VCCA Home Forums GENERAL DISCUSSION New User Forum 1937 chevy truck rear end

can someone tell me what i can do to get more speed out of my 37 truck as far as changing the rear end. top speed 45 pushing it 50

Thank you Scott

IF IT IS A 1/2 TON TRUCK I RECALL THERE IS A 3.55 RING GEAR AND PINION AVAILABLE FOR 1937-1939 MODELS TO REPLACE THE PRESENT 4.11.

Scott,

There is a popular aftermarket 3.55 gear set available for 1940 to 1954 1/2 ton trucks, however, I'm not aware of such a gear set available for the 37-39 1/2 tons. Chevrolet did offer a 3.82 gear set as an option for the 35 and 36 Master Deluxe passenger cars and the 35-39 1/2 ton trucks (GM P/N 602477). While this gear set would improve your highway speed somewhat, it is quite rare and would probably be very expensive, if you could locate one.

An option that I did on my 37 1/2 ton was to obtain a spare rear end from a 1940 1/2 ton and install the aftermarket 3.55 gear set in it. You'll need to shorten the propeller shaft and torque tube 1-1/2", and in order to mate up the propeller shaft spline to the transmission output U-joint yoke, you'll need to install a 40-46 1/2 ton transmission. The 40 rear end has the same track width as the 37, and the spring seats on the 40 are the same as the 37, so once the propeller shaft and torque tube are shortened, the 40 rear end fits right in. I'm not sure, but the same may be true with the 41-46 rear end, though I believe you'd have to shorten the propeller shaft and torque tube on the later rear end by 3".

The problem you have with the transmission is that the 37 uses a coarse spline on the U-joint yoke, and the 40 propeller shaft has a finer spline. You could conceivably fabricate a hermaphrodite U-joint with the 37 front yoke and 40-46 rear yoke. In my case, I had a spare 40 transmission and it bolted right up to the 37 with no modifications necessary.

The problem with the above procedure is that it requires obtaining a spare rear end and transmission, which are becoming more scarce and difficult to find.

There is probably more than one way to skin this cat, and, in fact, I believe there is a VCCA member who has posted in the past an extensive step-by-step procedure that he used to get a 3.55 gear set into his stock 37 rear end.

The above assumes a 1/2 ton truck. If you have a 3/4 ton or larger truck, that's a different animal.

On the 1/2 ton with the stock 4.11 rear end and 6.00-16 tires, at 50 mph, your engine is running at 2500 rpm, which is easily in the safe range for the 216 engine, if it's in good condition. With a 3.55 gear set and the same tires and wheels, your engine will be turning about 2550 rpm at 60 mph and about 2800 at 65 mph. In the physical world, you generally cannot get something for nothing, and, accordingly, your engine will be working harder with the 3.55 gear set to produce the same torque as the 4.11 required to propel the truck at a given speed. In the long run, this could result in more rapid wear on the engine. For what it's worth, I like the 3.55 gear set in my 37, and have put several thousand satisfactory highway miles on it with no troubles.

Mark

Thanks for your response. It is a 1/2 ton I was just told that a gear set from 1954 power glide rear end will bolt right in.The person that had the truck before me put new 14 inch tires on it might be part of my problem also,After reading your response

Thanks again
Scott

Remember that you need to base your engine speed/ground speed calculations on the rolling radius of the tire, not the wheel diameter.

I expect that whatever tires are on the 14" wheels do have a smaller rolling radius than the originals. Going back to original 16" wheels and 6.00 x 16 tires might offer some engine speed reduction.

There are numerous posts in this forum about updating rear axle ratios. Mark's guidance is on target. Yes, there was an optional 3.82 but I expect you have a 4.11. Before you make any major changes you should confirm what is currently in the truck.

With respect to fitting a 1954 Powerglide rear end it is nowhere near what I would classify as "bolt in". You would need to follow a similar process to the one that Mark described to install the aftermarket 3.55 gears.

I doubt if the 3.73 gear set from the 37-39 Master cars would fit. The truck housing is larger so I assume the ring gear and associated parts are larger. That would offer a 10% reduction which is noticeable if it could be done.

The 1954 Power Glide or any other 1937 and up passenger car rear end WILL NOT JUST BOLT IN.

Hi Gene,

Thanks for the confirmation.

Not having seen the difference between the "new 14"" wheels and the original 16" wheel I would suspect that would be a contributing factor to you problem. Here in Aus a lot of manufacturers have reverted to the 16" wheel but with a lower profile tire (less distance between rim and road) which then compares to a 15" wheel with a reasonable tire depth. Rolling diameter reduction results in a speed reduction but a final power output increase meaning less gear changes on steep hills.
Tony

There is no quick easy way.

The ring and pinion design in a 37 1/2 ton is the same as late 35-36 Chevy Master, late 35-36 Pontiac, and late 35-39 Chevy 1/2 ton.

Ring and pinion back to early 1935 (and maybe 1934) will probably fit with a different pinion bearing. I don't think this helps in any way when you are trying to get higher than 4.11.

These are spiral bevel gears, not hypoid.

To use any of the available aftermarket 3,55 gears, you will have to change your whole axle to a hypoid style.

1/2 tons got hypoid in 1940. Passenger cars got hypoid in 1937. All the parts (ring, pinion, etc,) are smaller in the passenger car axle.

Aftermarket 3.55 are available for either axle type.

The oft-mentioned Powerglide gears (and associated parts) fit the passenger car axle, not the 1/2 ton.

The 37-39 3.73 gears Rusty mentioned are also for the passenger car axle.

If you use a passenger car axle, you will need to find one 1937 or newer (better yet 1940 or newer) that is the right width, and then move/reweld the spring pivots to the correct spot if they arent already (most likely they arent). Ray W's 1936 tutorial covers this. I suspect you might need a different width axle than he used.

If you use a 1/2 ton axle, you will have to buy aftermarket gears because the Powerglide stuff doesn't fit.

Either way you will need to cut/splice a torque tube to get the right length and u-joint spline. Ray W covered this in his 1936 article.

In a 1937 I would do what Mark did. It looks like the least work.

Thanks for all your coments gives me alot to think about

Scott

chev nut
do you know who sells this ring and pinion?

thanks scott

Hi Scott,

There are 3 sources that are advertising the 3.55:1 ring & pinion sets for 1940 - 1953 trucks.

Chev of the 40s
The Filling Station
G&D Classified Ad

At one time I was considering this swap for my '37 Master coupe. I dropped that idea quickly when I realized that it was going to end up costing about $1200 plus a lot of work. One advantage I had was that I did not need to locate, buy, and ship a complete different rear end to start the conversion.

In my case it was only a 5% gain because my car has a 3.73 rear.

Someone DID indeed advertise 3.55 gears for 37-39 1/2 ton, and to the best of my knowledge they cannot deliver. I thought it was Patricks, but searching online now it looks as if it might have been Chevs of the 40s. It could have been anyone.

What the description actually said was that it bolts in to 40-54 1/2 ton, and 37-39 1/2 ton with "driveline modification".

When I was brand new to this rear axle, I contacted the vendor (whoever it was) and quizzed them about what "driveline modification" was necessary. They did not know and could not answer.

I now know what the answer is, and you will too when you start looking at how these rear axles are actually built. They are Spiral Bevel (not Hypoid) gears. The 1940 and later is Hypoid. There is absolutely no way the same ring and pinion could work in both a Spiral Bevel carrier and a Hypoid carrier.

Rear axle terms can be a bit confusing. The carrier is the big cast chunk that has the torque tube permanently attached. The case is the spinning piece the ring gear rivets to, and the axle housing is the piece that attaches to the rear springs.

On a Spiral Bevel rear axle, the pinion goes right in the center of the carrier at the axle centerline. This can be visually identified by the torque tube going into the exact center of the carrier.

On a Hypoid axle, the pinion (and the torque tube) are moved DOWN and to the RIGHT. The gears are cut special for the pinion to intersect the ring BELOW the axle centerline. This is the reason the two can never interchange, the gears could not mesh properly.

If you attempted to put the whole hypoid carrier in your axle housing it would probably fit. I am not absolutely sure of this, but I think it would. I suspect the axles would go in, too. The problem is the torque tube will be down and to the right from where it was. Down isn't a big problem, but having the torque tube offset to the right means it does not line up with the transmission and will not connect.

When Chevrolet went to Hypoid in 1940, they kept the torque tube in the center of the truck. They did this by moving the big hole in the axle housing (where the carrier and the pan bolt) to the left. This moves the whole differential mechanism to the left.

Now that the differential is offset to the left, there is a short axle shaft on one the left side and a long axle shaft on the right side. This is the reason the axle housing and axle shafts also need to be changed (as Mark suggested doing in his post).

So finally, there is the answer that the vendor could not provide. To make those 1940-up parts fit you have to make everything 1940 (and then cut and splice the torque tube and driveline to fix the length and spline differences).

It would be wonderful if someone actually made a taller ring and pinion to bolt in. Chevrolet made 3.82, but not many, and they are nearly impossible to get. Larry Jackson made a very few custom sets of 3.36, but when I spoke with him he said he will not be making more.

Thank you for your responses.

Scott