Bergie91

Hello, I am new to the forum and need some advise if possible? I have a 91 XJ with the NP231transfer case. The issue we are having is when we put it into 4wheel drive and head down the road, it starts jerking as if it is engaging and disengaging. Light on dash flashes as well. I tried searching other forums / threads but didn't come up with anything other than maybe vacuum issue? Thank you in advance.

4.3L XJ

Do you have a vacuum disconnect on the front axle?

Bergie91

I don't have the vehicle with me right now...Son is using it 100+ miles away. Just trying to gather some information on what to look for.

cruiser54

Are you shifting it according to the instructions on the sunvisor? While moving as it was designed?

TrailerTrash

Are you driving it on dry pavement in part time?

Bergie91

Yes, we have tried it a couple different ways. Stopped / and rolling.

Bergie91

No, snow packed roads and it only has full time 4x4...2H,4H,N,4L

cruiser54

That's PartTime

Very Red XJ

You should be dead stopped, place the shifter in Neutral, move the transfer case lever from 4WD to 4WD LOW, then place the shifter in drive or reverse as needed. If it grinds when you move the transfer case lever, leave it in 4 high and move the shifter to reverse then back to neutral and try the lever again. If you have traditional 4WD, do not engage 4WD and drive it on the pavement. Cleaning the linkage and spraying silicone lube on the joints in good Maintenace that will ease the operation of your transfer case

cruiser54

absolutely WRONG!!^^
The system was designed to "Shift on The Fly"

Here's how the factory suggests you shift the transfer case and I've been doing this since these things were new and I worked at the dealership. Quoted from the owner's manual. The suggestions in CAPS are mine.

"To engage, shift the transfer case lever from 2H to 4H while the vehicle is moving at any legal speed". I LET OFF THE GAS, THROW THE LEVER, TAP THE GAS AND LET OFF.

4L position: " To engage, slow the vehicle to 2-3 MPH , shift the transmission to Neutral, then shift the transfer lever to the right and pull firmly rearward to 4L".

TO SHIFT OUT OF 4L, SHIFT THE TRANSMISSION INTO NEUTRAL WITH THE VEHICLE STOPPED, SHIFT THE TRANSFER CASE LEVER TO 2H, THEN THE TRANS TO D IF YOU HAVE AN AUTOMATIC, OR INTO FIRST GEAR WITH A MANUAL, AND CONTINUE ON.

Revised 11/20/2014

cruiser54

We need to confirm whether this 91 has CAD axle FIRST, before throwing a bunch of bull**** out there. 91 could go either way and a malfunctioning CAD

4.3L XJ

I agree, which is why I asked he question

Very Red XJ

My bad - I need to drink a cup of coffee before I reply, My comment only applies to shifting from shifting from 4 high to 4 low on a 20 year + old jeep that dosent go into 4 low any other way . However, cleaning and lubing the linkage is good Maintenace that may help him

cruiser54

I've been guilty of the same.

Here's some photos that might help the OP.