Axle Question

[VaGent]

OK for what it's worth & not sure if it will work. I have a 1989 BII 2X4 with the A4LD tranny & 2.9 V6 engine. The axle ratio now is 3.45. I would like to swap it out for a 8.8 3.08 gear behind a 4.0 V6 A4LD transmission. Will this work without having to change out a lot of stuff. I'm trying to get better gas mileage & my wife will be driving this BII back & forth to work & she is "easy" on the gas pedal. Where I live I don't have any mountains so it will be mostly driven in traffic & opccasionally out on the open highway. If this will work, what truck/s can I try to find with the gear ratio & 8.8 rear end I need. Any help would be appreciated. Thanks

 

[Hahnsb2]

Bad idea, 3.08s behind a 2.9 auto will kill your gas milage and your transmission.

 

[rickcdewitt]

go 4.10

 

[97BlackBetty]

I would suggest 3.73's for in town driving. Problem with going with a tall gear like a 3.08 is that the engine has to work harder to turn the tires. On the highway, a taller gear is a better choice, because you are maintaining a constant speed, generally a fast one at that.

 

[VaGent]

I admit I am confused on this issue. I had 235/75R/15 tires on the BII to start with. I got at the most 14.5-14.9 in town. Out on the open road I got around 21-22 driving it sensibly around 65-70. I decided to go to smaller tires 215/75R/15 just see what would actually happen. My intown mpg went up to around 14.9-15.1 & the highway went to around 22.5. Not really that much to brag about. I did nothing other then change the size of the tires. The engine is tuned the best it can be for a stock motor & runs great. I have no bitch about it or the tranny either for what it is & used for.

I'm thinking hard about putting a 4.0 in it & using the same drivetrain I have now. I've heard the 4.0 gets better mileage due to being a stronger engine with more torque. If I do this should I stay with the same 3.73 gear or go to something else? Thanks for the help guys.

 

[Mutant Pony]

The improvement in mileage by going to a smaller tire proves that you need a lower gear. 3.73s and 235s work pretty good.
If what you need is fuel mileage- buy an econo box! Find an Escort, Aspire or Focus. You will get far better mileage than any RBV can.

 

[4x4junkie]

I agree, a 3.08 axle will send your MPG into the crapper for sure (and could wind up killing your A4LD too).

If you're running 235/75R15 tires, 3.73 or 4.10 will be the best ratios for mileage (and power) on a 2.9L.

And no, the 4.0L won't get better mileage than a 2.9L (not a 2.9 & the right gears anyway).

 

[kunar]

I admit I am confused on this issue. I had 235/75R/15 tires on the BII to start with. I got at the most 14.5-14.9 in town. Out on the open road I got around 21-22 driving it sensibly around 65-70. I decided to go to smaller tires 215/75R/15 just see what would actually happen. My intown mpg went up to around 14.9-15.1 & the highway went to around 22.5. Not really that much to brag about. I did nothing other then change the size of the tires. The engine is tuned the best it can be for a stock motor & runs great. I have no bitch about it or the tranny either for what it is & used for.

I'm thinking hard about putting a 4.0 in it & using the same drivetrain I have now. I've heard the 4.0 gets better mileage due to being a stronger engine with more torque. If I do this should I stay with the same 3.73 gear or go to something else? Thanks for the help guys.

heres the problem: you changed the size of the tire but did not change the speedometer. so with a smaller tire than stock, you are going less distance but racking up the same mileage on the speedometer. with a bigger tire than stock, you are going further without putting as much mileage on the speedometer. any calculations you have made are no good....

as far as the gears, you do not want gearing like that, it will do you no good. its not a crime to let the engine rev a little bit. you want 3.73's or 4.10's

 

[VaGent]

OK thanks for the information guys. I've got 3.73s front & rear now with the rear being LS. Guess I'll just keep the 235/75R15s & bite the bullet as I ain't going into anything smaller. It if looks like a 4x4. drives like 4x4 & runs like a 4x4 it has to be a 4x4. I cant' find used 4.10s for the front & rear anywhere so I'll just stay with what I have for now.