If you purchase a truck with the 3:31 gears and want to upgrade to 3:55 (aftermarket), is it a difficult or costly upgrade? I have no idea what's involved with a gear change. I seldom tow anything as heavy as a big 5th wheel....more general purpose trailers and a boat. I do plan on putting on a lift and running 37s. Sound like with the power this truck has, the 3:31 would be fine. The 3:55 upgrade is ~$1400 not including the ELA ($390). Normally I'm one to just order all of the upgrades even if I don't really need them, but this one has me questioning the additional cost.

Also, can someone kindly help me understand the difference between limited slip, non-limited slip, and ELA? Seems like a stupid question, but the standard from the factory is 3:31 non-limited slip. Is non-limited slip essentially a locked axle? If so, why is there an ELA option for the 3:31, unless that also upgrades the axle to limited slip so you have the choice of running either locked or limited slip depending on the situation. The order page doesn't make this entirely clear. Pardon my ignorance, but looking for a quick education....

 

no.. there are three choices

open - no locking or cross axle control, typical stock on most vehicles
limited slip - locked all the time via friction clutches.. slips when it needs to, ie when going around sharp corners (parking lot)
locker (ELD) - open, except when manually locked (thru electric control),this is forced locked.. disengages automatically above 20mph as I recall. does NOT slip going around sharp corners (parking lot).. recommended NOT to use on dry pavement as it puts high pressure on tires in the cases where sharp turns are required.

Sam

 

Thank you Sam. So, is it safe to say that there isn't a limited slip only option for the SRW trucks? The only two options I see are various flavors (gear ratios) of non-limited slip & ELA for the SRW models. Looks like limited slip is only available on the DRW if I'm interpreting the order page correctly.

 

Limited slip is indeed only available on the dually's when equipped with a diesel. Srw trucks in 17 and 18 inch wheel sets are available with 3.31 or 3.55 gearing. SRW trucks with 20 inch wheels gets you 3.55 gears only. No other gearing available. Electric lockers are optional.

The 6.7 has plenty of power to pull either gear set with 17 or 18 inch rubber. It likely has plenty enough power to do the same with the 20 inch wheel swap.

Regards

 

I found out about this at the dealer last night too. Whats up with the 3.31's and 20" wheels? The only option I supposidly can get is 3.55's on 20" wheels. Still haven't pulled the trigger yet - I can't quite get to where I want to be on the numbers.

 

3.31 only available with the 18s. I wanted the 3.31 and 20s, but it's not available. There are lots of 20" wheel sets available on fleabay so it can be done, just after you buy the truck.

 

JMO, but Ford has rated all the wheel combination's the same in load and tow capacity. Using factory supplied rubber, the 20" wheels with a 3.55 are numerically close to the 18" wheels when tire revolutions per mile are considered. 20 " tires on the 3.31 likely changes the final ratios enough that Ford will not go there. As I said, JMO.

 

Well, I have some comments but I'm sure some of you all know better so feel free to negate what I have to say.

1. Get the 3.55 with the electronic locking diff. Whether you get 2WD or 4WD, if you ever need to lock down both rear wheels and put power to the ground, you'll have it. With the open diff. you could get in a situation where you only have one rear wheel spinning and nothing happening on the other 3 wheels.
2. If you go 3.31 w/37 tires it is obviously possible but that's a really tall final drive ratio and I don't think I would do it, I would not advise anyone to do that. Seems like the torque converter would be unhappy after 50K miles of stress like that. Engine does have plenty of power but more power being poured onto a tall ratio places a lot of stress on the driveline.
3. If you go with the 37 tires you are aware that the speedo and odo will be off but if you search the forums you will find that it is possible to program the truck so that it is accurate. If you don't adjust there are a few systems in the truck's PCM and TCM that may behave odd over the course of a lot of miles. Everything is monitored and information is used more comprehensively than possibly any other engine control system that Ford has ever produced.

 

I've ordered a truck with the 3.31 and 18" tires and this topic is something I've been wondering about. If you have those gears and put bigger tires on ie. the 37's were talking about in this thread, is the transmission going to spend more time shifting at every hill and in strong winds? At least with this transmission you can lock out 6th so it wouldn't be constantly searching for the right gear, something that bugs me about towing with my '09 F150.

 

Are the tires the same size OD on a 20" wheel as an 18" wheel? If they are the same OD then it won't matter - both tires will turn the same revs/mile regardless of the wheel size. I am assuming the tire size is different between them, though, otherwise the logic of having 20" wheels with 3.55's only, without 3.31's being available, wouldn't be there.

 

I looked into this for my truck and was quoted from a Ford dealer about $2900 to do both axles. This was for a 450 going from a 4.30 to a 3.73 for better fuel economy, but I would think parts and labor would be close the same pricing for your set up. Having Ford do it will probably be more money, but figured it was a safer bet to ensure the integrity of the factory warranty.

 

Great post, Joel!

I just wanted to add something here. Traditionally you would be correct, one slipping wheel could limit the torque to the other wheel and get the truck stuck in many situations.

But all the SRW trucks have the AdvanceTrac system with it's form of traction control. This system is pretty advanced and is capable of braking the spinning wheel to force more torque to the opposite wheel that has traction.

In lots of off-road situations this may not cut it, but it's perfectly adequate for the vast majority of situations you'd encounter in normal driving.

I think the e-locker is a great thing; one I wish I had in my truck. But with traction control this thing does better with it's open diff than my '08 did with it's LSD.

 

Tom I thought you had a locker. In any event, I never thought about the traction control. That would be interesting to test. Have you had much experience with it? I'd be scared to death with an open diff. The LSD I had was junk as it was. Then again, I had no traction control system either.

 

The TCS only uses the brakes to act as an LSD in the SRW trucks. When one wheel starts to spin you can feel the ABS pump start to pulse. The truck then starts to move forward as the torque is transferred to the wheel that grips.

It's not as effective as the e-locker I'm sure, but it works pretty well for what it is.

 

Steve

I had the locker at the Ohio meet. I have the 20 inch wheels and the 3.55 gears. I pulled the hill with ease in 2 wheel drive. I would not be without the locker.

I have also pulled my fiver out of a low campsite up a small grade in some slick stuff in 2wd with the locker engaged. Drove it right on out and up the hill. I have 4wd and did not use it.

Regards