I need a good explanation of the differences between a limited slip and a non-limited slip transmission. I have a 2000 4.6 supercab and it has a 3.08 non-limited slip transmission. I don't hotrod and mainly use it as a commuter vehicle and intend to do some fairly light towing (2800# or less) over varied length distances. The 3.08 is fine for commuting and seems to have more than enough spunk to get out of its own way and will probably fair well at high speeds with good gas mileage. Will my 3.08 non-limited slip suit my needs without damaging anything because I really don't want to sink any more money into this truck. Please, no over-kill recommendations on improving what may not be a problem at all. I look forward to some positive feedback. Thanks in advance. HarleyF150

 

A limited slip differential (the gears in the rear end, not the transmission) has clutches that distribute power evenly to both wheels, limiting the amout of wheel spin.

An open differntial (non- limited slip) has fewer moving parts. It sends power the the wheel with the least resistance. As long as you don't spin your tires, (drag racing, snow, mud) an open differential is perfectly functional and less prone to noise and failure in the long run.

The gears you have in the differential are not ideal for towing. The gears are turning 3.08 times for every 1 time the wheel rotates on the pavement. They're acceptible for a small fishing boat or light trailer, but the ratio puts a lot of stress on everything from the engine to the rear end if you pull something heavy. A gear ratio of 3.55:1 or 3.73:1 would put less stress on your truck and get you moving with less noticable effort.

If you are concerned, all you'd need to change the gear ratio is a ring and pinion. It's a very common mod and only costs around $500.00 parts and labor. Going from 3.08:1 to 3.73:1 is the most noticable performance improvement outside of major engine tuning.

 

AjRagno, Thanks alot for your info, I think I'll go for the 3.55 which would more than triple my tow capacity (but at the expense of gas mileage?), or even a 3.31 would almost triple my capacity, do you think that the gas mileage would be about the same as a 3.55? Also, I guess I'd have to have the computer reprogrammed for this change by the dealership, (Cost?). How hard is it to install a new pinion and gear? Is this something I could do myself? I see you're from Minneapolis, I'm a transplant from Hibbing and now living just outside of Orlando,FL.

 

I'd go with what AjRagno said. If you're changing gears, I'd at least go to a 3:73. For around town driving many see an increase in MPG when stepping up to a taller gear. HWY you may see a little drop but you'd definetly be much beter off when your towing.

 

Good to meet you here. Part of me thinks it's too bad that you've moved away because Northern Minnetosta is so beautiful. Cold I know but, I go to Superior Nat'l Forest a few times a year and absolutely love it.

There's a very good RPM calculator here: http://4x4cyberstore.com/website/rpmchart.html It will tell you what your RPM's will be at with different gear ratios.

The difference between 3.08 and 3.73 is not going to affect the gas milage to an extreme but the performance will make it feel like a new engine. Another issue that will come up is that you will be higher up on the torque curve so the transmission will not down shift as frequently on hills, which is a big plus.

Removing the gears inside the differential is not very complicated in itself. The risk of doing it yourself however is that when you install a new ring and pinion, everything needs to be very precise or the gears will shred themselves and destroy the entire differential. You should leave this to a professional. Have it done at an offroad shop. They know more about this than just about any auto technician, including a Ford dealership.

You don't have to worry about re-programming the computer either. This will have no effect on it.


A Ford Motorsports ring and pinion are about $135.00. This is what they look like:

 

Changing gears on a late model will most definitly effect the computer. talk to Mike on the chip board, he can set you straight.

 

My truck came with the 3.55 open and it has plenty of get up and go and I get about 19 MPG on the highway on long trips not towing before I bought my truck I test drove a few to me the 3.08 just didn't have enough get up and go a 3.31 was better but once I drove one with the 3.55 I knew that I was going with one with a 3.55 gear.