Rear end question

[Dano4163]

I'm in the process of building a 1969 GMC c1500 1/2 ton. According to the paperwork that came with it the rear end is a 3.07 ratio. I would like to upgrade this to a 3.73 or maybe a 4.11 and also make it positive traction. I haven't tore it apart yet but I have been looking at parts. The question is would the ring gear be an 8 7/8 an also which would be the better ratio to use? I plan on using the truck as a cruiser and for shows mostly.

[michael bustamante]

i think it would depend on what tranny you would use. 3;73 is usually the best option for a cruiser with a 700 r4

[picklito]

8-7/8" yes.
You will need to look for truck 12-bolt parts not car 12-bolt.

As for best ratio, we'd need to know your intended rear tire diameter and which trans you will be running.

[Willie Makeit]

also, the 3.73 will require a Series 4 carrier where you have a Series 3 carrier now for the 3.08

[engineer_gregh]

What everyone else has said about tire size, transmission, and intended use above is dead on IMO. I have two half ton big block trucks, both with turbo 400's transmissions. One has a 3.73 posi and the other has a 3.07 open rear end. The 3.07 is comfortable at 65 on the interstate but the 3.73 I keep at 60 mph or under on the interstate. Both average 10 mpg and neither are daily drivers. There is a noticeable difference in out of the hole performance as one might suspect between the 3.73 and 3.08 rear ends. Hope this helps.

[hugger6933]

You also need to be aware that the Dana 60 rear made its way into some GMC's. you can tell it by the distinctive rear cover. you may need to do a google image of the two for id purposes just to be safe. But you said it has 3:07 rear gears i don't think the 60 had that high of a gearset I'm not too knowledgeable on them. Jim

[Dano4163]

Its not a Dana rear end,its a 12 bolt. I plan on putting a Muncie 4 speed in it with a 454. It had a 3 on the tree. I really want to keep it as a stick shift. The plan for now is to keep 15 inch tires on it also.