Gear Change

[quickv6]

I am going to change the gears in my truck to 3.42s. I now have 4.10s. How do I correct the speedo calibration and ECU. Can this be done with the chip so lock-up is not affected? 1994 2500.

[JohnC]

TCC lockup is based on transmission output shaft speed. Changing the final drive ratio will change the lockup speed.

The speedometer can be corrected by modifying the VSSB. The anti-lock speeds will still be off.

[quickv6]

Can the chip be reprogrammed for the gear change? If I put a recalibration box on the output shaft signal then that would correct the signal to the ECU and speedo both correct?

[JohnC]

Depends on what you mean by "correct". Lockup speed is based on engine torque, not road speed. If you fool the output speed sensor, you fool the PCM as well, but I'm thinking the ECM's calculated ratios will be off so it may complain (and lock you into second gear...)

Someon else went down this road a few years back. If you search, you may be able to find the thread. My recollection is after it was all said and done he was not happy with the result.

Try these threads:
http://www.thedieselpageforums.com/tdpforum/showthread.php?t=23139
http://www.thedieselpageforums.com/tdpforum/showthread.php?t=29298

[Warren96]

You may lose the ability to do HEAVY towing. Mine has 342's, but it never tows. Its used around town light duty, and as a people mover on the highway. Its highway RPM is 1800,the sweet spot for best mileage. Your gearing should be selected for what you use it most. Not many people like to tow a LARGE load at 65mph.

[quickv6]

You may lose the ability to do HEAVY towing. Mine has 342's, but it never tows. Its used around town light duty, and as a people mover on the highway. Its highway RPM is 1800,the sweet spot for best mileage. Your gearing should be selected for what you use it most. Not many people like to tow a LARGE load at 65mph.


I drove a 93 with 3.42s and the towing power with that gear was unreal. The 93 was a low mileage stocker and would pull at 65-70 no problem. My Truck will pull great at 50-55mph with the 4.10s keep in mind I have 498,000 miles on the clock now. I am looking to get that up to 70-75 with the new engine thats is intercooled with HX35W turbo.

I guess the bottom line is there is no real way to fix the issue. I really hate to put a shift computer on the truck when it should not be needed.

[quickv6]

TCC lockup is based on transmission output shaft speed. Changing the final drive ratio will change the lockup speed.

The speedometer can be corrected by modifying the VSSB. The anti-lock speeds will still be off.

If its vss based there is a way to trick it. I am thinking if its MPH based if its corrected directly off the trans and sent to the computer it should be the same. What am I missing here??

[More Power]

The vehicle PCM receives inputs from the VSS, VSSB, APP, CKP, and others. The PCM then outputs control signals to the 4L80-E.

As long as the VSSB has been corrected for the new gearing, I believe the 4L80-E should shift and lockup correctly.

Jim

[16gaSxS]

I went from 3:73 to 3:42 but I also have a standard duty 3/4 ton not the heavy duty. The 4th gear lock up speed did increase and it locks up about 53-55 mph unless your putting more power to it. You will not be able to to tow as heavy. I tow up to 7500 lbs with no trouble and I only have a modestly modified engine. I did tow two years in the pull off the 10k and it did fine not a DuraBux but I'm happy with it. I have towed a number of bumper pull campers from Yuma, AZ to Central Montana about 1300 miles and several mountain passes. Camper sizes from 24-27 foot up to about 7,000 lbs. I could pull up to 75 mph but MPG drop a bunch and the tranny is down shifting to keep at speed a lot. 65 mph the MPG is much better and down shifts are less 70 mph is ok but I don't tow at 75 mph. 75 is just to hard on the truck maybe with you new engine it won't be and on level ground. Here in the Inter-mountain West with my truck I'll keep it 70 mph or below towing. Hope this helps.

Marty