I share Jack's enthusiasm for OD tranny's. I like the low rear ratio for
torque and feel that going to a higher ratio' can be a compromise- trading low
end driveability for top end and not getting the best of either. This can be
more noticeable with a six than if you're running a 300 plus HP eight.
Since you're running a TH 350 now another option is a 700-R4 or similar OD
auto if auto's are your preference.
Grant
50 Chevy 3100
52 GMC 150
Jack Halton wrote:
> 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
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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