MB / M38 compatability..

charlesfitton · Post by **charlesfitton** » Sat Jun 16, 2018 5:31 am

Is it possible to swap out the rear diff from an M38/CJ2 and drop it in the floating axle dif in an MB/GPW?

...asking for a friend....

(Truth is - I donated a newer front dif to the project, and the tech didn't check the ratios as I suggested.
Now when it goes into 4wd, it winds up tighter than a bulls ass in fly season.

hoping that the easy fix is to drop in a read diff, too..)

radtech · Post by **radtech** » Sun Jun 17, 2018 12:17 pm

I think you can put M38 diferentials in an MB if both front and rear are from the M38.

charlesfitton · Post by **charlesfitton** » Mon Jun 18, 2018 5:10 am

Thanks - that"s what I'm trying to confirm...the front was already done, I'm hoping he can match the rear..

Post by **wesk** » Mon Jun 18, 2018 10:25 am

Charles are you asking about swapping the entire axle assembly from an M38 to an MB or just the differential.

M38:

Front: Spicer Model 25 5.38:1 Floater No steering bellcrank on it.

Rear: Spicer Model 44-2 5.38:1 Semi-floater. (axle retained in diff by outer bearing retainer)

MB:

Front: Spicer Model 25 4.88:1 Floater. Steering bellcrank mounted on axle housing.

Rear: Spicer Model 23-2 4.88:1 Floater (axle retained by flange bolts)

If you are only swapping the diffs then there should not be an issue so long as you truly have a Spicer 44-2 with 10 spline axle and not a later CJ spicer model 44 with the 19 spline axle. There is a slight difference in the inner axle bearing sizes and I do not recall what effect if any that has on the swap.

The side bearings at the diffs that support the inner end of the axles are:

MB Spicer 23-2: ORD# 705438, Timkin 24780

Timkin Brg 24780
https://cad.timken.com/item/all-product ... 4780-24720
Specifications
Series 24700
Cone Part Number 24780
Cup Part Number 24720
Design Units Imperial
Bearing Weight 0.4 Kg0.9 lb
Cage Type Stamped Steel
Dimensions
d - Bore 41.275 mm1.6250 in
D - Cup Outer Diameter 76.2 mm3 in
B - Cone Width 23.020 mm0.9063 in
C - Cup Width 17.463 mm0.6875 in
T - Bearing Width 22.225 mm0.8750 in

M38 Spicer 44-2: ORD# 705440, Timkin 25577

25577 Brg Timkin
https://cad.timken.com/item/category-15 ... 5577-25520
Specifications
Series 25500
Cone Part Number 25577
Cup Part Number 25520
Design Units Imperial
Bearing Weight 0.6 Kg1.3 lb
Cage Type Stamped Steel
Dimensions
d - Bore 42.875 mm1.6880 in
D - Cup Outer Diameter 82.931 mm3.2650 in
B - Cone Width 25.400 mm1.0000 in
C - Cup Width 19.050 mm0.7500 in
T - Bearing Width 23.813 mm0.9375 in

charlesfitton · Post by **charlesfitton** » Tue Jun 19, 2018 2:41 am

Thanks - I was thinking that just the diff assembly would do it - should I ever try a job like that.

now I need to confirm that the diff did actually come from an M38, and not a CJ2 or 3.

Surprised to see that the ratio is actually higher on the M38, I expected it to be the other way round..

f

Post by **wesk** » Tue Jun 19, 2018 9:57 am

The WWII jeeps used 6.00-16 tires and the M38 used 7.00-16 tires. The tire diameter dictated the gearing change.

The 19 spline axles came much later than the CJ2A & 3A. Just look inside the diff's spider cage and count the receiver's splines. If they are 10 per side your good to go.