, but worth checking anyway.

 

[divegod]

Brake Fluctutions

You've maybe got a rogue chilli stuck up yir flu!

onyack

 

[divegod]

Brake Fluctuations

Brakes who needs them anyway?