CBF1000

CBF1000 => Brakes and ABS/CBS => Topic started by: Rick on 26 June, 2020, 08:51:49 PM

Title: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: Rick on 26 June, 2020, 08:51:49 PM
Went for MOT test yesterday and the examiner failed it as the rear wheel did not lock up. Explained combined ABS system would prevent wheel locking roller but he was having none of it. I see that in Haynes mentions 'A sensor on each wheel is linked to a modulator unit that determines if a wheel is about to lock up, and if so releases and pulses brake pressure via the modulator until there is no danger of wheel lock'.  Your experiences would be appreciated ?
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: maxstu on 26 June, 2020, 09:29:33 PM
Not sure about this one. MOT tester trying to lock up rear brake? Never seen any tester do that in 42 years of motorcycle ownership.
How does that show effectiveness of brake? Surely its only got to meet a set resistance show on the large LED readout screen?to pass without locking up?
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: Rick on 26 June, 2020, 09:40:06 PM
Thanks Maxstu, I've owned this bike for seven years and never had a problem before and passed without any issues, unfortunately used this new garage to me, as usual chap off work due to Covid. I explained that I had never seen the wheel lock roller on previous tests, just went by reading as you say. 
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: jm2 on 26 June, 2020, 09:50:22 PM
Yes. The test (now, for a while) is to lock it.

The trick is to put the final bit on slowly so it registers the most (before locking) - whilst squirming on thr roller !
Gone are the big round dials.


Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: maxstu on 26 June, 2020, 09:53:33 PM
Tough call, Rick. I would phone the test station and discuss your concerns. And ask how one remedies such an issue to get a pass? Or ask the views of another MOT station? BTW all tests guidelines are online for public to read too...
 
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: maxstu on 26 June, 2020, 09:58:44 PM



Well l stand corrected  :003:

Sit on the motorcycle and locate the front wheel in the rollers of the brake tester, ensuring that the motorcycle is lined up in the straight ahead position and settled in the rollers.

Make sure that the roller brake tester is set to rotate in the correct direction so that the motorcycle wheel will rotate forward.

Start the rollers and allow the front wheel to stabilise. With the rear wheel brake fully applied (unless itís a linked system), gradually apply the front brake until maximum effort is achieved or the wheel locks and slips on the rollers.

Record the reading at which the maximum braking effort is achieved and release the brake.

Restart the rollers if necessary and gradually increase the front brake effort to about half the maximum reading and observe the way it builds up. Hold steady and check for fluctuations. Release the brake and observe the way in which the braking effort reduces.

In the case of linked systems, repeat the steps 1 to 5 for each control operating the front wheel brake. However, some linked systems are designed to only work above 10km/h and will not work in a roller brake tester.

Repeat the procedure for the rear wheel brake and any sidecar brake fitted.

Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: Rick on 26 June, 2020, 10:07:39 PM
Thanks JM2, but surely the abs system is trying to prevent a lockup, maximum braking takes place just before a wheel locks, that's where abs braking comes in, by applying cadence type braking many times faster than could ever be achieved manually.
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: Rick on 26 June, 2020, 10:29:13 PM
Thx Maxstu, the very much more powerful front brakes did jump out of the rollers, however the rear wheel didn't. The rear brakes seems to stop the bike within a reasonable distance, obviously with the linked system some front braking is applied at the same time.
 The whole point is to get good braking not just the rear wheel locked and skidding in sliding friction.

If I had applied the front brake as well as the rear pedal, whilst the rear wheel only was in the rollers the centre piston would have come in and given the full rear brake reading. But I didn't do this and just used the pedal, the combined system seemed to cause an unwelcome complication for the tester 
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: TerryR on 27 June, 2020, 06:59:16 AM
There is no centre piston on the rear brake and the front brake lever has no effect whatsoever on the rear brake.
There is a centre piston on the front brakes and it is operated by the rear brake pedal.
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: Rick on 27 June, 2020, 08:57:11 AM
Thanks TerryR, Although my bike has got 3 pistons on the triple rear brake caliper, same as the front,  I was wrong in  my understanding that the front is linked to the rear in the same way that the rear is linked to the front. How could it be! there is only one brake fluid supply line to the rear caliper. Just shows benefit of discussion.
I would appreciate more feedback on original post about experience of others at MOT test and if rear wheel locks when carrying out roller test on abs models.
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: jm2 on 27 June, 2020, 12:58:14 PM
*Originally Posted by Rick [+]
Thanks JM2, but surely the abs system is trying to prevent a lockup, maximum braking takes place just before a wheel locks, that's where abs braking comes in, by applying cadence type braking many times faster than could ever be achieved manually.
Ah but the abs disengages at very low speed - or you'd never be able to fully stop.
DON'T try it yourself; on a loose gravel surface apply too much rear at moderate speed and abs will work flawlessly and keep everything stable, as you come to a halt the rear will lockup and you may loose it altogether.

Maximum braking effort is achieved just before locking (hence why cadence braking works) and the mot says to lock the wheel.  The trick is to go slowly at the end (just before locking point where the roller detects it has been stopped).
If you can't lock the wheel on the roller (why not) you aren't getting through maximum braking effort.

C-ABS does makes interesting testing figures (especially on the old dials) but doesn't detract from the test - I do believe you are allowed to add the alternate brake in if required for the (lock) test; but these bikes do not need it (5x front pistons are plenty for the test - I seem to remember testing another bike of mine on the rear only front operation and it achieved very good braking effort if really leaned on).

You ought to be able to get the abs working on a road at speed (try 50mph, clutch in, and load the rear brake).
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: Art on 27 June, 2020, 03:14:03 PM
and the difference in locking the rear wheel on the roller and stopping the bike on tarmac is?
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: jm2 on 28 June, 2020, 10:44:35 AM
?

The original poster (OP) didn't expect the roller to lock with abs.

- Although I (mis) used my phone to type that reply and it seems I didn't see some (any?) earlier replies.
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: Rick on 28 June, 2020, 12:43:49 PM
Thanks, Just need feedback from owners who take their abs bike for an MOT and report as to how the rear brake behaves during the roller test, does it lock up ? Presumably this would cause the bike to jump out of the rollers, mine didn't.
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: Rev Ken on 28 June, 2020, 07:38:12 PM
*Originally Posted by Rick [+]
Thanks JM2, but surely the abs system is trying to prevent a lockup, maximum braking takes place just before a wheel locks, that's where abs braking comes in, by applying cadence type braking many times faster than could ever be achieved manually.
If you read a little further the manual gives the efficiencies needed and there is no requirement for any wheel to lock.

1.2.2.
'Brake efficiency'
Most motorcycles have 2 brake controls, one operating the front wheel brake and the other the rear wheel brake. One control must achieve an efficiency of at least 30% and the other control 25%.'

Oh and if a wheel does lock it is assumed that it reached the 30% figure.

(When I was in charge of the branch that was responsible for MOT testing there weren't small roller testers available and the usual method was to tie a spring balance to the front forks, get the owner to sit on the bike and apply each brake in turn while ratcheting the bike forward reading the spring balance. Alternatively you could use a ramp and lift one end up gradually with the bike on it - interesting! Oh and it is still legal to use the spring balance method if your authorisation was before the new requirements were introduced. I tested several 'pendulum' testers as used for cars, but they didn't work as on my 400 Superdream I could lift the rear wheel when braking, giving false readings and was considered a little dangerous for some testers.)
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: g5guzzi on 28 June, 2020, 09:34:40 PM
The garage i use on bikes with  linked brake systems take the brake reading
for the front brake effort and the weight of the bike on the front wheel then take the same  readings
 on the rear  then work out if correct brake efficiency has been reached.
Locking the wheel is not essential.

 
Malc
Title: Re: 2009 Mk 1 abs, Should the rear wheel lock up whilst on MOT Roller
Post by: jm2 on 30 June, 2020, 05:53:55 PM
*Originally Posted by Rick [+]
Thanks, Just need feedback from owners who take their abs bike for an MOT and report as to how the rear brake behaves during the roller test, does it lock up ? Presumably this would cause the bike to jump out of the rollers, mine didn't.
Well mine was apply all the way to lock-up - now whether or not that was to get as far as I could and locked was obviously passed that point I can't know. It certainly completed that test element.
Yes, as said earlier, it squirms about !

Sorry Ken, obviously my mot station can't do mental maths or doesn't need to with their testing machine.
- but it begs the question, 30% of what (for the front).  Surely if you've two equally naff brakes it can't pass?