3/4 ton 1964 rear gear ratios?
 

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?

Re: 3/4 ton 1964 rear gear ratios?
 

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.

Re: 3/4 ton 1964 rear gear ratios?
 

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?

Re: 3/4 ton 1964 rear gear ratios?
 

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.

Re: 3/4 ton 1964 rear gear ratios?
 

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?

Re: 3/4 ton 1964 rear gear ratios?
 

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.

Re: 3/4 ton 1964 rear gear ratios?
 

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

Re: 3/4 ton 1964 rear gear ratios?
 

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.

Re: 3/4 ton 1964 rear gear ratios?
 

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

Re: 3/4 ton 1964 rear gear ratios?
 

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?

Re: 3/4 ton 1964 rear gear ratios?
 

Thank you Jeremy - a picture is worth a thousand words :)
So what do the numbers on your tag translate to and how do you read them?

Re: 3/4 ton 1964 rear gear ratios?
 

60-66 gmc 1500 trucks use a dana 60 rear. the gear tag will read like this 4.09 or 45-11 or sometimes both of these #s if it is a 4.09 ratio. a second tag will have the limited slip oil only on it. these tags are not always present however. They often broke off or were not put back on. The Eaton ho52 is a chevy 3/4 ton and one ton single wheel rear that was only used on gmc 2500 series. The eaton tags appear to be a part # tag, I have never seen a gear ratio tag on an eaton. Factory option for the dana 60 is the power lock limited slip, and the detroit no spin for the eaton. BTW the detroit is not a positraction it is a mechanical locking diff , the wheels can not go slower than the driveline. differentiation occurs when the outside tire goes faster than the driveline.

Re: 3/4 ton 1964 rear gear ratios?
 

OK guys - just found out from the previous owner that this 64 3/4 ton truck is 4:10 geared and is a Positraction rear - dumb question, but I thought Positraction was a Chevrolet term, so did GMC call this Dana posi-rear something else or is Positraction really the correct way to say it?

Is is considered to be an un-common option to get a posi on a 3/4 ton like this in 64?

Re: 3/4 ton 1964 rear gear ratios?
 

I should have read this before posting my latest questions - this is a HUGE Help. I will have to wait until I get delivery of the 64 truck which is about 2 weeks off yet to determine whether mine is a Dana or Eaton, but it sounds like a Dana w/ Powerlock but not sure....this is all so different than my 1/2 tons so I am going to enjoy learning a lot of new GMC information from you guru's about these heavier duty trucks and their differences to the 1000 series counterparts....thanks again Barry

Re: 3/4 ton 1964 rear gear ratios?
 

Checking a 66 owner's manual, it makes mention of the PowrLok, Positraction and No-Spin. So it does not seem GMC REFERRED THE PowrLock as a Positraction. The Powrlock can be identified by it's 4 pinion design and 2 piece split case. What applications the Positraction was used in I can't tell you but possibly Barry may know. Pete Chronis Northern Cal.

Re: 3/4 ton 1964 rear gear ratios?
 

Positraction is eatons and later gm corporate name for their clutch type limited slip used originally in cars and non dana 1/2 ton rears. Dana/spicer makes the four pinion power lock used in the dana 25,27,30,44,60,70. GMC used them often in the 44 and 60 from 60-66. You can still buy the powerlock and detroit for the danas . You also can get a new detroit locker for the old eatons if you use later GM 14 bolt axles. I run 3 detroits ONE in a 72 K20 eaton 1 in a 89 wrangler with a D44 and 1 in the 66 GMC D60.I also run 4 powertlocks the 60 and 65 gmc's And in a 60 CJ-5 The 72 also has a powerlock in the front d44

Re: 3/4 ton 1964 rear gear ratios?
 

OK - I will look at the original documents and literature that came with this truck when it was bought new and check the tags on the rear end to see what I have - will post pictures and info once the truck gets here from Kansas about the 15th or so of Feb - Thank you

Re: 3/4 ton 1964 rear gear ratios?
 

What kind of gears are in my 61 1000 series pickup would you know???

Re: 3/4 ton 1964 rear gear ratios?
 

The most common gear is 3.07, but if you don't see a tag on one of the bolts you can count the ratio directly and be certain.

Crawl under the truck and put matching marks on the pinion yoke and differential housing. Jack ONE rear wheel off the ground, chock the opposite front wheel, put the transmission in neutral and the parking brake off. Can you turn the wheel easily? If yes, you have an open rear. If the wheel is difficult or impossible to turn, you have posi. In that case, jack BOTH rear wheels off the ground.

If you have an OPEN rear, turn the wheel exactly TWO revolutions and count (or have a helper count) the number of complete driveshaft revoutions and estimate any fractional revolution as closely as possible. The number of driveshaft revolutions plus the fraction is your axle ratio

If you have POSI, turn either one of the wheels exactly ONE revolution and count the driveshaft revolutions the same as for open.

Ray

Re: 3/4 ton 1964 rear gear ratios?
 

Anyone know how to read the numbers on these round tags like 63 Rous Fire posted above?