binding driveline when in 4x4

[shawn]

so i by this '91 elininator - no front ds - now i have 1 in and it fits and is a good length - when i put it in 4 wheel it feels like the whole driveline is binding up and when it is rolling (even in neutral) it comes to a stop quickly. -t- case hooped ? -been a great truck in 2 wheel drive but this is disappointing. --

[Eagle]

The fact there was no front driveshaft is what we call a "clue."

 

Have you verified that the front and rear axles have the same gear ratio? If not (which is what I suspect will be the case), they will be fighting each other in 4WD.

[shawn]

it had not occurred to me (ever) that they may not b the same ratio. but it does make perfect sense judging by the way it was behaving. -

my bad - really baaaaaaaad. will see what i can do about making lemonaid after the weekend ------ any other thoughts ?

[mvusse]

I'm pretty sure I posted the possibility of different gearing for the axles in a different thread, but can't remember if that was you or someone else.

 

Either way, that would be my first guess as well.

[Eagle]

I can't think of a good reason for a previous owner to have a 4WD truck with no front drive shaft -- unless he swapped one of the axles and wanted to be certain he wouldn't accidently put it into 4WD and break something.

 

If the front axle is original and un-tampered with, there should be a tag with the gear ratio. The rear axle probably will not have a ratio tag, so you'll need to resort to other methods to determine that ratio.

 

Let us know.

[shawn]

eagle - i think u hit the nail on the head - i had heard that the rear axle was rebuilt but it never occurrred to me that it would b with a different ratio. :bowdown: :bowdown: -------nothing in that guys CL ad was true and i was blindsided. (live and learn i guess).

will look for that tag on the front axle in the morning. as it stands now i have a great 2 wheel drive truck - but thats not going to get me to the alpines.

it seemed to be dragging its rear wheels when in 4x4 and even when in nuetral coasting it would come to a fairly sudden stop.

[BLHTAZ]

even when in nuetral coasting it would come to a fairly sudden stop.

That [to me] is a pretty sure sign that the gear ratios are different. If there was a t-case problem, you would notice it in 2wd as well because the drive power goes through all of the primary t-case parts even when in 2wd.

[Geonovast]

You could jack up one side of the vehicle(on level ground, and chock the other wheels), getting one front and one rear wheel off the ground *assuming you don't have a locker*. Turn one wheel, and if see if the other one goes the same speed.

[mvusse]

For that to work, the vacuum disconnect on the front axle needs to be engaged, which will need the engine running for vacuum. Also transfer case in 4wd (high or low) and transmission in N.

[shawn]

thanx guys - 4 the very intelligent help. and i will do just that sometime today so i will know 4 sure what I'm dealing with. what i will do about it I'm not so sure yet.------the mind reels.

[Eagle]

It's a '91 -- does it have a front axle disconnect? The last year for the disconnect in the XJ was 1990, and I always thought the Comanche was the same. So if it has a disconnect, there is a possibility that the front axle isn't original to the truck.

 

Nonetheless, you could put all four wheels up on jackstands so no tires are touching the ground. Start engine, shift transfer case into 4WD and the front disconnect will engage. Turn off engine and the disconnect should remain connected. There's no spring in there -- it'll stay connected until the vacuum sitch sees you're back in 2WD and pulls the shift fork the other way.

[Pete M]

Yup, almost all MJs had the vac disco. To my knowledge, only the 86 models with the all-wheel-drive option had the non-disco.

Apparently the vac disco survived into '93 on Cherokees. '93 is the last year in car-part.com that give the choice of vac and non-vac. '94 the choice disappears and I assume the vac disco was gone for good. But, if you search the nation's junkyards for a vac axle, the vast majority of the results that turn up are '90 and '91. '92-93 become increasingly rare so I imagine that Jeep was in the process of dropping it.

[Geonovast]

Yup, almost all MJs had the vac disco. To my knowledge, only the 86 models with the all-wheel-drive option had the non-disco.

Apparently the vac disco survived into '93 on Cherokees. '93 is the last year in car-part.com that give the choice of vac and non-vac. '94 the choice disappears and I assume the vac disco was gone for good. But, if you search the nations junkyards for a vac axle, the vast majority of the results that turn up are '90 and '91. '92-93 become increasingly rare so I imagine that Jeep was in the process of dropping it.

 

My dad's got a n 91 XJ with the vac disco, at first I thought the axle had been replaced, but the entire system is there and it could very well be factory.