21 and 23 Spline
The photo to the right shows 21 (left) and 23 (right) spline inputs side by side. Carb and EFI 4cyl Pickup and 4Runners have transmissions with a 21 spline output. V6 and Turbo trucks have transmissions with 23 spline outputs. Both input and output must be the same spline count. For a single transfer case setup choose the gear set that matches the spline count of the transmission you are using. For dual transfer case setup we recommend using stock 2.28 gears in front and 23 spline 4.70 gears in the rear case.
Why mix 21 and 23 spline in the same dual case on 4cyl trucks?
All 4cyl Toyota trucks have the 21 spline output, except for the Turbo 5sp trucks. Many people run dual transfer case setups with 21 spline inputs in both units of a dual transfer case without problems. An even stronger setup is to put a 23 spline gear set in the rear of a dual transfer case. As the motor power comes out of the transmission, the torque is more than doubled when it goes through the first reduction unit of a dual transfer case. This means that torque going to the rear input of a dual transfer case is about double that of the front. If you purchase your gears and dual adapter at the same time, get the 23 spline dual adapter and 23 spline gear set. Using 23 spline components in the rear of a dual case setup is stronger yet costs the same as 21 spline components. If you use a 23 spline gear set in the rear, you must have a dual adapter with a 23 spline coupler. If you purchased a 21 spline dual adapter, you can replace the coupler in order to use it with 23 spline gears.
4.70 Gear Kit Parts List
21 or 23 Spline input gear w/bearing
Low range gear
Counter shaft gear w/bearing
Transmission output seal
Rear output seal
Front output seal w/felt and retainer
Shift fork clip
Drain and fill plug gaskets (2)
Complete gasket set (5 pieces)
Marlin Crawler shift knob
During disassembly and reassembly we refer to different transfer case housing sections by number. The photo below shows each of the covers and its number.
As you take apart your transfer case we recommend you label each part as it is removed.
Step 2: Remove 7 bolts and cover #4.
Step 18: Remove 4 bolts, remove shifter
base (top shift) or block off-plate (forward
shift) depending on model.
Step 20: Remove detent plug, ball and
spring from both sides of upper case. Rotate case
on side, then spring and ball will fall out.
Step 21: Remove remaining 4 bolts holding
cover #1. Two bolts are located on the front side,
two are on the rear side.
Step 25: Slide cover #1 forward and remove.
Retrieve two shift fork roll pins from bottom of
Step 32: Remove 4 bolts and main shaft
Step 40: Remove snap rings from input and
counter shaft gears above. The remaining parts
will not be used during reassembly.
Step 45: Slide thrust washer over main
shaft until seated onto face of low speed gear.
Line up notch in washer with ball.
Step 46: Slide 6308N bearing onto main
shaft. Press bearing until it contacts thrust
washer. Install snap ring onto shaft.
Step 49: Using a grinder or file, remove
inside radius on shift forks(s). The roll pin must
also be ground down to clear the larger 4.70:1 low
Step 51: On 79-83 models only, replace
C-Clip on 2wd/4wd shift fork with new clip
provided in kit. Clip is not used on newer cases.
Step 52: Insert roll pin into low range
shift fork. Shaft can go in two ways, install as
Step 56: Using end mill or hand grinder
clearance case as required to accept new 4.70
Step 57: Place counter shaft and bearing in
clearanced housing. Rotate counter shaft to check
for proper clearance. Gear should not contact
housing when spun.
Step 62: Sometimes it is necessary to
clearance cover #1 near the input gear as shown.
Test fit to see if this is necessary. Clearance up
to 1/8" as needed.
Step 63: 79-83 cases only. Install roll pin
into shift block. Note position of shift block
fingers and shift rod. Assemble as shown above.
Step 65: Slide cover #1 onto cover #2.
Carefully tap cover #1 with hammer until cover #1
seats on cover #2.
Step 72: Insert interlock pin into either
detent spring hole. (Skip this step if installing
a twin stick) Turn the case on it's side and tap
if needed to get pin into place.
Step 73: Make sure the interlock pin is all
the way into position. Here is can be seen and is
not yet in position. Push the pin in until it can
no longer be seen.
Step 74: On 85-88 EFI models only, place
pin just far enough into shift block so that you
can pick up the block.
Step 75: Use the pin to place shift block
into transfer case. Slide shift rail into shift
Step 76: Note position of detent notches on
2wd/4wd shift rail.
Step 80: Lightly press the front output
seal in from the front of housing #5 as shown,
pressing it down about 1/2" beyond the
housing. Then place the felt atop the seal, then
the metal ring atop the felt, and then lightly
press the metal ring until it is flush with the
housing. The metal ring will push against the seal
moving it into position.
Step 86: Apply grease to inside and outside
of both both front drive cage bearings. Slide
bearings onto main shaft.
Step 101: Install cover #3 onto the back of
cover #2. Be careful to align oil transfer tubes
in the cover. Install 10 bolts into cover #3.
Torque to 29 ft/lbs.
Step 104: Remove speedo lock bolts and tab.
Using a screwdriver remove the speedo drive gear
from cover #4.
Step 106: Install cover #4 onto the back of
cover #3. Install 7 bolts into cover #4. Torque to
Step 110: With the case on it's side, drop
in one detent ball.
Step 111: Now drop in a detent spring after
Step 112: Apply silicon to the threads of
the detent plug and install. Flip the case over
onto the other side and install the ball, spring
and plug the same way.
Step 113: Install 4wd shift light switch
into cover #1.
Step 114: Apply silicone to the spines
inside both flanges.
Step 115: Install flange. Note, the
silicone will bulge out just a bit. You should see
a slight bulge on each of the splines.
Step 116: Install the main shaft nuts and
tighten to 90 ft/lbs. Using punch, drive the stake
nut into the main shaft as shown above. Repeat for
8 X 1.25 mm bolts with 12mm head: 10 ft/lbs
10 X 1.25 mm bolts with 14mm head: 29 ft/lbs
30 mm front and rear flange nuts: 90 ft/lbs
No brake in is required for 4.70 gears, we do recommend replacing the oil after the first 1,000 miles and every 30,000 miles thereafter. Conventional or synthetic oil may be used. Again, we recommend 80/90W GL5 or equivalent.