MOT advisories - Slight fluctuation of brake effort

Hi guys
I took my 1996 ST1100 AT ABS for the first MOT since I have had her as I bought her as an MOT failure. You may have read about my problems with the ABS, which are not over, but I will deal with that later.
She passed but with the advisories of slight fluctuation on ALL the three discs, can someone tell me exactly what that means? How can they separate the two front brakes on the one front wheel?
I have looked into this and opinions differ between warped discs to unevenly worn discs to dirt under the disc mounting to sticking pistons etc..........Thoughts from those who know!?
What's weird is that I have not noticed any bumping or juddering through the lever/pedal and braking seems fine!
Will she fail next time if I don't sort it and is it a dangerous problem waiting to happen that will get worse?
Cheers guys!
James

The way I understand that is that there might be a slight warp in the discs, if you are riding the bike and on application of the pedal or lever do you feel a vibration or pulsing? Why don't you take the calipers off and clean them up, and eliminate that before you go to the expense of new discs, bearing in mind the bike is 20 years old and unless you have had the bike from new you won't know if the discs have been replaced at some point, it will all depend in how the bike has been stored, whether garaged all the time or left out in the crap UK weather.

Jamesgss said:

She passed but with the advisories of slight fluctuation on ALL the three discs...

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"Slight" could as well also be caused by corrosion, like water trapped underneath the pads the last time the bike got garaged and then left there for some time.

How can they separate the two front brakes on the one front wheel?

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The way I understood the CBS, are front and rear brakes not fully connected, if depressed only gently one can make use of rear or front brakes independently .
Uneven drag of rotors is also audible, when you lift the wheel off the ground and spin it by hand (I'm doing that every time I've reinstalled a wheel or worked on the brake system, spin the wheel and tap briefly on the brake lever to check for instant response and instant release of the callipers, as well as listen for any uneven dragging noises, indicating warped or corroded rotors)

the only real way is to dial indicate the rotors. even the I would think that .004 in. would be the max. Calipers usually stick when hot. Basic check (do not remove anything, on bike check) that I would do is grab a screwdriver and gently pry the pistons in. If all the pistons move in that part is good. Now (with the pistons in )check the caliper slides by pushing the caliper inward and outward. It should move with some resistance but should move.

The next time ask which rotor is out, what test did they do, what spec did they find that was out of range and what are the specs...and get it in writing. I think that they just looked at the rotors and are making it up as they go along!!

I got curious about what "fluctuation" means and downloaded the inspection manual. The closest thing to what you were given is reason 1(d) on page 48, "excessive fluctuation of brake effort with steady application of the brake."

Warped and worn rotors are covered in an earlier section that I'd hope requires that the inspector determine through measurement. It's unfortunate that they don't provide you with any information on what was being tested when they saw this, because it would go a long way toward narrowing down the source.

One thing I would look into whether or not the inspector took the behavior of the bike's linked braking system into account. The inspection manual points out that "In the case of a linked brake system, it may not be possible to apply the brake of the wheel not being tested prior to starting the test" but doesn't make clear if that means only the brake for the wheel being tested should be applied or if both should be applied simultaneously. If the inspector applied both at once while testing the front wheel, it will show some amount of braking initially from the outer pistons and more after the delay valve allowed fluid from the rear to push the center piston. This is the intended and expected behavior but could be considered a fluctuation. My own opinion, which is worth exactly what you paid for it, is that the test should be done by applying only the brake for the wheel being tested.

--Mark

Gentlemen
Took her for the re-test, and she passed at last even though the ABS still does not work!
Asked him about the fluctuation in the braking effort and he said that it is very much up to the discretion of the tester if they put in an advisory, which surprised me, but also that the slight warping of the disc was probably as little as a 'thou' and should do nothing about it until I could feel it through the lever/pedal.
I felt slightly annoyed at that on the basis it was still perfectly smooth and safe and yet if I had decided to sell it, it would undoubtedly effect it's value
All I need to do now is sort the ABS, but that's just a minefield!
James

PS, as advised, I asked him about the tolerances when testing, what test was used, etc and he couldn't tell me! Just not to worry about it!! I thought it was a little slapdash!
James

I had this years ago with a mot tester, had bought bike without ticket, went to local mot guy, everything fine except the discs were warped...........bull...........nothing wrong with them imo, no judder etc, but guess what he had on the shelf.........yes you guessed it a shiny set of disc for sale!!!!, so not happy with this went to another tester the day after passed no problem.

Went back to the first guy and demanded a refund but no joy, quoted me the mot tester can use his discretion crap.

Just the way of it sometimes.

Thanks Caddyman
Think it us outrageous that they can effect the value of a bike when it is purely his discretion. This was the main Honda dealership! The only reason I went there was in the first place was because the bike had not been on the road for some time and thought the paperwork would look better in its history file, wrong!!

I bought my 1300 with less than 300 miles on the clock from my Honda dealer, it was 3 months old and was traded in by someone who thought it was too heavy, I took it to my local Honda dealer for its servicing and when it needed its first MOT I thought I'd take it there as if it needed anything serious it would be covered by warranty. It passed without any issues and they tried to charge me the test fee and an hours labour, as you know the test fee is a stand alone charge I told them my thoughts and they backed down, had they insisted my next call would have been VOSA.

They are now closed for business and my bike has never been back to a dealer. One of the Honda mechanics does the work on my bike in my garage and has done since it was new. It is now nearly 13 years old.

JamesGss

My opinion on main dealers is not positive im afraid, the price of servicing is far too high, mainly I think due to high overheads of running said shiny dealership, its bad enough being bum raped for the price of spares never mind having any work completed!!.

Im happy to tackle most jobs if I have the tools or can make something to sort the problem.

The ST1100 is ideal for the home mechanic with most jobs being straight forward, wksp manual and you will be sorted, pic's with the camera or phone is a handy way of keeping yourself right.

Cheers
Chris

Coming round to that thinking! Only thought initially it would be good until I know the bike better but seems they don't have any 'out of the box thinking'!
Unless everything works according to the manual all the advice they ever give is "buy a new one"!
Cheers lads.
James