I just picked up this truck. I have the 8.8 open axle (non-limited slip) I understand that they have the 31 spline axles. What can I do to make this a limited slip rear. Is it as simple as buying the unit and having my mech install it. It's a 3.73 gear.

 

Yes, buy a LS differential and have your mechanic exchange them. Typically, you will also need some level of installation kit.

 

Throw a 4.10 in there while its apart.

 

Well, after investigation, I'm going to stay 3.73; I will be towing a sled trailer and a 4.10 would be a bit much. Can I keep my ring and pinion and just put the posi unit in.

 

Just talked to the guy that did my 01 Lightning, he's got a new Ford Trac loc posi and will install it for $375, or thereabouts. Not bad. This guy is a top-notch installer. Comes highly recommended. Doing this will make me feel a lot better towing a trailer in the winter.

 

Yes, that's fine. Good luck with your installation.

 

Well, the Trak-loc is in and it certainly changed the characteristics of turning and accelleration. Kinda' reminds me of my SVT Lightning....kinda'. I had the guy put Mobile 1 gear oil in. Now, there's another factor in the mix. I am thinking about some 18x9.5 Roush wheels with 285/60-18 tires. These are around 1.5" taller than my stock NASCAR wheels. The new wheels measure 31.5" tall vs. 29" for the stock wheel/tire setup. What will this do to the speedo and trasmission shifting. Will I loose power if I don't chip it to make up for the taller tire.

 

Going with the taller tires will change both the speedo/odo and shift patterns. If it's a 1998, you can get a new VSS gear and that will fix it. Getting one with probably one less tooth on it then the one that's there now should fix you up.

You might notice a bit more of a 'bog' off the line or starting from a stop..... I've got 3.55 gears and went to a 31" tall tire from the stock 29" ones.... I swapped out the VSS and all is fine again.

I even tow a #4500 travel trailer and it has plenty of grunt to it... Well, I do have the 5.4.... The only things I've added was a 3" cat back single exhaust and a drop in K&N... Still pulls strong and I'm pulling around 2500 rpms @ 62 mph while in third and towing.... Seems to be the perfect match for my setup.

Just as an after thought, if you had gone with the 4.10 at the time you had the LS installed, your taller tires would be giving you an effective gear ratio of right around what you had with the 29" and 3.73 gears...... Oh well......

Good luck!

Mitch