Warped discs?

[yorkie_chris]

Noticed now that the pads are bedded in on my new front end that all is not well with the front brakes.

At higher speeds the whole front end shudders, and at lower speeds you can feel them grabbing on and off again, kangaroos like mad below 30 with normal braking force.

There's no obvious pulsing of the lever, but there is a lot of travel when moving, even though the brakes are rock solid stationary on the second pump of the lever.

Discs warped?

If so then straightening by motoliner any good?

If so then can anyone lend me some TL/busa/SRAD discs untill they can do them? :-)


Cheers

[flymo]

Sounds like it. Do you have a dial indicator that you can use?

[yorkie_chris]

Yes can get hold of one tomorrow.

Got any idea what the straightening services are like? These have loads of meat left on them.

[flymo]

Yes can get hold of one tomorrow.

Got any idea what the straightening services are like? These have loads of meat left on them.

Never had any discs straightened to be honest but for ?30 its gotta be worth a try.

[Robw#70]

Getting discs straightened is ok when they are bent, but Imho not worth it when they are warped, they have warped from heat which has changed the characteristics of the metal so even if they can be made better I think the problem will come back with use.

Most pads nowadays rely on material build up, ie they grip on their own material, which if when new pads are bedded in they dont lay consistently can give the symptoms you describe, cleaning the discs off and linishing the pads, then re-bedding them in can help.
We had lots of problems like this with Ap discs, which was mainly cased by the pad material, ie race pads that were used on the road never got up to the correct temperature and weren't used hard enough

[yorkie_chris]

So then if they're not running out then how should I run in the pads when they're linished?

Also how much runout is acceptable?

I'm not sure the discs are warped by heat, could have easily been knocked about in the car when my mate collected the wheels and discs for me.
How do you tell the difference?

[zadar]

if surface of rotor is warped you can throw them in garbage.if bent it is inner aluminum part.most like by your lever coming in.what happens is rotor wobbles and spreads pads apart.than you need more lever travel to get pads back to it.if not moving it will seem normal.
it is easy to fix bent rotor,you can do it yourself without taking anything off.take calipers off.bolt piece of wire to fender mount and bend wire to pint right at rotor.find bent spot and kit it with punch and hammer in opposite direction.hit right bellow buttons at aluminum inner part.

[yorkie_chris]

A method to fix things using a hammer. It's rare I'd EVER use that sort of method .... honest....


The surface of the rotor #looks# pretty much as new, so I'll get that dial gauge anyway and give it a belt.

[richwill68]

Mate, I hate to bring everything back to basics but it may help.

1 Is everything installed properly? Wheel, discs, pads, calipers, all aligned and correctly tightened?

2 Check discs for runout. Bear in mind they are (or should be) semi floating rotors so will tolerate about 2-3 mm without too much of a problem. If they are warped, bin them and get more. Do not have them straightened, bent, punched or anything else! Remember you rely on these things to stop you, sometimes in a hurry, so take NO chances, ok?

Hope this helps

Regards

Rich;)

[yorkie_chris]

Yes everything is alligned and tightened, the wheel shows very little runout so it's not that.

The discs were showing up to 50 thou" runout, by zadars method this is now down to about 5thou.

Still felt a little pulsy, but I put this down to the uneven deposits of pad material, the lever remained firm at speed.

Will see what happens when the pads bed in a bit more.

[yorkie_chris]

Yes I know there's a slight risk, but these discs are serious overkill on the SV anyway, good enough to stop a 190mph 'busa so they'll be right on a slow, light SV even if slightly weakened.

[flymo]

Also how much runout is acceptable?


SV service manual quotes 0.012in (0.3) mm as an acceptable upper limit to run out. So, you were out to start with and within now.

[yorkie_chris]

Well tried zadars approach, and managed to get them down to an acceptable runout...

but this didn't improve matters much, so went to see a professional mechanic friend of mine, who reckons the rivets are knackered.

[Robw#70]

suzuki dropped the prices of their discs recently and quite a few are now cheaper than most aftermarket ones so worth a look

[zadar]

rivets will not make problem with lever travel.

[yorkie_chris]

There isn't a problem with lever travel now, they still grab on and off though when used, even though I cleaned the rotors and pads back and bedded them in again.

[zadar]

ok,let me put this way :)
rivets have nothing to do with any brake performance.

[yorkie_chris]

Whats wrong with them then?

Slowing to a halt they still shudder like mad

[flymo]

ok,let me put this way :)
rivets have nothing to do with any brake performance.

Yes they do, they form the join between outer disc and center. If the outer disc heats up and goes tighter on those rivets then warp can be the end result.

Thats why EBC race discs come with two sets of rivets (removable ones). The secondary set have more clearance so that when the fisrt set tighten up due to shrinkage you can swap them over.

I've never heard of knackered rivets though, how can they be knackered. Tight I can understand but knackered, dont think so. One racers trick I've seen done before was to loosen of those rivets with the ball end of a brake lever in a vice. Personally I wouldnt bother, if they are warped I'ld get a new set.

[flymo]

Whats wrong with them then?

Slowing to a halt they still shudder like mad

There must still either be a small amount of warp in them , or its down to the pad material build up as Rob says.

It might only be 5 thou runout, but if the runout is sudden in one particular spot then they will still judder.

[richwill68]

Hi Chris,

By rivets do you mean the bobbins which connect the rotor to the inner carrier?

A common problem with these is for the Belville washer at the rear to break up allowing the rotor to move about more freely. This will give you quite a clatter. Good news is you can get replacements from Stealth products.

Regards

Rich;)

[flymo]

the rotor moving more freely would actually be desirable in this case, I think its the opposite, they are likely now too tight.

I had a VERY loose set for years on a FZR400 race bike, clattery as hell but extremely smooth braking.

[yorkie_chris]

They're very tight, the disc does waggle a bit, but its stiff movement with no clatter

[zadar]

Whats wrong with them then?

Slowing to a halt they still shudder like mad
if your front chatters when braking rotor surface is warped.
loose or tight rivets makes no difference.loose will make rotor self center and tight is fine as long rotor spins straight.

[zadar]

They're very tight, the disc does waggle a bit, but its stiff movement with no clatter
what is waggle?

[yorkie_chris]

Side to side movement of the steel part of rotor

[zadar]

side to side movement is fine if rotor is spinning straight between pads.
if rotor moves side to side but also moves pads than that is problem.it means it is bent.

[yorkie_chris]

Ready for use as frisbees then

[zadar]

Ready for use as frisbees then
just make sure your dog does not try to catch it :)
borrow set of rotors and try.

[richwill68]

the rotor moving more freely would actually be desirable in this case, I think its the opposite, they are likely now too tight.

I had a VERY loose set for years on a FZR400 race bike, clattery as hell but extremely smooth braking.

Quite, just trying to cover all the bases. Recently had a problem with the washers on my discs and had some vibration at the lever as a result. I agree, fully floating discs are very noisy but give good braking results (hence their use on race machines) but road discs tend to be semi floaters.

To recap then, the rotors are within acceptable limits for warpage, the surface of the rotors is not suspect, the pads are fine, the calipers and pistons fit correctly and move freely, suspension is not at fault, wheel and bearings are fine as is the headstock and its bearings. Maser cylinder is ok, brake fluid is new, system is well bled and brake lever pivots are all free. If this is the case, there shouldn't be any problem with the brakes.

Hope tis helps,

Regards

Rich:)

[yorkie_chris]

I give up.

New ones ordered.