Uneven disc wear and pulsing brakes.

**erik** · 25th March 2006, 19:51

Does anyone know if you can get floating discs reground?
My right front disc varies in thickness from about 4.245mm to 4.22mm as you go around it and causes the brakes to pulse. I mostly notice it when coming to a stop at lights, but I did some higher speed testing and I think it's noticeable there too, so I need to do something about it.

I'm guessing you can't, particularly seeing as it's a floating disc?

Luckily the Bandit shares discs with quite a few other bikes by the looks of the EBC catalogue, so I should be able to get a second hand one.

**John** · 25th March 2006, 19:54

check that the carrier isnt warped, because this is often mistaken for warped rotors - if thats the case take it to an engineer and they can fix it up, Thats what I think would be what your feeling because .02mm shouldnt be noticeable.

Checked your pads?

**erik** · 25th March 2006, 21:04

I tried to check the discs runout, but realised it was pointless because if you push them then check them again, you get a different reading (seeing as they're floating discs). But I didn't think to check the carriers.
I checked them just now though, and they're only 0.12mm out on the right disc and 0.15mm out on the left disc, far less than the available floating movement and below the runout limit for the single disc bandit (which I guess uses a non-floating disc?).
0.02mm doesn't seem like much, but I can't think of anything else it could be. I tried pushing the bike carefully and noting the position of the wheel where the brakes seem to grab, and it seemed to coincide with thick side of the disc. I also tried removing one caliper and checking each side individual for how it felt at low speed and it seemed like it was ok when the right caliper was off.
I don't know what to look for on the pads other than make sure the thickness is ok (which is it).

**John** · 25th March 2006, 21:25

Dissasemble the entire front end and put it together straight with correct torque check your speedo spindle and carrier because they can missalign the disk if not put on correct, dont know if it applies to the zeal but on others it does - give the pads a quick sand with the roughest paper you have.

**imdying** · 25th March 2006, 23:36

Anything over about 2 thou of disc thickness variation isn't a good look, and will be noticeable at the lever. I know that sounds an incredibly tight tolerance, but even cages are that suceptible

**erik** · 25th March 2006, 23:51

Originally Posted by imdying

Anything over about 2 thou of disc thickness variation isn't a good look, and will be noticeable at the lever. I know that sounds an incredibly tight tolerance, but even cages are that suceptible

you mean 0.002 of an inch? that works out to about .05mm which is about twice the variation on this disc.

**imdying** · 26th March 2006, 13:06

Ideally, you would have no DTV.

**What?** · 27th March 2006, 07:07

Originally Posted by erik

Does anyone know if you can get floating discs reground?

Check the manufacturer's spec's for minimum thickness. Many modern discs come out of the factory right on the minimum, so can not be skimmed.
If there is scope to skim them, shop around for a good price. Avoid Midas - no-one costs more than Midas.

**imdying** · 27th March 2006, 11:19

Originally Posted by What?

Many modern discs come out of the factory right on the minimum, so can not be skimmed.

Really? Can you cite one example? You could remove them from the carriers and have them parallel surface ground. Pay to find out how much the rivets are first though.

**keza** · 27th March 2006, 12:00

u will find they are probably at min thickness of 4.5 if so not worth doing as below spec and will warp do to being so thin

**Ixion** · 27th March 2006, 12:10

On which subject , why DO bikes have such damnably thin disks? Cars have much thicker rotors, that can be skimmed (often several times).

The extra weight of a few more millimetres would surely be of no real significance, outside the racing world?

**imdying** · 27th March 2006, 12:17

Because they don't need discs that are any thicker. They go to all the trouble of multi piston calipers to reduce swept area, drilling holes to reduce weight (and increase outgassing and face scrape), hollow axles, hollow cast wheels etc, that adding extra weight in the discs doesn't really excite them. The discs only wear out quick if using shitty or mismatched pads, or if racing. If you're racing, then everythings wearing out, so no biggy there. They're road bikes after all, most seem to get past 50000kms on a set of disc alright.

Them minimum thickness should (according to SAE standards iirc) be engraved/stamped/whatever into them.

Now depending a lot on the manufacturer, disc aren't usually much more than twice the price of a decent tyre, and they last more than twice the time a tyre lasts... so it's not so bad.

People are typically a lot more wah wah it's too expensive when the slowing down bits wear out, but they're happy to drop a grand on a titanium exhaust can.

**Ixion** · 27th March 2006, 12:29

Well, 50000 km doesn't seem very much at all. And twice the price of a "decent" (read jolly expensive) set of tyres seems an awful lot. With a double sided front disk set up , that can be more than $1000 to replace.

:spudgrr:

.Plus the rear .

A good argument in favour of drum brakes I guess.

Personally I couldn't care less about hollow axles and such like, seems quite pointless for the few ounces it might save. Will we next see riders taking laxatives and emetics before a ride to save a few more ounces?

This sort of thing is why bikes have become so fiendishly expensive to maintain.

EDIT : Do Moto Guzzis have these silly wafer thin rotors? They seem more sensible than most about such matters. What about Harley Davidson ?

**imdying** · 27th March 2006, 12:44

Yep, eat to many pies for breakfast and the difference between a K5 and K6 GSXR is lost!

50000kms is probably 10 years use for the average sports bike (from just perusing sales etc), of course slower bikes would last longer. $300 for a good rear tyre on my bike, a disc is approximately twice that. Having said that, I've done three sets in the 25000kms on my current bike, discs are far from worn out.

Drum brakes are arse... they expand away from the shoes when they get hot, which is why they dissappear when they get pushed, they also have a tendency to lock a lot more than discs. Discs on the other hand expand towards the pads, which is a lot better than the alternative.

Bikes aren't that expensive to maintain, but like performance cars, if you use them to their full (read high) capabilities they wear out faster.