3/4 ton 1964 rear gear ratios?

[GMCNUT]

Hey guys - I bet someone will know this - I am buying a 64 3/4 ton 100% untouched original truck from another 6066'r and I want to know what gears to expect this truck to have - it is equipped w/ 305E and original 4 spd w/ no mods ever, so whatever gears GMC would normally install should be what this truck has. It is a decked out truck w/ lots of expensive options from the factory, so I am curious what hear set would be optional too and if there is any external numbers or anything that would tell me?

[bigblockv6]

The 3/4 truck would come with either 4.10 or 4.56 ratio,if it hasn't been removed over the years there will be a tag attached to the rear diff cover identifying the ratio. As far as what ratio was optional I don't think that really was the case, there were just two ratios available for that tonnage model. Unless the truck was a special order and the customer specified their choice of available ratio you got what ever ratio the dealer ordered. I know when my father ordered out 68 K2500 he never specified what gear ratio he wanted and the truck came with 4.56 ratio which he felt was just too low for his needs comparing it to his 62 that had 3.54 gears that seemed more than adequate with all the torque of the V6. Pete Chronis Northern Cal.

[GMCNUT]

Originally Posted by bigblockv6

The 3/4 truck would come with either 4.10 or 4.56 ratio,if it hasn't been removed over the years there will be a tag attached to the rear diff cover identifying the ratio. As far as what ratio was optional I don't think that really was the case, there were just two ratios available for that tonnage model. Unless the truck was a special order and the customer specified their choice of available ratio you got what ever ratio the dealer ordered. I know when my father ordered out 68 K2500 he never specified what gear ratio he wanted and the truck came with 4.56 ratio which he felt was just too low for his needs comparing it to his 62 that had 3.54 gears that seemed more than adequate with all the torque of the V6. Pete Chronis Northern Cal.

Thank you Peter - I was afraid you would say that. I want to run up and down the road with relative ease and ability to cruise at 60+ MPH speeds....a 4:10 or worse, a 4:56 would drink gasoline like crazy seems like. So where can I get 3/4 ton gears to replace the originals that would get me a higher highway ratio like 3:42 or something?

[bigblockv6]

That would be a 3.54 ratio for the Dana-Spicer 60 in your truck, the 3.42 ratio is for corporate GM differentials. In your application this will require a carrier change as well
You can get all the changeover parts from vendors like Reider Racing, Randy's Ring&Pinion,West Coast Differentials
,Summit Racing to name a few.

Pete Chronis Northern Cal.

[GMCNUT]

Originally Posted by bigblockv6

That would be a 3.54 ratio for the Dana-Spicer 60 in your truck, the 3.42 ratio is for corporate GM differentials. In your application this will require a carrier change as well
You can get all the changeover parts from vendors like Reider Racing, Randy's Ring&Pinion,West Coast Differentials
,Summit Racing to name a few.

Pete Chronis Northern Cal.

OK; so when you say "change the carrier" you don't mean the whole rearend do you? I want to keep it stock, so I can't just swap out the ring and pinion?

[bigblockv6]

The carrier is what the ring gear bolts to and it is the actual differential, you will have to change it to the corresponding gear ratio. Pete Chronis Northern Cal.

[63_Rouss_Fire_Co_GMC]

Just took two photos of the tag on my 63 1-ton panel. I was always told it was a 3/4 ton with 1-ton stuff. Attached two images but the tag reads "2439 376".

Jeremy Cooper
Winchester Va

[BarryGMC]

Thats an Eaton HO 52 3/4 ton or single wheel one ton. It probably has 4.56 gears. Way stronger than a dana 60. Look for a 4.10 carrier out of a 67-72 chevy if you want friendlier gears. Also GMC put lots of power lock limited slips in the dana axles.And most of them seem to be 4.10 ratio in the d-60. This carrier works with the 3.54. Look for the Oil tag on the cover.

[GMCNUT]

Originally Posted by bigblockv6

The carrier is what the ring gear bolts to and it is the actual differential, you will have to change it to the corresponding gear ratio. Pete Chronis Northern Cal.

Got it - I knew that but had a blonde moment when you said carrier for some reason - thank you Peter!

[GMCNUT]

Originally Posted by BarryGMC

Thats an Eaton HO 52 3/4 ton or single wheel one ton. It probably has 4.56 gears. Way stronger than a dana 60. Look for a 4.10 carrier out of a 67-72 chevy if you want friendlier gears. Also GMC put lots of power lock limited slips in the dana axles.And most of them seem to be 4.10 ratio in the d-60. This carrier works with the 3.54. Look for the Oil tag on the cover.

Thank you Barry - very helpful - I was not sure what a 64-66 GMC 3/4 ton would have model-wise for a rear end - this is my first 3/4 ton GMC.
Do you know how to read the numbers on the tag?