Help! MOT failure due to bent disc.

Copper · Post by **Copper** » Thu Dec 12, 2013 7:10 pm

Hi

Took my R1200S for its MOT last week it failed as one of the calipers had partially seized.

I stripped own both callipers freed the pistons (one was stuck) bled the brakes and put it all back together.

Took it for a retest today and its failed as a brake disc is warped according to their fancy new brake tester!

I cannot feel any pulsing at all when braking and have taken the disc of and cannot detect any warp in it. It binds very slightly when I rotate the wheel.

Is their machine too fussy, can I do anything to fix, & it how much is a new disc?

Regards,

Jon

slparry · Post by **slparry** » Thu Dec 12, 2013 7:22 pm

have you tried taking the disk off and cleaning the posts?

Copper · Post by **Copper** » Thu Dec 12, 2013 7:44 pm

Hi,

I have, I'm going to give it another go.

I've just taken the discs off and placing them together I can feed the thinest feeler gauge I have 05? between them in places buy its difficult to tell if its seperating the discs. To the naked eye the look fine how much run out is allowed?

Regards.

Jon

Bikerhoss · Post by **Bikerhoss** » Thu Dec 12, 2013 8:03 pm

The Dept of Trans MOT testers manual says reasons for failure include:-
m. Excessive run out or distortion of a brake disc.

To me, that is totally down to the tester, One might allow more than another, Doesn't really help I realise, sorry

slparry · Post by **slparry** » Thu Dec 12, 2013 8:24 pm

Perhaps they're misreading their new machine

... have you considered a different tester?

Copper · Post by **Copper** » Thu Dec 12, 2013 8:36 pm

I think thats my next step I can't find anything wrong with the discs.

I've just freed up all the floating bobbins.

Going to clean up the posts and re fit.

Surely If I can't feel when braking it it can't be a problem?

Jon

Copper · Post by **Copper** » Thu Dec 12, 2013 9:38 pm

All back together.

There might be a slight run out but its pretty hard to tell.

Will get a second opinon.

Jon

McBoxer · Post by **McBoxer** » Thu Dec 12, 2013 9:48 pm

It might be worth arming yourself with the manufacturers run out figures - if you can get hold of them. Talk to your friendly dealer and ask their advice

Corvus · Post by **Corvus** » Thu Dec 12, 2013 10:22 pm

What exactly do they use to check for run out?

Is there wear in the area where the pad contact? I wonder if that area is showing some run out, but checking at the outer edge is showing true? Just a thought.

SP250 · Post by **SP250** » Thu Dec 12, 2013 11:21 pm

If they are floating discs on the mounting posts the machine they use to check runout might not be capable of working with the side float and interprets it as a warp or buckled disc.

Just a thought.

Herb · Post by **Herb** » Fri Dec 13, 2013 6:00 am

I hate to say it, the R1200s does have something of a reputation for buckling discs. Definitely something to keep an eye on, even if you can get it through the MOT in its current form.

My tester is an old boy who uses a scale and a winch, so a bucked disc would be harder to identify. It might be worth asking around to see if you can find a garage that does things the old fashioned way.

Corvus · Post by **Corvus** » Fri Dec 13, 2013 6:47 am

SP250 wrote:If they are floating discs on the mounting posts the machine they use to check runout might not be capable of working with the side float and interprets it as a warp or buckled disc.

Just a thought.

On that note, are the wave washers present?

If you take one of these discs off the wheel they are remarkably easy to distort with your bare hands.

Then there's the dreaded post (or turret) erosion.....

There ain't nuthin worser than an eroded turret.

Corvus · Post by **Corvus** » Fri Dec 13, 2013 6:56 am

Herb wrote:I hate to say it, the R1200s does have something of a reputation for buckling discs. Definitely something to keep an eye on, even if you can get it through the MOT in its current form.

My tester is an old boy who uses a scale and a winch, so a bucked disc would be harder to identify. It might be worth asking around to see if you can find a garage that does things the old fashioned way.

Hear hear.

The only thing is.... It will be noted on the failure sheet. PITA.

I wonder if it is run out we're dealing with? I mean, how do you go on with a more conventional floating disc, as found on a typical jap sports bike. They float around very freely. What method are they using to distinguish deliberate run out as opposed to a warped disc?

Copper · Post by **Copper** » Fri Dec 13, 2013 5:20 pm

Hi,

I have taken the bike to another garage they have confirmed there is excessive warping.

I phoned a company called Motorliner who claim to be able to straighten discs as soon as I mentioned BMW the chap said he couldn't straighten them and added "I bet your bike was fine until you took for the mot!"

Phoned motorworks they dont have and 2hd discs and a new one is £200!

I've trawled the internet looking for a way to fix them mostly full of people warning not to try and fix them, microscopic fractures etc.

Then I found this article (scroll down through the first few posts) and look at the fix from the user "Ferchja"

http://www.vfrdiscussion.com/forum/inde ... rotor-fix/

It seems to make sense. I'm going to give it a go, I just hope it is the disc and not the posts!

Corvus · Post by **Corvus** » Fri Dec 13, 2013 5:36 pm

Copper wrote:Hi,

I have taken the bike to another garage they have confirmed there is excessive warping.

I phoned a company called Motorliner who claim to be able to straighten discs as soon as I mentioned BMW the chap said he couldn't straighten them and added "I bet your bike was fine until you took for the mot!"

Phoned motorworks they dont have and 2hd discs and a new one is £200!

I've trawled the internet looking for a way to fix them mostly full of people warning not to try and fix them, microscopic fractures etc.

Then I found this article (scroll down through the first few posts) and look at the fix from the user "Ferchja"

http://www.vfrdiscussion.com/forum/inde ... rotor-fix/

It seems to make sense. I'm going to give it a go, I just hope it is the disc and not the posts!

Your disc set up is not like his though. It is radically different.