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Re: Replacing rotors (query)

To: John Bartholomew <jdb70@juts.ccc.amdahl.com>
Subject: Re: Replacing rotors (query)
From: Robert Allen <boballen@sky.net>
Date: Sun, 17 Nov 1996 10:57:57 -0600
Thanks, John, 

for putting so much effort into your reply for the list. After thinking about 
it 
for awhile, I think you are right in your description and, with a set of both 
internal and external micrometers, you could set the clearence to .004. My 
thinking is if you cleaned everything up and installed the new (or old) 
bearings 
dry, you could use the external mic to find the exact distance between the to 
axle-bearing races. Then you use the internal mic to get width of the spacer. 
Without a great amount of difficultly (and a claculator) I could figure out the 
difference and collect the shims to leave .004 clearence. I must assume, 
however, 
that once you bolt everything back together, you can 'sqwish' .004 out and have 
the assembly bolted up tight. I mean, it would olny take .002 per bearing or 
.001 
for each roller and each race. Not much!

So me-thinks Santa might need to bring me a good set of calipers. I've got a 
local 
tool shop that is pretty good unless I can support some internet commmerce from 
the recommendations of this fine list.

So, I should either get the 'C' right with dial gauges or just chuck the 
spacer. 
Other than a testicular-level desire for more tools, I can justify it with the 
woes of a fellow club member: He spun the outer-bearing axle race and the 
insuing 
heat *burnt* the end of the sub axle off. And he was 1,200 miles away in the 
middle of nowhere. I had to *send him* my kingpin assembly off my 'C' just so 
he 
could get back home and owe me his next female-born child. I suspect a proper 
amount of shins to snug up the axle-bearing races and the bearing wouldn't of 
spun. And as our cars get older, the axles aren't getting any thicker.

I feel a little wiser, thanks.

Bob Allen, '69MGC/GT, Kansas City

John Bartholomew wrote:
> 
> Robert,
>       Thank's for sharing your views with me.
> 
> >Whoa there! I would like to hear some dialog on those lousy shims. Three cars
> >and several years ago I read carefully the instructions on those shims that
> should
> >be fitted between the outer race and the conical spacer. And I read all the
> >details on measuring the gap --- and I decided it was all a bunch of hooey.
> 
> Let me share some ponderings with you...............
> I too have read, digested and followed those directions from the shop manual.
> I followed them, to the letter! Even got myself a dial gauge and spent
> almost a full day swapping shims. Even got some new ones mic'ed em up and
> selected the exact ones for the job. I could never get the end float just
> right on one side. I fought the thing for hours! Finally I swapped the
> castled nut and hey presto it was OK, I finally had the 4 thou end float.
> Having got it RIGHT, I was hard pressed to believe this was really
> necessary, I mean 4 thou! Was I to go through this misery again and again in
> the future? What about all the machining tolerances can the bearings be that
> critical? I don't believe they are today, I don't believe the US car makers
> even use a spacer between the bearings do they?.
> My personal belief is that those darned BRITS (I am one also), were working
> to a perfection point that is beyond reasonable limits. Those tapered
> bearings, I doubt, needed to be set up that precisely, perhaps they did at
> one time, who knows.
> I have worked on a 79 B that even had the spacers removed from the hubs I
> never knew it, I was not aware of any handling problems.
> Why would you need that spacer anyway? The hub is designed so that the
> bearing cages seat in the casting thus defining the center lines of the two
> bearing surfaces with one another. The rollers themselves take the full
> thrust and provide the rolling surface interface with the grease. Like you
> suggested, seat the bearing, back the nut off a hair, put in the pin and
> away you go much easier and far quicker. Providing a spacer and shims does
> afford a RIGID assembly alignment and perhaps extends bearing life. If they
> were hundreds of dollars new, I could understand the need, but I am only a
> lowly engineer what do I know I didn't design it. I just follow the
> maintenance instructions!
> 
> >
> >I think that trying to measure .004 play is impossible because:
> >1) Once the new assembly is packed with grease you won't feel any and
> >2) what you do feel is (acceptable) play in the kingpin.
> 
> I do think it is possible to make the determination of where the movement
> is, king pin or axle, but the assembly should be dry, free from grease, to
> make that judgement.
> 
> >
> >So what's the scoop? Why would just the British have the shims and are they
> really
> >important with modern bearings? If someone want's to tell me the dire
> consequences
> >of losing the shims, I guess I'd like to know when they might be showing
> up. They
> >haven't in 30,000+ miles.
> 
> Was there a possibility that the bearing manufacturing and hub manufacturing
> tolerances could not be held well enough by the various suppliers and so it
> is was deemed necessary to provide that fixed datum afforded by the spacer
> and shim arrangement? I have no idea what the 60's manufacturing goals were,
> labor was probably cheap and materials at a more cost conscious level?
> 
> I do know I have never had a wheel bearing go out! I have however, replaced
> bearings as a preventive measure and a means of getting to know my machine
> more intimately. Besides I like to play with tools and get my hands dirty!
> 
> Comments from the net, from the more knowledgable?
> 
> John Bartholomew. San Jose CA.

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