Ford Build Thread: FrED the Ford. '98 E350 7.3 4x4 The More We Explore's Adventure Van

[sixstringsteve]

Good feedback. I got a quote to do the gears up front. If I brought them everything, including the gears and install kit, they said $400 labor with the axle assembled, $350 with the axle apart. That seemed like a lot. I'll have to do some more digging and see if I can get some better quotes. If I do go with new gears, I'd rather have them swapped in while the entire axle is apart anyway...

I was worried the 4.10s would rev too high on the freeway and give me poor MPG. It's all a balance between mpg, power, towing, and being unloaded.

I plan on a mild tune at some point. There are a few van guys who have custom tunes set up for the 7.3 vans. I need to do more research in this area still. I don't need a dragster, but I only hear good stuff about tunes.

 

[bryson]

You know Carl does gears for a lot less than that...

 

[sixstringsteve]

Ah, I wasn't sure if he did dana axles. I'll hit him up.

Six states in Orem said $175. That's a lot. Eater than the first guy I called.

 

[Gravy]

Most stock 7.3 f250s come with 3.73's and 265 or 285/75/16s
put some 35's on there and you're going to want 4.10s
No intercooler and a milder tune in a van. You'll REALLY want lower gears while towing.
Keep your revs up and loading the motor less will keep the EGT's down and keep reliability up.

 

[sixstringsteve]

using the grim jeeper gear calculator:

with 35s
3.73 - 70 mph will be 1780 RPM
4.10 - 70 mph will be 1956 RPM


with 37s
3.73 - 70 mph will be 1683 RPM
4.10 - 70 mph will be 1850 RPM
4.30 - 70 mph will be 1941 RPM


It sounds like 1800-1900 RPM is the ideal RPM range while cruising.

 

[Jesser04]

My old man had a 97 crew cab dually 5 speed and it would run about 2800 at 80. He'd get average 13-15 mpg. I'd definitely go with the 4.10 or maybe even the 4.30's.

 

[sixstringsteve]

I found two 2005 f350 10.5" sterling 4.10 rear ends. One has a posi (62k mi) and one doesn't (unknown miles). Both are the same price Which one would you buy?


Does the posi actually do anything, or is it pretty worthless? If I buy an axle with a posi in it, and it ends up being worn, is it going to screw anything up to keep running it? I imagine the clutch discs will just wear out and it'll behave like a normal open diff. Are the ring and pinion gears any different than the open diffs? Could I still swap a truetrac in there?

 

[bryson]

The limited slip does use a specific carrier, but if you're replacing it with a Truetrac you'll be just fine, as the Truetrac replaces the carrier. The factory limited slip diff uses the same gears as the open diff version of the same ratio, so they'll work either way.

 

[sixstringsteve]

You guys are awesome. Any disadvantages to purchasing the one with the posi/limited slip in it?

 

[bryson]

If the limited slip works and feels tight I don't think you can go wrong. But, I don't know the specifics of the Ford LS diffs - general reliability, etc. All I know is that if it's a clutch-type diff you need LS compatible fluid or friction modifier additives.

If you want a traction aid for sure, I'd buy the factory LS one. Worst case scenario is it doesn't work (catastrophic failure isn't likely IMO, it would just get much less "limited" as clutches wear out) you pull the diff and replace the carrier with a Truetrac down the road. Best case, it works great and you save several hundred dollars by not buying a new diff.

Also, a worn out LS would act just like an open diff, and could probably be run that way for a long time.

 

[TRD270]

I had a limited slip in my '98 2WD Cummins loved that thing when tooling around on dirt. It did hook up at a bad time once though, wheel started spinning posi hooked gripped while in full boost which led to a shattered clutch. I'd still take the posi

 

[sixstringsteve]

Cool, thanks for all the feedback. I dropped the front axle off st six states to get 4.10s, and I'm picking up my 4.10 rear 10.5 sterling tomorrow. It'll be nice to have all that done.

 

[Greg]

Far as your 35's vs. 37's debate... I had 37's on my GMC and IMO they made the truck much less driveable on the freeway to the point that I wish I had stuck with 35's. Putting 37's on your van would be crazy, especially with the intention of towing a trailer. I'm sure in your mind you're thinking about clearance under the van, diffs, etc... but I think you'll loose so much more than you'll gain with 35's. Just because you could, doesn't mean you should.

 

[sixstringsteve]

Good feedback. A lot of the van guys with 37s seem to love them. When the time comes, I'll see if I can find anyone local with 35s and anyone with 37s and see if I can swap em on and see how they feel.

 

[Bart]

I loved the limited slip in my 02 Superduty. It worked great. Only problem was when it would get warmer, after a long haul, it would semi engage in town. At first I thought the rear end was going out, but found out it was just the ls.

As for 37s vs 35s, I would never run 37s on a daily driver. One of the reasons I sold my 03 DMax was the tall lift and 35s. I got very tired are climbing in and out of the rig, and the taller tire, especially a 37, will make it less friendly around town. JMHO.

 

[Kiel]

I loved my 2001 superduty 7.3 on 37's with 4.56. Towing power was great once I stopped lugging it below 2200 rpms. Before that towing up a grade it would hunt between overdrive and starting getting turbo surge. It was a beast of a truck and towed 6500 pounds no problem at any speed up any grade. I'd never do 37's again though 35's and down

 

[Marsh99]

I think 37's would look awesome, but 35's will be more practical.

 

[jeeper]

another vote for the 35's. Fuel mileage, towing ability, drive quality, ect will all be affected greatly between the 35's and 37's. My 7.3 (idi, not PS) was slow when pulling the hills on 35's. I went to 37's and it was miserable! I went down to 33's and had much better experiences.

 

[sawtooth4x4]

my 2006 F350 has a limited slip. it works nicely. especially when it's slippery out

 

[sixstringsteve]

Darn you guys and your practical advice!