Speedometer Calibration

I swapped 4.88's into my Jeep to replace the 3.73's. Now I have to calibrate my speedometer. I know I need a speedometer cable gear with more teeth to slow the speedometer down, but how many more teeth??? Is there some simple calculation to figure this out? Who carries the parts to do this? Thanks in advance

EDIT: This is for a Dana 18

 

Anyone?

 

If your speedo was right with the old gears. Then you could do a little math. If you cold get the speedo gears. I did it once. but I couldn't tell you how. I would take it to a speedometer shop. They may have to put a gear reduction on it.

 

Here is some general info, without knowing more about what gear numbers you presently have.
There are 2 different possible drive gears (inside the transfer case) that drive the driven gear at the cable end.
Because of tooth counts, you cannot mix the 2 series or damage will occur.
Generally speaking, when a CJ5 V6 had 3:73s swapped for 4:88s, you removed the 16 tooth driven gear (3:73) and replaced it with a 22 tooth driven gear 4:88
Unfortunately, the gears are getting very hard to find, are no longer availble new, so used is the only option, in light of an NOS ebay find.
This will only get you close, as tire diameter plays into this mess as well.
You simply don't have the option of trying one gear, one tooth at a time, as gears were not made for this application in that range (16, 17, 18, 19, etc).
If your removed 3:73 is 16 tooth SW #448856, then you should be able to run a 22 tooth SW # 448495 without having to change the inner drive gear.
If you can furnish your currrent numbers, as well as the numbers of the gears you want to run, I can tell you whether they will match together or not.
There should be some previous member discussion on this topic as well.

 

Thanks much, that helps a lot. I guess I'll just have to go take it apart (which would have happened anyway) and see what I've got