UFO brake question

Bernie Benz b.benz at charter.net
Mon May 12 08:00:37 PDT 2008


Do you know of the SJ shop’s set up for UFO machining? What ever it  
is, they must be introducing residual stresses in the rotor that is  
relieved over time and temperature. To test this, put a newly  
machined rotor pair of known runout in your kitchen oven at 500 deg F  
for 10 hours, shut it off and when cool, remeasure runout. If no  
change, you should have a good pair. If change, shim to true and they  
should be good to go. Stop machining rotors!


On May 12, 2008, at 12:21 AM, Steve Scalmanini wrote:

> No Q, Bernie.  I know you've had great luck with your UFO's but  
> mine and many others hasn't been as good.  I follow your advice,  
> though, to not replace them.
> Turning has always trued my UFO's to within .001" TIR and then each  
> runs for 3-15 months before wobbling again.  I've never tried your  
> shim technique but I'll give it a shot some time.  I made a tool  
> over a decade ago to measure runout.  (Aluminum bar that holds a  
> dial indicator on one end and can be clamped to the anti-sway bar  
> with a Vice Grip.  I posted it's design once.)  So I'll try shims  
> some time and post the results.
> Have you ever tried steel shim-stock (available from machinist  
> supplies - looks like a loooong feeler gage - available in plenty  
> of thicknesses)?  An appropriate thickness could be cut and adhered  
> adjacent to both sides of each appropriate hole in the mounting  
> surface of the rotor, perhaps with a thin coat of Permatex (the  
> alcohol-soluble brown goo.)  Then the shims might stay in place if/ 
> when the rotor was removed.
> I've confirmed several times over the years what you posted years  
> ago that UFO warpage can be felt in the brake pedal starting at ~ . 
> 002" TIR, and by the time it gets to .007" it feels like the front  
> end is shaking apart.
> I've never messed with the heat-'em-up technique for fear of making  
> them worse or some other aspect of Murphy's Law.
> Steve
> PS:  My front-end rubber is still original at 245K so that's the  
> next project on the car list.
> Sun, 11 May 2008 16:20:07 -0700, Bernie Benz wrote:
>> What’s your Q? I’ll throw one back at you!
>> Why do you think that they need repeated re machining? IMO, it’s a  
>> waste of good material and the trueness derived for normal wear.  
>> Mine at 225K have never been re machined, are dead true, and I  
>> believe will remain so for another 250K.
>> Bernie
>> On May 11, 2008, at 3:29 PM, Steve Scalmanini wrote:
>>> If you don't know where to get your UFOs turned (in San Jose, CA)  
>>> from a
>>> post years ago, it's on Chris Miller's site.
>>> I have 3 extra sets and every 3/4/5 years I send or drop off the  
>>> 6 not
>>> on the car to get turned.
>>> Steve
>>> Ukiah, CA

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