I posted this in the Sport Trac forum but haven't gotten a response yet. I just bought a 2004 Sport Trac 4x4 Auto. I put it into 4x4 on a gravel road just to give it a little workout. I drove for a couple hundred feet and then stopped. It was definitely in 4x4 with the amount of traction I got taking off. As I was driving along about 35mph, I hear a whine building up and then a loud clunk you could hear and feel in the drivetrain. Then it would start to build up a whine and then another clunk same as before. It sounded like something was binding up and then popping loose. I went to some pavement so that I could hear better without the gravel crunching under the tires. I know my 4x4 system is not made to be run on dry pavement but I figured just going straight for a few minutes to hear better wouldn't hurt anything. I put it into 4x4 and went perfectly straight, never moved the steering wheel, and the same thing happened except much worse. I thought the whole drivetrain was going to fall out. When it's not in 4x4, there is no whine or clunks. The vehicle drives great and gets good gas mileage. This is the first time I've had it in 4x4 more that just the few seconds when I bought it. Please help diagnose my weird clunks. Any help or ideas would be much appreciated.

 

I am no 4x4 expert, But It sounds to me like two different gear ratio's front and rear.

First thing I would do is lift it and do a manual ratio check by marking the driveline(s) and rotating the wheel 1 revolution, and counting the drive line revolutions. Both front and rear to ensure they are the same.

-Enjoy
fh : )_~

 

That thought popped into my head but I discounted it thinking that no one would be stupid enough to change gears in one without doing both....I'll have to check that. Thanks. Any other suggestions?

 

It's nice to know you have that much faith in the human race, I wish I did, Unfortunately there are some pretty slimy people out there and it's been done before!

That's all I can think of, I'm sure others will respond when they come online.

If you figure it out, please let us know, I'd really be interested in hearing the results.

-Enjoy
fh : )_~

 

Good suggestion. Also make sure all tires are the same.

 

All the tires on the Sport Trac are the same size 255/70 16. The front two are new and a different brand than the rear. The rear tires are pretty worn and not much life left as far as the tread depth goes. Does this sound ok or will it cause a problem?

 

Measure the height of the tires. That can be a reason, though it sounds to extreme to be just wear difference.

How long (feet) does it take before it makes the gawd awful clunk.

Remember finding the cause is step one, finding whatever is letting go (clunk) will be step two.

If there is a ratio difference (be it gears or tires) something is winding up and then letting go... That could be splines or TC chain if so equipped. Regardless, it's damage that needs to be located as well.

-Enjoy
fh : )_~

 

Well, the one time I did it on pavement it made two clunks in about 75 feet. I put it in 4wd HI and then started going really slow straight ahead. The first 30 or 40 feet everything was fine and then clunk. After a few more feet, I kept rolling forward but put it in 2wd. And then after about 75 feet came the really big clunk. Maybe that one was worse cause I was going really slow and almost stopped. I have not put it in 4wd since that happened.

 

The distance leads me to believe gear ratio ... To many drive line revolutions to be just a transfer case.

But I know NOTHING of the sport trac, (don't even know what it means )it could be something else.

-Enjoy
fh : )_~

 

Here's the latest that I've found out. I asked this question to a Senior Master Technician with 30 years exp and he seems pretty certain that it's the difference in circumference between my front and rear tires that is causing this. He says that a gear ratio difference would cause continuous binding and clunking and not intermittant like mine. I don't really want to buy two new tires but it sounds like maybe I'm gonna have to unless someone else can offer any other suggestions. I'm still gonna check the gear ratios when I get home.

 

Both are a ratio difference.

One way to find out, Measure the tires.

But like I said, I am no 4x4 expert, 4x4's have never been my thing! Just a personal pref.

I do hope thats all it is!

-Enjoy
fh : )_~

 

different size tires will cause thisproblem. speaking from experience.

 

Well, all four tires are the same size, but the front ones are brand new and a different brand than the worn rear ones. I guess I'm getting two new tires for the rear.

 

Two new rear tires fixed my problem.....Thanks for the responses.