Automatic 3 to 4 Speed 4WD Transmission Swap

[Marshy]

Hi Guys and Gals!

I have a 1986 Pathfinder with automatic transmission. This is my first visit and use of this site. Hopefully someone here can answer some questions here on an automatic transmission swap.

After I purchased this ultra clean Arizona rust free rig, I kept looking for the overdrive button that is usually found on the shifter or some where else on the dash, but to no avail. Then I thought the electric shock switch which puts the shocks in a off-load mode might also be a dual function switch turning off the transmission overdrive. No such luck….finally discovered that 1986 was the year they switched transmissions from a 3 speed auto transmission to a 4 speed with overdrive. Apparently I have the 3 speed model with no overdrive, hence the reason for no overdrive switch on the shifter :-)

The transmission works great, but without overdrive the motor is running running over 4K+ RPM at highway speeds of 70MPH. This is hard on the motor and overheats the vehicle in Arizona's hot summer climate in no time, especially with the AC running. I've changed to a dual core aluminum radiator which has helped to a large degree with the heat, but still the trusty Pathfinder is not a very good highway vehicle in this day and age where 75-80MPH is the norm on USA highways.

My wife just learned how to drive an automatic and so we'd like to keep it that way, but wondered if the later 4 speed automatic would be a clean easy swap on the vehicles engine and transfer case?

Otherwise we just have to resign ourselves to the fact this is a local driver and not much use on the highway except for short spurts.

Any transmission advise on how to install the later 4 speed automatic in a 3 speed configuration would be greatly appreciated, such as years of transmissions that will work and whether it's even possible without changing the transfer case and drive shafts.

Thanks,

Marsh

[atraudes]

You probably won't get many replies here, unfortunately. The majority of active members are R50 owners and only a handful have done this type of work. I'd recommend hitting up the folks at http://www.nissanpathfinders.net/. There's many more WD21 owners there and they will have much better information on drivetrain options.

That said, I suspect it's possible to do a straight swap and for not too much pocket change. You have a Jatco 3N71 transmission which gained an overdrive in 1983 and was used in quite a few vehicles (namely the same-year sister Nissan Pickup).

Good luck!