Hello all,


Great site, lots of good info here.

First off, this truck is a 1996 xl crew cab, very basic work truck with high miles.

I'm looking to squeeze a bit more out of each gallon of diesel and wondering how difficult it is to swap out my 4.10 gearing to 3.55 or maybe even 3.08. I drive my truck mostly around town, but a few times a year i tow a 7-8000lb 31 foot Airstream trailer. I have a 5 speed manual transmission, and on this decoder it classifies it as a "5 speed H.D. Overdrive" transmission: http://www.ford-trucks.com/article/i...de_Chart_.html

I'm assuming its the Mazda transmission. I've starting filling up my stock tires up to 80psi and keeping my foot off the gas, keeping the rpms as low as possible.


I travel frequently to El Paso, TX where there are salvage lots all over the place, I'm thinking I might be able to find a good used set of gears. Is this the kind of thing I can remove from a salvage truck with basic tools out in the salvage yard? I've replaced injectors in this thing and I'm somewhat mechanically competent.

Thanks for lookin!

Changing R&P sets takes a pretty good mechanic. Jeep shops swap R&P sets all the time and generally do a good job.

You should be able to locate 3.55s pretty easily. Maybe you might do very well by finding a whole junkyard axle witha lower ratio and swapping it on. Otherwise places like Rick's Ring and Pinion sell kits.

I'm pretty sure you can get 3.55s for Ford 10.5" axles but 3.23 or 3.08 is limited to the Sterling 10.25" and in rear axle only.

Thats a damn good idea about replacing the whole axle from the salvage lot. 4.10s just seem like overkill for what I do with this truck. Thanks

The lower the ratio, the better the MPG.

No free lunch. Lower ratios are tough on automatics.

Note that Ford has now made 3.55 standard of new pickups.

Is it a 2wd or 4x4, a dually or single rear wheel?
The OBS could be had with 3.55 or 4.10 gears.
I honestly wouldn't want to go much higher than 3.55 on a truck that size. If you plan on leaving the engine stock it will have a hard time getting out of the way even with a stick if you went all the way down to 3.08 gears. With a few simple mods to bump up the power you could run higher gears easier. Since you have a stick you have even more options.

Its 2wd, SRW. Only simple mods like DIY intake, high pressure crossover, and hopefully soon a new downpipe. I'm thinking 3.55 is what I'm looking for.

I'd go for a 3" Downpipe & a straight pipe the rest of the way back. Might even think about a DP Tuner PCM flash for 60 tow to give it alittle boost in power without getting too crazy & hurting things.

I'm thinking about doing the same thing as you are with the truck in my signature...

If you are 4x2 SRW, check your axle. It might be the Sterling 10.25" rather than the Ford 10.5"

Randy's Ring & Pinion has 3.08s for the Sterling but I think only does to 3.55 for the Ford 10.5".

If you are 4x2 and fuel prices are getting you down, you should at least think about a slam. DJS makes a 3" front - 3/4.5/6" rear slam kit that is easy to install. I found it to be worth an extra mile per gallon. Put an air bag in the rear to compensate for the spring leaf you lose back there.

I never had any luck improving MPG with exhaust. I have a 4" exhaust for it doesn't help MPG a bit.

I don't think a commercially available chip will help your MPG unless your truck is an egregious fuel-hog to start with. I tried 'em and always lost MPG. Today I run a special custom MPG chip. It is one of two in the country - the guy who burnt it runs the other one. I got it in trade for some testing work. I helps me get an additional 0.75 MPG.

As far as I know it should be a 10.25 if it's on an OBS. From what I understood the 10.5 wasn't around till the Superduty came out & the 10.5 uses a metric bolt pattern.

Personally I'm a firm believer in a free flow exhaust & intake. It might not get another MPG or two but it let's the engine breath better which is always a good thing. It also paves the way for a chip if you want one. I've delt with & driven a few Powerstrokes stock & modded & there is a night & day diffrence with the chip. I know my buddy just put a DP Tuner on his truck with the 80 ecno he has no problem merging onto the expressway usually without any smoke either. But with the stock setup he would sometimes have to floor it to make it down shift & wait till it got up to speed to merge with traffic. In other words the engine doesn't have to work as hard to get moving up to speed. Not sure MPG wise crusing, we drove about 70mph on the Ohio Turnpike & got 19-20mpg the whole time with his DP Tuner set in 80 ecno. We didn't try it with it set in stock to see what it would do but with the amount of traffic the added power was nice to have if we needed to get out of the way in a hurry.

On another story when I got the IDI it had a 2.5" exhaust coming down to a gasser muffler then the tail pipe was only 2.25" big. The tail pipe was smaller than the manifolds... It also had a large fiberglass topper on the back that was promptly removed. With just a straight pipe & a normal open pickup box I could see 16 mpg on a regular basis in the summer. The last owner said the average he normally saw was 14mpg. So I'm not sure what did more, the straight pipe or removing the topper but all I know is that it picked up a MPG or two.