front disk brake runout Heritage Special

[gggGary]

I have a bit of pulsing in my front brake, a slow pulse not chatter. My thumbnail sez about once a wheel rotation or so. I put a dial indicator on the disk. I used a bolt in the fork leg caliper mount to make a stable dial indicator mount. and got about .007" of run out did little manual search and on the early 73-76? system Yamaha spec'd .006" (.15mm) max. On the later system (this bike) the manual specs .02" (.5mm)!!!! That seems like a pretty loose spec and a heck of a change. I grabbed a disk I had laying around mounted it and came up with the same run out so then I grabbed a mag wheel mounted it and came up with about the same run out on that wheel too. Anyone else measure this? I checked at the inner and out edge of the disk. I marked high and low on the disk and wheel and then rotated the disk 180 degrees and rechecked the run out and it appears to be the wheel's disk mounting flange not the disk where the run out is located. Anyone else explore this? I did a test run with the mag wheel and got little if any pulse. Am I chasing the wrong thing?
Edit; fork seals are good, pads are thick and light colored. Caliper mount slides are free, finger pressure moves them. I cleaned the disks with carb cleaner and paper towel twice.

Checked a third bike with mag wheel that one has .004", better than the other two.
The mounting flange on the spoke wheel hub was out about .0025 did a little file work and got down around .0015 put her back together the disk is a bit better now down to about .005" and will test run it when the rain quits.
I am guessing that the specs and what I measured are why yamaha went from a dual piston solid mounted to the single piston floating caliper. They couldn't keep the disks straight enough to keep them from pulsing. It seems that all the newer dual piston bikes run floating rotors now.

 

[XSLeo]

In my factory manual that covers the TX-A, XS-B,C,D the spec is .06 not .006. Most any of them should work fine.
I would use brake cleaner instead of the carb cleaner. Sanding with a cheap sandpaper, the good stuff leaves residue, in a circular pattern to clean the rotor. A light sanding of the pads to can help.
I have found keeping the rotors and pads clean works very well to prevent porblems.
If you can find someone to turn them, going past the 6.5 mm minimum spec isn't much of an issue.
They use the same caliper and pads on the XS1100. The rotors on the XS1100 are 5 mm thick. So if the same calipers and pads work with a 5 mm rotor on an 1100 then they work fine on the 650, been running 1100 slotted rotors on mine. They work just fine.
As far as changing the parts around by the factory was more a cost saving thing than a better brake thing.
I think the main reason the new style brakes are better is because the brake pads are larger. More pad= better brakes.

 

[gggGary]

That's good to know about the 5mm on the 1100 the stock rotors weigh a ton. Do you need to shim the calipers in with a thinner rotor? I guess it would depend on where the material is removed. I wasn't worried about the carb cleaner since the rotors were off the bike. Like you I tend to sandpaper the rotors anytime they are off the bike. The eBay guy who turns and drills em claims they need to be ground, he is using a surface grinder. Says brake lathes don't like the stainless which sounds believable but what do I know? I may drill a set myself for one of the other bikes. I tried a hole tonight it was easy, I used about a 5/16" to start, low speed, oil and bit of pressure and it went right through, making nice spirals as it cut. I have a XS750 nose and think with dual disks the smaller rotors should be plenty.

 

[gentlemanjim]

I know a aguy that will true them up for you if you wish.

 

[XSLeo]

I didn't shim mine. With the floating caliper the caliper centers itself. Running two you need to adjust the right fork leg a bit before tightening the axle clamp bolts. The caliper bracket can be close on one side. Only need a bit of adjustment, just enough to keep the bracket from rubbing on the rotor.

 

[Grinder]

I'm also running XS100 slotted rotors but the ones I picked up at my local salvage yard are the same thickness as the stockers. (7mm)

 

[gggGary]

GJ thanks for that offer. The run out was in the hub not the disk and since it is well within specs I will leave it for now.

From the Yamaha ABCD manual.

.006" on the online converters I checked. .

06 would be a pretty big wobble? Heck I think the later spec of .02 is huge. I am pretty sure you would feel.02 as a pulse.

Marginal relevance alert;
The old CB900s were very sensitive to axle spacing/tightening and would warp the rotors if it wasn't set just right. The tool kit included a feeler gauge. Once warped the pulsing was awful, made the bike act like a pogo stick under braking.

Hmm a bit of a mystery on the XS1100 rotors. I sometimes see complete XS11's for $300 but the shed is ALREADY bulging.

 

[XSLeo]

There may be a difference in the thickness between the standard and special XS1100. The specials being a more sporty bike might have the thinner rotors. Less weight, better handling.
The standard being more of a tourer may have thicker rotors, packed up with bags, fairing and stuff. The thicker rotor won't warp as quick under heavy braking.