What's my rear end?
 

Hey all, so I have a still relatively new 150, and I'm wondering what I got here. It's an '08 Scab 4x4 5.4L with the 18 chrome clad wheels. The rear is a 3.55 "Regular Axle". Does this mean I have a non-ls? Not sure what they meant by regular? Also, what would my diff be? the 9.75 or 8.8? I'm guessing what I have is a 3.55 non ls 9.75, but not sure. Also, I was considering going 4.10s, but don't know if it's worth it. I'm very happy now with off the line accel, and I like the top end I have. I know taller gears mean lower top end, but I did see a comment in another thread that top end would possibly be increased. Not sure at all how that's possible though. If I did go the 4.10 route, what would I be looking at for cost of gears and install considering I'd have to do front and rear. I'm sure it would be a pretty high number....

the v6 and the 4.6 v8 have a 8.8 the 5.4 has a 9.75

Yes, you have a "open" diff. The 4.10's will help with accel. and midrange. My truck with 3.55's on the dyno would run 125mph in 3rd, so unless you are wanting to run 130mph+ the 4.10's will be fine. The downside will be that the truck will turn more RPM on the highway reducing those mpg's, but in the city they should go up. I had gears for my 98 4x4 priced for $1600.

Yes thats what you have

and yes 4.10s is what alot of people go with and are happy with

Alright, great, thanks fellas. I figured that's what I was dealing with here. I would like to go with 4.10s, however where the truck is still so new I think I'm gonna run with what it's got for now.

Now by being an open diff, that means I get 50% power to both rear wheels all the time, correct? As in power would never be diverted to another axle in say snow or mud, it's always being evenly distributed? I should know this considering the last time I layed a small patch there they were, two beautiful marks left behind me, not a single line :devil:

If you laid 2 tracks it's more than likely a LS diff. if it were open you would have had 1 track.
under normal driving conditions only one wheel is driving the vehicle. when the wheel "slips" the other wheel will lock in to help drive the vehicle. If it were an open diff. then the power goes to the wheel of least resistance.
I have done a lot of research on the regearing and I am going from a 3.55 to a 4.10's with an Auburn hp diff. the gears I chose are motive. The reason I am doing the gear swap is I tow a 7,400# trailer.

If the axle code on the door sticker is 19, it's open 3.55, if it's H9, it's LS 3.55.

I always thought that the power going to the wheel of least resistance under normal driving IS ls, therefor when that wheel slips, power is diverted, limiting the slip of the wheels. And so I thought in an open diff, power goes to both wheels all the time, 50/50, not slipping ever so in a slipperey situation you could potentially get stuck easier. If it only went to one drivewheel what good would that do you?

With an open diff, the power goes to the wheel with the least traction, the other wheel just sits there, when you have unequal traction coefficients between the 2 wheels. LS will engage the clutch pack under these conditions and get the other wheel moving.

to get power to split 50/50 to each rear wheel would require a locker. That is why, when someone with a locker goes around a sharp turn, their tires chirp.

Here ya go, this is a pretty decent web site. It should help.

http://www.houseofthud.com/differentials.htm

Wow, you really do learn something new everyday! Thanks everyone for all the great info, and that website is awesome talking about the ls and open diffs. So now the question is, do I want a locker? What are the advantages, I know the disadvantages are it puts more stress on drivetrain, inside tire can wear more due to spinning, but what gains are there?

gains = TRACTION! And actually there is not really any big "tire wear" issue any more. Detroit has made a new revised locker that allows for the inside tire to spin a little bit more (as long as you don't gun it).

Lockers will get you over and through much more difficult stuff. They will also give you a better launch and better traction. I have ordered some 4.88's and a detroit for my truck personally.

99 4.2 differentials...
 

i have a 99 4.2 extended cab. i wanna know what rear end it is and what gears are in it ? my buddy is selling me a 8.5 with 3.73s and a traction lock i think the rear end is out a 88 5.0 because it bolted up to his 67 mustang, will this rear end fit my truck or if not will the gears fit my rear end...

Jorge, with a 4.2 you have an 8.8" rear, get the axle code off the door jamb sticker to see what the ratio is and whether it's limited slip or open.

That depends on what you are using it for.

If you do a lot of driving on snow and ice, it is kind of as double edged sword. When you lose traction on ice wit only one wheel, the on that keeps traction helps keep your vehicle traveling in a straight line. If you are using a locker or even Ls, when both rear wheels break loose on ice, especially on the highway, things get a lot more interesting.

They are great for mud and offroading though.