Left front brake rotor stuffed; how important is it to replace both rotors?

[pyrocam]

I have had a bit of pulsing/shuddering in the front of my cbr600 so built myself a poor-mans runout indicator* and found one of the rotors is well over the limit (.4mm) I understand replacing the rotor and the pads is ideal, but do I need to replace both front left and right rotors?


ps, is the legal limit .3 or .03mm on overall runout?[/COLOR]



*Just to give me some idea of how bad it is, I will get the shop to run a more accurate test when I'm in for another peice of work I'm getting done

[vifferman]

Nup.
My VFR800 has two mismatched front rotors - they're not even from the same model! Pretty sure they're both Hondas though...
Oh and they work fine.
However, when I first got the bike, it had the same problem as you've described: brakes shuddered and whatnot. Turned out the pads on the non-VFR disk were kapotnik. A quick change and they were fine.

[schrodingers cat]

Obviously too much run out is a problem because it knocks the the pads away from the disc so you need a big (scarey) handful to get them back creating heat and friction.
Is it worth asertaining why the disc has that runout? You may be able to knock it straight again. It may be mismounted.

Otherwise, in the real world, no. So long as both friction surfaces are in similar condition then you'll be fine

[pyrocam]

yeah its only been noticable since a crash a while ago, getting pretty bad and noticable now that I'm riding around in the wet though. chur

[DesmoDAZ]

If they are bent they are bent and stuffed if they have a bit of runout you can get them surfaced by engineering shops that have a magnetic flywheel plate on a lathe even if they are fully floating. Coombs in Ch Ch here touched up my 320 full floaters for about $65 a rotor. A big problem with brake shudder is pad material build up on the rotors from where you stop with hot rotors and the pad material sticks to the rotor at the point where the caliper is, multiply this by many stops with hot rotors and you get uneven build up of pad material. I had rather big shudder issues on my st4s 320s with gold line brembos, changed steering head bearings, changes fork oil and bushings, had rotors surfaced, tried 4 different pad brands and compounds, re ballanced wheel and tyre and had wheel checked for runout, all good, still shuddered.
Did one track day at Ruapuna and by the end of the 3rd lap the shudder was gone, The fully hard work out your braking system gets on the track simply cleans the rotors of uineven pad material buildup. I now run organic front pads and this has kept the shudder problem away for the past 7000k street use.
he

[pyrocam]

bugger, its .03 (ish) so both rotors would probably fail anyway.
nearly $1000 to replace both (incl pads)
wow

[MSTRS:Me]

Nought wrong with used rotor/s. Try these guys... vicwreck@iinet.net.au Way cheaper than anything local.

[Squiggles]

ebay

[schrodingers cat]

If they are bent they are bent

Not always.
I think the reason you're noticing the problem in the wet is because you're using less pressure and can feel the pulsing

Its worth trying knock it straight - it doesn't cost anything.
Mark where the run-out begins and ends wit a vivid and the middle (high/low) spot.
Measure at the outer edge of the disc, the middle and the inside. This will help you understand the shape of the what you're dealing with.
Remove the disc and lay it on a big solid Flat piece of wood (on the ground) and use a hefty deadblow or softface mallet. Let logic dictate where you thump the disc. Refit. Measure. Repeat.

If you fuck it up you haven't lost anything and you have sucessfully avoided an evening of bad television.

Worth a crack Nigel

[pyrocam]

Assuming I cant fix the rotor (likely) has anyone had any experience with cheap chinese rotors? I found these
http://cgi.ebay.com/Brake-Disc-Full-...item3a59730364
I am worried that if they used the wrong metals etc they could be dangerous, $300 NZ vs $1000 NZ there must be something up

[MSTRS:Me]

I wouldn't go there...

[CookMySock]

Its worth trying knock it straight - it doesn't cost anything. [....] If you fuck it up you haven't lost anything and you have sucessfully avoided an evening of bad television.

Fully agree. Call us back yard bashers if you like, but if it feels good, do it.

Steve

[Flip]

Just one small thing. These look like floating discs, the disc is free to float around a bit because it is not hard bolted to the disc carrier and hub.

[Crasherfromwayback]

On floating discs...sometimes the disc can simply be not sitting on the mounting rivets properly (as in not square). Try cleaning up the mounting rivets and see if it improves things. We had a 250 Hornet here we got much better by doing this.

[AllanB]

F1 Engineering in Hamilton. They offer a fixing service (depends on the condition of course) and can supply rotors etc.

Or get onto the web and find a new set of EBC or Galfer etc rotors for a fraction of the stock ones.

Try

www.denniskirk.com
www.bikebandit.com

pop in your bike year and model, US $ of course so allow for the conversion etc.

Watch out on E-bay for suspect new ones out of China - I'd stick with a known brand name as you know they are using the correct grade of metal.