Hey guys I'm new to the forum and actually just bought the truck last week. Had a bad front differential and so we replaced it with one from the junkyard said to be good. Everything was packed in greased on the front differential. We put it all together and I drove the truck after also replacing the rear driver brake line. In 2 wheel drive the truck operates flawlessly. Shift correctly doesn't f*** and everything moves smoothly. When I put the truck in 4 H or 4 L it will go about 15 to 20 feet and slow down to a stop. If I hit the gas it will move a little but something is keeping it from driving. Again its fine into will only in 4 wheel it happens both in forward and reverse. No strange noises are heard. Any suggestions? Thank you

 

Welcome to the forums Joe.

What year, engine, and transmission are we talking here? Do you have full time 4wd or part time?

The front drivetrain always rotates when the truck is moving, the hubs don't disconnect. Just the transfer case is engaged or not.

 

thank you for the quick reply. Its a 1999 Dodge Dakota v6 automatic. When I put it in neutral and engage 4 H or 4l it does say part time. yeah I'm wondering if it is something with the transfer case or something with the new differential that we put in. It's an issue I've never seen or ran into before.

 

New differential?

Did the gear ratio match what's in the rear???

 

- that I do not know. I bought the truck used and the guy threw in the port for me. He had bought it for himself to install but did not have time to install it. Is there an easy way like a serial number I can check on the bottom? Or is it something that I would have to have taking apart to find out.the only weird thing is that again I can move 15 or 20 feet which would be multiple revolutions inside the differential. I was think it would bind up a lot shorter than that.

 

on a 31" tire, 15 feet is 1.85 turns and 20 feet is 2.47 turns.

The difference between a 3.55 and 3.92 gear is 6.56:7.25 rotations for 15 feet, and 8.76:9.68 rotations for 20 feet.

Both are less than 1 rotation apart, and given system slop, I'd say you have a mismatch.

 

There might be a tag on the differentials.

Jack the truck, all 4 wheels, put it in gear. See if it binds.

There isn't that much difference for it to lock up immediately. There is some play in the system to begin with and tires can slip a bit, fortunately, or you'd probably blow up your t-case.

I can't really think of anything else that would do this to tell you the truth.

Add up all the play in the transfer case, the differentials, the u-joints, and front CV joints like Magnet says.

That's it. You have mismatched gears.

 

Im betting its a different gear ratio. You said the front diff was bad when you bought it. What exactly happened to it.

 

Another one for mismatched gear ratios.

You can find the ratio your truck came with from the glovebox sticker, buildsheet, and there should be a tag on one of the bottom bolts of your dif.

Also check to see if the tag is on the dif you swapped in.

You could be running 3.55 gears with 3.92 or similar.

 

So I checked the codes at the bottom and in the glovebox, called the dealer up and got re assurance the ratios are in fact the same. What it appears to be is the truck was sold me me with different front and rear size tires. From me having fwd all my life I didn't realize the impact. Stupid mistake.

Now 4h and 4l engage properly, but the truck pulls to the left. It almost drives at a / angle, can anyone think of
A reason? It does make considerable noise while in high for the short distance I went.