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[oletrucks] 81 GM Truck OD tranny

To: oletrucks list <oletrucks@autox.team.net>
Subject: [oletrucks] 81 GM Truck OD tranny
From: J Forbes <jforbes@primenet.com>
Date: Mon, 08 Nov 1999 19:00:06 -0700
Hi...I'm back in lovely Sierra Vista, my stay in Las Vegas was
pleasant.  I got to see the new (mid 2000?) Suburban and Tahoe, which
are based on the 1999 Silverado (which is what I drove up
there...thanks, Janet!)

The tranny used in some 81 (possibly other years?) GM trucks, with
overdrive, is a New Process 4 speed.  This is the transmission that was
used in Dodge CARS and light duty trucks in the 80s.  It is based on the
A-833 4 speed car transmission, but 3rd is direct, and 4th is
overdrive.  They do this by switching the shifting of 3rd and 4th, and
making what would normally be 3rd gear and overdrive ratio.  The 81
Chevy truck service manuals are ambiguous...the overhaul sections shows
pics of a Dodge type tranny, with the funky Dodge input shaft.  But, the
Chassis Service manual shows a cutaway drawing of the tranny with the
normal Chevy input shaft!  I have never seen one of these beasts, so I
can't tell you whether or not it has a Chevy tranny bolt pattern on the
front, but it might...so it could be a straightforward swap.  You would
need the special floor shifter that comes on it in trucks...or possibly
adapt a Dodge car od shifter.  I don't know about the driveshaft yoke,
or the speedo cable, etc...

I've also seen a neat late 80s Mexican Chevy truck 4 speed, I don't know
if it was an overdrive or not...but it was a Ford Tremac aluminum top
loader, with a floor shift similar to that used on the big "normal"
truck 4 speeds.  Had a special bellhousing, with a hydraulic clutch, and
some other neat features.  Good luck finding one!  I saw it at a friends
shop, a fellow from Mexico wanted an automatic (not available there),
and the 4 speed was leftover from the swap.

Jim  (who favors a simple 3 speed automatic, mild rear gears, and the
torque of a big block)
ORIGINAL message:
Along the subject of this thread I see an ad at Stovelbolt Engine Co for
NP 4
speed from a 81 GMC that bolts in the same is the Saginaw. The seller
gear is OD. Anyone familiar with these?

Grant G
50 3100
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959

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