Hello all. I'm looking for some guidance.

I have a 1999 Expedition which I bought used locally. It has a 4.6L without the tow package (2WD). We have been using it to tow our camper the past 2 yrs after installing a hitch receiver, elec brakes, trans cooler. When not towing it is our 3rd vehicle for special events (people hauler, other vehicle broken, etc.).

Background complete, now my question. I want to get better performance when towing and have considered performance tuners, better exhaust, K&N air cleaner, etc. My first thought is to replace the gear ratio to the stock ratio for tow package equipped Expeditions (3.55 I believe). What is entailed with this? Has anyone had this done? Costly? Does it cause problems with speedometer calibration? Any other thoughts welcome short of selling the truck since it is almost paid-off and is otherwise a solid vehicle.

Thanks in advance for your help.

 

To check your stock ratio, look at the axle cose on the door jamb sticker. We have a code translator in the articles section... it will be the same as an F150. Next you may need to crawl under the Expy to look at the rear end ring gear size, it should be an 8.8," but you could also expect to see a 9.75," as well. The tag hangs off the diff by one bolt. You're interested in the second line on that tag. It has the ratio and ring gear size stamped on it something like this:

XXXXXX XXXX
3 31 8 8 XXXX
or
XXXXXX XXXX
3 55 9 75 XXXX

When replacing the gears you'll need a complete ring gear/pinion set for your rear end size, as well as a installation kit. If you've never done this before (and it sounds that way) it may be best to have a mechanic do it, unless you have a few rear ends to practice on, or don't mind paying more to "experiment" as it were. The tolerences you're working with require feeler gauges and dial indicators for proper fit-up.

I'd recommend actually going with a 3.73 gear set if you tow often. It will increase the life of the engine and tranny, as they won't have to work as much. This does depend on the weight of the trailer, too. The specs for a '99 should be very similar to a '01... look in that section here at FTE to assist you with determing the tow weights between the gear sets. It looks like the 3.73 set raises the GCWR about 1,000lbs...

I'd supposed you could spend under $500 to have one differential done including parts. People around here have spent either side of that and been happy with the result. The materials should be between $150-250 w/gears, install kit and fluids, it's more about quality as far as the price goes. It should only take a mechanic a couple hours at the most to set it up and put it back on the road.

The speedo will be out of cal withb a gear swap. I'm unsure about the '99 Expy's speedo cal location. It could be an ECU function or it may be a gear in the tranny tail shaft or rear diff. Someone else will have to give you that info. If it's an ECU change, an after market tuner will help for about $300-500. Not only can you change the gear ratio with a tuner, you can program in a few extra horses, too.

Opening the intake and exhaust, making them less restrictive, will help,but the biggest bang for the buck without going to some forced induction is the gears.

Hope that helps.

-Kerry

 

I appreciate your taking the time for so much info. I'll check the things you recommended. You are correct in that I'll probably have a shop do the work. Do you think that it would be better to have the Ford dealer to do it or is this kind of thing getting too far "outside of the box" for them?

 

You might talk to their rearend guy, me may do it on the side cheaper. That's how I got the 3.55's put in my Mustang.
What size tires do you have? I would go with 3.73's or 4.10's. If I ever get the Money, I'm gonna put 4.10's in mine. The 3.55's aren't enough with the 17" wheels.

 

Well, after shopping around for possible replacement trucks, I decided to go the cheapest route which is to switch to 3.73 gears in the rear end. I had previously loaded the Edge programmer and will use the software to re-calibrate the speedo.

I guess my decision was based on the fact this is not a full time vehicle for me and my family (we have gas sippers for that including my almost indestructable 1995 Taurus GL with the 3.0 L Vulcan V6, 210,000 miles and goin' strong) and I couldn't justify a big ticket purchase especially since the truck has been so reliable.

The work is being done by a local shop whom I trust and don't mind paying extra (total $900 parts and labor) to get the job done right the first time.

Our first trip will be up Afton Mountain (I-64 outside Charlottesville, VA) this week. I'll post a follow-up when we return. Fingers crossed!

 

What gears do you have now? What is the tire size.
I'm going with 4.10's in mine when the funds allow. I have to do front and rear, so mine will be double the cost.

 

Yes what ratio did you decide on? I am curious, I have the ultimate highway gears in my van 3.08 and would like to swap mine as well. It sounds like we use our trucks the same way.
For those that have changed how has your mileage been since the swap?

humpty

 

Sorry about the dealy in responding. We've been having fun camping.

Anyway, the gear swap has been performed. The original factory ratio was 3.31 and it has been modified to 3.73. I had previously installed the Edge Evolution software and it has properly recalibrated the speedometer to the new ratio.

The performance when towing has improved substantially. As for Afton Mt. (the U.S. 250 shortcut, not the gentle slope on I-64), well, it was still a bit of a slow go. It took a bit of learning to drive with the new ratios, but the transmission no longer had to downshift as often as before the modification.