I have a 1996 Ranger Supercab, 4x4 4.0L 5speed manual with 200,000 miles. It has developed some sort of drivetrain problem, at about 65mph the drivetrain slips/clunks in 2wd or 4wd, it is a rather violent clunk and will happen repeatedly if I continue to drive over 65mph. It is not the slip yoke (just greased it) or the carrier bearing (replaced it) on the read driveshaft. It was having the problem both before and after these repairs. It is not specific to the front or rear, I drove it with only the front drive shaft in place for a day and it had what seemed to be the same problem. While it did not clunk, if felt like it went out of gear for a moment at 65mph. With only the front driveshaft in place the engine RPM’s and speedometer shot up, but there was not power going to the wheels. I let off the gas and felt everything hook-up again. It did this repeatedly if I tried to drive above 65 mph. Under 65 mph there were no problems.

These symptoms occur in 4th or 5th gear at the same ground speed, I do not want to try to go that fast in 3rd, the truck does have 200,000 miles on it. I do not think it is the clutch slipping, because the speedometer shoots up when the problem happened with only the front drive shaft in place. If it was the rear differential, then the problem would not occur when I was using only the front, unless I have two different issues. It is not specific to a single gear, but occurs at the same ground speed in 4th or 5th.

Anyone have any ideas what the problem could be?

 

I'd have to think it's the transfer case. You seem confident in the tranny and it doesn't sound like a differential problem based on what you desribe. Along with that, keeping in mind the things you have already ruled out, it would seem to leave the TC as the prime suspect.

 

I'd agree with the transfer case as well. Some models of Fords had the speedo connected to the TC. In either case if it slips out, then that might be why the speed increases but none gets to the wheels. And since the transfer case supplies power to either axle either in 2 or 4X4 I'd guess that's as good a place to start as any.

 

Thanks for the fast replys. Any ideas about what could be going wrong in the transfer case or how I can go about testing it? I normally do the work on my vehicles myself, and have had good success. This problem just has me a bit stumped.

Thanks again.

 

I think I'd start by checking the oil. Looking for metal shavings. This would point to excessive wear on the parts inside. You could look for excessive "play" in the front drive shaft with it in 2WD and front hubs unlocked. Not sure what to look for other than that inside the truck.
The only TC I've seen that has went bad was because of a bad seal, and after it dumped all the oil it ate the gears inside. By the time I saw it, you knew it was bad. It was grinding even at 5 mph and the drive shafts were wiggling all over.

 

I was under the truck this weekend, and did not notice any excessive play. I will check the fluid tonight, and check the play on the front driveshaft. I am still trying to picture what could cause the symptoms I am experiencing, but the more I think about it, the TC makes sense. Fortunately I have an extra one, but it is still on the parts truck.