CUCV gearing

[Draco-87]

Ok guys I have an 85 cucv with a 700r4 transmission with 31" tires thinking of going up to a 33" tire. I tow a m-101a2 trailer so I'm wondering what gear ratio would be best for the trailer towing and for highway cruising.

 

[Warthog]

And which CUCV do you have?

 

[Draco-87]

I have the 1009, I was thinking about 3.73 gears as an all around set up

 

[Keith_J]

Leave it stock at 3.08:1. The 700R4 has a little lower first gear, with a proper throttle valve cable setup and kickdown switch, the transmission will drop out of lockup and OD when you need to pass. This combination will be perfect for accelerating at highway speed.

You have enough torque at lower engine speed for off-roading with the 208 transfer case. You need a lot more than just lower axle ratios for extreme rock crawling.

 

[Warthog]

The stock M1009 has 3:08 gears. With 3:73 it should be a good combination. There are many websites that have gear calculators to help make your selection.

 

[wayne pick]

If you plan on pulling a trailer up steep highway grades the 3.73 gears are still way too high with a 700-R4. At 55 MPH, the engine will be barely running and lugging @1415 RPM. We all know that the 6.2s "sweet spot" is at about 2200 RPM. With 4.11 gears it will run @1715 RPMs and is a much better choice, but still falls short of the 2200RPM goal. unless you add a turbo to a 6.2-700-R4 combination, even with the 4.11s the 6.2 is short on horsepower for pulling grades with added weight to the truck. A 700-R4 is really a 5 speed trans when in lockup. The above axle ratio calculations were taken from www.grimmjeeper.com/gears.

 

[Skinny]

Sounds like you will either keep that converter from locking and really heat up your ATF or it will be constantly hunting between 3rd and 4th which was one of the major 700R4 killers back in the day. I'd probably drop a set of 4.56 CUCV axles in it with that setup rather than regear the 10 bolts which are useless anyways. Price wise you would be pretty close on both so why not gain the extra strength...

Another thing too in the meantime is just keep in in D range to avoid lugging the engine. Keep it out of OD unless going down long grades (which you may want D range anyways for as much engine braking as possible).

 

[wayne pick]

Skinny is right on with the D60 axle suggestion. I failed to mention it because there is some cost and fabrication involved to make it work on an 09. The 700R-4 and 4.56 combo gives you the best of both worlds, highway cruising speed, within reason, and low end grunt when you need it. The D60 axles will last forever with a 5200# 09 sitting on them, and gives you a true king pin front end, and better tire choices. Adding a big aux trans cooler is a good idea to keep trans temps in check. Excessive heat, as said above, will toast a 700, new or old.