I have been using overdrive transmissions for years and they have a big
advantage in that you can keep the 3.90 for torque but drop to 2.73 on the
highway when cruising with no load.
The 5 and 6 speed trannies common today have up to .50 top gear for which we
can probably thank EPA/CAFE/OPEC so the net result is the same or better, but
these trannies are rather costly in most cases and present some problems in
adapting to old trucks.
The Borg-Warner and Saginaw overdrives from the 50's and 60's are relatively
inexpensive, adapt pretty easily to the truck drivetrains, and are what I call
a "true" overdrive in that they use a solenoid-engaged planetary gearset, a
free wheeling clutch, speed governor to prevent damage from engaging at too low
a speed, and a kickdown for passing. The nice little extras with these units
are clutchless shifting and free wheeling.
Downside to this type of OD is that they are pretty much swap meet items these
days and parts can be tough to find.
www.Chevytrucks.org has a HRM '75 reprint discussing the Saginaw OD 4-speed
conversion. This is what I use in my old truck and I highly recommend it.
------Original Message------
From: Steve Parham <thebttmline@yahoo.com>
To: oletrucks@autox.team.net
Sent: May 9, 2000 5:09:10 PM GMT
Subject: [oletrucks] the need for speed
Hi all!
I've been browsing the archives and it appears
that most folks obtain higher highway speeds by
replacing the rear end - replacing the standard
3.90 gears. This is what I've been planning to
do also, but before I do I was also wanting to
consider keeping the 3.90 gears and adding
overdrive. My transmission was replaced with an
automatic (350) by a previous owner.
To say I'm an amateur mechanic is probably an
overstatement. This truck is an education for
me - (one which I'm thoroughly enjoying). I was
hoping someone could give me some of the pros and
cons of a new rear end vs. overdrive to help me
with this decision.
This truck will become my daily driver. The highway
speed limit here is 70 mph. I just want to be able
to cruise comfortably at 80 so I can go with the flow.
Thanks for your help,
Steve
__
_____|L\___ Steve Parham
(_,._____,._) 55 3100 1st
---`'-----`'-- Knoxville, TN
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
Jack Halton
51 GMC 1/2 ton
Winter Park FL
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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