Warped discs

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Warped discs

Hi,

I've just done the cable tie trick to check to see if there any movement in my discs, there appears to be about 1mm of movement in the right disc and 0.5 mm in the left. How much is acceptable?

I had a problem with my brakes yesterday and someone has suggested it could be the disc pushing the pistone back into the caliper. The discs came of a set of wheels i bought off ebay, so not too sure of their condition

Any help would be much apreciated.

cheers

Will

What bike?

None. simple as.if they are pushing the calipers back, they would basically be unrideable when braking.

The bike is a ZX6R.I was riding yesterday, and one minute the bike would be fine and the next i would be able to pull the brake lever all the way back to the bar, then it could go back to normal again.Someone sugested that if the disc was warped, it could push the pistons back in to the caliper, which would result in the brake lever needing a couple squezes before it went back to normal.

Sometime the bobbins can seize and freeing these will remove the run in the disc.

captainkev wrote

The bike is a ZX6R.I was riding yesterday, and one minute the bike would be fine and the next i would be able to pull the brake lever all the way back to the bar, then it could go back to normal again.Someone sugested that if the disc was warped, it could push the pistons back in to the caliper, which would result in the brake lever needing a couple squezes before it went back to normal.

I'd bleed your brakes if I were you.

captainkev wrote

The bike is a ZX6R.I was riding yesterday, and one minute the bike would be fine and the next i would be able to pull the brake lever all the way back to the bar, then it could go back to normal again.Someone sugested that if the disc was warped, it could push the pistons back in to the caliper, which would result in the brake lever needing a couple squezes before it went back to normal.

You can't feel it when you brake ?

Strip the brakes, clean all the pistons etc, put em back together, fresh fluid, bleed, and see what thats like...............Oh and dont forget the WD40

I bled the brakes this morning and they were fine, at the worst point yesterday, i had the brake lever all the way back to the bar and the bike still hadn't come to a stop. Could it have anything to do with the wet weather and the brake needing to bed in to the new discs?

captainkev wrote

I bled the brakes this morning and they were fine, at the worst point yesterday, i had the brake lever all the way back to the bar and the bike still hadn't come to a stop. Could it have anything to do with the wet weather and the brake needing to bed in to the new discs?

Possibly, but it does sound more like there's air in there, if your in any doubt get your local bike shop to have a look.

You mention you have bled the brakes? I assume this is from the calipers? Does your master cylinder have some where to bleed from?If it does, cable tie your front brake on overnight, then try bleeding from the Master cylinderAir will always/99% of the time (eventually) make its way to the top

1mm run out on the brake disc doesn't sound too bad, although it may be on the limit of the manufacturers spec. MY ZRX had 3mm run out at one time and it didn't really cause any adverse effects other than a bit of a pulse. I doubt it's the cause of your problems TBH.

What 6R is it, older F or G model? If it is whatever you do it wont improve much, they just arn't great brakes. If you really need shit hot brakes go for a set of aftermarket iron discs such as AP.

If you can lay your hands on a Haynes manual for your bike, captainkev, it will provide you with the maximum allowable runout for the discs.On the Pan, it is 0.3mm

If you had a warped disc, you'd feel the judder in the lever. If you're near west London, I can recommend a trip to SRS who have straighten discs for me in the past (do a search as I don't have their address right now).

I've got slightly warped disks on my ZZR600 and they just slightly judder under braking, judder a lot more under really heavy braking.However - at no point do they push the caliper back far enough to cause the lever to move/fail.It's bound to be air/shite old fluid in your system. I'd flush a whole new can of oil through to make sure it's flushed through.P.S. New brake disks are approx £130 per side for EBC. (well they are on my ZZR)

Splat wrote

If you had a warped disc, you'd feel the judder in the lever. If you're near west London, I can recommend a trip to SRS who have straighten discs for me in the past (do a search as I don't have their address right now).

Its an 2005 ZX6R, it doesn't judder much, however, I do alot of trackdays on it, any it is much more apparent when braking hard from high speeds (120mph+). I did speak to a company today who i thought might be able to check and straighten them, however they said that disc cannot really be straightened, and they will become warped again quickly. But i will try and find SRS, what area are they in?I think the wierd braking issue must have had something to do with the rain as it did not do it the day before when it had been dry, and there has been no problem today either.One other question, when replacing discs, do you have to replace both at the same time or is it ok to replace just one? should brake pads be replace too?cheers for all the help everyone

The older ZX-6R's had pretty crap brakes which would bind quite frequently - I seems to have to get mine sorted at almost every service.

rydalong wrote

If you can lay your hands on a Haynes manual for your bike, captainkev, it will provide you with the maximum allowable runout for the discs.On the Pan, it is 0.3mm

What he said. On my 400 it is 0.4mm. I am willing to bet that both your discs are scrap.

If, for example, you have two used discs that were both used as the left disc, is it ok to swap one over to the other side and use it as the right hand side disc?

There is an acceptable level of runout for discs. Its usually printed in the workshop manual or sometimes on the disc itself. You say you can feel it juddering so it sounds warped (as long as your wheel bearings, shock bushes etc are fine).Sounds like they're scrap.

sweepdoggydog wrote

If, for example, you have two used discs that were both used as the left disc, is it ok to swap one over to the other side and use it as the right hand side disc?

It depends, some are handed.

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