I have a 1998 F150 with the 4.6
Is it an 8.8 rear end? Also what speedo gear would I need with a 3.73 gear and a 33" tire

 

I have the same year and engine. Yes it has an 8.8" rear end. As for the speedo gear for going to a taller tire, you will probably have to pull the one you have (5 min job) and count the teeth, then try the next one or two down in tooth count. A taller tire will effectively raise (lower numerically) you rear end ratio.
The speedo gears for the 97,98 trucks go for about $8.00 each and are available at most mustang parts suppliers. Unless you need the aftermarket 23 tooth gear for going to 4.10 and keeping the stock tire hight, (like I did) it goes for about $15.00.

check this place out for gears http://www.mustangparts.com/drivetrain.htm

Just one of many suppliers.

 

mikeintx,
I just realized what ratio you were asking about. If you currently have 3.55 and you go to 3.73 with taller tires you may not have to change the speedo gear. The taller tires will bring your effective ratio closer to where you were and the existing speedo gear may be your best bet. If you have 3.31 then you will have to try 1 or 2 different gears. When you start changing tire hight you may never get a perfect reading speedo with the available gears but you can get pretty close. Of course there are much more expensive alternatives from compainies like Truespeed involving electrical devices installed on the VSS harness.

Feel lucky, for those with 99 and up models changing a speedo gear isn't an option.

 

I currently have the 3.08 but I plan on putting in a 3.73 and a trac loc. I guess I will have to try some different speedo gears

 

There are a couple of mustang and 4R70W sites out there that have calculators just for figuring out what speedo gear tooth count to get verses gear ratio and tire hight. I seemed to have deleted their web sites but I'm sure you'll find them in a search.

Good luck

For the same price you can go to 4.10 with ford racing gears (silent). The difference in economy from 3.55 to 4.10 was about 1mpg but the difference in rear end torque was incredible.

 

Yeah I was thinking about 4.10's but I do alot of highway driving so I was leaning toward a 3.73. What kind of RPM's are you doing around 70 MPH?

 

I'm at 2000 on the nose at 60mph and just offhand I think its around 2300 or so at 70mph (in O/D). But that is with stock 30" tires. If you want 3.73 and you go with 33" tires you may have to get 4.10 to get an effective ratio close to 3.73. Otherwise you wiind up with an effective ratio closer to the stock 3.55. Either way it will be a big change from 3.08.

I just looked at Randy's Ring and Pinion and the calculator says that 3.73 with 33's is just a hair off of 3.55 with stock 30's. It will also let you know what RPM's you will run with each combo.

Here's the site: http://www.randysringandpinion.com/c...latorsind.html

The ratio for your tranny is 1.0:1 in 3rd and .70:1 in O/D(4th)

Good Luck

 

Thanks for the info. I just picked up a 4.10 and a trac loc. Now I just have to find some time to get them in.