Ulf,
In Low range the driveshaft turns 9.04 times for 1 revolution of the tires. In Hi range the driveshaft turns 6.50 times for one revolution of the tire, so Hi range has the speedometer cable turning SLOWER, so the adaptor speeds it back up by 29%.
I drive all of my 2-speed rears the same. I start with the transmission in 2-low then go to 3-low then 4-low then 4-hi, which makes 4-Hi kind of like having OverDrive. The difference between 4-low and 4-Hi is .71 (6.50 divided by 9.04 = .71 which means your engine will run 29% slower to maintain the same speed you were running in Low range).
You should be able to lock your existing adaptor into Hi range with a piece of tie wire. No need to buy anything, or you could put a choke cable on it and move it manually for whatever range you are driving in.
I hope this helps clear it up...
Mike B
