I wanted to know if anyone has swapped out and 3.73/4.10's for 3.42's? I currently have a 6spd and 3.73's with stock tires, and do alot of highway speeds (75-80). The tach is way up there 23-2600, and the fuel mpg is way down at those speeds (14-16). In the past (01 and older) 3.55's and a taller tire helped with the revs quite a bit. With the truck I have now taller tires are not an option. Just wanted to know if any one had any input? I'm scheduled for Monday for the swap. Thanks in advance.

 

I'd like to hear how much it helps the mileage. No matter how you slice it, 80 MPH has the same amount of wind resistance with any gears. That's the big drag you're facing. Slowing down does more for mileage than anything else.


John

 

I'll definatly keep you posted with the R's and mpg. I agree with the drag point. I would like to add that our business also had 2 '95 reg cabs, manuals one had 3.55 and the other 4.10, and hands down the 3.55 would get better milage goin the same place as the 4.10. But there was nothing that could stop the 4.10's other than 86 miles per hour (rev limiter). Slowing down the truck is a great suggestion also, I get low 20's (mpg) round 65. However I generally travel 5-700 miles one way non-stop, and head home the same distance. Goin is easy, goin home I have a tendancy to get in a hurry.

 

I get my best compromise mileage at 1800rpm which is about 64mph.

I can do 1900 (about 67mph) without TOO much of a hit. But 2000 (about 70) cuts into my average pretty bad.

You mention 2300. EEK!

 

3.42 w/ stk tire =2450@80 or 1840@60
3.73 w stk tire =2670@80 or 2000@60
you'll be looking @ $1k+ in parts + labor on a 4x4 to drop 200 rpm.....


then again my truck turns 1650@ 60 and 2200@ 80, sure is nice turn'n lazy rpm's and not having a 3rd inj event... 800+ miles per tank on average....

 

The swap is goin to cost about the same as a new set of tires (1400.00). I put alot of miles on my trucks(1-4000 miles a month), so I figure this is decent experiment to try. In addition to runnin empty, I also pull a 30 foot livestock trailer(at lower speeds) so I'm doin it more out of curiosity. Anything to help with the $3.00 per gallon fuel.

 

The best MPG gain I had was upping the tire pressure from 55 to 80 all around. Picked up 2 MPG. Rides fine.

 

Slowing down the motor is it. Anythig over 2000 RPMS on the highway is not for fuel economy in a diesel. I am not saying the wind resistance at 80MPH has nothing to do with it (it does) but, you ARE going to see an increase in fuel economy if you are able to slow the motor down with a gear swap.

 

Where are you getting the 3.42's? Been looking to do the same thing, just haven't been able to find them.

 

There is a link in the "who else does not like their 6 speed" thread.

 

That is awesome, I am very interested in how this little experiment works out. I know I sure miss the 3:55 and taller 5'th in my '99. This thing really revs on the highway, I'm seeing similar milage.

 

I didn't see 3.42's for the front though.

 

Th front is a different axle, and depending on what year, should be a Dana60


Edit: Rear ring and pinion's are the same for the front. IN other words, if youfind aR&P for a rear Dana 60, it will work in teh front



TEH=THE

 

Both axles on an '06 are AAM axles.

 

$1400 ???? WOW!!! Who is doing your R&P swap? R&P about $180-$200x2=$360-$400 for gears. That is leaving you $1000 in labor plus some fluid and a couple of seals. OUCH. I hope they are using ______