Hey all, I'm new to the Excursion realm but I'm loving it. I have a '05 w/6.8 and was looking for some good performance mod suggestions. She already has a 7" lift and running on 37x12.50 on 17's. I know I'm never going to get good mileage but I would like to get a little better and maybe more power.

 

What gears are you running? With 37's and stock 3.73 gears it would be torture for the trans, going to deeper gears would wake it back up.
And Welcome to the site!

 

Thank and yes, 3.73s. if I go to 4.10s tho, would that weaken my mileage on the highway?

 

If you have 3.73 gears and are running 37" tires your effective gear ratio is 3.18. With that low of a gear and with the heavy tires I would imagine that you are lugging the motor and putting a lot of strain on the trans. According to the online gear/tire calculators you would need to go to 4.38 gears to return your effective ratio back to 3.73 and a new set of 5.05 gears would give you an effective 4.30 ratio. In your case I think going to a numerically higher gear ratio would most likely help your mileage some because of how bad your current setup is, gear wise that is, the truck looks good.
My truck also has 3.73's and stock 31.5" tires. When we tow our 9-11k ToyHauler it drops out of overdrive on the slightest incline. My plan is to upgrade to 35" tires and regear to 4.88 to bring my effective ratio to just above 4.30, a much better ratio for towing heavy. I'm not expecting much of a mileage drop as my new gear/tire combo will have the V-10 operating in a more efficient RPM range.

 

Tom, thanks for the info. I will look into regearing the beast then. I'm also looking into a banks system for it thru my local off road store. You've got a good looking rig as well.

 

Tom, have you looked into doing this yet? How much $ to swap out front and rear axle ratios? Do you have limited slip on rear and does that add to cost?

I really like the looks of the 2004 KingRanch 18" wheels like you have and would also like to step up the size/diameter of my tires. But of course, this is a towing beast and it is very important to keep the RPMs in the correct range.

 

If you're looking for better mileage on the freeway, get some 4.30s. They will even out to the 3.73 gear ratio and make it much easier for your trans to get and keep your truck moving.

If you tow often or plan on towing, you'll need either 4.88 (which will put you slightly under) or 5.13 (which will put you slightly over) to even out to the 4.30 gear ratio the V10 loves so much.

 

Forest, I had called around to a couple of area shops that rebuild diffs and was given estimates (not quotes, said they needed to pull covers and take a peek to give a quote) of around $2200-2400 for both axles to go from my 3.73's to 4.88's. The cost would go up if they found any surprises once inside, of course. My rear diff is a factory limited slip but I gave that info so I don't know if that added cost or not. Since that time I have been told of another shop that may be able to do it for just under 2 grand but my recent good luck has made that call unnessesary.
Forum member Jasonodsky had posted a link to an ebay auction (not his) for a set of EX axles with 4.88 gears and a rear locker. After that auction ended without any bids I got in contact with the seller and after several questions about the axles, gears, wear patterns and such were answered we worked out a deal where I would pick them up for $1300. This past weekend my wife and I made the trip to WI to pick them up, our fuel, tolls and room costs came to less than the freight shipping estimates I had gotten and we got to spend two days hammering along interstates and enjoying each other's company, a win-win!

The '04 SD 18"s were a nice find and the timing was right. I plan to move up to Nitto Dura Grappler 305/70R18E (35") tires and have always preferred OEM wheels over aftermarket but I didn't want to have to run $pacer$ so these single year Superduty wheels are perfect. Like you I tow heavy also and my 3.73's have had our truck out of overdrive way more than I liked. Otherwise the rig has performed flawlessly in over 4k miles of towing. After playing around with online tire/gear calculators I had decided to change to 4.88 gears with the new 35" tires to wind up with an effective ratio of 4.39. Everyone seems to agree that the V-10 loves to work with those 4.30 rears.
Now it's just a matter of saving up for the new tires and some other goodies like stainless braided brake lines and Rancho 9000's. I hope to have everything swapped over for July's vacation.

 

Tom, that will be a very nice looking rig with the bigger tires. Way to score a pair of axles as well!

Your estimate(s) of $2200 - $2400 are what I have been hearing.

 

I saw that auction, sounded like the seller did not know anything about the axles or what lockers they had in them. Hope they end up working out for you.

 

I have been looking at this kit
D50 & 10.5" 4.88 Gears + Master Bearing Kits

Is that everything my mechanic will need to get the job done?
The price seems pretty good and my guy does great work for a low labor cost. I may re-gear real soon if that is all it takes.

 

from the pic, that looks like everything, but I'd be prepared to spend more. That would be a good time to go over all your outer bearings and seals as well and you may need to replace those. Also a good time to get one of the later aluminum diff covers and upgrade while your diffs are apart. I like the lube locker gaskets for putting the covers back on. seal up good with no silicone and they are reusable. Just make sure your guy has all the stuff to do diffs and has done them before. Not all mechanics do/have.

also, from that link, I never realized jbg sold stuff for the newer trucks... I've ordered stuff from them for my 79 before.

 

When I regeared back in '07 (I know prices have gone up on everything since Nobama has taken office)...but back then I paid $1500 total for both front and rear axle gear swap.

I was fortunate to find a local shop here in Fort Wayne that had a 40+ year Dana axle employee that also worked at the performance shop (the owners father-in-law).

That guy was the guy that did the gear swap on my Ex...

Parts cost me right at $1000 at the time and labor was $500.

I realize the OP is in CA...where things just cost more than a simple mid-west town...so I wouldn't be surprised by a $2200 to $2500 price tag.

I agree that re-gearing that beast with 37" tires will be your single biggest bang for the performance buck...

I'd re-gear first and see how you like the performance boost before deciding on Banks kit...

I tow a 9000# TT all over the country with our V10 and 4.30's...I have yet to find a hill/mountain/grade steep enough to stop this combo...the V10 is a strong towing motor...

Good luck,
Joe.

 

Good to know.
My guy has done gears before.

Any advantage to aluminum diff covers other than they look cool?

How much do the Aluminum Covers and Lube Locker Gaskets cost? Where do you get them?

 

I went with the '08 Super Duty rear diff cover. I think I bought it for like $50 or something like that.

for me the advantage of this cover is that it provides some added surface area for cooling the diff fluid since I tow a 9000# TT all over the country...

Here's a picture



New '08 SD differential cover - Part #8C3Z-4033-A you will also need 5/16" - 18 x 1.25" bolts with flat washers

Never thought about swapping the front cover since how fast do you normally drive in 4x4 to generate any appreciable amount of heat?

Joe.