Gear Ratio and Speedo settings

[UpNorth_10]

Hi All,

I am changing my gear ratio on my FL70 from 3.90 to 4.33 over the holiday's. I talked to the freightliner dealer and they said that there are some dip switches on the speedometer head that can be changed to make the speedo read correctly with the new gears. I have a direct final drive in the tranny and am running 11r-22.5 tires. Does anyone know what the correct speedo-head settings are??

any help is much appreciated.

Thanks

Up North

 

[NEVERHOME247]

You are correct. There are dip switches on the back of the speedo head. You will need to get the dip switch settings from the dealer. There is a chart in the factory service manual. It has a formula that takes the ratio,tire manufacturer and tire size,etc. This formula gives you the new PPM (pulses per mile) You then cross the PPM to the chart which will give you the correct dip switch settings. If you are doing the work yourself. If you talk to them, they should be able to make you a copy of the chart. If they are doing the work, they should recalibrate your speedo head. Hope this helps.