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RBT Indicates excessive fluctuation of brake effort

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jscho84233
L Plate Warrior



Joined: 17 Jun 2010
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PostPosted: 17:13 - 17 Jun 2010    Post subject: RBT Indicates excessive fluctuation of brake effort Reply with quote
Hi,

My 2002 Bandit 600 has just failed it's MOT because of excessive fluctuation of braking effort. Thing is, I've just fitted brand new disks and pads. I told the tester this, and he put the bike back on the RBT to show me the problem. With the rollers started, and the brake lever applied at a constant pressure, and the needle does fluctuate quite a lot, from about 40kg to 80kg.

Another thing is, last week, I took the bike in for an MOT at a different garage, and it failed on a completely unrelated thing (shock absorber bearing, which I've replaced), and it passed the brake test there fine. The tester there said everything else was fine, and would have had no advisories for anything else (including slight fluctuation of brake effort.)

So how can it pass at one garage, and not another? If the tester at the first garage noticed fluctuation, but decided it wasn't excessive, surely I would have got an advisory for it?

The reason I didn't just go back to the first tester for a retest, the tester is on holiday now for two weeks, and as I've got next week off, I didn't want to wait for him to get back off holiday!

Does anyone have any thoughts on what could be going on? Riding the bike, there is absolutely no sign of judder in the lever when the brakes are applied, it's very smooth. I'd be grateful for any comments! Thank you.
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DrDonnyBrago
World Chat Champion



Joined: 03 Jan 2010
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PostPosted: 17:24 - 17 Jun 2010    Post subject: Re: RBT Indicates excessive fluctuation of brake effort Reply with quote
jscho84233 wrote:
Hi,

My 2002 Bandit 600 has just failed it's MOT because of excessive fluctuation of braking effort. Thing is, I've just fitted brand new disks and pads. I told the tester this, and he put the bike back on the RBT to show me the problem. With the rollers started, and the brake lever applied at a constant pressure, and the needle does fluctuate quite a lot, from about 40kg to 80kg.

Another thing is, last week, I took the bike in for an MOT at a different garage, and it failed on a completely unrelated thing (shock absorber bearing, which I've replaced), and it passed the brake test there fine. The tester there said everything else was fine, and would have had no advisories for anything else (including slight fluctuation of brake effort.)

So how can it pass at one garage, and not another? If the tester at the first garage noticed fluctuation, but decided it wasn't excessive, surely I would have got an advisory for it?

The reason I didn't just go back to the first tester for a retest, the tester is on holiday now for two weeks, and as I've got next week off, I didn't want to wait for him to get back off holiday!

Does anyone have any thoughts on what could be going on? Riding the bike, there is absolutely no sign of judder in the lever when the brakes are applied, it's very smooth. I'd be grateful for any comments! Thank you.


How long have the discs and pads been on there? Have they been bedded in properly?

If they aren't bedded in properly then you can get a build up of brake pad material at certain points on the discs making the "braking effort" fluctuate. You can normally feel this though tbh.
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jscho84233
L Plate Warrior



Joined: 17 Jun 2010
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PostPosted: 17:30 - 17 Jun 2010    Post subject: Reply with quote
I put them on the day before it went for its first test, so just over a week. I figured that bedding in might be an issue, but didn't wanna ride it very far without an MOT and tax! I might just risk it and take it out and use the brakes a lot and chuck it in for the retest to see if it makes a difference.
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DrDonnyBrago
World Chat Champion



Joined: 03 Jan 2010
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PostPosted: 17:37 - 17 Jun 2010    Post subject: Reply with quote
jscho84233 wrote:
I put them on the day before it went for its first test, so just over a week. I figured that bedding in might be an issue, but didn't wanna ride it very far without an MOT and tax! I might just risk it and take it out and use the brakes a lot and chuck it in for the retest to see if it makes a difference.


Hmmm, how did you bed them in? Just used them and hoped for the best or did you try and follow the manuf instructions?

It is worth cleaning out and greasing up your calipers (red rubber grease by castrol) as this may help, but basically I'd start over with the bedding in.


Rub the disc surfaces with some rough sandpaper (aluminium oxide based) to remove the glaze and pad material from the discs and then finish off with some fine paper to smoothen them out. Wash them well to stop bits getting underneath the pads (perhaps take the wheel out first) and spray everything with an aerosol type brake cleaner.

Then bed them in from scratch using the manufacturers instructions...

It will be something along the lines of:

'Perform 25 to 30 trial brake applications, each of approximately 4 seconds, using around 50% of normal race pressure' - Ferodo car brake pad instructions.


Of course you could always take the scenic route to the MOT station and do this on the way Thumbs Up .
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jscho84233
L Plate Warrior



Joined: 17 Jun 2010
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PostPosted: 17:53 - 17 Jun 2010    Post subject: Reply with quote
Ok, thanks, I will try rubbing down the disks and bedding in again. I did go through the procedure on the packaging the disks came in, they were quite different to what you have quoted though. I still don't get why it passed the day after i fitted them, and failed a week later though...
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