How in the world do I find out what rear end I have? I know from the axle code that I have 3.55. I am wanting to go to 4.10 but am unsure of what to buy. Everyone talks about 8.75 inch this and 9.5 inch that, but I am confused. Any help is much appreciated!

 

The '97 on 4.2L and 4.6L have an 8.8". The 5.4L has a 9.75".

 

Thanks, that sure does make it easier! Hope to have the new gears by the end of the week!

 

I have a 02 F150 with the 7700lb payload package(7 lug wheels etc...) and I can't find a tag on the rear diff. I want to order and install a set of 4.56's, but can't tell if it's the 9.75 or the 10.25. I was told that the 9.75 cover has 10 bolt holes and the 10.25 has 12 holes. I'm not sure if this is true because I'm also told that the 10.25 was only in the super duty,..And my cover has 12 holes. How can I tell prior to disassembly???

 

My F150 rear axle has 12 bolts and it's the 9.75". Don't the 10.25" have 14 bolts??

 

Well, mine has the 10.25 (according to the tag) and it has 12 bolts. Super Duties also have the 10.25, but it is (I believe) a full floater as opposed to the semi floater in the 7700's and LD250's. The 9.75's could also have 12 bolts but are still different on the inside. The only reason I know all this seemingly useless crap is because I wanted a truck I could put a slide-in camper on. And all these GVW and GVCW numbers come into play, not to mention actual payload. Hope this helps.
Gary

 

I ordered my 02 SC 4x4 with the 7700 lb package for the same reason. I have 27ft 5th wheel that the truck "carries" just great. Plenty of truck(spring, frame, cooling, shocks etc...) but the 3.73 was the lowest gear I could order, and 3.73's with 265x75x16 AT tires does not make for good towing. Opened up(at or near WOT) it pulls first gear up to 45 and second up to 65-70. I want to pull at around 60-65 for mileage purposes, but the slightest uphill run drops me back to second. So I decided to order and install a set of 4.56's. That's when I ran into the "which rear diff" do I have problem. I have been all over the rear diff, and so far can't find a tag. I have a tag telling me to use 75W140 SYN lube, and a tag with what looks like a FoMoCo engineering number on it, but no tag that says 9.75 3.73 or 10.25 3.73? The door code tells me it's a 3.73 limited slip but ???!!!

 

http://www.fordf150.net/howto/decode.htm

 

The door code translates to 3.73LS. This much I know. I need to know if I have a 9.75" or a 10.25" so I can order a new set of gears. So far the FORD dealer can't find a listing for a 10.25" in a 150. Only in the "Super-Duty's".

 

Will I notice a big difference as far as towing power and take off if i go from 3.55 to 4.10? Half of my miles are driven on the highway, the other half are to and from work. Is 4.30 too low to go?

 

bmw -- the tag with the engineering number should be the one that shows the size... it should have digits like 9 75 or 10 25 or 8 8 -- no decimal... on my 4x4 it's hanging off a bolt on the passenger side of the diff cover.

 

Wow, I'm amazed at how many people are getting new gears. I hadn't seen much talk of gears until recently on this site and now a lot of people are looking into this .

Well, for those who don't know...this is one hell of a mod...especially for automatics. Actualy for automatics, it's a MUCH NEEDED mod

 

There is a lot of action on this subject. Myself i am going to switch from a 3.55 Non LS to a 3.73 LS. I will be pulling a medium size Popup camper (plus all the supplies that go along with a 3 day trip).

So i wanted to beef up a little from the 3.55 and i wanted the extra traction that a LS would give me. I also would like to keep some of the mileage that i get now.

I have larger tires then stock (265/75/r16 vs 235/70/r16).

So any thoughts on the change.

 

fdpike, I would take a look at 4.10's if you are going through the trouble of installing 3.73's. I used to own a V6 powered 150 4X4 with the 5sp and I liked the truck, but it had zero torque, at low rpm anyway. Granted, I had 3.31's and 255-70-16 tires, but the truck absolutely fell on it's face with any kind of a load. Those 265's you have are quite a bit larger than the stock 235's, so a 4.10 rear would seem perfect, my .02!
Gary

 

I am torn on the whole subject right now. I do need as much trq as I can get, but also like gas mileage and decent RPM at highway speed.

I do like my 265's, my 4x2 sits up much higher then the other 4x2's I park next too and as high or even a little higher then the stock 4x4's.