Hello,

I have a 1999 automatic XLT 4.0 V6 2wd. Rear end is currently 8.8 open 3.55 gearing.

I have a 3" suspension lift and was planning on running 31" or 32" tires although I'm willing to go smaller. I do plan on highway towing and some off road. It also is my only transportation vehicle so I need it to get the best of all worlds.

What gearing should I upgrade to? I was thinking 4.30 would be the best option so that I get more torque than 4.10 but am not wearing the transmission as much as 4.56.

I was also originally going to get a lunchbox locker, but since I am redoing the gearing, is there a better option?

What should I do?

 

I wouldn't do Lunchbox locker, just ford limited slip(trac-lok) would do, and a 4.10, these would be available as stock from wrecking yards or ??, 1993 to 2012 Ranger would be direct fit

That should give to about a 3.65-3.70 ratio(31-32" tires) which would be good for MPG and towing with an automatic, I might go higher ratio with manual trans, but automatics have torque converters to pick up any slack

Lunckbox lockers are good, just not for "sometimes" use, they can be "grabby" when cornering especially on slippery surfaces, which can cause loss of control
When you go around a corner differential MUST be unLocked or you will drag outside wheel or spin inside wheel.
Lunckbox works by torque, so if you accelerate around a corner then differential locks and you have a problem

 

Okay, cool

So a ratio of 3.7 is optimal? If I find 4.30 gears, is it going to be too much work on the engine or tranny?

Do you think it's better to swap the entire axle or will just new gears be good?

Correct me if I'm wrong, I need these parts?
Axle Ring and Pinion
Trac-Lok

 

I think you will find the whole axle cost(used) and installed(you do this part) will be less money than ring/pinion and differential swap.
But price out both.

Ring and pinion is not plug and play, these need to be shimmed or rear end will whine, grind, clunk and wear excessively.
It is a good thing to learn, like any knowledge, but it is one of those areas that most don't use over and over again
While I think it would be good to know how to butcher a whole cow/steer, all knowledge is good, I really just want to eat the steaks so.............I pay to have that part done, lol.

If you can't find a used axle with specs you want then yes, go with ring/pinion differential replacement

Ratio 3.73 was optimal for both MPG and hauling loads, wasn't great at either
4.10 was better at hauling but lower MPG and top speed
3.45 was better for MPG and top speed, but lower torque for hauling

 

I'll look into cost.

Yeah, I agree. I've done all the work on my truck so far and intended to do this, but I can see the tolerances are very critical, so I'll take it to someone.

Now, I'm considering several things regarding the differential. I will be towing a lot on the highway and also through sandy desert areas. I may encounter ice as well though as I plan to travel to different areas of the country. What would be the best option (if price is not an obstacle), a clutch-less limited slip like the Detroit Trutrac or a selectable locker like an ARB? Also considering this is my daily driver.

With the ARB I get the benefits of an open differential, but also more traction when I really need it. Or just all around more traction with the trutrac? I've seen very mixed opinions. I don't want my handling or maneuverability to suffer.