Gear Ratio Question

[K5-Matt]

I believe my transfer case is a Dana 20 with 4 speed manual transmission. I know that the front end is the original Dana 44 but the rear end has been changed from the original GM Corporate 12 Bolt to a GM Corporate 10 Bolt. The back end is not a limited slip differential. I want to know what was the original gear ratio in the Dana 44 and the GM Corporate 12 Bolt. I believe it was a 3.73 but the front differential is taged as a 3.07. Needless to say the front and back do not match. Did the '73 K5 Blazer come with a limited slip differential? I am wondering if I should swap out the rear end for a limited slip rear end and then match the front and back gears. Or just change the back to match the front.

 

[StevoandaRedK5]

I don't know if this is true for all '73, but my K5 came with 3.73's and a posi in the rear.

 

[4X4HIGH]

First off what size tire are you running. Since you currently have mix matched gearing it would be wise to make your gear selection based on the tire size you have now. If you are running larger than the factory tire i would definately forget about 3.07 gears. If you're running a 33" tire you would be good with a 3.73 gear and if running a 35" tire you'd be best with a 4.10 gear.

Are you opposed to buying new wheels? The reason i ask is because probably the single best mod you can do to a truck IMO is to swap in a 14ff but that means 8 lug wheels and then doing an 8 lug conversion up front OR finding a matching pair of axles (preferably with the gearing you need) and swap a complete set of axles in instead.

 

[79rustyk10]

First off what size tire are you running. Since you currently have mix matched gearing it would be wise to make your gear selection based on the tire size you have now. If you are running larger than the factory tire i would definately forget about 3.07 gears. If you're running a 33" tire you would be good with a 3.73 gear and if running a 35" tire you'd be best with a 4.10 gear.

Are you opposed to buying new wheels? The reason i ask is because probably the single best mod you can do to a truck IMO is to swap in a 14ff but that means 8 lug wheels and then doing an 8 lug conversion up front OR finding a matching pair of axles (preferably with the gearing you need) and swap a complete set of axles in instead.

X2! and if you have a 4 speed manual, you probably have an NP 205 transfer case. However it could be a np203 also but I think those are kinda rare with a manual trans.

 

[K5-Matt]

It could be a NP 205 transfer case. How would I find out?

 

[K5-Matt]

First off what size tire are you running. Since you currently have mix matched gearing it would be wise to make your gear selection based on the tire size you have now. If you are running larger than the factory tire i would definately forget about 3.07 gears. If you're running a 33" tire you would be good with a 3.73 gear and if running a 35" tire you'd be best with a 4.10 gear.

I have 35" tires on the truck now. And I've been told that a 4.10 gear ratio would be good. But the manual transmission give me more torqe than the automatic transmission in the lowest gear 6.55:1. So I may be able to get away with 3.73's. What do you think?

Are you opposed to buying new wheels? The reason i ask is because probably the single best mod you can do to a truck IMO is to swap in a 14ff but that means 8 lug wheels and then doing an 8 lug conversion up front OR finding a matching pair of axles (preferably with the gearing you need) and swap a complete set of axles in instead.

What do you gain by doing this?

 

[K5-Matt]

I don't know if this is true for all '73, but my K5 came with 3.73's and a posi in the rear.

I think the rear end has been changed. I'm thinking rather than changing the gears, I'll just change the whole rear end to a LSD and match the gears front and back.

 

[brooks294x4]

upgrading to 8 lug, which would mean a 14 bolt in the rear and either a Heavy Duty dana 44 or a dana 60 up front, will make your vehicle a hell of a lot stronger and able to take the abuse with less failure of parts.