Programbo

Hello. I hope everyone is well today. I'll try to keep this brief but want to explain my question as detailed as I can. I am looking at a 1995 Grand Cherokee Laredo to buy and it is in very nice clean (Garage kept) condition with low miles. I went to look at it briefly last weekend and just took it on a quick spin around the block. Apparently this particular model or type Laredo only has 4HI, N and 4LO as choices for the transfer case. No 2WD option.

It was in 4HI when I drove it and I wanted to make sure the 4LO worked but when I was parked in P and tried shifting the transfer case through N to the 4LO setting it started making a terrible grinding. Neither I nor the current owner knows anything about Grand Cherokees (I have only owned older XJs) and we did not know you can't or shouldn't shift the transfer case with the engine running and in Park. Since I have owned XJs for 25 years and they allow you to shift freely between the settings with the engine running and in P it never occurred to me a '95 ZJ wouldn't do the same. It only was grinding maybe 3-4 seconds or so before I put it back in 4HI. Afterwards it seemed to drive fine.

My question is: Could this have caused any serious damage to the transfer case or transmission? I have very bad anxiety disorders and OCD so I have been worried since then I could have damaged a very nice ZJ. Someone told me the gears in those '95's are very study with large teeth and made of hardened steel so 3-4 seconds of grinding shifting settings most likely didn't do anything. (They actually said the odds were "slim to none") I plan to go back this weekend and buy it after a longer road test if all seems fine but would appreciate any encouraging (Or not) input from knowledgeable ZJ guys.

Thanks in advance!

dave1123

That would be the NP249 transfer case and it's only constant 4wd. With the transmission in park, there should be nothing spinning to make it grind, however if the linkage is rusted and not used a lot, it may not have been fully engaged in low range when you tried to take off or the jeep was rolling when you shifted it. The transfer case is all straight cut gears with no synchronizers so if the gears were not fully engaged they can grind.


Shifting to low range should be the same as the XJ's NP231 you're familiar with but people who own ZJs may not have every used low range, especially ones that are rarely driven. I'd say a low mileage 95 fits that category.

wingless

+1

The transfer case has this zee linkage. Over time the grommets used to retain the arms while permitting rotation deteriorate.

A $10 kit permits swapping all the old grommets to new for proper operation.





Note that transfer case requires all four tires to have identical outside circumference, same brand / wear / pressure. When mismatched the transfer case viscous coupler will fail, requiring a rebuilt replacement to restore normal operation. A failed viscous coupler will case dry pavement tire chirping when doing tight figure eight turns.

97grand4.0

[QUOTE=dave1123;3474158]That would be the NP249 transfer case and it's only constant 4wd.

The OP is saying there is No 2wd option...If he just put the transfer case in N wouldn't that be 2wd?

wingless

This video shows normal NP249 shifting.

Programbo

[QUOTE=97grand4.0;3474196]N on this one seems to make nothing working. There was a digital display on the dash which showed what wheels were engaged and in "N" none were lit. I guess since it's full-time 4x4 that setting (N) would be for towing or pushing or something? It only has a high or low 4x4 and Neutral settings.

dave1123

Because the gears for high and low are different diameter, they have to pass thru a neutral in order to mesh since they're turning at different speeds. This is true with your t/case in the XJ also. It's also convenient for towing, but that's not it's designed purpose.

As wingless stated, the bushings on the linkage are probably gone. This allows the linkage torque shaft to move around way too much.

Because both axles are constantly driving, any difference in driveshaft speed between the front and rear, like in turning, must be compensated for by slippage in the viscous coupling. Even tires of different diameter, even just tire wear, will cause a difference in driveshaft speeds. The fluid in the viscous clutch heats up when it slips and eventually will stop functioning. This is why the 249 is not popular and is expensive to repair. It's a good case if taken care of.

Programbo

Thanks for all the feedback on this particular transfer setup. It's definitely different than what I am use to on my old XJs. So in general based on your guys knowledge does anyone think I caused any damage with the 3-4 seconds of grind the other day? It seemed to drive fine after that. I'm going to give it one last test drive and buy it tonight if all seems well. It is in great shape and spotlessly clean.