I have a 94 f150 (4x4, 5.8, E4OD, excab) that currently has 3.55 gears in it. The previous owner put a 6" lift on it and 33's and I feel that the 3.55's are a bit too tall for it. According to the gear calculators 4.10's would put it back to a stock feel/ ratio but I am worried that 4.10's will negatively affect fuel mileage and highway driveability. I was thinking about finding a rear axle from the junkyard with 3.73's to see how that changes the feel of the truck. My question is did ford every put 3.73's in these trucks stock? It seems like all I can find are 3.55's and 4.10's.

Anyone running a similar set up with either 3.73's or 4.10's? How do they seem to do towing, driving on the highway, fuel mileage over the 3.55's, etc?

 

3.73's are pretty rare and there isn't much difference between them and 3.55's. IMO not worth the hassle or expense even with a junkyard axle.

4.10's are going to get you as close to stock as possible. If you're worried about gas mileage, keep in mind that with 33's and 3.55's your engine has to work VERY hard to get the truck up to speed. You won't have to use as much throttle to get to speed with shorter gears. Also, your truck won't have to downshift to get over any little hill. In all probability, your gas mileage will go up or stay the same. I would be very surprised if it went down.

 

Right. Consider this
Larger tired effectively makes the overall gearing from crankshaft to the ground taller so by putting 4.10's, lower gears in, you are just returning the overall ratio to close to what it was factory
As far as mpgs go. There is a mystical balance between gearing it low enough so the engine doesn't work too hard an gearing it too low so the engine revs more than necessary and wastes gas
Overall in my opinion if 3.55 feels like to high of a ratio for 33's. Don't bother with 3.73. 4.10 is most likey what your looking for based on what I think your saying
I have 29's and 3.08 gears and I've considered swapping to 3.73
I think it's better to let the engine spin a bit faster and not work as hard especially in town
I think highway is where u might notice mpg drop if any

 

The 3.55's seem really tall if you are in alot of stop and go traffic. It takes alot to get her going. Once your moving it's not bad, even pulling a trailer. 4.10's would definitly take alot of strain off the motor and tranny. Maybe I will try and find a 4.10 axle from the junk yard and see how I like that. I would only be concerned about my highway mileage. I am sure it would go up around town.

 

3.73s were never a factory option in these trucks so don't bother looking. You need 4.10s period and you can expect an increase in fuel milage with them and another after you recalibrate the speedo for those larger tires, because I'll bet $$ that wasn't done by the PO... nobody seems to think it's necessary but they all complain about crappy fuel milage. HOW TO RECALIBRATE THE SPEEDOMETER ON 92-96 FORD F-SERIES AND BRONCO .: Articles

 

Another option, if you're interested, is to remove the lift and run 31's... Would be more cost effective, and these trucks are still capable in the dirt in stock trim.

 

WOW! I had absolutely no idea that the speedo could be recalibrated without using some type of tuning device or going back to the dealer. Does this apply to just OBD-II, or would it work on my '97 Speed Density?

Also, can you enlighten me on the effect that the actual calibration has on MPG. Other than throwing the odometer off in terms of manual MPG calculations (which can easily be taken into account), I don't understand what effect it would have. Is there something to do with the engine fuel management or something? Or, are you just saying that most people just go by the odometer reading and don't take into account the discrepancy caused by taller (or shorter) than stock tires?

 

^^^^Hes saying people just go by the odo reading, and when youre speedo is off, it wont read a mile accurately.

For comparison, my 95 has a 302 and 33s. I went down from 3:31s to 4:10s this past spring, and ive GAINED 2mpg because of it. The engine doesnt work anywhere near as hard to get moving, and is back in the correct area of the powerband when at highway speeds. Before it was always up/down shifting on the interstate, now it sits in OD and is happy about it.

 

This isn't really an option, I would spend just as much money taking the lift off as I would regearing. I don't really need the lift, I would have never put it on to start with, but in order to remove it I would need to find stock radius arms and all the stock brackets for the front axle. I would basicly need a stock parts truck.

If I can find a rear 4.10 axle at one of the local junkyards to swap in for $150 then I can pay a shop to swap out the front gear set and only be in it about $800.

 

This applies to all OBD-1 Ford trucks built after 1992 including the '96 and '97 HD trucks in the old body style.



It affects milage in three ways..

Since the ODO is accumulating fewer miles than actually travelled the math used to figure out fuel milage is off.
And since the speedo is reading slow you're actually driving faster than you think which will consume more fuel.
And also because the speedo is off the calculations used by the engine computer to determine how much fuel to add is wrong and the tranny shift points will be wrong... since all this is speed sensitive.

People use all sorts of methods to guesstimate how far they have travelled from road milage markers to a GPS to adding a percentage to what is displayed, but it all works better when the speedo is as accurate as possible.

 

^^ Excellent. Thank you very much!

My speedo is actually a little fast about (64 speedo MPH = 60 actual) since I have slightly shorter tires. I take it into account when I drive in terms of speed and also adjust when I calculate mileage for MPG. The math is pretty basic and I can get it to within negligable error limits, but it would be nice to not have to do the mental gymnastics and be more accurate at the same time.

I've wondered about things like the shift points being speed based or RPM based, but in my case it didn't seem to make any significant difference - although the OD to 3rd downshift at cruise speed may have more of an effect than I realize. If nothing else than for drivability reasons, I'm going to attempt to recalibrate my speedo this weekend. I'll monitor the MPG for a few tanks to see how far off I've been or how much effect it has.

 

Depends how much you drive the truck, and how long you plan on keeping it... MPG should improve if returned to stock, tires would be less, it should be more practical as a truck, and it should put less stress on certain parts. Price vs. cost. Short term vs. long term. All things to consider...