hub/brake runout advice?

[jwvand02]

Car is an S5 FC if that is important.

Over the winter I put new GT-1 high strength hubs and PBM knuckles on my car, as I had a wheel bearing failure that tore a bunch of stuff up.

First track day, I had a lot of brake judder. I tried changing front rotors and that didn't really help much, but there were a bunch of complicating factors that I couldn't work through during the day.

Having gotten the car back in the garage, I'm finding that I have a ton of brake rotor runout on both front hubs (10 thou on one side, 18 thou on the other) and indexing/changing rotors does not improve it. I did my best to measure hub runout with the hubs still on the car, and it looks like the hubs themselves have some significant runout (5 thou on one side, 8 thou on the other).

I'm now trying to do my best to measure the hubs on other surfaces to try to figure out where the runout lies but I'm just beginning that process. I've looked into using brake runout shims as well but so far can't find enough info to find one that will definitely work and there's not one specced specifically for the car, and even then they don't seem to be designed to take up more than 6 thou of runout.

I have access to a lathe, and am going to try mounting one of the hubs to my old spindles and measure to see if that makes a difference. Posting this as an open-ended call for any other advice, as I don't really have time to get new hubs from rhdjapan and the mazda ones are f-ing $550 (!!!) a piece. Also may try new bearings and inspecting to make sure the race is seated.

[freeskier7791]

It sound like to me that the snout on the spindle is out, can you check perpendicularity of the snout?  As a side note I am working on getting FC hubs made since they are so hard to find.

[jwvand02]

It sound like to me that the snout on the spindle is out, can you check perpendicularity of the snout?  As a side note I am working on getting FC hubs made since they are so hard to find.

This occurred to me, but I really don't have any good way to measure to that level of accuracy. Less than one 1/100th of an inch at the outside of a 13" brake rotor translates to a thousandth or less at the spindle.

With that said, I actually have made a lot of progress on this problem. I changed two things, and I'm genuinely not sure which did the trick, and frankly with it working well diagnosing what went right isn't a huge priority.

First, I revisited how I was installing the hubs. The FSM procedure is really weird and I started looking around for "unofficial" advice from experienced people who are running these types of hubs at high loads. What I found was that I was likely way over-tightening the bearings, Timken's advice to get it in the neighborhood was 50 ft-lb to seat, back all the way off, 10 ft-lb, then back the nut off a quarter turn. The way the FSM reads is you want to be able to hang a couple pounds off of the wheel stud without it moving, which requires cranking the bearing down way tighter than that.

The other thing I did was source blank brake rotor rings from Coleman racing, which I've anecdotally seen more than one person recommend. I have been running Z1 motorsports sprinkle slotted brake rotors with the Ronin Mandeville kit and it seems likely that Z1's quality control and metallurgy is not great. If I did it over I'd probably go to RacingBrake for my rotors.

I'm tempted to measure the current runout and maybe swap the Z1 rings back on, but like I said the brake feel is vastly improved and I'm mid-season so having the damn thing working is all I really care about right now.

FDF makes a kit that swaps the whole front suspension out, and their knuckle uses the bolt-on 350z wheel bearing. I really wish someone made a replacement knuckle that did the same thing but without the extreme drifting suspension and steering geometry.