Looking to do a rear end swap. From a open 3.08 to a 3.55 LSD. Any ideas or suggestions.

 

LS any day.

 

I don't know what to tell you except go for it. You won't be disappointed

 

why are you wanting 3.55s? what engine tranny and wheel size are you running?

 

4.0L Auto with a 0.75:1 OD with a 3.08 rear end and 28.8" tall tires. Doing a little math, that puts my engine at 1482.2 RPMs @ 55 mph with a 3.08 ... With a 3.55 the engine will be at 1708.4 RPMs @ 55 mph. I believe that the tall gear and tires are whats giving me my transmission problems.

 

You might want to consider going to the next gear and get a 3.73. They are pretty common and not to hard to get your hands on. It's a good all around gear for freeway and city driving, and would give you a little more room later on if you ever wanted to go to larger tires, as well as a little peppier truck. Just my opinion.

 

Don't know if this will help your decision or not, but I had 4.10's in my Ranger and now 3.73's in my Taco. If you're planning to be on-road much more than off-road, I'd say the 3.73's are what you'd want. In the Ranger, I'd turn 2500 RPMS at 60-65. I can go considerably faster in the Taco and not touch 2500 RPMS. Again, it's going to be based on how/what most of your driving will be.

 

^^^ The gearing in the transmission also makes a difference, you are comparing 2 completely different trucks....

 

Good point. I hadn't considered that.

 

No prob, but I have often thought about that too, another factor is that manufacturers gear a vehicle to stay within its power band, every motor is different, so gearing would be different too. Just some food for thought. :)

 

yea I'd definitly go with either a 3.73 or more likely a 4.10. If you like to cruise at 80-90 then go with the 3.73, but if you run mostly on the highway between 65-80 or under then go with the 4.10s. You're truck and you will love them. 4.10s are what come factory on most of the newer trucks and they have about a 29 inch tall tire stock. Even the 4.0L likes to stay up around 2500RPMs at least and definitly above 2000 when cruising. Lower than that and you are lugging then engine and killing gas mileage.

 

No, a 4.10 to low. 3.73 or 3.55. Well see what i can fine.

 

ok, well keep in mind you can use any ranger axle for a bolt in swap from 93-07 either a 7.5 or an 8.8 although with the 4.0L I'd go for an 8.8. But you can use any of them as long as it's 93 or newer.

 

Iam just going to change out the chunk not the whole axle, just to let you know.

 

AnyOne Else ??

 

Yes I have some input!

First off.. a 4.10 is not too steep. Don't assume it is and that you'll use more fuel as a result.

The 4.0L motor is a short stroke motor. The piston speed is lower in relation to other engines. This means that the torque curve is higher. And to make adequate torque you need to rev the motor.

If you have a scanner that can read data live you'd see that engine load and fuel trims are actually **more** when lugging the engine! Do *NOT* assume that a higher rpm will consume more fuel. Often times is doesn't.

The slower you operate the engine (35-55mph) the more advantage you'll see in milage from a steeper gear. You'll find yourself pushing the pedal less to get the same effects. Now by the same token.. if your a heavy footed driver and push 80-85mph out on the freeways? (like around here) then a 3.55 or a 3.73 might be a better choice.

That said, I'd suggest a set of 4.10s, or 3.73s and a detroit true trac diff.
If you can't afford the TT then get a ford LS.

Rich

 

get your self some 3.73's and a LS. that will do your truck good. That was my setup stock and it got my good mileage and the tranny never ran hot. Purely highway driving between 70 and 75 would get me 20+ mpg.

If you drive just on the highway then maybe 3.55 would be okay but 3.73 is going to help you a lot around town over those 3.08's. you won't need to press that pedal down nearly as much to get the same mph pickup with the 3.73's.

LS is not really needed if you don't go off road or tow. You live in georgia so snow is not a problem. If you tow or offroad then get a LS. The open diff will suit you perfectly if 100% of your driving is on pavement.

 

wydopnthrtl, i wasn't assuming anything...

 

Heres what I come up with while running my 28.8" tires (3.08@55=1482rpm / 3.08@80=2156rpm) (3.55@55=1708rpm / 3.55@80=2485rpm) (3.73@55=1795rpm / 3.73@80=2611rpm) (4.10@55=1973rpm / 4.10@80=2870rpm) Here what i get for the 27.9" Tire that i my switch to (3.08@55=1530rpm / 3.08@80=2225) (3.55@55=1763rpm / 3.55@80=2565rpm) (3.73@55=1852rpm / 3.73@80=2695rpm) (4.10@55=2036rpm / 4.10@80=2962rpm) With my STOCK TIRE SIZE (3.08@55=1617rpm / 3.08@80=2352rpm)

 

Sorry for being presumptive myself. I just would'nt go with a 3.55 on a 4.0L ford. The piston speed is just slow.. the TQ curve demands rpms. Or at least *my* foot does. Which btw.. I'm getting 21-22mpg now with 4.10s

Anyway, Here is a decent little online calculator. (enter data at the bottom)

http://www.csgnetwork.com/multirpmcalc.html

Regards,
Rich

 

based on those numbers you posted 3.73s would be the highest you should go and a 4.10 would seem to be ideal... If 80 percent of the time in your truck is spent doing 80+ on the highway than the 3.73s should be fine, but if youve got a good amount of city driving or under 50MPH driving, or if the time spent on the highway is really around 70MPH then the 4.10s would be perfect.