Hey guys,

Sometime in the near future I'm going to be getting some custom tunes and gauges. Just wondering...before I do this, is it a good idea to re-gear for my new 37'' tires? Or would I be able to get away with stock gearing and just use the tuner to program the truck for the larger tires? Would this put extra stress on the tranny? I have stock 3.73 gears.

Thanks

 

Nice truck.....IMHO it depends on what you are using the truck for???
Towing.....yes a gear drop would be beneficial.
Stop and go around town.......perhaps?
Lots of off road use and hill climbs (fun)...... I'll say yes.
Lots of highway........no.

Lots of things to consider, as doing both diffs is not a low dollar change.

I tow a lot with my 3:73's (15,000 lbs) on 20" wheels and it does quite well !

 

It will put more stress on your trans. but i have seen many people running 38.5s on stock gears...i have 35" all-terrain tires on my truck and i can break em loose from a 20 roll on pavement. So you can probably get by with the 37s for a while.

 

IMO the gears should have been done when the tires were put on. Some 4:10's will get your speedo closer to correct and save some wear and tear on the trans. Might as well go for a Detroit TruTrac while you're at it. And an 08 diff cover. And some traction bars. Ever here of Kelderman?

 

dang... what setting do you have the SCT X3 set at ? what gears ? stick or auto tranny ?

 

Thats when its on the performance tune that comes with the xcal...its auto with a BD converter. If im not mistaken the performance tune locks the conveter up pretty early on. It's been a pretty peppy truck since i bought it even when it was bone stock...it doesnt have a problem hittin 33 or so lbs of boost on hills, which is worrysome with no studs.

 

I have close to 40,000 on my 37's and 3.73 gearing. I have towed over 18,000 lbs on a 700 mile trip, and many shorter trips with alot less. The 37" tires are not that much taller then the stock 275/65-20 (about 34.5"). To correct the speedo you will have to get a Tirepaq. My advice is to stick with the 3.73 at first, unless like previously mentioned, you do alot of towing. I'm also using the SCT tuner with custom tunes by Matt. With my setup the rpm's are at 2000 when cruising at 80mph which is where most of my driving is and is also at the peak of the torque curve. I put on my stock 20's and drove a 1600 mile trip and used more fuel then I do with the 37's (rpm's were higher with the smaller diameter tire at cruising speed). You will notice very little difference in power with the diesel drivetrain and 37's. If I did more towing I would only upgrade to 4.10 and not any lower for the sake of fuel economy.

 

Thanks for the reply. If I do swap gears I would be looking into a detroit Tru Trac for sure, and most likely a cover.
And no, I have never heard of Kelderman?

I tow probly every other weekend however it's a only a 12ft single axle enclosed trailer. In it is a water barrel, two dirt bikes, toolbox and some gear. Loaded, I could not tell you the weight...Other than that I don't do much highway, mostly around town stuff, however I live out in the country so around town aint quite stop and go...

And I'm pretty sure I would only be doing the rear diff? Right? How much should I expect to pay for that?

Thanks for the reply. Would I not be able to correct the spedo with an SCT tuner (Or Spartan, havent decided yet!)? And your right, since I put the new wheels on I haven't noticed much power difference with the diesel, but that's not my concern. I just don't want to be putting any extra stress on the trans.

Now, why exactly does it put more stress on the trans? Is it because the trans is always shifting trying to find the right gear? Since I put the new wheels on I have noticed that sometimes the tranny will shift when normally it wouldn't have, however I don't find it a big deal because if I slightly adjust my driving style, it hardly ever happens....

 

And I'm pretty sure I would only be doing the rear diff? Right? How much should I expect to pay for that?



If you ever plan on using 4x4 you need gear ratios to match or you will be out of control or break something

 

Like mentioned, you will want to do both instead of just the rear. For what you are towing I would just go with an SCT, custom tunes, and spend the gear $ on gauges or something more useful. The only way to correct the speedo is to take it to a dealer (so I've heard) but they will charge like $75? plus most will only reprogram for up to 35" tires, or get a Tirepaq then you will always have the ability to make adjustments in the future. I often tow 2 seadoos, 3 standups on a 4 pos. trailer to Laughlin, alot of uphill from where I'm at and about 5,000 lbs. The tranny doesn't even notice the extra weight, the concern is putting too much stress on the internals, gears, etc. with larger tires but like I stated the oem tires are not much smaller then 37's and it came with 3.73's.

You need to do the trans strategy relearn to "fix" the unusual shift pattern, take a look in the tech folder for instructions.

 

Alright thanks the info. My last truck (f150) I put 33s on, and the dealer couldn't even program those tires, so I doubt they'll do 37s.

Now on SCTs website it says you can "adjust tire size- rev/mile'' (Livewire). Will this not do it?

I will look into the trans strategy relearn.

Now I'm still just wondering, what approximatly would I expect to pay for front and rear gear swap?

Thanks

 

The SCT (Xcal3) adjustment is for trans shift strategy only, does not program the speedo. Not sure about the Livewire.

 

Motorman.......when I checked last year for gear changes from Ford, the quote for front and back was about $3,200.00 cdn. I am sure south of our border it would be a bit less ?

 

Okay thanks. I'm in Canada too.

Rotun, I can't find/not entirely sure what to look for, concerning the trans stategy adjustment. Do you mind posting a link?

 

anyone, trans strategy adjustment?