63' Chevy C30 Dually Rear End Identification

[OldYellow63]

Hey guys, I have a 1963 Chevy C30 Dually that I want to swap the ring and pinion out of. We did the "turn the tire twice and count how many revolutions the driveshaft makes" and found it has somewhere around a 5.13 gear ratio in the rear. The truck motor screams at 4,000rpms at 70mph. I want to buy a set closer to 3.23 that will take the rpms at 70mph down to a more acceptable 2500rpm. Trouble is, my dad swapped multiple rear ends in and out of this truck back in the 80's and has no idea what rear end it's running now. I found a stamped number of 3766686 with a "D" under it on the rear end but haven't had much luck with google searching. I would like to order a gear set on Amazon if possible. Any help is appreciated. Thanks in advance.

*I've attached some pictures below*

[Nanook]

I am not an expert but it looks like a HO52...

[Nanook]

If it is a HO52, parts are expensive and the best you'll do gear wise is 3:90.

[Short 3/4]

You have a 5.14 ratio. Your rear is an HO52 or more likely HO72 (center section is interchangeable between the two). The only other ratios available are 4.57 and 4.11. You will have to find a used one. Best place to find a 4.11 is in a late 60's early 70's truck,
Good luck, Tom

[OldYellow63]

Thanks so much guys. I'll try to find out how much I can get a set of 4.11's for it. 4.11's would drop the rpm at 70mph from 4000 to 3200. Might be worth it if I can get the gears cheap enough.

[Short 3/4]

Looking at the picture closer, center section does look like an HO52 as Nanook said. If truck is original 1 ton the housing probably an HO72, but really does not matter as all interchangeable. Only difference is bearings in the center section, which are mostly available , but as mentioned, not cheap. Heard rumors of 3.90 ratio for years, but never actually seen one, so not going to say for sure ether way.

[aerotruk63]

[OldYellow63]

Thanks Short, after mulling it over more, I really want to get down to around a 3.23 vs 3.90 or 4.11 for cruising on the highway. I'm thinking of just switching out the entire rear end for something more appropriate for what I need. Hopefully I can find something in the junk yard. Might be able to make up the loss a little by selling this rear end on Craigslist to the rock crawler guys for a couple hundred bucks.

Aero, I see you posted something but I can't view it. It just has a little square with an "x" in it.

[allchevy58]

Have you checked into a Gear Vendor overdrive? That's probably what I'm going to do my 64 C30, it has 5.14 ratio. Truck looks good, have to get together.

[Captainfab]

The only way you are going to get a gear higher than 4:11 is to change the entire differential. Personally that's what I would do regardless. The last time I bought the one pinion bearing it was about $240. And that was over 25 years ago. Finding a 10.5" 14 bolt with 3.73 gears isn't too difficult. With a Dana 60 or 70, you can get 3.54 gears.

[vince1]

With 5.14 gears wouldn't the driveshaft speed be a little excessive at 70MPH?

This happened on an empty Kenworth gravel truck but I saw a drive shaft come loose and trash the hydraulic tank after the driver threw it into neutral down a long steep grade.

[urmyboyblue]

Look for a 14 bolt rear. You can probably find one that will match the spring to spring distance on yours. However, you may have to shorten your drive shaft. That is all I had to do when I swapped.

[62c30]

i have a 62 c30 that i just swapped out the Eaton for a 14 bolt out of a 1981 one ton with 4.10 gears, bolted directly in.

[factorystock]

A 4.10 Eaton pumpkin is the easiest and cheapest swap ( just need to find one for a C 30, however I've heard C 20 pumpkins, much more plentiful, are the same), no modifications will be necessary, except the speedo will be slightly off. As Short 3/4 ton mentioned, much more common in 69-72 C 20's with V8 automatic, harder to find in any other model. Never seen or heard of the mythical Eaton Ho52 3.90. The good news about a complete rear axle swap to a higher ratio is your truck has leaf springs, which are used on all newer 1 tons. ( IMO 3.73 would be best, any higher ratio 3.20-3.50 you'll loose pulling power in a heavy truck)

[Short 3/4]

Originally Posted by allchevy58

Have you checked into a Gear Vendor overdrive? That's probably what I'm going to do my 64 C30, it has 5.14 ratio. Truck looks good, have to get together.

This is the ultimate setup. You keep the low gears for heavy hauling, but still have OD for the Hi Way. Plus you can split the gears on that wide ratio 4 speed, giving you 8 forward gears.

[OldYellow63]

Would love the Gear Vendors set up for the Muncie 4spd I have. But $3,000

[Captainfab]

You could change to a NV4500 for about half of that cost. And change the differential for a bunch less than that.

[cscott719@yahoo.com]

If my information is correct, the 3.90 gear was only used one year, 1955 and only on Napco front axles. The reason, I believe is that in 1955, Napco did not have a half ton axle ready for the 4x4 conversions, but they did have a 3/4 ton axle with 8 lugs. This axle was based on the HO52 housing used in the 3/4 ton trucks from the factory. It used the same Eaton drop out. The trucks came with 3.90 gears in their half ton rear ends. As a stop gap until their 1/2 ton front axle was ready, the Napco Power-Pak was shipped with a 3/4 ton front axle with 3.90 ring and pinion installed to match the 1/2 ton rear axle in the truck. They also included a set of wheel adapters, so the owner did not have to carry 2 different spare tires. In 1956, Napco had their 1/2 ton front axle ready and that was used on all 1/2 tons until 1960, when GM redesigned the front suspension and installed their own "corporate" 4x4 system. I don't think they actually built the axles and transfer cases, but they were installed on the assembly line, and were not converted 2wd pickups. Until 1957, all Napco 4x4 conversions were done by the owner of the truck and at dealers. After 1957, Chevrolet installed the Napco conversion at the factory through 1959. So, as far as I can tell from bits of information here and there, the 3/4 ton Napco front axle is the only place you would ever find a set of 3.90 gears.

[andyh1956]

Originally Posted by Short 3/4

This is the ultimate setup. You keep the low gears for heavy hauling, but still have OD for the Hi Way. Plus you can split the gears on that wide ratio 4 speed, giving you 8 forward gears.

I've read for a long time that you can "Split the Gears" on GV od's & they make your trans "8 or 10 Spd", but can you really PROGRESSIVLY shift thru the gears, or is it just being able to split the gear your using?
Kinda xample of what I' talking about is like a Fuller 13 spd & a 15 speed.
The 13 spd has two ranges, and you split the last 4 gears, all progressive & only use 1st once.
However the 15 spd has 3 ranges & 15 forward spds, but you shift it either 3-5-5 or 5-3-5, so it only has 13 PROGRESSIVE speeds.

[Short 3/4]

Originally Posted by cscott719@yahoo.com

If my information is correct, the 3.90 gear was only used one year, 1955 and only on Napco front axles. The reason, I believe is that in 1955, Napco did not have a half ton axle ready for the 4x4 conversions, but they did have a 3/4 ton axle with 8 lugs. This axle was based on the HO52 housing used in the 3/4 ton trucks from the factory. It used the same Eaton drop out. The trucks came with 3.90 gears in their half ton rear ends. As a stop gap until their 1/2 ton front axle was ready, the Napco Power-Pak was shipped with a 3/4 ton front axle with 3.90 ring and pinion installed to match the 1/2 ton rear axle in the truck. They also included a set of wheel adapters, so the owner did not have to carry 2 different spare tires. In 1956, Napco had their 1/2 ton front axle ready and that was used on all 1/2 tons until 1960, when GM redesigned the front suspension and installed their own "corporate" 4x4 system. I don't think they actually built the axles and transfer cases, but they were installed on the assembly line, and were not converted 2wd pickups. Until 1957, all Napco 4x4 conversions were done by the owner of the truck and at dealers. After 1957, Chevrolet installed the Napco conversion at the factory through 1959. So, as far as I can tell from bits of information here and there, the 3/4 ton Napco front axle is the only place you would ever find a set of 3.90 gears.

Thanks for the great info, makes perfect sense.There is one of those early Napcos in town here, and always thought it looked odd with a 3/4 ton front and 1/2 ton rear