Warped rear disc

rustychain

rustychain

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My R1150GS has just failed it's MOT on a warped rear disc. 🙄

"One of the worst I've seen" according to the tester (he would say that, wouldn't he???)

The disc looks fairly young - definitely not the original and it has minimal wear. I had noticed a pulse in the brake pedal but hadn't put 2 and 2 together.

What should I look out for as I replace the disc and pads to avoid a repeat?
 
Last edited:
rustychain said:
What should I look out for as I replace the disc and pads to avoid a repeat?
Click to expand...
Make sure that the surface that the disc mounts on is spotlessly clean and that the new disc sits flat and stable on it. Dirt under one of the mounts will cause it to warp when you tighten the bolts. When you tighten the bolts, go around doing them all up a bit at a time - don't swing the torque wrench on one while the others are loose. And (obviously) ensure that your replacement disc is decent quality. You might need new bolts as they can get chewed up when you remove them - better to have some available than end up waiting for some while your bike has no rear brake :)
 
Service the rear caliper, esp the sliding pins. A replacement disc is only about £40 so replace it and carry on riding
 
Thanks for the responses.

Possible daft question time - should a warped disc be visible to the eye?

I've rotated the rear wheel and can't see any obvious run out. Is it the disc surface that gets warped? Are we talking microns?
 
If the warping is visible to the naked eye when you spin the wheel the bike's probably unrideable! Amount of run-out can usually be measured only with a dial test indicator or something similar. Or, of course, felt through the lever/pedal as pulsing.
 
sproggy said:
If the warping is visible to the naked eye when you spin the wheel the bike's probably unrideable! Amount of run-out can usually be measured only with a dial test indicator or something similar. Or, of course, felt through the lever/pedal as pulsing.
Click to expand...
Thanks - my first warped disc so on a learning curve!
 
Disc removed from the wheel without any dramas.

I think I've found the culprit - one of the rubber covers to the sliding pins was kaput. Replacements on order (not cheap for what they are!).

I don't want to ask this question as I think know what the answer will be. The rear of the offside pad had circular oily patches (presuming brake fluid from the pistons.). Rebuild time or fit new pads and see if it magically fixes itself with the pistons retracted?
 
Yes, but carefully clean the seal grooves as any dirt distorts the seal. Use red rubber grease on the seals as I have found that using brake fluid as a seal lube isn’t good as scraping the groove with a metal implement can scratch the metal and over time it reacts with the brake fluid going all furry- again distorting the seal.
 
rustychain said:
My R1150GS has just failed it's MOT on a warped rear disc. 🙄

"One of the worst I've seen" according to the tester (he would say that, wouldn't he???)

The disc looks fairly young - definitely not the original and it has minimal wear. I had noticed a pulse in the brake pedal but hadn't put 2 and 2 together.

What should I look out for as I replace the disc and pads to avoid a repeat?
Click to expand...
My 1150 GS has just failed its MoT for warped FRONT discs.

Shocking as it's only done 105,000 or so gentle miles :).

Any advice on best source of replacement discs and brake pads and what other bits (bolts and the like) would be much appreciated. Thanks.
 
simondippenhall said:
My 1150 GS has just failed its MoT for warped FRONT discs.

Shocking as it's only done 105,000 or so gentle miles :).

Any advice on best source of replacement discs and brake pads and what other bits (bolts and the like) would be much appreciated. Thanks.
Click to expand...
I like Brembo discs and pads
Replace with oem bolts and wavy shims
Check the orientation of the mounting posts on the wheel hub, they can wear down (and shrink in material 😳😉)
 
theoneandonly said:
fuck knows , not been that way for a while , haven't been to see Wilf ( ex Bracken ) either !

what that now means , is i'll end up there next week !
Click to expand...

Well you see one without seeing the other., I thought Wilf was only open by appointment .,
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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