Question: tire/gear ratio?

Mogman

Member
May 3, 2020
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Papalote, TX
I am sorry if this has been asked before but I could not find it..
I am thinking of transplanting the original LMM dash cluster in my HMMWV conversion and would like to know if the speedo correction can be made.

The HMMWV (M998) has a gear ratio of 4.915:1 and a 37" tire, can this be programmed?
 

JoshH

Daggum farm truck
Staff member
Vendor/Sponsor
Feb 14, 2007
12,927
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Texas!!!
Yes, the speedometer calibration is located in the ECM speedo section. You correct it by changing axle gear ratio and tire revolutions per mile. You can also change pulses per revolution of the speed sensor if it isn't the same as the stock Duramax reluctor, but if you're doing a complete powertrain swap, you won't need to alter that parameter.
 

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