Thread: Confusing ratio results after TF change

Did you swap the speedo drive gears? Sounds like no.

Different cases can have different drive gears fitted, they can be swapped out reasonably easily.
But the speedo drive is on the output. Internal gearing won't affect speed measurement. Only your rpm.

Originally Posted by lux201

Hi All,

I have a D1 300tdi with an R380, standard 3.54 diffs and 33s. I put in a 22D (1.410) LT230 as I was hoping it would pretty much correct ratios so suit tyre change as the 1.211 was out by about 8-9%.

With the 1.211 my 100kph (on the dash) was actually about 108kph at the wheels.

Now though, my ratios are way out *the other way

With the 1.410 my 110kph (on the dash) is approximately 103kph at the wheels and if I travel at 110kph at the wheels im sitting on about 3000rpm.

I am wondering if someone could have put 1.667 gears into a 22D case?

calculated here: - Ashcroft Transmissions - Ratio Calculator

The speedo drive gears are in the rear output housing of the transfer case. Changing the ratio in the transfer case, as with changing the gear selected in the gearbox, doesn't affect the speedo reading, because the speedo reference is the speed of the tail shaft.

However Stock Disco tyres are about 29" diameter, while stock Defer tyres are about 31" or 32" diameter. So the speedo drive gear for a disco has a different tooth count (ratio) to that used in a defender transfer case. The tooth count is to suit the tyre diameter, not the transfer Hi/Lo ratio.

The speedo gears are easy to change, the transfer case doesn't need to be opened.

Ok cool. I will swap the speedo drive and hopefully this will sort out the accuracy of my speedo. (so long as i'm running 1.4 gears)

I guess my main concern has come from the ratio calculator. according to the calculator I should be around the 2650rpm at 110kph but instead im at 3000rpm at 110kph which more closely matches the calculated result of running a 1.667 ratio transfer case.

Is it possible for the gears from a 1.667 LT230 to fit into the casing of a 1.410 transfer?

That sounds about right for 1.410.. My old 130 was doing about 3000rpm at 110kph, and was flat out with no more to go down hill and a tail wind at 125/130kph.. That was also on 285's. if you had a 1.667:1 ratio in there, I doubt if you'd have found 100kph.... Cheers.