[DeTomaso] rear suspension survey-long

[JDeRyke at aol.com]

You have about 20 questions here; I'll answer one: I converted one spare 
upright for our '72 street car to tapered roller bearings over 10 yrs ago, 
simply to compare them to a properly sized stock ball bearing on the other 
side. To convert the upright, I bored the front bearing recess 5/16" deeper so a 
standard lip-seal could be pressed in on top of the outboard tapered 
bearing. To make the seal work properly, I discarded the stock cup-shaped axle 
spacer and fabricated a spacer that fit the axle chamfer and was the right size 
to slide through the seal. This is a weak spot in most such conversions 
since they always use a lip-seal that only rubs against a stock cup-washer; 
this does nothing but keep out (most) dust & dirt. Lip seals are designed to 
rub around a shaft inside them.

On the inboard side, there is no available tapered bearing that fits the 
smaller stock bearing recess so the hole must be overbored. I used the same 
size tapered bearing as in front, seated against the step created by the 
overbore. To maximize the stub-axle span between bearings, I made a thin 
extension cup in back and pressed it into the upright behind the bearing, then added 
a lip-seal in the extension. I turned & polished the companion-flange to 
fit inside the seal. Again, this worked perfectly- no water/corrosion inside 
since installation. 
Since tapered bearings cannot stand much pre-load, I only torque that stub 
axle nut to 10 ft-lbs. The stock nut is mechanically locked in place by 
drilling & tapping a 1/4-20 hole thru the flange and screwing in a long allen 
bolt. The bolt shank goes thru one of the spanner-nut slots, locking it in 
place in spite of the light torque on the nut. The locking allen is then 
safety-wired. This is easier to see in the article illustration than to describe. 
30,000 miles, several track events, driving in rain- no adverse effects seen 
by disassembly & direct inspection.
All this is a highly machining-intensive conversion, takes special tools, 
and IMHO does nothing to increase reliability- the other upright with stock 
ball bearings AND A PROPERLY SIZED STUB AXLE has given the same service at 
much less cost and risk of one or more of the the machining cuts being done 
wrong. I realize this is a single example so statistically, it may not be 
significant. But from owners, you aren't going to get much different- most of us 
only HAVE one car to work with. 
Bottom line: tapered rollers are a waste of your resources, from someone 
who's done it. An estimate of the costs of my labor etc would be around $1500 
per upright- and no, I wouldn't bother doing it again. A set of stock ball 
bearings on an oversized stub-axle so the press fit tolerance is 
0.0005"-0.0009" -within specs for the ball bearings as published by the bearing mfgr, 
works at least as well plus is probably more efficient (e.g- less heating), 
since spot-contact from rolling balls is always less than line-contact from 
rollers. No real-racecar in the world uses tapered rollers in its rear 
uprights; all use ball bearings. 
All this was documented in a POCA Newsletter article, with photos, in 
August 1998, with a 3000 mile follow-up done in June of 1999. Periodic checks 
since then have shown no wear or corrosion, in either upright assembly to date. 
Good luck- J Deryke


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