macaziod

Ok so I have aquired a frankestien XJ,
My problem here is I am going down the freeway at 75mph (my wife beside me in her camry), my speedo is reading 95ish, my RPMs are at 2800 or so ???????
Here is what I know I have.
-2001 XJ
-4.0L
-aw4 tranny
-NP242 T-case
-30 or 31 tooth speed sensor gear
-31*10.50R15
-My Build sheet from the dealer says I have 3.55 gears ??? but I dont know for a fact.

Should I have a different speedo gear put in, or maybe the previous owner put different gears in??? not sure and would appriciate any help.

emptypockets

Not really sure what you're asking. My speedo is also off on my xj. I used my GPS to figure out about how fast I'm actually going and just use some basic math skills when I'm driving. I don't see any need to change anything if you can subtract.

Khyren

You may have 4.10's bets bet is to do the standard gear ratio check by picking up the rear and counting the rotations of the pinion compared to one turn of the tire. or you can pull the diff cover and look for the ratio stamped on the ring gear.

macaziod

Thanks Khyren, I will try that, It just seems odd that the speedo shows I am going a lot faster than I really am. I was thinking about changing the diff oil anyways, cause I am pretty positive that I have Track-Lok, so I was going to add the friction modifier, just in case the last owner didn't do it.

macaziod

Yep did that little spin the tire trick and found my pinion went around about 4 and half times, so I guess I got 4.56 gears, so now I am looking for a 42 tooth speed gear.