I have a 07 Ram 1500ST with the 3.7, six speed, 9.25 rear axle with the 3.21 gears.

Since I moved to the mountains of East Tennessee, I no longer need the very tall highway gears the truck came with and would like to go to 3.90 final drive ratio with a detroit locker. Both easily available from Randy's Ring and Pinion. At under 1k for parts, it is far cheaper than trading this truck in on a 4x4 since resale kind of sucks.

However, to make this change seemless, I will need to calibrate the speedo. On my older Dodge trucks, I simply swap out gears at the transmission. Is there an electronic speed sensor on these new trucks? do we have an easy procedure or does it require a visit to the friendly local dodge dealer...

Or I could just drive the 68 Utiline, 318/727, with 3.90 suregrip factory axle...but it doesn't have a radio and heat and wipers aren't so good...

Howard

 

As long as you're not changing tire sizes, you don't have to re-cal anything. The speedo runs off a ring on the outside of the carrier and will not change with ratios. The only thing that will change relevent to speed is your driveshaft rotation.

 

What he said...

But I question getting a true locker in the rear of an IFS daily driver. It's gonna be ratchet city around turns. I think you'd be better suited with an Detroit TruTrac or an Auburn LSD...

 

I guess the TT913A368 might be the better choice here. Nice to know the speedo won't need correction...

Howard

DET187C-172A Detroit Locker for Chrysler 9.25" differential. The Detroit Locker provides maximum traction for off-road or racing use. The heavy-duty case and internals provide a dramatic increase in strength while giving 100% torque to both tires. The mechanically-operated unit works by locking while under power and unlocking when you let off the gas, allowing you to turn. Unit comes standard with a one year warranty against workmanship defects

TT 913A368 True-Trac limited slip for '97 and newer Chrysler 9.25" with 31 spline axles. The True Trac limited slip uses a worm-gear design to bias torque from one tire to the other, providing extremely smooth operation. Since there are no clutches in this unit, there are no parts to wear out and no need to run limited slip additive in your oil. Tractech warranties this unit for one year against manufacturing defect.

 

Yep, and unless they've done some major re-working of the internals since I had a set about 10 years ago, the "unlocking when you let off the gas" doesn't always happen and they almost always lock when you start to accelerate coming out of a turn. I think the changing of your attention towards the TT is a prudent move...

 

3.7L with 3.21??? I cant even imagine! I had the 5.7 with 3.55 and thought it was a dog.

 

20 miles a gallon, will haul a ton of gravel up the mountain I live on, just have to downshift for speed bumps...that's why I want 3.90 gears...plus it will get stuck on wet leaves...