Part time 4wd


#1

can you guys explain how the part time 4wd works in the 1990 Cherokee?

remember, I m an idiot, so go slow…


#2

When you move the lever to the 2wd position, all the power goes to the rear wheels only. In 4wd, the power goes to all the wheels.

I don’t know exactly how the transfer case in the Jeep works, but in the Tercel i had, in 2wd, all the power went to the differential at the front of the transmission. The transmission had a tailshaft that was not used in the 2wd mode, but when you shifted into 4wd, you basically slid a splined collar over the tailshaft that locked the tailshaft to the driveshaft going to the rear differential.

Your Jeep doesn’t have a front differential built into the transmission so as I understand, the tailshaft of the transmission has a sprocket for a chain. The chain goes around another sprocket that the rear drive shaft is connected to. There is some type of coupling that engages the front driveshaft to the sprocket when you shift into 4wd, probably similar to the splined collar that the Toyota used.


#3

Transfer cases

All the transfer cases used on the Cherokee were chain driven with aluminium housings. Command-Trac was standard on XJ models built with 4WD.

1984–1987: New Process NP207 Command-Trac, part-time only, 2.61:1 ratio with low range
1984–1986: New Process NP228/229 Selec-Trac, full-time/part-time, 2.61:1 ratio with low range

NP228/229 has a vacuum switch for 2wd/4wd selection on the fly and a separate manual lever for low range

1987–2001: New Process NP231 Command-Trac, part-time only, 2.72:1 ratio with low range

NP231 has the following settings: 2HI, 4HI, N, 4LO

1987–2001: New Process NP242 Selec-Trac, full-time/part-time, 2.72:1 ratio with low range

NP242 has the following settings: 2HI, 4 full-time, 4 part-time, N, 4LO

As you can see, the NP-231 and NP-242 transfer cases had slightly different control functions…

For “part time” 4WD, some means of disengaging the front axles (so they free-wheel) must be incorporated…When the Dana 30 axle is used in Dodge pick-ups, they had a somewhat Mickey Mouse vacuum actuated system of disengaging the front axle shafts …


#4

No experience w/the Jeep, but my Ford 4wd truck is part-time-4wd. The transfer case has one input shaft (from the transmission) and two output shafts; one output is the rear driveshaft, the other is the front driveshaft. In 2wd only the rear driveshaft spins, which in turn drives the rear diff, then the rear axel shafts. The front driveshaft just sits there not spinning at all. So the front axel doesn’t spin either, the front wheels just free-wheel on the hub bearings, like a normal rear drive car.

In 4wd mode both the front and rear driveshaft’s turn. The front driveshaft turns the front diff, which turns the two front axel shafts. The disadvantage of this arrangement is the driver has to get out of the truck and twist the front hubs (using a little handle at the center of the wheel) to lock them up so the turning front axel will actually drive the front wheels. Otherwise the front axels would be turning but not accomplishing anything. Plus if the aren’t properly engage to the wheel, they can bind up. So its necessary to lock the hubs anytime you are in 4wd mode.

This manual hub locking procedure doesn’t seem like a major inconvenience, and for the most part it isn’t. But sometimes I’ll be driving the truck in 2wd and it gets stuck in the middle of a big puddle of water and mud. I can’t just walk out there and twist the hubs to lock them, b/c I’d be in up to my knees in water and muck. So I’ve had to sometimes crawl out the door to the hood, up along the top hood, lay down on the hood, and reach down and unlock the hubs that way.


#5

mine must be the np231, I have 2H, 4H, N and 4L.

I can shift into 4H on the fly, but have to stop put the regular gear selector in neutral before shifting into 4L. or so I m told.

I wish people would leave the owners manuals with the car, it should be a stinkin law…


#6

Is it worth $20 to you?

http://www.ebay.com/itm/1990-Jeep-Cherokee-Wagoneer-Owners-Manual-User-Guide-Reference-Operator-Book-/230818281750?pt=Motors_Manuals_Literature&hash=item35bdd77916&vxp=mtr


#7

. I don t do ebay yet. but I probably would pay 20 bucks for one. I wonder if the Chrysler dealer would order me one? I dread to think what a shop repair manual would cost…


#8

eBay is your friend…

This is a CD. But printed books are available too…You can search eBay without being an active buyer or seller…


#9
1984–1987: New Process NP207 Command-Trac, part-time only, 2.61:1 ratio with low range 1984–1986: New Process NP228/229 Selec-Trac, full-time/part-time, 2.61:1 ratio with low range

NP228/229 has a vacuum switch for 2wd/4wd selection on the fly and a separate manual lever for low range

My 84 GMC pickup had the NP207 transfercase also. And it had the Vacuum switch. I’d suspect the Cherokee also had the Vacuum switch.

And a side note…New Process Gear is no longer around. They closed their doors last year. At their peak they were the largest builder of 4wd transfer cases in the world. 51% owned by Chrysler…and 49% owned by GM. When Iacocca took over as CEO to rescue Chrysler…New Process Gear was one of just two plants owned by Chrysler that was making money.