sumncguy

I pull about a 5k dry travel trailer. I just bought a 09 6.7l QC st 4x4 .. was wondering how its going to do over hills .... anyone got the 6.7 wiff 3.42's ?

I dont plan to mod this truck at all .. got the ST cause I want simple. But if its real crappy, I may have to go to the 3.92 ....had thost on my 05 Thunder Road 1500 .. pulled like a charm.

anyone ?

MJDiesel

I just switched from 3.73s to 3.42s and the 3.42s are not high enough. I was worried about towing performance, which is the only reason that I did not look into 3.08s. I probably could have easily gotten away with 3.08s by using 5th more often at gravel road speeds, which is better for the transmission. Oh, well. Live and learn. At least the 3.42s are better than those stinkin 3.73s!

rich

only thing i heard anybody say bad about the 3:42's was guys towing heavy with 6 spds std tranny. i wouldnt get them in auto. dont believe the rtio in your 1500 is avzilabe should just be 3:42, 3:73 and 4:10's. dont know fore sure since i wont buy a new truck for a long time

sumncguy

Your right rich ... those are the options available ... for a new purchase .. but couldnt I just have the 3.92's installed .. I bought the truck already. If not then maybe Ill have to go to the 4.10s .. but those are gas killers, no ? Ooops I mean "Fuel" killers .. got to get with the diesel speak

How much did it cost for your swap MJDiesel ?

MikeyB

Only three ratios available for the AAM 11.5". 3.42, 3.73 and 4.10.

You gotta remember that the 6.7L is a torque monster and should not have any issue towing that weight with a 3.42/6spd.

And you can always downshift to 5th when hitting the steep grades.

MikeyB

rich

if its an auto the 3.73's will work fine

MJDiesel

$1200 with labor. I don't think that it will ever pay for itself with fuel savings, but the pickup drives much better now. Then again, I might actually keep this Dodge a while and put 100s of thousands of miles on it, so i minght break even sometime!

sumncguy

Freekin Dealers !

I got my build list today from Dodge ..

Surprise ....

6-Spd Automatic 68RFE Transmission
Man Shift-on-the-Fly Transfer Case <----really like this better then electronic
5,200# Front Axle
3.73 Axle Ratio
11.50 Rear Axle
Anti-Spin Differential Rear Axle
Conventional Differential Frt Axle
Engine 6.7L I6 Cummins Turbo Diesel

Totallyrad

MJ, would you mind telling me what rpm you're showing at 70mph with the 3:42's?

PaulDaisy

I think the OP said that TT weight is 5k lbs? Why are we talking different gear ratios? The truck won't know the difference with 5k trailer I think.

rich

5k trailer the truck will not know its their with the 3;73's

MJDiesel

2050 or so. It has the245/75R17 tires.

MJDiesel

After doing the math, it shouldn't be that high, maybe 100 rpm less. I will have to give an updated report after another drive. I towed about 12,000 lbs today and it did well.

sumncguy

Ok .... Heres the trucks I owed and the tow story ..
05 Camper weighted about 4k
08 Camper weighs about 5k

03-06 towed both


03 QC 4.7l 3.55 - sucked hard ... constant downshift especially going up grades, but also noted on flat ground (wind, traffic, mergers etc etc). Encounter this behavior whether towing or not. Gas mileage sucked both towing and not

05 QC 5.7l 3.92 - Sweet. Great combo .. nice pulls, almost no downshifts at all (hills, towing etc), gas mileage pretty good.

06 Mega cab 5.7l 3.73 - ok .. but lots of downshifting while pulling the camper. Frequent downshift on hills whether towing or not. Gas Mileage ok not towing ... 12-18 maybe a little more on the highway. 8 miles to the gallon while towing.

I have been paying close attention to the tranny behavior ... turns out the dealer was wrong and this truck doesnt have 3.42's .. it has 3.73's according to the build list ... in places where the Mega cab(3.73) would down shift, this truck holds tough. I may loose a few mph's going over a hill with a steady throttle, but no down shift.

Im dieing to pull something with it .. cant take the camper out ... too much going on at work right now.

That Cummins is givin me a woody ... wanna work it .. ya know ??

Totallyrad

That's interesting, I'm running stock tires, 3:73 rear and 2050 is what I'm turning at 70mph. I would have thought it would be a couple hundred less with the 3:42.