I have a 98 Exped 4X4 with a 5.4 and the code on the door is H6, 3:73 LS. One of the reasons I bought this unit. Something just wasnt right though. When driving home from Thanksgiving I had my wife write down the odo#s at the mile markers. When we got to the tenth mile, my odo said 8.9 miles. The previous owner didnt say anything about changing gears or rear ends and he seemed like an honorable man with nothing to gain by lying. He was very well off.
Does anyone else have this problem? I have the standard size tires. Im wondering if I had a set of 3:55's in the back. I need to know before I put it in AWD.

 

well i have 3.55s and my speedo reads right on so i dont think that is your problem

but seriously tho, i would NOT try putting it in 4wd until you get this figured out b.c if you do have two different gears (front and rear), you will tear your transfer case up very fast.

Other thing to consider is that mile markers arent exact, but i think you already realized it, thats why you went on a 10 mile scale.
-Patrick

 

Jack up the rear axle.

Place a mark on the driveshaft.

Rotate the rear tire and count the driveshaft rotations per complete revolution (or was it the other way ....). Anyway, it's easy to figure the gear ration just by observing the relationship between the input and output rotations.

BTW, does the 98 have a PSOM (don't have the service docs with me)? If so, you just have to enter in the correction factor to correct odometer and speedometer.

Steve

 

We're having record breaking rain here so Im waiting for some time to work on the Xped. We've had 12" of rain this month or something insane like that, and its raining right now.
What is a PSOM? Your help is appreciated.

 

Also, I checked the rear axle cover bolts for a build tag and there wasnt one. Ford still puts those tags on dont they? I'm left assuming that if the tag has been taken off someone messed with the rear end. I would guess that if the diff was surviced by the dealer they would put the tag back on when they were done changing the fluid.
Does anyone have any experience with synthetic gear oil? Does it really help?

 

There should have been two tags on the rear axle. One gave the build data including the ratio, the other said to use only synthetic lube...

PSOM= Programmable Speedometer/Odometer Module.

Steve