Looking for a thread about crewcab with t400 rear axle gearing. Mine is to low need more cruising sp

[Wrenchless]

86 crewcab dually 454wth400 14 bolt rear end. The truck is revving to go 65mph on freeway. I'm running 215/75-16s and would like to be able to drive 80 like all the other crazies on the road! Any ideas about a good axle gear set to achieve this would be much appreciated.

 

[Frankenchevy]

If you don’t want to fit a taller tire, it’s really an easy equation.

5280/tire circumference in feet=rotations per mile

Target rpm/rotations per mile=rear gear at 60mph

With your tire a 3.55 will go 60mph at 2500rpm.

To do 80 at the same rpm, the math comes out to 2.67. Something close to that should work, but acceleration will be compromised for sure.

There are several calculators to do this math for you online. It’s theoretical though. Converter slip is dependent on your individual stall and fluid temp. Tires aren’t always exactly what the numbers say either.

 

[AKguy]

Might look at a Gearvendors overdrive unit. I switched from 4.10’s to 3.73’s and still plan to install a Gearvendors unit next winter.

 

[Wrenchless]

I was thinking maybe a 3.42 and not be revving so high. I'm used to driving my wife's 95 dually with O.D. auto , when I get in the 86 it feels like it's in low range ! No fun to cruise. I'm not really trying to go 80 ! Thanks for the formulas. Gear vendors are cool but pricey, and my buddy has had to rebuild his twice!

 

[Frankenchevy]

I was thinking maybe a 3.42 and not be revving so high. I'm used to driving my wife's 95 dually with O.D. auto , when I get in the 86 it feels like it's in low range ! No fun to cruise. I'm not really trying to go 80 ! Thanks for the formulas. Gear vendors are cool but pricey, and my buddy has had to rebuild his twice!

3.42 at 80 would still be at or over 3000rpm with your tire.

 

[HotRodPC]

Is this is a 2WD, I'll assume so since you mention both are C30. My vote, and if it were me, I'd keep the low gear. To have the better of both worlds, both LOW gear AND highway cruise, I'd convert to a 4L80-E. The controllers are no longer $1000 like they used to be. Maybe $500 or so, but still all worth it in the long run. With the gear vendor, lots of mods and very expensive, with gear change, still not cheap and you're giving up low end torque and pulling power. Don't give up a thing and gain highway driveability.

 

[V30crewcab]

you can get a 3.23 ratio for the 14bolt, but they are kinda hard to find. I don't think anyone makes it aftermarket, just have to find some original takeout gears.