VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Rear End Gearing

Looking to talk with someone on changing the gear ratio on my 1940 Special Deluxe. At 55 the engine sounds like it's doing 70. What are the alternatives: Overdrive?, Gear Ratio Change? or?, It would be nice to do 65 on the Interstates with the engine doing a comfortable RPM.

Thoughts on this Please....

Wes Marquis

There was an optional ratio - 3.7? - and there was an aftermarket Truckstell overdrive used in the torque tube. And, there is a later Bendix kit that goes in the torque tube also..You can use later powerglide 3.55 gears or '53, '54 stick shift gears - 3.70. Don't know if the entire PG or '53, '54 center section will work on the '40 as in later models. If so, you could use the entire '50 PG setup because the brakes will match your front brakes..

Plan #1...find a street rodder that removed the torque tibe and rear axle housing from a 1940 Master 85 (cheap model with leaf front springs)Had a 3.73 ratio and makes 65 MPH a breeze.Install complete unit.

Plan #2...find a 1941-49 with optional 3.73 ratio.The ring gear and pinion and be installed in your 1940..Not common find.Those are the only parts that you will use.

Plan #3...Find rear end out of 1950-54 Power Glide.Remove ring gear and pinion and case ring gear bolts to and install in your existing rear end.This will be a 3.55 ratio.

Plan #4...Same as above but gears from a 1953-54 Stick.Will be a 3.70 ratio.Gives little better "power" than the 3.55 with little sacrifice in RPM'S.

The 1940 torque tube is a one year "length" only.The differential carrier is part of the torque tube so the later gears can be used but not the housing, etc...The case that the ring gear is bolted to must be matched to the ring gear and pinion on the PG gears and the 1953-54 stick...this is important.The rear axle banjo housing (from whel to wheel) also fits 1940 only.

With your present 4.11 ratio your engine is turning over a little more than 3000 at 60 MPH.With the 3.73 gears will be about 2750.Doesn't sound like much on paper but makes a world of difference.While making the change would advise replace the drive shaft bushings inside the torque tube.When worn the produce a vibration thru the body of the car making it sound as if the engine is really churning.(note Oakie busing kit in Filling Station catalog).

Actually if your 1940 is "as new" it should cruise at 60 MPH with little fuss.Just don't compare it to a modern car.

The filling Station catalog has a Ring Gear and Pinion 3.55 ratio for $400, recommends an install kit for another $300. Sounds like a direct replacement. Looking in the shop manual, it dosen't seem like rocket science to do, is this something I'm being naive about and really needs an expert? Any comments will be really appreciated. Thanks

Wes Marquis

I have a '40 chev and used Chevgenes' option 3 and it worked fine. I took a 54 powerglide ring & spider gears w/bearings and mounted it in the '40 banjo. He is correct on the driveshaft length and you will have to rivet the 40 drive shaft to the powerglide ring and pinion. I did put in a new pinion bearing plus driveshaft bearings and seals while I had it apart. Follow the book on ring and pinion adjustment and you will be fine. The difficult part is 'back' recovery from wallowing on a concrete floor. Email me off-line if you need any more info.

. The 3.36 ratio is available for half thru one ton trucks from 34 - 39 and passenger cars 35 - 36, from Larry Jackson.
. If you have a passenger car, use 3.55 power glide gears.
. If you have a Ton & half truck, use a Brownie and isolate with motor mounts.
For details click here. http://home.znet.com/c1937/RPM.htm

Isthere any way one can tell at a glance from the exterior what ratio these rear ends are ie how do you identify them at a swap meet apart from counting turns?

The "code" for the gearing is stamped into the front of the center carrier.Right side....between the studs in area inline with the right axle tube.There will be two letters followed by some numbers ,the numbers are the date made and the letters the ratio.

As an example aa 1952 car will have K for the first letter .Indicates 1952.The next letter will be L or M for the 4.11 ratio.The 3.55 ratio will have the letter S or T.

(the second letter identifies the ratio and the plant that made the diff.)

In 1950 the second letter would be A or B for 4.11 and don't have code for 3.55

In 1954 the first letter would be M the second would be L or M for 3.70 and S or T for 3.55

1949 first letter G, second would be A ,B or C for 4.11 and D, E, and F for 3.73.

I would assume that 1953 would have used the same second letter ID as 1954...etc.These were the codes that I had handy.

thanks Chevgene, Ill be out there prepared!