<VV> Rear Wheel Bearings

[James Davis]

Hi Bob,
    As you know, I am new to Ultra Vans with only 5 years experience 
(67,000 miles).  I have been, however, a owner of a 65 Corsa since March 
1965.  Fred Leary first wrote about removing the press fit in the late 
model hubs in a 1977 tech tip for the UVMCC newsletter (now called the 
Ultra Sounder).  It sounded like perfect for on roadside repairs.  The 
typically Ultra Van carry 1,400 on each hub as opposed to 800 lbs on a car 
hub so rear hub failures are quite common.    Any deficiency in the hubs 
design or setup is greatly magnified by Ultra Van usage.

   It was thought that when the hub assembly with the press fit removed, 
the clamping force of the yoke nut would hold the assembly and prevent the 
inner races turning on the shaft.  That has proved to be incorrect. I 
assume it is because of thermal expansion.  Most Ultra owners carry a 
optical pyrometer to measure hub temps. Typical temps. for me after a 
couple hours of interstate cruise are 200 on the left and 250 on the 
right.  The right runs hotter because the torque convertor exhaust into the 
right wheel well. If I check the temps after coming down a mountain pass 
the temps usually run 60 degrees higher due to the brake drum heat.  Due to 
the loads, I would assume the bearing temperatures to be somewhat higher. 
This temperature differential leaves the bearing assembly without 
preload.  100 ftlbs; 20 pitch nut on a 5.8 inch shaft is about 0.0001 inch 
shaft stretch.  Steel expands at  0.000062 units/degree, so 100 degree 
differential would remove the nut preload.  That my theory why the inner 
races turn on the shaft.  The heat produced by the friction of the race on 
the shaft soon melts the grease allowing for the bearing to fail.

  All I know is everyone I talked to that had removed the press fit for the 
bearings has had a bearing failure.  The previous Ultra Sounder tech 
editor, Norm Helmkay advised me on how to rebuild my hubs for my 
UltraVan.  Norm has 150,000 miles plus in this Ultra Vans.  Gene McMasters 
who has personally put over 600,000 miles on his coach said under no 
circumstances remove the press-in-fit.  The most vocal of Ultra owners, 
Walt Davison (who has average 20,000 miles per year for the last 25 years) 
said I would regret it if I removed the press in.  Actually he was much 
more emphatic above it.  As an engineer, I was thought is much better to 
learn from someone else mistakes than from your own.
Jim Davis



At 12:24 AM 1/6/2005, BobHelt@aol.com wrote:
>In a message dated 1/5/05 6:03:20 PM US Mountain Standard Time, jld@wk.net 
>writes:
>
>>The tech tip on sanding down the shafts is still listed in
>>the Ultra Van tech tips (available online and searchable at
>>www.corvair.org/chapters/ultravan/ ) but it is definitely NOT recommended
>>by anyone who has tried it.
>
>
>Why is that, Jim? Please explain.
>Regards,
>Bob Helt