re programming ECM after a axle gear ratio change

[mpaulson]

I changed my 07.5 from the 3.73 to 4.56 and did nothing other than the gear swap. No programming at all. Never noticed any issues back then. This was with the 6.7 and the 68 RFE. Loved it for towing back then. Speed is/was picked up off the sensor that counted the ring revolutions on the rear diff, not affected by a gear ratio change.

 

[EDankievitch]

I’ve up sized to a set of 295-70 -18 tires. My speedometer was off a full 4.5 mph. I bought a programmer off Amazon from procomp that allows me to set the speedometer for any tire size. Also allows me to change rear end ratio. It made a huge difference in my shift points and Mpg’s all for the better.

 

[Larry E]

2013 RAM 2500 4x4 TD. I just swapped out of the 3.42 for the 4.10 to tow a new toy hauler. Main purpose was to 'save' the transmission and have better overall towing with the new load. Problem I have is the transmission has an issue with shifting from 5th to 6th. At times it will shift rapidly back and forth and pop the CEL. I lock it in 5th and cruise at 62 mph and don't worry about minor rolling hills and I actually get better gas mileage at the higher RPM but light pedal compensates.
But I wondered if a reprogram is/was necessary.

Larry

 

[cerberusiam]

Maybe not absolutely necessary, but, really should be done for optimal trans performance sans a trans tune. Pretty sure the 68RFE uses the output shaft speed sensor like the 48RE for shift points. A gear change will impact the shift profile, using a 3.42 profile on 4.10's is bound to change the way things work. Should be able to set the gear ratio in the BCM then let it relearn, if that doesn't help then probably time for a trans tune and a few parts, that will help "save" the trans as much as the gear change.

 

[Ozymandias]

Jep, program the new axle ratio into the ECM will definitely help, that program point is there for a reason even if people denying it.