Well I'm finally diving into the 6.7 world! Now I'm not new new to them seeing as my father has owned three but I've finally decided to make the jump.

I found a truck local for an incredible price, 2012 f350 srw with 100k on the clock for 25k. There is only one problem, the truck comes with 3.55s instead of 3.73s like the dealers website states. The truck will be used to pull a 39ft newmar mountain aire 5th wheel with a gvwr of 20k.

I've researched pretty heavily and I know a srw 4x4 with 3.73s will pull up to 21,700 lbs but I will obviously need to change the gearing.

Is this a difficult task? Or better yet, is it even possible to do the switch?

 

Congrats on the new truck. On the gear change, I wouldn't. I regularly tow my toyhauler that weighs just under 20k loaded with my truck that has the same rear. No problems with gearing at all. Give it a try before you go messing with a perfectly good rear. I'm betting you forget all about the swap after one tow session...

 

Thanks! That is the kind of info I'm looking for! I appreciate the quick response and kind words!

 

I would try it with the 3.55's before changing them. The 6.7 has some grunt to it and might pull better than you think. The cost to change will be in the neighborhood of $3,000 give or take some.

 

Glad to help. Lots of guys with lots of different experience here so ask away.

 

this

You've bought a freight train. No need to regear it.

 

Rodney will know better than I , but I found if in mountains locking out 6th gear aliviated any problems I "thought " I had pulling heavy with 3.55's. Rest of time just cruised and enjoyed

 

I know a lot of guys manually shift or lock out gears situationally so there must be something to it. I think Joel says he shifts manually every time he tows heavy. I'm not sure if it's me being lazy or what but I put it in drive, hit the tow/haul button, and let the truck do it's thing. Over 22k miles towing 16-20k and never felt like I needed to do more. To be honest I will say that on occasion, starting off on a hill from a dead stop, I've felt like more gear would be nice. It's just not a necessity.

 

I switched to manual shift mode before I tuned/deleted my '11 if I found it shifting gears. After I started running the H&S transmission tuning, that problem went away.

 

You know what I noticed as far as shifting frequency is how much better it tows in cruise control. On the highway, it will hold speed and 6th gear and save a boatload of fuel with cruise vs. without.

 

I really should care about mileage...shrug. Smash the accelerator is all I know.

 

I don't either or I wouldn't be towing at 75-80. However, with a 26 gallon micro-tank I barely make it 2 hours before stopping to refill. Cruise seems to cut back on that just a hair and the truck tows better to boot.

 

That's one thing I like about the Fiat...31 gallon tank vs. 26 gallon. I can get a little more range out of it.

 

I'm looking forward to next year when I have a proper adult size tank instead of my current "fun size" LOL. Even the shortbeds are moving up to 34 gallons in the 17's with the long beds going 48!

 

Nice...

I've spent a lot of time on freeways this spring in 70 mph zones trying to get around RVs doing 55 - 60 mph. Most RVs can do the limit or near the limit but those who can't can cause some difficult and dangerous driving for others. I already know that the people doing way under the limit think that they are being really safe, I just don't agree with them. Seen way too many crazy things going on around these extra safe drivers.

bruce...