4.10's gonna kill me with this setup?

[70torino429]

MPG-wise?

Thinking of buying a Sterling 10.25 rear-end for my newly-acquired '94 but since I drive the truck a lot on the highway, I don't want to throw my fuel mileage out the window completely, 1 or 2 mpg drop wouldn't concern me though. The 10.25 I'm considering has 4.10's in it though, which is the slight dilemma.

It's a 4.9L, with an M50D trans (will probably switch to a ZF if this trans. doesn't hold, but we'll see..) and currently has 3.08s in the stock 8.8. So, anyone done a gear change in a similar setup? Loving the 17-18 MPG I'm swinging on the highway now, but also want a little more power for occasional towing, maybe 3.55 is the ticket.. but, I'd like to get more opinions than just mine, lol.

For those wondering why I want the 10.25, I plan on setting this truck up to tow the "toy" and also doing trips halfway across the country with a bunch of equipment and such in the bed and no trailer and quite frankly, I've beaten some 8.8's to hell doing this with other similar trucks of mine and would rather play it safe on the cheap.

 

[5.0Flareside]

try to find a rear with a 3.73 in it. i know someone that just put 4.10s in his F150 with a 300I6 and is strongly regretting it. he is wishing he put 3.73's in.

he originally had 3.08s also.

 

[LEB Ben]

I personally think 4.10's would be a little strong, especially going from 3.08's. I think I'd strongly consider the 3.55's, although I didn't know the 10.25 had a 3.73 gearing available...so that might be worth looking in to.

 

[Fellro]

The 3.55 and $.10 are the most common. I have seen listing for 3.73 in my 92 book, as well as 4.56, but when you look up parts, they aren't shown. Myself, if you want better pulling power, but maintain some economy, I would go with the 3.55 over the 4.10. The 4.10 will pull well, but the rpms end up being plenty high if you want to run with most of the traffic. Might not be as bad with an overdrive trans.

 

[crzybil87]

yea id go with the 3.55's 4.10's arent really highway gears

 

[LEB Ben]

4.10's arent really highway gears

That statement can be somewhat misleading. Depending on tire size and weight of a the vehicle, 5.38's could be a 'good' highway gear if it pulls your effective ratio back in to spec. Say you're running 44's, 3.55's would be terrible to run on the highway and would cause you to use more fuel, because your effective ratio would probably be somewhere down around 2:1...but if you bump up to 5.38's, you'll probably be back around an effective ratioin the 3.50-4:1 range. That being said, for stock tires, you're right.

 

[crzybil87]

I stand corrected its been so long since i had actual stock tire on that 4.10's could be highway gears ive been so used to running big tires with 4.10's i just forgot what my gearing does with stock tires. I stand corrected

 

[Fellro]

I have 4.10's in the 86, it hits the governor at 75.... It pulls real well at 65-70 though. It is happiest at 60-65.

 

[conanski]

The highway milage you get depends alot on the transmission, the manuals have a relatively shallow overdrive ratio(0.80:1) so you really don't want as much axle gearing as you would with an AOD/4R70w for example that have 0.67 overdrive. Combined with the I6's powerband optimal gearing is in the 3.55 to 3.73 range with tires up to about 31" in diameter.

 

[70torino429]

Thanks guys, ended up passing on that axle anyways since the guy cut the shock mounts off of it.

I think I might just rebuild 8.8 and buy a 3.55 gearset with a locker for a little more oomph. It's plenty peppy around town with 3.08's, but with a 3-4k lb. trailer and/or a lot of weight in the bed it takes quite a noticeably while longer to get going.