Advance Adapters 50-9702 - Manual (Page 2)

GM TRUCK 4SP MODEL SM420 TO
JEEP DANA 300 TRANSFER CASE
ADVANCE ADAPTERS INC. P/N: 50-9702
P.O. Box 247, 4320 Aerotech Center Way New Item: (3/93)
Paso Robles, CA 93447 PAGE 2 OF 3
Telephone: (800) 350-2223 Fax: (805) 238-4201 Page Rev. Date: 03-19-93
SPECIAL NOTE: The components packaged in this kit have been assembled and machined for specific type of conversions. Modifications to any of the components will
void any possible warranty or return privileges. If you do not fully understand modifications or changes that will be required to complete your conversion, we strongly recommend
that you contact our sales department for more information. This instruction sheet is only to be used for the assembly of Advance Adapter components. We recommend that a
service manual pertaining to your vehicle be obtained for specific torque values, wiring diagrams and other related equipment. These manuals are normally available at automotive
dealerships and parts stores.
GM & CHEVY SM420 TRUCK 4 SPEED 1948-67:
This transmission can be identified by a cast iron case length of 10-1/2". The casting numbers on the side of the case should
be GM #3761930 or GM #3813389. The transmission has a shift cover that bolts over the top of the transmission that
has a shift cover part number of GM #591568. The P.T.O. opening is on the left hand side of the main case and the
transmission is a non-synchro first gear.
The transmission you select will need to be disassembled and machined for a snap ring that will retain the rear main bearing.
Your adapter kit includes a new set collar that can be used in place of the snap ring and if installed properly, will do the
same job as the snap ring. Make sure the collar and the clamp screw secure the shaft from any forward movement. The
drawing will illustrate the dimensional data for installation of a groove that must be cut into the shaft for holding the rear
bearing in position. There are a few stock applications where this snap ring will already be in place and the transmission
will not need the new snap ring or set collar.
The right side of the main case will need to be ground off for clearance of the front output yoke on certain installations.
We recommend a trial fit with your transfer case and front output yoke so that any modifications that may be required can
be done before final installation into the vehicle. This is also a good time to set up the shifter linkage for the transfer case
controls.
The early Chevy truck 4 speeds were equipped with the small front bearing retainer that is 4.648" in diameter and must
be used with either early truck bellhousings or late model car-type bellhousings. The late model truck bellhousings all use
a 5-1/8" retainer size that will not be compatible with this transmission.
We changed the design of these SM420 kits to incorporate a spud shaft design in 1988. Prior to this time, we manufactured
a completely new main shaft for all SM420 transmission conversions.
First Gear ....... 7.05
Second Gear ... 3.57
Third Gear ...... 1.70
Fourth Gear ... Direct
The Dana 300 transfer case has a seal around the input sleeve collar that will prevent any transfer case fluid from entering
into the transmission area. In order to prevent transmission fluid from escaping between the adapter and transfer case,
we have supplied you with a new gasket that must be used. The original transmission that is being replaced, normally has
a rear seal that prevents the need of having to use a gasket between the adapter and transfer case.
On installations using a 2-piece main shaft, make sure that the coupler and the output shaft do not bottom out. We have
found on occasion that a transmission output shaft may be slightly longer than we have allowed for; and when coupling
into our new spud shaft, we find a small amount of interference. The adapter housing and spud shaft must be assembled
to the back of the transmission without interference.
DO NOT FORCE THE NEW TAILHOUSING ONTO THE
TRANSMISSION. If assistance is needed, please feel free to call the number listed above.