warped discs through underuse?

[zebedee]

a colleague of mine has had to replace some brake discs after only about 1200 miles to pass the MOT, and the garage are saying it is through underuse. Does this sound realistic, or more likely there was something wrong with the discs?

Says he hasn't been thrashing the bike or doing trackdays etc

cheers

Edited by zebedee on Thursday 31st August 09:14

[kawasicki]

He may have had corrosion where the pad has been near the disc. When the brakes are used the corroded area is weaker and wears away leaving a low spot on the disc. It wil not be easy to rectify this problem. Note for future - take the pads out if you leave the bike for a long time without moving it!

Other reasons for "warped" type behaviour include uneven deposition of brake pad material on the disc. This could possibly be fixed by using aggresive brake pads which will wear the disc down to a fresh layer. This happens when you get brakes very hot with a pad that cant really cope.

I'd put my money on the first cause. You may not see rust on the disc, cause one they've been used the rust disappears, but the low spot remains.

Shane

[zebedee]

thats an uneven brake disc though, surely, rather than a 'warped' one. If they warp through underuse, do they have to throw the ones on warehouse shelves away after a year or two? Sounds like rubbish to me - if a disc is sitting somewhere at an ambient temperature, don't see how it could warp. If subjected to harsh heat cycles, then maybe I could understand it, but this seems to be the opposite

[John Laverick]

There is no such thing as a warped disc!!

A vibration will occur for one of two reasons:

a) Pad deposits

b) Run-out on the mounting face casing varying disc thickness [pad/disc rubbing during roation causing wear].

I would imagine in this case it was pad desposits and it may have cleared given time.

The best idea would be to check the disc [and mounting face if possible] using a clock or dial gauge for run-out and then seek advice regarding the allowable tolerance from a specialist.

On a car the tolerance is typically 0.1mm or 4 thou

Hopt this helps

[zebedee]

it would, but his bike failed the MOT on it, so they had to fit new discs, much to his annoyance. He has retained them and is returning them to the manufacturer, on the assumption that they were faulty, given the low mileage and general lack of use

[fergus]

kawasicki said:

He may have had corrosion where the pad has been near the disc. When the brakes are used the corroded area is weaker and wears away leaving a low spot on the disc

I think you've been reading too much MCN How do you get a 'low spot' on a disc? I suggest you attend Metalurgy 101!!! 'Corrosion' (on the surface) is highly unlikely to do this.

[Adetuono]

John Laverick said:

There is no such thing as a warped disc!!

Obviously never had an Exup then.

[dern]

John Laverick said:

There is no such thing as a warped disc!!

Yes there is. Granted your other explanations are more likely but you can warp discs. Never had one on a bike though.

[fergus]

I suggest you read the following aticle in detail. It's very informative....

www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

[dern]

fergus said:

I suggest you read the following aticle in detail. It's very informative....

...never the less I took the discs off my westfield after they felt 'warped' and gave them to an engineering firm who skimmed them for me after measuring the run out was more than could be accounted for by pad material transfer alone.

[Steve_T]

fergus said:

I suggest you read the following aticle in detail. It's very informative....

www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

Top read!

[bimsb6]

Steve_T said:

fergus said:

I suggest you read the following aticle in detail. It's very informative....

www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

Top read!

some is however irrelevant to bike discs as he is refering to cast iron car discs not the more flimsey
discs fitted to motorcycles which tend to be steel .