5 lug to 6 lug 14 bolt with GMT900 20's

[daddy_dandy]

I have a 97 2WD GMC GMT400 with 3.73s. I got a hold of some GMT900 stock 20s with practically brand new tires. Yay! All I gotta do is put 2500 rotors on the front (easy) and slap a new axle in the back. (which I have no idea how to do) At one time I had 285s and my mileage took a major **** with the 3.73s. What gear ratio should I be looking for in a 14 SF? I do a ton of highway driving, about 70 miles a day.

All comments, recommendations and tbi are welcomed.

 

[6chevy9]

why not go back to the 285s? also are the new tires taller than the old ones? that may compensate for the 373 gears and give you more options.

 

[daddy_dandy]

I'm on stock GMT400 rims and they are beat to ****. Currently running 225/75s right now. The tires are stock size for the GMT900 20's which I believe is 275/55. Not absolutely sure though. Rims are at my dads, otherwise I'd just go look. I have to get a new rear end because the GMT900 rims are 6 lug and my axle is 5.

 

[6chevy9]

yeah i knew your reason for the axle swap. but a question for you on that. why not a stock 4x4 10 bolt? are you towing with it or somthing? you could more than likley find a used 4x4 10 bolt with a ratio you want for cheap used and its the same lug pattern as the GMT900. im not too sure about the options with a 14 bolt.

 

[daddy_dandy]

I feel pretty lucky I haven't blown my current 10 bolt up. I've beat on it and haven't taken great care of it either. If I'm going to change the axle out, goin 14 bolt. A 4x4 10 bolt is cheaper but I'll be pissed if I blow it up.

 

[RSTahoe99]

You should be able to get a GMT400 rear out of a Z71 (14 bolt) for 200 bux hear in town, check craigslist, there is a place in Lewisville that has one. The only difficult part would be finding a 6 lug w/ the 3.42s most have the 3.73s

 

[daddy_dandy]

So you think I should get 3.42s? Even with the larger rims?

 

[RSTahoe99]

it really boiles down to total height of tire and wheel combo. If you didn't like the mileage of your existing set up with stock rims and tires and the new set up it the same height the gas mileage will still be the same. If your new setup rims/tires is taller than your old ones then stay with the 3.73's and your mileage should be better.

taller the total height the steaper the gear needed

 

[daddy_dandy]

Ok, Thanks man. Guess I need to measure the two and figure what I need to buy. Currently getting 20-21 MPG on the highway, so can't really complain either way.

 

[6chevy9]

yeah i think you would like the 373 still with those tires.