Hi all,
I've started to plan mods for my truck (I have an '01 4x2 S'crew), and there is a wealth of info here. I've been able to answer a great deal of my questions just by reading the forums, but I have a few questions I can't find the answers to.

Before I go into the questions, you should know I have the 4.6 engine, the automatic, and the 3.55ls rear axle. In addition, I’m running on stock tires – 30” in diameter. In addition, I split driving in town/highway miles about 60/40. The speed limit in Nebraska is 75 on the interstate, which means most people are pushing 80, and I’m usually right there with them.

I might add as well that I have a slight whine from the rear under hard acceleration – only noticeable right before the shift points – and it sounds like that’s not uncommon, and that there’s probably a good chance changing the rear gears might not make that go away.

I’ve been checking into using rear gearing to “wake up” the truck a bit, and so I know my choices from Ford Racing are the 3.73 and the 4.10. (I plan to have Troyer work his magic under the hood as well someday – as I said, I’m just researching the “what-ifs” for modding my truck). Anyway, the 3.73 is about a 5% change in gearing – which doesn’t seem like much, and the 4.10 is a little over 15% change in gearing – which will add around 300-400 rpm at 75mph. I know I could probably adjust some of this back with tire size if I needed to – but I’ve lowered my truck (1”/2”), and I’d rather not raise it back up with bigger tires. (Although I suppose it would fill the wheel well a tad better.)

Okay – so now the questions.

First, I’ve read posts where guys think the 4.10 might not be the best for cruising speeds of 70mph or more – will a 4.10 be too hard on my engine?

Second, is going to the 3.73 enough to wake up the truck in town?

Next – I know that Ford Racing doesn’t make a 3.89 for the 8.8 rear – but Jeg’s does – what would be the drawbacks for using these gears? Reliability? I ask because the 3.89 seems to be the happy medium between the 3.73 and the 4.10.

Finally – Would you guys buy used gears? I keep looking at different deals, and I see some used ones that are low miles that are way cheaper than new – but is it just a crap shoot?

You have now officially made it to the end of my post! Congratulations! (And thanks for putting up with my rambling . . .)

 

4.10's would be fine in your truck. i had 4.10's in my ranger off road and it only had a 3.0. Tach ran at about 2500 or so at 70mph. I have heard that the 4.6's really get better as they open up in the higher rpms. i do not know if this is true or not but my truck has 4.56's in it and it does great out on the highway.

 

I would also agree with 4.10s. It may be worthwhile to simulate what your engine would feel like by driving at an equivalent RPM with OD off - this is what I did before I got the 4.56s, and it worked out very nicely since my gear swap (3.55 to 4.56 = 28%) almost exactly matched the D/OD ratio (1 to 0.7 I believe). It may help you decide if your engine will be too wound up for your tastes.

I wouldn't buy used gears because 1) they have to be a matched set, and you may not know that they are for sure; 2) you won't know how well the guy before set them up, so they could look OK but could be on their way to looking like crap after x? miles, and 3) gears aren't that expensive not to buy new. With a 2wd, I imagine you wouldn't save more than $150-200 on a set. If you have to go back into your rear end before that truck dies because of your used gears, you just paid for a new set and then some. Definitely put in new bearings, seals, etc. while the diff is open.

Gas mileage hasn't suffered but a few tenths so far (2 tanks). This weekend I will be going to Florida so I will see if the extra 4-500 RPMs I pull will substantially decrease it.

Good luck -

Mike

 

Thanks for the input guys. I tried driving with the O/D off, and it seemed a bit too much - but I have time to decide, and this definitely helps. I'm thinking about playing around with the percentage change of tire sizes/gears until I get what I'd like to see from stock. Here's my reasoning:

Both of you are running 34.5" or so tires - about a 15% change from stock 30" tires. Both of you are also running 4.56 gears - about a 28% change from 3.55 gears. That means your total change from stock is 13%.

If I leave the tires the same (30"), changing from 3.55 to 4.10 is about 15% - so I'd be changing % (and rpm) about the same as what you guys have already done. It sounds to me like I won't kill my truck by going to the 4.10 gears, and I can always adjust back from there with tire size if I think it's too much. With the 4x2, I can't go as big as you guys, but I think I could get away with a 32" tall tire if need be, which could cut it back in half.

Still, many options - but thanks for putting me on the right track for parameters of what guys are doing with their trucks.

Also, thanks for the input about buying new gears. I kinda figured that was the way to go, and it was nice to have it reinforced.

Thanks again!