I need a quick answer to a question about gears. What gear ratio came in a '77 K5 with a 350/TH350?203 combo? I need to figure out what gears are in the 12 bolt I have.

Pull the cover and check the numbers. Could be a few different ratios most likly 3.73's

Thanks.

373's

My 77 Jimmy with 350/th350/np203/12bolt came with 3.08's.

it will most likely be 3.08's with that combination...

3.07 is standard ratio. 2.76, 3.73, and 4.11 are optional.

'77 K5 Jimmy Brochure (http://brochures.slosh.com/1977gmc/jimmy6.jpg)

most blazers came with 3.07's, trucks came with 3.73's

Mine was a truck..

Same here my diffs were out of a 74 pickup

Newb question but anyone know the gear ratio cut off for lower gears, 12 b (3.73and down) D 44 (3.90 and up)???????

The carriers for a 12 bolt are 3.73 and down or 3.73 and up. I have a spacer that will allow you to run 3.73 and higher on a 3.73 and lower carrier that I don't need, that's if you need one.
The dana 44 is 3.92 and up or 3.92 and down.

Three 'carrier' (case) offsets for the truck 12-bolt:

up to 2.73
2.76 - 3.40
3.73 - up

Dana 44:

up to 3.73
3.92 - up

Three 'carrier' (case) offsets for the truck 12-bolt:

up to 2.73
2.76 - 3.40
3.73 - up

Dana 44:

up to 3.73
3.92 - up


I didn't know that there was a 3rd carrier for the 12 bolt.. What would that have come in? I can't see a truck coming with 2.73 gears.

ive seen many late 70's early 80's with 2:73's when the gas crunch was on car companys were looking for any way they could to increas gas mileage. Which inturn affected performance just go to the junk yards aqnd look in the glove boxes of gm products