89 Square Dually 2wd, need lower highway RPM

[johnnydefacto]

Hi guys, I am a brand new Squarebody Dually owner. I am 36 but have had a love for the Square since I was 3 when my Uncle would drive me around in his 78 C10. I have had the truck for a couple weeks but have been using this site to learn as much as I can. This is my first post:

1989 Crew Cab Dually 454/TH400 2wd 4.10's. 235/75/16s

My new tire wheel combo will be about 31" tall tire (31.39"). I will not be doing any heavy towing, but will be driving long distances at highway speeds often, cruising around 70-75, sometimes towing a 5000 lbs boat at around 60. I really need to get my freeway rpms down. I have a tach being shipped so I can get good numbers soon, but I can just hear and feel the motor screaming at 60 mph. i have the Dana 70hd. Lowest gears I can go apparently are 3.54, or 3.42 online somewhere). I really wanted to go lower, 3.23 or 3.08, but that is starting to look impossible.

Now I am looking at trying to find a 4L80-E tranny, with 4.10 gears what will my final drive ratio be? If it is not low enough then I can gear down to 3.54 or 3.73s, but this will be quite a bit more expensive than just a gear swap.

Also looked into a gear vendors but wow, way too much money.

Any help would be appreciated.

thanks

I will post pictures as soon as I get home in a few days....

 

[foamypirate]

Hi guys, I am a brand new Squarebody Dually owner. I am 36 but have had a love for the Square since I was 3 when my Uncle would drive me around in his 78 C10. I have had the truck for a couple weeks but have been using this site to learn as much as I can. This is my first post:

1989 Crew Cab Dually 454/TH400 2wd 4.10's. 235/75/16s

My new tire wheel combo will be about 31" tall tire (31.39"). I will not be doing any heavy towing, but will be driving long distances at highway speeds often, cruising around 70-75, sometimes towing a 5000 lbs boat at around 60. I really need to get my freeway rpms down. I have a tach being shipped so I can get good numbers soon, but I can just hear and feel the motor screaming at 60 mph. i have the Dana 70hd. Lowest gears I can go apparently are 3.54, or 3.42 online somewhere). I really wanted to go lower, 3.23 or 3.08, but that is starting to look impossible.

Now I am looking at trying to find a 4L80-E tranny, with 4.10 gears what will my final drive ratio be? If it is not low enough then I can gear down to 3.54 or 3.73s, but this will be quite a bit more expensive than just a gear swap.

Also looked into a gear vendors but wow, way too much money.

Any help would be appreciated.

thanks

I will post pictures as soon as I get home in a few days....

The 4L80E has an overdrive ratio of 0.75:1, so you can multiply your rear end ratio by the trans overdrive ratio to get your true final ratio in overdrive. For the 4L80E and 4.10s, that works out to be 3.08 (the equivalent of 1:1 in top gear for a TH350/TH400, and a 3.08 axle).

 

[yevgenievich]

For highway and mild towing, I find 4l80e and 3.73 rear gears to be a good match.

 

[johnnydefacto]

For highway and mild towing, I find 4l80e and 3.73 rear gears to be a good match.

thanks guys, I appreciate the help. Now looks like I am going to have to decide between 3.73's now and do the transmission swap next year, OR 3.54's now and save up for a good gear vendor (doing some research now to try to find one that is automatic so I can have a 6 speed automatic at the flip of a switch... not sure if that is possible).

Loving my square body. Dream truck for sure, it has been fun so far. Thanks for your help.