I have a 99 F150, w/ 3.73s, but it has open diff, what would be my best choice in replacing the diff, I don't need anythign expensive like an air locker or anything. Any suggestions are welcome.

 

If the 99s still have an 8.8, which I'm sure they do, then there are several options as far a "posi" type unit. You could get a used traction loc (factory unit) and rebuild it, the rebuild kit is about $70 from ford. There is also the True Trac, which I beleive is available from through Ford as well, I have heard good things about them. The auburn is also available for an 8.8, but they are not rebuildable so once it wears out it makes a nice paper weight.

I've often wondered if you can put the clutches in an open unit and convert it to a posi, maybe someone can comment on that idea.

 

5.4's come with the 9.75" axle, not the 8.8. Sorry I can't help with any suggestions...

 

Sorry, didn't see that in the signature.

 

As of right now, Auburn and Ford motorsports make the only limited slips for the 9.75" rear end which you have with the torquey 5.4. You don't really want to replace the diff as that is a whole different problem since you would have to find an entire new axle assembly with the 5 on 135 mm that ford likes to use. Detroit and Powertrax do not make anything at this time for the 9.75 so go with the auburn. Klaibs

 

Its cool - we all miss stuff sometimes. I've been guilty of it myslef a time or two... Thanks for the info on the 8.8 though!

 

Thanks for the info, right now I'm leaning toward getting a stock posi unit from ford (I do have the 9.75), as it is significantly cheaper, and I'm pretty sure thats the same one they use in the lightnings, and I"ve never heard of any problems with them.

 

Does anyone know the ford part number for a stock 9.75 posi unit?

 

I HAVE THE OPEN DIFF. DOES THAT MEAN ONE WHEEL IS TURNING ALL THE TIME, OR THAT THEY BOTH WILL SPIN, BUT JUST THE ONE WITH THE MOST TRACTION WILL PULL? MY QUESTION REALLY IS: WILL BOTH THE LEFT AND RIGHT SIDE TIRES TURN UN-SIMULTANEOUSLY GIVEN THE TRACTION THAT IT HAS? SORRY FOR GETTING SO TECHNICAL. ANY HELP WILL BE GREATLY ACCEPTED.

 

Open diff means that normally both wheels would be spinning. but the wheel that spins easier will recieve more torque. so as soon as one wheel starts to spin, it will keep spinning and the other one will not. thats also why it will only do 1 wheel burnouts. hope this helps, kinda hard to explain.