All:
First, I'd like to thank all of you who responded to my inquiry on axles.
Sending out an APB on FOT surely produces results, and I am grateful to many
for their time, particularly Ed Barnard and the Derby's.
In the interest of keeping the flame burning, I'd like to share the results
in hopes that it may help another of the brethren.
It turns out the axle was not bent. The custom outer flange had become
damaged over time, and caused the run-out that we presume resulted in such a
large vibration. Bottom line, with some modifications and a bit of
machining, we were able to save the axle without having to replace the pair.
Here's the saga. We removed the pair in December and spun them on a
driveline balancer. This showed 40/1000 run out on the right axle, enough
to cause a molar-loosing vibration. We suspected that the axle shaft was
bent, but couldn't understand how a 1.125" billet shaft could bend,
particularly because I don't remember running over any Pooch-cars in the
past few years. I did notice some damage to the pilot on the outer yoke,
though, and wondered if that was the cause.
We pulled off the outer yoke and dropped the axle into a lathe. Lo and
behold, it was straight as an arrow. Suspicions then turned to the damaged
yoke.
A bit of history. The axles were custom made around 1991 using Chevrolet
shafts and larger Spicer inner and outer yokes, larger bearings and bigger
U-joints. The Spicer outer yoke had been re-drilled for the Spitfire/GT6
bolt pattern, and the pilot modified. The pilot is the circular ridge which
protrudes from the mating surface of the yoke; it's purpose is to center the
yoke into the cavity of the differential's stub axle. The pilot on this
Spicer yoke had obviously been too large in diameter, and had been turned
down to fit the stub axle. Because of the casting (slightly off-center), it
was razor-thin in one quadrant. At some point in time (probably lying under
the car changing a rear end) it had been drawn up slightly off-center and
crushed the too-thin edge of the pilot. The result is that the yoke was
bolted off-center to the stub axle, so that the centerlines of the stub axle
and the axle half-shaft were off-center to each other, the latter actually
rotating around the former.
We found a new set of yokes with the correct pilot diameter. A NEAPCO part
for hopping up Toyota's, they have only been available for a couple of years
and so post-date the custom manufacture of these axles. We re-drilled the
yokes for the Spitfire /GT6 bolt pattern, and installed them on both axles.
We went back to the balancer, which showed minimal run out, barely enough to
register on the machine.
Although we haven't run them at the track, all indications are that this
will solve the vibration problem. I'll let you know after the VDCA event in
Kershaw, SC next month.
Again, many thanks to all, and Godspeed.
Sincerely,
Rob Stewart
'67 Spitfire #6
-----Original Message-----
From: owner-fot@Autox.Team.Net [mailto:owner-fot@Autox.Team.Net]On
Behalf Of Rob Stewart
Sent: Monday, January 03, 2005 4:13 PM
To: fot@Autox.Team.Net
Subject: Spitfire Competition Billet Axles
All:
I'd like recommendations and any information available on procuring a new
set of billet steel axles for my vintage race Spitfire. I haven't had to
look for these in quite some time and don't know who is still making them,
or what the experience (good or bad) folks have had with the various
suppliers.
Any information is greatly appreciated.
Best regards,
Rob Stewart
1967 Spitfire #6
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