The Stovebolt Site Forums The Shop Area Engine Shop Napco gear ratios

Hello all,well I finally started on my 63 Gmc 3/4 ton.The diffs are out and apart,and I noticed the front had been rebuilt at one time,looked like a gear failure.Any how the font is a 375 ratio and the rear is a 410 is this normal?

Definetly not normal. They should both be 4.56, or at least within .01 of each other. According to my 4x4 guide, neither ratio was available for a GMC that year in a 3/4 ton. It sounds like the axle have been changed. Question-Is the front open or closed knuckle? If it's open, then it's a '69 or later axle. You definetly need to get both diffs with the same ratio. T-case damage can result with the difference that you currently have.

Thanks for that 55 ,what exactly do you mean with open or closed knuckle :confused:

It's closed the orig.just talked to a diff shop ,they are going to build me two fresh ones with 373 ratios !

On the earlier 4x4s, they had a closed knucke that used king pins and a ball shaped enclosure around the outboard U-joint. The ball is 2 peice, with a felt wiper type seal between the 2 parts. There is a plug on it to allow for addition of gear lube for the joints.
Open knuckel is what was used on later trucks, it's still used on the F250/350 4x4 ans the Jeep Wrangler. Basicaly, there is no enclosure around the U-joint, so it is "open". These axles are usually equipped with ball joints in stead of kingpins, with the later 1 ton GM/some Dodges being the exeption. These have a much tighter turning angle than the older closed type.
If you're looking for a stonger axle, rather than 100% originality, go to the open type. They have larger/stronger spindle mounting, and are less prone to breakage. GM axles up to '77 are the best, though some 3/4 tons use the beefier Dana 44 axle up to '87. Any 1 ton front axle up to '91 will be very strong, too. This would be an open kingpin style Dana 60.

This ones for Bill. I crawled under my 63 GMC 4x4 burb to see if I could identify the transfer case. I had been looking for the input and output seals. You suggested Napa and they found them and sent them to a store in Niagara Falls which is close to me. Even though I couldn't identify the case I got the seals anyway. I will be away from 11 March until July at which time I will send the truck to my buddy in a tranny shop and he will see if the seals are right or not. Too bad I have to wait so long. OK after all that, my question is, when I crawl under again where should I look for a tag or anything to identify the case? Could I post a photo of the case and someone identify it?
Thanks in advance.
EB.

Don't mean to hi-jack a thread, but it is regarding the old NAPCO axles.

The rear axle is the same as my "eaton" axle I have on my one ton (from what I understand). The front looks very similar, but with the knuckles at the end.

Am I correct in saying that both the front and the rear have the "third member" that can be pulled out? If so, are these interchangable from front to rear? If they are, then isn't the front axle pinion turning in the oposit direction of the rear, and is that good for the pinion gear?

Very nuby question, I don't know much about 4x4's and just a little about axles. Thanks.