VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 differential chage 4:22 to 3:78 ,,, 38 MD

would it be easier to put my backing plates and brakes on a 38 master rear end rather than remove gear set and shaft from a 4:22 and replace with 3:78 ? in other words replace the hole thing rather than take both apart and proceed that way ?

Hello bigpine38,
The amount of work either way is six of one half a dozen of another. To replace brake lines or to NOT replace brake lines. Are the wheel cylinders leaking? Are the brake shoes in good shape? Is the brake hardware original or new? Are the axle bearings in good shape? Are the axle seals leaking? All of this comes into play when working on the rear differential.

( Were you able to get the speedo gear from the trans?)

I performed this change a few years ago, but I used the original banjo. I guess it depends on the condition of either set-up, bearings, seals, that type of thing.

There is also something you should check while you have this apart. There is a gap between the spring saddles and the axle tube. If it is excessive it may cause a chatter when the clutch is engaged.

What I did was check it with a feeler gauge. Had a local machine shop remove half that amount from each half and used shim stock to create the necessary gap to allow the torque tube to rotate as it moved up and down on the spring.
There is also a procedure for greasing the saddles...With the full weight of the car on the spring, inject grease. Once the grease appears, lower the car onto jack stands under the frame and allow the rear axle to hang, then inject grease again.

Well I guess thats it in a nut shell...keep us posted.

A 1938 does not have the "metal" spring saddles. It has rubber bushings. 1937 was the last year for metal. The banjo housing is different in other way from a 1938 . The wheel tread (distance between wheels) is wider on a 1938 and up.
If the 3.73 ratio assembly the banjo housing can not be used on a 1938.

Yes I picked up a 37 and 38 complete rear differentials, have not looked at 37 yet but 38 has 41 teeth so I assume I'm good to go ..I had the 38 MD car going 60 with stock diff. and I thought I was going into orbit with engine screaming..about 45 it was OK ..is the u-joint hookup hard to get in like a model A ? I could transfer all the new brake parts to the other axle and put the it in as a unit ..what do ya think ..sc

It CAN NOT be a 1937-1938 COMPLETE differential as they are not the same. The banjo housing, which runs wheel to wheel is NOT the same for 1937 and 1938. The center section and drive shaft and torque tube are the same and CAN be used.

I picked up one each a 37 complete diff and a 38 complete diff..= two ,I will sell the 37 as I do not need it.also I will sell 1936 6 lug setup

Hello Chev Nut,
Thank you for high lighting the difference between the '37 & '38 differentials. I really wasn't aware of the mounting/width difference.

The increase in the rear "tread" made different fenders necessary. The 1938 rear fenders has more budge to them. After acout 1940 Chevrolet only sold the 1938 style fender for replacement and was to be used to repllace the flatter 1937 fender.
Chevrolet came out with an all new car in 1937 but for some strange reason retained, for one more year, some of the old features. Examples woud be the straterator, valve lifter helper springs, rear spring to axle mounting and
bendix style starter.

good info Gene!
never knew the 37 fenders were a different shape from 38`s

My installation of a 1938 center housing (3.73) into my 39 master deluxe is completed thanks to you guys and y tube for all the information, at first it seemed like a job that I didn't want to touch,but it was actually pretty simple,just a lot of greasy hands and cramped positions.The car is not even the same now I start out in 1st gear instead of second.

39 chev busy..How did you get diif. out ,I looked at mine a 38 MadDog with 4:22 and it looks like the diff. is captured by the springs,did you take off rear spring mount off frame and then slide it out ?? I picked up a 1938 3:73 complete rear axle,thinking of transferring my good stuff from the 4:22 to the 3:73 and put in the new unit as a one piece ? is there a bearing front of torque tube that should be replaced ?

There is a bushing and seal replacement available for the front of the torque tube.

The seal helps stop the gearbox oil running down into the rear axle.

1939 front driveshaft bushing and seal

The rear of the springs can be undone at the shackles by undoing the centre bolt, the side plates then come off a taper on the end of the pins easily.

I un bolted the u joint,and dropped the torqe tube down,( easier than bolting back but not that bad,I guess a special tool helps,I don't know though) I thought it would be complicated at first to someone like me who never did it before,but if I had to do it again--piece of cake.