Right now I have a '97 4.6 4x4 with 35s and open diff 8.8 with 3.55s. To me, the truck isn't a dog, but it could be a lot better. I offroad some, but not a ton and tow here and there but that could change soon. Right now I get about 12.5 mpg in the city (90% or more of my driving), and about 13.5 mixed.

Might have the chance to swap out for a 9.75 rear end with newer 4.56s, and new brakes. I've read that I would have to shorten my driveshaft since the pumpin sticks out further, but I've also read that if I'm lifted I might be able to avoid this. Would this strickly apply to suspension lifts? Because looking at my driveshaft it does look like it might be pulled out some. Few more questions... would my mpg increase at all? everything else should line up with the axles right? (both drum) And as long as I don't use 4WD until I can get my front gears swapped I shouldn't have any problems right?

Honestly, it seems more than worth it. It would save me a drum brake job, and relieve my tranny. I just want to get everything sorted out before I jump on it.

EDIT: Forgot to add, the 9.75 has a tru-lock LS clutch package, and Motive gears

 

You definitely should get 4:56s or 4:88s. I have the 4.6 and HAD 3:55s so I know what its like. TRUST me.. new gears and that truck will be completely different. Your 8.8 is more than strong enough for whatever you want and you could find a decent locker on craigslist sometimes for less that $200. I have my 8.8 and 4:56.. not to toot my own horn, but when I wanna smoke em I can.

BTW! I have an edge.. and my AVMPG is 16mpg. That is mixed my friend..

 

i thought about that same thing a while back and the drive shaft will need to be shortened about an inch like you said.

but like brad said i got an 8.8 ls diff for 150 off craigslist with 3.73 gears and it was brand new. gonna put some 4.56 in it and be good to go.

and im at around 11mpg city now

 

since you have a body lift, you have done nothing to the driveline length...


it's a simple swap, and you'll be able to find a truck in a wrecking yard with a 9.75 rear axle so you can snag the driveshaft

 

Well I'd be able to get the entire axle for a little more than the cost of the LS and the gears alone. Which is much cheaper than the last quote I got of about $600 per axle. Especially If i'd able to sell my old 8.8.

Jerame, I could get my driveshaft shortened for about $60. With the old JY driveshaft, wouldnt there be a good risk of it being out of balance?

 

yeah, only a driveline shop should shorten the driveshaft unless you want lots of vibrations...

 

Yeah i'd have it shortened by advanced driveline. My brother and some of his buddies have used them before and have had good results.

 

If only i had my stock 9.75 driveshaft tube that i threw away after lengthening the rear driveshaft after putting the fabtech kit on my truck... i would have given it to you, and you would've had to only pay labor for the job and not the new driveshaft tube. i'm kicking myself now that someone would have had a use for it, lol.

 

damn..lol oh well.

wait so, theres more to shortening the driveshaft than just the cut and weld? how much does a new drive shaft tube usually cost?

 

No,
they'll just use your drive-shaft and cut it.

Phil

 

well, they're not going to cut 1'' off your current tube and reweld the ends back on... it wouldn't balance correctly that way. they're going to give you an entire new piece of tube in the middle.

i recommend replacing the u-joints during this time as well.

I paid $198 out the door for my driveshaft to be lengthened and new u-joints by central FL driveshaft in lakeland.

they charge you by the foot for the driveshaft tubing.

 

hmm, alright. I just replaced the stock u-joints not too long ago though with greaseable ones, so I prob won't need those. I thought they only replaced it with another tube when they lengthened it? They just use your ends from your old one again. But when they shorten it they just cut the ends and take some off? Maybe not though

 

Your exactly right.
Any good reputable drive-shaft shop can shorten your drive shaft and balance it perfectly.

Phil

 

If you look closely at your driveshaft you will see that the ends are of two different diameters. At least mine is. The shop that shortened mine told me that they can not shorten it more then the length of the smaller diameter part of the tube. Any shorter and they have to build a new one. While you have it out of the extension housing take a good look at the slip yoke. If it is scored replace it and the bushing and the seal.

.

 

All looked good when I replaced the u joints a few months ago, but i'll definately take a look at all that again.

Picked up the axle today, i'll have to clean it up and paint it before I throw it under the truck but nothing bad. Suprisingly there wasn't even any rust besides a little surface rust inside the drums where they'd just been turned but that should clean up fine too. This 9.75 looks beastly compared to the 8.8

This may be a dumb question, but how do I know how much to shorten the driveshaft? I've read it's usually around an inch, but it'd be nice to know for sure. Also, all my brake cables should bolt or sit right in where the existing ones were on the 9.75 right? He left a few on there but I figured if I could just use mine it'd make it a little easier.