4 wheel drive problems

[19bigt51]

I have a 1989 dodge W250, 4wheel drive automatic, This truck is just used for dump runs and snow plowing, Problem surfaced during last snow storm of the year last winter. In four wheel drive it jumps violently when moving or even trying to start off. When i shift it into two wheel drive it drives fine. The front drive shaft and drive knuckles on each wheel are in good shape. as wll as universal joints.

1. is there a chain drive inside the transfer case and could this be my problem?

2. if so how much of a job is it to change this?

3. What else should i look for.

I have had no prior experience with four wheel drives so i am pretty green in this area.

Any help is very much appreciated

[CanukGMC]

Is there a difference in the jumping in 4hi or 4lo?

[19bigt51]

4 low i assume because of the lower gearing makes the jumping/bucking much more pronounced than 4 high.

it does go into either low or high easily but as soon as i give it the gas to move it starts jumping/bucking.

The engine runs great and as i said in two wheel drive it has no problems

[wafrederick]

Check the fluid level in the transfer case also and it uses Automatic transmission fluid if you want to know.

[CanukGMC]

Check tcase fluid for burn as mentioned and open up the front diff and see how everything looks in there. It probably needs the gear oil changed anyways, open it, look for metal debris, inspect the ring and pinion for broken teeth (causes irratic driveline behaviour) and turn it a few times to feel for grinding or anything odd.

[19bigt51]

Good, i will start with the differential and see what we can see. This will probably take me a few days because of commitments so please check back i will post what i find. What goes on in the transfer case? is it easy to open up without removing the whole unit from the truck, looks like ten bolts around it to split the case and remove the drive shaft. Thanks, i did not realize that it took ATF as well.

[CanukGMC]

Originally Posted by 19bigt51

Good, i will start with the differential and see what we can see. This will probably take me a few days because of commitments so please check back i will post what i find. What goes on in the transfer case? is it easy to open up without removing the whole unit from the truck, looks like ten bolts around it to split the case and remove the drive shaft. Thanks, i did not realize that it took ATF as well.

It's a pain in the butt to work on normally, honestly (beacause of the guts involved and the awkwardness of working under there) it's easier to remove it to split the case, it's more complex than a diff and might as well get done properly. If the tcase is anything like my old np231 it has an aluminum drivechain that connects the right side (rear axle output shaft) to the left side (front output shaft to the front diff). I've heard of those chains stretching and being at the point of causing issues but I'd work back from the easiest point first which is the differential. The age of the truck if it was the transfer case it'd be easiest to just pull it, buy a junkyard case (with a 30 days warranty) and swap it. Rebuild kits cost more (and need special tools and alot of labour) than a junker xfer case.

Also if you can get at it try dropping the front diveshaft and seeing how stiff the ujoints are to flex, I had some go on my old ford that didn't have play but were nearly seized (couldn't even budge em buy hand) solid. If the truck has enough age maybe the mounts under the tranny\tcase have rotted out and the ujoint on the front of the tcase is seized and when it forces it to turn and flex it fights it and causes a bucking action. Just throwin ideas out for ya, good luck with the diff check and let us know, I'll wait for your response.

[clutch492]

Pull the drain plg on the transfer case. It usually has a magnet on it and will have metal on it. If the chain is bad, it will have large chunks of metal on it. Also, use a magnet and insert it into the case. If the chain is as bad as I think it is, there will be a lot of metal.

It is not real difficult to change the chain while it is in the truck. Remove the back of the case and (while removing the main shaft) remove the chain from the front output sprocket. assembly is not hard either, except to make sure that you seal it with the proper type of sealer. Silicone is not correct. Use the "3M gasket eliminator". A thin layer is all that it needed.

You do have a bad chain.