importance of hub cleaning & measurements of Timken hub assembly

I was doing front brakes and one wheel bearing today and took a few measurements along the way.

 

on the side where I was just swapping the rotors and pads I measured the following rotor run-out values:

 

new rotor + old hub (as-is) > 0.012"

new rotor (Eurorotor/Brembo) + old hub after hand wiring brushing 0.007"

new rotor (Eurorotor/Brembo) + old hub after wiring brushing + repositioning the rotor 0.005"

new rotor + old hub after cleaning with a Dremel mounted wire wheel 0.003"

above + a second scrubbing with the wheel + manual sanding with paper 0.001"

 

on the other side I installed a new Timken hub assembly and new rotor:

 

first mounting 0.003" WTF. I would have expected better with new parts

 

repositioned rotor 0.001"

 

I'm guessing the rotors were contributing about 0.001" and the new hub was adding 0.002". By repositioning the rotor on the side with the new hub I was able to cancel out about 0.001" of runout. I would have expected better from a brand new hub.

 

before I made the measurements, I never realized just how much run-out can be introduced by just a little rust on the hubs. I pretty much had to polish the old hub before the run out dropped below the factory limit of 0.002". I'll know tomorrow if the run-out was a major contributor to the large amount of dead travel in the brake pedal that has been bothering me for years.

update:

 

the brakes feel much better, as expected. the dead travel is now what I would expect, and doesn't vary in strange and random ways anymore.

………….before I made the measurements, I never realized just how much run-out can be introduced by just a little rust on the hubs. I pretty much had to polish the old hub before the run out dropped below the factory limit of 0.002"……………...

 

Thanks for posting this. Given that the runout limit on the discs is 0.002" it is interesting to see how far out of whack things can get with rust on the hub.

I'm suspecting this is my problem as well - how does one measure runout? Can it be done without jacking up all 4 wheels?

the measurement is usually done with a dial gauge and a mag mount. you can measure one wheel at a time. the procedure is to jack up a corner, remove the wheel and brake caliper, install a couple lug nuts to clamp the rotor, place the mag mount on the strut and the dial gauge tip about 1/2" inboard from the edge of the rotor. the dial gauge should be kept perpendicular to the rotor and slightly preloaded. zero the gauge and spin the rotor.

the measurement is usually done with a dial gauge and a mag mount. you can measure one wheel at a time. the procedure is to jack up a corner, remove the wheel and brake caliper, install a couple lug nuts to clamp the rotor, place the mag mount on the strut and the dial gauge tip about 1/2" inboard from the edge of the rotor. the dial gauge should be kept perpendicular to the rotor and slightly preloaded. zero the gauge and spin the rotor.

 

What kind of dial gauge/mag mount are we talking about here? Have never used one.

 

I already ordered 4 new Detroit Axle hubs, based on reviews here that they "work". Will probably just hope for the best -has to be better than putting rotors blindly on worn-out rusted hubs like I've done so far. Every week I learn something new I'm doing wrong

I like Mitutoyo brand, but for this sort of measurement you can use a cheaper knock off unit. harbour freight, princess auto etc... usually have a house brand that is good enough for a better or worse type measurement. as for the mag mount, it doesn't really matter what brand you go with as long as the joints can be locked firmly.