Swap rear axle ratios

[guyonearth]

Would there be any bad repercussions if I swapped the 3.73 axle in my 2WD '97 Astro with a 3.53? I know the speedo might be off, but it's already slightly off now.

[moneymaker]

The computer has already been programmed for the original gear ratio, wheel and tire size for the correct shift points in your transmission. You can change all this, but my recomendation is to buy a power programmer and reprogram with the new ratio and wheel and tire size so your shift points won't be off, plus the speedo.

[guyonearth]

Can you recommend which device to get and where to get it?

[Gary]

The gear ratio I think your talking about is 3.42's and not 3.53....right??.The 3.73's are just about the best all around rear end gear you can get with these vans.Are you sure that you have 3.73's by the RPO code??.The 3.42's are more common in these vans.If you do end up taking them out make sure you list them for sale here if they are in good shape and watch the guys here fight over them.

Yeah-I edited the post to correct the statement of 3.43's to 3.42's.Well a senior moment. Ya know ya reach a age when you don't have so many teeth to count in ya head.......so rear end gears get much harder.

[Gus_Mahn]

I doubt you'll notice much of a difference. Acceleration will be slightly slower, and fuel mileage may be slightly better. Cruise rpm should be 200-300 rpm lower at 70 mph.

I deal with Mustangs quite a bit. To those considering a gear swap, I recommend only swapping gears if you're going to swap 2 gear sizes. Ford example 3.08:1 stock gear, next size gear 3.27:1, I'd recommend 3.55:1 as the minimum swap gear. I'dealy I'd recommend 3.73:1 for stick shift and 3.90:1 or 4.11:1 for automatics.

In the case of an Astro, I think 3:42 is close to ideal for those not pulling trailers, but 3.73 is close and pulls trailers better than 3.42's. I believe the next smaller GM gear is 3.31:1. I'm not sure if a stock Vortec will pull this gear in high winds at highway speeds. If this is the case, you may actually lose fuel mileage at highway speeds.

[guyonearth]

I meant 3.42, I'm not sure what I was thinking. I was hoping for slightly better mpg if possible. The van has tons of power, that's hardly the problem.

[Gary]

I meant 3.42, I'm not sure what I was thinking. I was hoping for slightly better mpg if possible. The van has tons of power, that's hardly the problem.

What is the gas mileage??.When was the last tune-up??.Did you use Delco parts??.Last change of fuel filter??.I suggest you need to look at "the big picture" of a gas mileage issue before a radical gear change.And one which might be a move in the wrong direction.

[Mr_Bowtie]

Like what was stated above if you wanna do a gear swap don't both with just one step up or down in gears as that would be pointless. If your going to swap the 3.73s out for some gears with better gas mileage then you might consider go down to 3.23 or even further down to 3.08 gears. I personally think it all comes down to vehicle maintanence and how you drive the vehicle more then just final drive ratio. Buy yourself a vacuum gauge and make yourself stay off the gas pedal and drive 5mph slower.

[91astroluv]

Well a senior moment. Ya know ya reach a age when you don't have so many teeth to count in ya head.......so rear end gears get much harder.

Yeah and I hear when things in your rear start getting harder rather than the thing in the front, That's when you should begin to worrrrry!!!