Rear End Posi

[asonfry26]

Just wondering what are my rear end options for and 87 2wd model. I would like to go with a something other than the stock 3.08 in it now but also incorporate either a posi or LSD...Thanks

[hatzie]

Which axle?

[piecesparts]

I and my son are running 12 bolt axles with 3.73 gears under our 84 and 86 SWB trucks.

[asonfry26]

I am running a 10 bolt rear...drivetrain is an LSX 5.3, carbed with mildly built th400. Just looking for a better gearing for that racing feel...will 4.10 be too low of a gear for driveability. And will i need posi rear for better performance. Thanks

[INSIDIOUS '86]

Go to 355 or 373's depending on how much "racing feel you want"
Posted via Mobile Device

[piecesparts]

Originally Posted by asonfry26

I am running a 10 bolt rear...drivetrain is an LSX 5.3, carbed with mildly built th400. Just looking for a better gearing for that racing feel...will 4.10 be too low of a gear for driveability. And will i need posi rear for better performance. Thanks

How tall of tires are you going to run? A 400 with 4.10s is a stump puller, but gas mileage is not in your fuiture.

[djunkie]

I've got 3.73's with a Detroit Tru Trac setup in my 10 bolt. Ive also got a 700r4 trans though. Tires are about 27" tall overall. Honestly in over drive on the freeway it's tacking about 2400 at 65-70 mph. With a turbo 400 it would be screaming. My mileage dropped a little when I got rid of the 3.08's. But it was a night and day difference power wise. Truck is a lot quicker and more responsive.
Posted via Mobile Device

[asonfry26]

Thanks folks. That is just what i needed. I think I will go with just a 3.73 gear. Im committed to the th400 since I have 3 of them and they are a cinch to rebuild although the 700 would be nice.

[beamn7]

I yanked the 3:08's out of mine and put in 3:73's Richmond's with a Auburn Cone Clutch carrier. Very happy with it. I had a THM400 in it for awhile but decided to go back to a 700R4 after swapping the gears. Tires are 31's and at 70 mph I'm getting about 2000 rpm where I was getting about 3000 with the THM400. 700's are easy to build too, just make sure you use a 85 or later model at the bare minimum but a 87 or newer model is better yet.

[notyo_cheez]

It's been suggested to me that unless you have overdrive 3.08 is the lowest you'll want for the street. The 700R4-equipped trucks employed 3.73 off the assembly line because of the overdrive. You'll run out of room on the highway with a low gear and only three speeds pushing it. Fuel economy? What's that?

Not sure if the 10-bolts have 30 spline axles, if so you can get an Eaton posi or LSD carrier and use the same gear and pinion. Call a friend to help you with this upgrade or find a local shop who can do it for you. A shop in Houston quoted me $850 for a posi conversion a number of years ago for a Dodge project I was working on, but lucked out and found an entire 3.36 assembly for $150 instead.

This is really beyond my depth so I stand to be corrected if I'm wrong. Unless you want to burn tires, gas and a bigger hole in your pocket go for it, or keep your 3.08 peg leg and change the oil when it needs it.

[beamn7]

Believe it or not alot of the factory 700'd trucks came with 3:08's as well, mine being one of 'em. Thing would almost idle down the freeway! 3:08's were good when I wasted the 700 and put the 400 in but once I wasted the one legger rear I opted for the 3:73's. Built a 700 for it not long after doing the rear since now she was screamin' down the highway....

[asonfry26]

I guess I will just pony up the dough for an LSD.3.42 may be a better comprise. I running 20 inch 245/50 tires. There is a guy on this forum with an awesome flat black square pro street with like 15 inch rears. He has definitely got me thinking.

[slinginrods]

I am running the 3:08 700 combo and I hate it! It's getting 3:73 posi as soon as I can.not sure if the 700 will hold up to the 406 I built.plus I got a nasty converter already for a th350 so I'll probably go with a th350 .I ran as much as 4:56 on the street,high way was out of the question but damn thing would pull so hard it would flatten your eyeballs !!
Posted via Mobile Device

[beamn7]

I hear ya there! Hated the 700/3:08 combo too. Very happy with the 3:73/700 setup. Great around town and on the freeway. Just a good all around set up in my opinion.

[djunkie]

Originally Posted by beamn7

I hear ya there! Hated the 700/3:08 combo too. Very happy with the 3:73/700 setup. Great around town and on the freeway. Just a good all around set up in my opinion.

Same here. Feels like a whole different tuck now.
Posted via Mobile Device