Title says it all. Just went from 3.73 to 3.42 rear end in my '06. Not sure if the speedo needs to be corrected or not though. Anyone know where/how the trucks measuring speed?

I know the dealership can do a quick OBD II update if needed but figured it would be better to find out here first.

Thanks!

 

I am thinking that these trucks read the speed from the tone wheel on the rear differential carrier, which is still going the same speed as the wheels, therefore the gear ratio change will not have affected it.

 

No need, they do use wheel speed sensors.

 

Excellent. That's exactly what I was thinking. I called two dealers and both wanted to recalibrate even though I told them I wasn't certain it needed to be. First dealer wanted $45 second wanted $125. SOBs.

Thanks for the info!

 

So, are you seeing an improvement in fuel mileage? If so about how much?

 

f you have changed tires, you may need to adjust. You can always verify the accuracy with a GPS,but do it with a trip and then compare the actual distance with your odometer.

 

Best I have ever gotten on my way into work was 17.5. I saw 20.5 the first day with the new ring and pinion!

So far I am really happy with them. The truck is a lot less jerky now driving around unloaded. Also the 6-speed tranny is more livable. I just don't feel like I'm shifting 6 times in 20 seconds now.

The only reason I'm driving the truck around is to get 500 miles on the diff fluid before changing it. The truck is 99% tow vehicle for me. Problem is going 65-70 I'm only getting about 10.5 mpg towing. I'm not towing that heavy ~9k lbs but its a car hauler so the wind resistance is pretty bad. I don't think I'm going to miss the torque reduction as the loads not that heavy but I'm really hoping I get a decent fuel econ improvement.

I'm towing about 600mi next weekend so will report back with results!

 

My 2009 has that ratio in it from factory Plenty of accleration best mileage so far is 16 local 20 on a trip . My old one 1999 was 4:10 ratio Best around town 13 and 16 on a trip .

 

Overhead or hand calc?

I doubt you see an improvement towing. Since you have 8.3% less torque multiplication and it takes "x" tq to maintain a certain speed your motor is now going to have to work harder than it did before.

The 3.42 gear swap is not for people who tow, it's for those who live empty. There is a reason 3.42's have a lower tow rating, for the same weight it's more strain on the motor/drivetrain.

 

My truck was purchased new 2009 with the 3:42 ratio and it has a tow package as well. I think It might be a little sluggish towing on the hills that's why we have a Tow Haul transmission package with it . I think on the straight away it will be OK but I may have to drop down a gear on the hills . Just have to watch the RPM Maybe a Pyromoter is in order . It might help . I think a travel trailer will work fine but perhaps a heavy equipment /car hauler trailer might require a bit more careful attention to ones driving .
Don

I hand calculate my mileage every time ...Around Town 15.3-16 Trip was 20 MPG The over head is always higher

 

You'll be fine towing. just keep it out of overdrive if the rpm's are down on hills. I have a Gear vendors on my '02 and it gives me about the same as you'll be with the 4spd. keep the RPM's at around 1800 to 2100 and you'll pull the hills fine. I get about 14 towing a 6k 5r. Pulling 9k though you might wish you kept the 3:73's and added an overdrive trans. Be interesting to see how your trip does.

 

I agree with you I know I need to keep the RPM's around 1700 on a hill but this is what the transmission is designed for ... I have an airstream with a ball hitch . It weighs aprox 5600 They pull very nice I am told I haven't pulled it yet .
I think if I were towing cars or pulling an equipment trailer I might want the 4:10 or 3:73 . I have a 99 with 4:10 in it Never lacks power but a bit heavier on fuel . Big difference in 10 years ... you first notice you can talk without yelling at one another .

 

I was told by a dealer service manager that the towing ratings are based on sound db limits. Not sure what that means/method exactly but my 5th gear with a 3.42 pull EXACTLY like the OD of a 4.10.
I think it would be better to qualify such statement rather than a blanket statement.

If you pull a 20k# trailer all the time then I agree the 4.10 is better but we pull a 5-7k# and another 2-4 bed payload. The 3.42 works well for us. The 6 speed gives us a great selection to find the correct gear when we hit the hills, which is less than 10% of our driving.

My '04 4.10 ratio purchase has cost me about $4000 in extra fuel cost. That came right out of my pocket. The tow rating of the DRW 3.42 is nothing short of misleading!!! Based on my experience, it must be calculated at using 6th gear only. So just realize that if you're towing over 10k#, you won't be using 6th gear. So do your rpm calcs with 5th.

For this reason, we are swapping our '04 with 4.10 for a 3.42 rear. But then again our '04 isn't stock. The edge/juice gives us up to 405hp/805FtLbs. Having options is good. Also, the 48RE is a good tranny. This truck is barely broke in with only 97kM on it. But it's just been turned over to our crew that travels. 3 mpg extra saves us about $1500/year.

 

I think that if I am towing on the flat It will be better mileage than the 4:10 but if I hit the hills it will probably be the same I will know after a couple of trips though won't I. I have a 99 with 4:10 and that was 13 MPG towing a trailer and 16 empty ...I am hoping the 09 will be a bit better . We'll soon see

 

Look into the performance of an Edge/Juice or similar mod computer. We have a 99 too. It only has 215hp/420ft.
Our results with Edge/Juice on our '04 was amazing.