Hello Members,
I'm going to be purchasing a toy hauler sometime in the next 6 months and have realized that my truck has a 3.15 rear end, which limits my towing capacity to around 7,500 lbs. If I change it to a 3.55 rear end it increases the towing capacity by about 1,000 lbs. Is there anything else I should be aware of when making this change ? I have the 3.5 Ecoboost motor. Thanks a bunch.

 

Do you need that extra 1000 lbs of capacity to tow this trailer?

You could just lock out the top 2 transmission ratios and get pretty much the same result as a gear change. IMO you won't see enough of a difference going to 3.55 to make it worth the bother so I'd suggest you go to 3.73 or 4.10.. especially if you tow in the hills a lot.

 

Hi Paul, thank you for your reply. I'm not familiar with locking out transmission ratios, how is this done ? I will be definitely towing in a hilly area, so I really need a lower ratio rear end. Do I need to do anything to the transmission if I change to a 3.73 ? Thank you

 

You can use the M mode on the trans and shift yourself or use the - (minus) on the shifter to lock out gears while in "D".

 

Thank you very much

 

What year is your truck?

The 6sp transmission in the newer trucks has a lower 1st gear ratio that compensates for that relatively high(for a truck) axle ratio, with the end result being good off the line performance like a truck with lower axle gears plus a deeper OD ratio
Or at least that is the theory, the downside of this new arrangement is excessive transmission shifting when towing and/or climbing grades which generates heat and shortens trans life, so I still think that is a poor axle ratio for towing in the mountains.

 

My truck is a 2014 and I ordered it with the Lariat tow package, but not the upgraded package which would have given me a higher rear end ration than the 3:15. So it is sounding like you are in favor of changing to the 3.73 rear end. Is that correct ?

 

My $.02 - The 3.73 is as tall as you want to go for a daily use truck. It will make a big difference in your towing and daily driving coming from a 3.15 ratio. The truck will tow nicer, accelerate better unloaded, but lose a little mpg.

 

Thank you Turbo Dog for your input, I'm now convinced that the 3.73 is the way to go.

 

My 2014 has 3.55 gears, I wanted 3.73 but couldn't find one with the other options I wanted. Good luck and enjoy your time out on the road

 

Hi Turbo Dog,
Since you have the 3.55 gearing, do you think it is adequate for towing a 7,500 lb trailer ?

 

A little older truck but mine is a '93 with a 460 and a 5 speed. It's got 4.10's and spins 2200 rpm at 60. I personally don't think you've got enough engine to pull a 7500 lb trailer.

 

X-2

My vote is to get the trailer and then decide whether to re-gear the rear. Chances are good that 'dialing-in' the hitch will cause more issues than the differential gearing. After some experience under the belt with the trailer, then take a pulse - check to see whether re-gearing is necessary or just a tweak to the tune will due. If the truck just needs some tuning to shift a little better and lock the TCC some more, that will likely cost a lot less than a re-gear.

Swapping the differential gears is neither a cheap option nor something a 'shade tree' mechanic should tackle on their own. So that is another factor to consider in the decision.

As a reference point, I just took my SOB truck from a 4 speed slushbox with a 3.73 rear to a 5 speed manual with 3.42's and am completely happy as the RPM's are now exactly where I want them for the different modes of use (highway cruising or towing) and my left foot controls the amount of transmission slip. The reason I decided on the tranny and differential swaps was from *experience* towing the trailers with that truck and not from an Internet poll based on theory. Just say-in


Actually, might want to consider focusing more on the toy hauler's road manner characteristics where some trailers pull well, and some are better off as RV Park Queens. As another reference point, a family member bought a ~7,500# TT that was marginally friendly behind a 3/4 ton truck. Pulling it with a 1/2 ton SUV rated for 9K# and a 7 speed tranny was pure white-knuckle 100% of the time. I dubbed that TT the 'Tow Pig'. After less than a year, Tow Pig was sold and replaced with another ~7,500# TT that behaved well behind the 3/4 ton truck. Not so surprising was that Tow Pig was a RV Park Queen before my family member bought it . . .

 

Holy Cow! Just realized that this thread was dug-up from over two years ago!

Am sure that the issue was resolved by now . . .