Speedo Gear Re-Calculation

[ParadiseMJ]

Greetings,

 

I took the MJ to the mountains to get a couple of Christmas trees yesterday for it's first real road trip. Highway, long uphill grades, side roads, dirt roads, steep downhill grades, some distance on no roads. I used mile markers (sometimes reliable) and a GPS (poor signal in Feather River canyon) to calculate my mileage. (side note: the truck ran beeee-you-tee-fully the whole way with out a single clunk, whine or glitch)

 

When I swapped trannys last summer (BA-10 to AW4) I also swapped in a 94 231J. I have the D30/D44 combo with 3.07 gears. I have older BFG T/A/ KO's 31x10.5 R15's all around.

 

I know the exact mileage as I've taken the same trip, summer and winter, several times in the XJ and my sons Ranger. My mileage on the odometer says 151, round trip...but I know it's really 188 round trip. The speedo says ~48 when I'm really going 60. I figured the speedo/odo is off by ~21-22%. Can anyone tell me where to find a speedo gear calculator to correct the numbers here, and exactly which parameters I need to get it right and install the right gear??

 

[HOrnbrod]

With that setup on an 88 (3.07 w. 31") the correct speedo gear is 27 tooth, p/n J3212727, long shaft.

 

http://gojeep.willyshotrod.com/HowtoSpeedoGears.htm

[ParadiseMJ]

Boom!

 

Thank You.

[Eagle]

When you swapped the tranny and transfer case, which speedo gear did you use?

[ParadiseMJ]

At first I used the speedo gear from the OLD t-case, a 231amc. Now I have the gear from the newer 231J. The old one was too small, no contact, didn't register at all.

[Eagle]

At first I used the speedo gear from the OLD t-case, a 231amc. Now I have the gear from the newer 231J. The old one was too small, no contact, didn't register at all.

 

So what transmission and what gear ratio were in the vehicle that t-case came from? And what size tires? The gear you have was (supposedly) correct for that tire size and axle ratio.

[HOrnbrod]

At first I used the speedo gear from the OLD t-case, a 231amc. Now I have the gear from the newer 231J. The old one was too small, no contact, didn't register at all.

 

I guess you know there are three positions stamped on the speedo gear housing; 26-31, 32-38 and 39-41 teeth. The housing must be rotated to the correct position corresponding to the number of teeth on the speedo gear to mesh. Me thinks you might have had it in the wrong position for the small gear you tried?