Mark, a while ago Jerry (GremlinGTs@aol.com) told us about a Mopar 4-speed
overdrive trans that can be easily used in Chevys. 4th gear is a .73
overdrive.
I can send the magazine article as a (2.9Meg) Word attachment, if you are
interested.
Here is some of the exchange:
***********************
Date: Sat, 3 Mar 2001 09:38:51 EST
From: GremlinGTs@aol.com
Subject: [oletrucks] <Tech E - Long> Using Mopar 3-spd OD trans in Task Force
truck...
( Lister's Disclaimer - I'm not the originator of this article, just
passing it along, I make no claims expressed or implied as to it's technical
reliability, cost, etc. :?) )
( Article based on author's restomizing a '58 1/2-ton Apache p/u, former
utility truck )
I picked up the February issue of Petersen's Custom Classic Trucks
magazine awhile back, which has a number of interesting items in it. One is a
'57 Chevy Suburban artist's concept with a Nomad/Cameo theme. Neat! The other
is a tech article on using the Mopar A-833 New Process aluminum 3-speed with
Overdrive trans ( used in '70s era Plymouth Dusters, etc ), the article which
I just got around to reading.
One of the biggest problems for driving an original old Chevy truck is
the horrendous rear gear ratios which aren't meant for high-speed driving,
and changing out the gears is an expensive and involved job if no one in your
area is capable of it. So, what to do? The old OD trannys would be nice, but
parts are hard to find, and expensive. So what's left? By utilizing this
tranny from a Mopar, you get the OD you need ( .73 Final Drive ratio), with
a more modern tranmission, and it's almost a BOLT-IN. Here's the good points:
ADVANTAGES
1) Fairly easy to still find
2) Uses Chevy bolt pattern to bolt to original Chevy bell housing
3) Uses Chevy 23-spline driveshaft yoke ( original's were 18 )
4) Transmission is exactly the same length as original 3-speeds from late
'50's/early '60s, no need to replace driveshaft
5) Aluminum casing, lighter weight ( there are cast iron A-833's, which
are 4-spd but aren't OD, and are more common than aluminum types, but DON'T
USE )
6) used behind Mopar small blocks as well as slant six, so can handle the
smaller v-8's as well.
7) Has built-in back-up light switch
Ok, that was easy enough...any bad points? well, it's never TOO easy...lol!
Here's the other stuff :
DISADVANTAGES
1) need to have front bearing retainer turned down on lathe to fit (or
buy a replacement, P/N 452696 )
2) Speedometer will need to be recalibrated, it was designed to run off
the rear axle ratio, even when going thru the transmission, so the OD will
affect the reading. They suggested using a Dakota Digital instrument cluster
to replace the original cluster - read, more money
3) Have to use a floor shifter, so gotta cut that hole in the floor!
Luckily, it appears to all be in the trans floor plate, so it won't mess up
your main cab floor anyway.
So, that's about it. The author figured his engine would be turning about
3,100 rpm with the original truck axle ratio, with the Mopar OD trans, it
would turn 2,670 in OD. (3100 X .73 = 2263) He swapped his axle ratio for a
3.90:1, though.
Even keeping the 4.11, a 430 rpm savings is a big deal, allowing you to
cruise on the highway easier at 60, than winding it out at 50. I'll probably
be looking to find one of these myself, for a future conversion project,
although I have an automatic in my '55 TF Suburban at the moment.
As I mentioned, at the top, I have no direct experience or knowledge
about this conversion, so talk to a tranmission shop about these OD units
before attempting it. I intend to talk to my Trans guy, he's a real winner
who knows alot about gear-boxes, has raced cars as well, so he should know
about these Mopar units, and how well they'll stand up to a daily-driver use.
I already have two original OD units, one a rebuilt '57, the other a '58
which needs alot of work and is missing the expensive solenoid, so this might
be a better way to go with a modern unit. well, time to hit the road, and get
busy. Everyone have a good weekend.
Jerry Casper
Woodbridge, VA
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
****
Here are additional comments from a Mopar loving friend of mine:
These are very rugged transmissions. I do not know about the conversion to a
Chevy, however. It does make sense as I was once given a Mopar clutch disk
from a big block Chevy drag racer. I don't know what his application was but
it tends to make sense that the A-833 is a bolt in.
The gear ratios in the transmissions produced from 1975-1980 are 3.09, 1.67,
1.00 & .73 ( these were considered a 3 spd. with overdrive). Earlier
transmissions had a final drive of 1.00. The earlier versions had a course
and a fine spline. The course unit was considered a "Hemi" 4 spd. as they
were standard on all 6 pack and Hemi cars.
Internal parts are readily available from Chrysler. Shift rods for some
applications can be tricky.
A great resource is the Mopar Performance Chassis manual ($20.00 from any
Mopar Performance dealer).
*******************
Dennis McGillis
Vintage Chevrolet Club of America
Orange County Region
949-551-4821 phone
949-551-1162 fax
949-533-7211 cellular
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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