Just wanted to know if there is an easy way to find out which rear end I have. I would like to know what gear ratio and also if It has a limited slip or not. It is a 2001 Screw 4x4 W/ 5.4L Auto also a Lariat if that makes any difference.

 

Check the drivers door jamb for the build tag. On it you will find an axle code that will tell you what you have. There is also a tag attatched to one of the bolts on the diff itself with all the info you need.

 

When you look at the axle code, 18 is a 3.08 ratio and 19 is a 3.55 ratio. these are the most common, if the code is different it is most likely the 3.31 ratio. If the 1 in the code is replaced by an "H" than it's limited slip

 

Thanks guys I will look in the door jamb first. Thanksagain

 

H9

 

Your rear axle is a Sterling 9.75.This is the rear they put behind all the 5.4L,as far as you axle gearing it's probably 3.55 or 3.73.

 

Since yall are on the subject. I have checked mine and it says 18 on it. So I figure that means I have a 3.08 w/o limited slip. The problem is I have a 1998 4.6 4X2 and I just upgraded tire sizes from 235/70 16 to 245/75 16. Somone tell me if I am wrong on this...This means I now have an effective gear ratio of something like 2.93. My truck can't hardly move uphill.

What is the best ratio to move to, and whay type of rear-end do I have so that I may order parts.

THanks

 

Yes, those suck. You have a 8.8". Personal preference would be 4.10's. This would surpass your tire change reduction and substantially increase performance/towing.

 

How, do I know if I have an 8.8 or a 9.75 rear end, as some vehicles are 98 f-150 2wd and they have 9.75, and I just thought that most f-150's had the 8.8. Is there a code for that too? I have made no mods to mine, it is stock. I bought the truck used, so I don't know if the 9.75 was an option for that year?

Thanks,

Mike

 

19 – 3.55 Non-LS
18 – 3.08 Non-LS
H9 – 3.55 LS
B6 – 3.73 LS
check this link for info on decoding you door jamb sticker

 

4.2s and 4.6s have the 8.8". 5.4s have the 9.75". If you want to double check, there is a tag under one of the cover bolts. The second row of information includes the size numerically. Even easier, the 9.75" has 12 bolts on the cover.

 

OK,

Now that I have new tires and will be getting new gears, I am sure that I will have to calibrate my speedo. In my 98 f-150, do I have the gear that needs to be swapped, or can I do this with a tuner, dealer ECM flash...etc.

old tires: 235/70R16 Diameter: 29"
new tires: 245/75R16 Diameter: 30.5"

old gears: 3.08
new gears: 3.73

I have used many calculators and I think that I will might be able to keep trak of speed with RPM's, but this in inconvenient and not very accurate.

I have checked many threads and searched, but didn't find my specific vehicle and saw each of the options listed above for other year models.

Thanks ahead of time for any help.

Mwkatm

 

1998 needs the gear. Try this:

http://www.f150online.com/forums/lin...ges/speedo.htm

 

Max,

Thanks for the link, looks like for my set up, no matter which drive gear I have, I just need to count the teeth on the driven gear and increase the number of teeth by 15% (at least that is what my math tells me). I do have a question though. Where do I get them, will a dealer have them, the link you sent me has part numbers for gears, however I have no clue which company's website I am on when I am there.

Again, I really appreciate all of your help, and by the way, I have installed my new 3.73 gears and I absolutely love them, its like I have a new truck. NO more sissy downshifts on tiny hills. I'll bet it even runs better when the ECM gets a better idea of how fast I am driving so it can calibrate shift points, and timing adjustments.

Thanks,

Mike

 

You're Welcome ! Yes, gears really wake a vehicle up and give it a whole new attitude. A bunch of places sell the gears. The Ford or Ford Racing pieces are quieter than some. Try here:

www.steeda.com/store/-catalog/speedometer.htm
www.redrider.us/ford_aode_parts.htm

Most Mustang parts dealers sell them. Try a general browser search for ["mustang" and "speedometer gear"] or search here for "speedometer gear" and several pages of member experiences on F-150s will pop up.