Truck unsafe when put in 4X4
 

Tried to search for any previous thread without success. So I'll try and describe problem and what we know.

It's a 2006 F250 FX4 V10 Supercab. I recently bought it so I don't know much on the history. It has 64k miles on it.

When you engage the 4x4 switch on the dash and the tires get good traction front and rear the truck bucks and shakes. It act almost like the front and read diffs are out of sync or different gear ratios. (That could be) We have put it up on a rack and everything spin freely in the front drive line. Planetary gears work as they should, hubs lock as they should. All drive line u-joints turn freely.

First thought it someone blew out a front diff, got the wrong one at a salvage yard put it in and then sold the truck. Truck came through a small dealership from auction. With the very low miles and how things look underneath I would not suspect this, but it's possible.

Second thought, which I know less about, is could this be in the transfer case going to the front end?

Under power the truck bucks and wants to pull hard to the right. When you let off power it is just as bad and wants to dive left. In 4x4 it is unsafe to drive.

Hope for some experts on her to help me figure out what needs replaced.

Thanks
Eric

If you had it on the rack what were the gear ratios? Mark the tires and driveshaft with chalk and count the rotations. It's very possible the rear axle was swapped.

Are you using 4x4 on dry pavement? The 4 wheel drive system is not designed for use on dry pavement it will bind up. The tires need to have some slippage such as what use on snow, ice or sand will give you.

Paul

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This sounds like a gear swap gone wrong, or at least halfway done i.e. rear axle swapped for lower gearing and front never changed.

Thanks for the input. I hadn't considered that the rear axle only could have been swapped, as I was focused on the front. My mechanic put it on the rack to quickly check the front end u-joints etc at no charge, but I have access to the rack this weekend and I can take more time to check both axle ratios.

I do understand it is not a system for dry pavement, but even in snow and wet roads it bucks and pulls. I have had other 4x4 Fords and this one has something screwed up. My usual mechanic is very good, but he had never been inside one of these transfer cases, so he was unsure if there was anything in it that could cause this type of problem. Seems the general concensus is I have a problem with ratios in either the front or rear axle. i do have the original window sticker, so I can look and see what was originally installed.

I'm thinking someone might have changed the rear for some reason and I don't think the truck was used in 4x4 much so they may not have even considered what they were causing.

I'll investigate the axle ratios next

Thanks and any other thoughts are appreciated. I haven't had this truck long, but I do really like it and it's solid. So worth the effort to straighten it out and drive if for 15 years

I'm not trying to start an argument. Find another mechanic if he/she can't figure out what's wrong with your truck. My truck was dripping coolant. I couldn't figure out if it was a hose, the manifold, etc. When I took my truck in to my former mechanic and he couldn't tell me where or why my truck was dripping coolant. "We tighten some stuff up. No charge". You just lost me as a customer. I went to my new mechanic. I had a cracked intake manifold. You go to a mechanic or shop to get your vehicle repaired.

Definitely sounds like someone swapped the rear gears or axle and now the ratios don't match front to back.

I can put mine in 4H on the interstate and it drives perfectly. Yes, it will bind in turns on pavement but should not going in a straight line.

Could be a jumping transfer case if it's worn. I had similar symptoms in my old dodge when the chain stretched, in 4wd it would hop and pop as the chain slipped and grabbed. Start with spinning the tires and counting driveshaft rotations to see if it's the same front and rear to rule out gearing differences.

I dont feel that this truck has enough miles for Chain stretch in the T case.
I'm pretty sure someone swapped the rear axle to get better towing performance and didn't bother or didn't know to change the front axle to the same ratio.

I dont think it is mismatched front and rear differentials.
I do think something is in need of service like the front axle u-joints in a bind.

the outcome sbould be interesting
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subscribing... interested to see how this plays out... im with the others that it sounds like a gear mis-match between the front and rear...

the one thing i didnt see in the OP posts was if the truck was SOTF or Manual T-case... if its the manual theyve been used on numerous vehicles (across different brands) over the years with a very good track record for durability.. Ive heard complaints about issues with the SOTF versions but only about mentions with the solenoids.. never really specifics..

To answer the above. Tires are all brand new, less than 1000 miles, all matched and the size stated on the data plate on the truck.

All u-joints seem to be fine and turn freely. I am not using the 4x4 mode, with the exception of on really icy spots where I could not get going (we live in snow country in NW PA) When I do use it to get moving I immediately turn it off and it is rarely used which is why I did not find the problem until now.

The truck is at the local 4x4 experts in town this morning to see if they can figure it out. This was suggested by my usual mechanic. It is the electronic shift package, not the manual lever. They mentioned they have seen a solenoid fail or not fully engage causing problems but did not rule out the ratios on the axles as a possibility either.

Thanks for everyone input and thoughts. I will keep you up to date so we all can learn from my challenge!