Posted by Clint Dixon on Monday, September 18, 2023 at 19:52:36 :
In Reply to: Speedo Drive Gear for Transfer Case posted by Glenn in Maine on Monday, September 18, 2023 at 16:07:50 :
Correcting faulty speedometer readings by swapping driving and/or driven gearing internal to the transfer case:
The (speedometer) drive gear in the transfer case is referred to as the "Gear". The (speedometer) driven gear exiting the transfer case is referred to as the "Pinion". There were two available gears used for the Power-Wagon - one with 5 teeth and one with 4 teeth. There were three available pinions used for the Power-Wagon - one with 14 teeth, one with 15 teeth, and one with 16 teeth. The choice of gear and pinion that were factory installed in the transfer case all depended upon the tire size, as well as the differential gearing, that the truck was ordered with.
The normal combination for the (somewhat rare) small 7.50x16 tires would be to have 4.89:1 differential gearing. This would require a 5 tooth gear and a 16 tooth pinion for the speedometer to read correctly. The normal combination for the (more often found) 9.00x16 tires would be to have 5.83:1 differential gearing. This would require a 4 tooth gear and a 14 tooth pinion for the speedometer to read correctly.
Then there were two additional oddball possibilities that are quite rare as most trucks used the tire size and differential gearing mentioned above. The first oddball combination was found on trucks equipped with 7.50x16 tires and the 5.83:1 differential ratio. Why anyone would have ordered this option is beyond me unless they wanted to drive the truck VERY slowly working in a salt mine or something. This combination required a gear with 4 teeth and a pinion with 15 teeth.
The second oddball combination was found on trucks equipped with 9:00x16 tires and the 4.89:1 differential ratio. I doubt one will find a large quantity of trucks equipped this way as originally delivered from the factory. This combination required a gear with 5 teeth and a pinion with 14 teeth. This is the desired combination for those swapping out 5.83:1 gearing in favor of 4.89:1 gearing for higher road speed.
Parts manuals show that that these gears and pinions were used for several years in both transmissions and transfer cases of various vehicles.
I have spoken to individuals who have swapped gearing in their transfer case to correct speedometer inaccuracies with good results. Another, possibly easier way, to correct a speedometer reading, especially if one are not already thinking about rebuilding the transfer case, is to install a speedometer gearing adapter inline between the transfer case and speedometer. One source is at this link:
https://speedometercablesusa.com/gear_box_adapters.html
Junior
From Chris Case: Speedo Drive Gears 5x16 works perfect for Michelin 11.00x16