VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 1940 ratio change

I have 2000 miles on the rebuilt 1954 235 in my 40 town sedan and its going good. No oil consumption and quieter mechanically with its hydraulic lifters. Thanks to help from Chevgene and others here. My next project is to try a ratio change. I have found a 54 auto rear and disassembled it. One of the differential pinion gears is scored on the thrust surface. Everything else looks good. My question is can I run it or do I need to find a different rear end?
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You can try to smooth off the high spots and use it, you may also be able to use one out of the rear end in the car.

Thanks for your reply. The carrier has matching grooves in it as well. So, I would have to change out the carrier and spiders. Not sure if I can do that with the 54 ring gear. I also read on here somewhere that there was a change in the tooth profile for spider and side gears. Not sure when. Would have to be changed as a set?

The only time that gear spins is when slipping, such as on snow or ice, and when cornering. It does not do any high speed spinning so it should be OK to reuse. While you can use one from another differential I prefer to keep the gears that came together as a set rather than mixing.

Fuzzy,

I did that job on my '36 PU. It's described here:

https://vccachat.org/ubbthreads.php/topics/334876/1936_Chevy_3.55_rear_gear_conv

As described in the article I'm an amateur gearhead, not an "Expert", but I found that all the 1937-54 differential internal parts are the same. So you can substitute a good gear from another rear end. It's a very easy rear end to set up because the pinion is located by spacer shims, not a crush sleeve.

You are going to love the 3.55 gears. Even my bone stock '36 engine pulls the 3.55 gears easily.

Ray W

The side and axle gears were "changed" in 1946. You can install the set of for in any of the years as long as they have the same tooth pitch.
The most simple to make the change would be to install the complete torque tube and rear end in your 1940. The problem is the 1940 torque tube is a one year 1940 length only.
I believe there is a problem mating the 1954 pinion gear to the 1940 drive shaft and a kit was available at one time.
The carrier or case, the part the ring gear is bolted to must be used with the 1954 ring gear and pinion.

I was under the impression that I could bolt the 54 pumpkin with torque tube and propeller shaft to the 40 banjo housing using the 54 gear set with 40 axles. I thought I read that somewhere here. Thanks for your help Gene

oh crap. I measured and with the 40 rear end still in the car, it(the 54) looks to be about 3 inches too long. Wheel base on the 40 is 113 verses 115 on the 54. This isn't going to be as easy as I thought.

It never is....

"This isn't going to be as easy as I thought."

Fuzzy,

Did you read the article?

https://vccachat.org/ubbthreads.php/topics/334876/1936_Chevy_3.55_rear_gear_conv

Actually it is easy because you don't have to change the driveshaft socket from 10 to 17 splines as is required with a pre-'40 driveshaft. You can do it!

The '40 driveshaft female rear socket is 17 spline and so is the 3.55 pinion. If installing the 3.55 pinion in the '40 driveshaft doesn't appeal to you the article shows how to shorten the driveshaft and torque tube that you have with nothing more than a small metal lathe and an AC "Buzz box" welder.

There is a rivet that retains the pinion in the driveshaft. You will drill out one end of it to remove the rivet. A new rivet is easily made from a soft hardware store bolt shank.

Ray W

"I believe there is a problem mating the 1954 pinion gear to the 1940 drive shaft and a kit was available at one time."

Gene,

According to my '38-'64 parts book 1950-54 car with powerglide trans ring gear and pinion sets are all the same part number 3705262. Is that correct? If so his 3.55 pinion will slide right into that '40 driveshaft and he'll be cruzin in the fast lane soon.

Ray W

the 1940 uses a different coupling pin than a 1941-1954. This is the pin that locks the splines on the drive shaft and pinion gear together.
different for 1953 and 1954.
I believe all will work but may take some minor egineeering.

Gene,

From the work I did on my 3.55 conversion I learned that the driveshaft diameters are different in different cars so the rivets (coupling pins)will be a different lengths. I made one out of a hardware store bolt on my project. There is no shear force on it. It just locates the pinion fore-aft in the splined socket at the back of the driveshaft.

Ray W

I did read your article Ray. It is a good one. I was hoping not to have to shorten torque tube and drive shaft. I did all that on my 37 buick. Went from a 4.44 to a 3.60 out of a 53 Roadmaster. I have another 40 parts car and as soon as I can get the third member out of that I'll see what minor engineering is involved with changing the late pinon into early shaft. I have welder, lathe, and big hammers. Not afraid to use any of them.

Fuzzy.

I think you will find that the '54 pinion is a perfect in the '40 driveshaft. You're in like a tall dog.

The only "Engineering" required is making a replacement rivet the length of the '40 driveshaft diameter to locate the pinion shaft. A piece of cake for a guy with a lathe.

It's nice to meet other guys with real shops on this forum. We are not typical. There is a guy named Kevin Smith in Australia I met here. Right now he is adapting a modern water pump bearing and shaft into a '36 water pump. He's documenting the process so I can duplicate it.

Even though I've had it for 50 years I still find my '36 PU an interesting project because there is always another improvement that can be made on it.

I'm very interested in how this works out for you. Can you let me know by email? raywaldbaum@gmail.com

RW