Rear end info -- 68 Shortbed

[JJchamp48]

This is hat I've got:
-- 68 shortbed stepside Chevy 1/2 ton.
-- HD rear coil springs.
-- Factory 4:11 rear end. (for some reason I thought it was Posi but am not positive. factory option #4H04CA). I have not gotten # of diff yet.
-- Powerglide tranny was factory. Someone swapped it out w/ a 3 spd, but I have orginial tranny.
-- was 6 cyl, po installed 350 which blew up. I am installing a 65 Vette 327.
-- tires are 275/60/16, 6 lug

What I want to do:
-- I live in the mountains but don't climb them regularly
-- Being rural, I don't drive in the city much, just on trips to town.
-- most of my driving is 55 or better
-- I will be travelling in truck to races, kid's college, visit family, etc which will be mostly interstate speeds.
-- I want a cruising gear more appropriate for my use

This will not be a daily driver. I have a GMC for any heavy hauling, firewood, etc I need to do.
I was thinking about 3:42 but was told I needed a smaller carrier to switch to that ratio.
I am also thinking swapping rear ends would be easier, but not sure which ones interchange.
Any help would be greatly appreciated.

[Shaky]

It sounds like you have your hands around it.

I'm assuming the 3-speed is a turbo 350 (maybe a 400). If so, 3.42s and that transmission is a good combo for what you want to do.

The bad news is that I've never seen a factory 3.42 on all the trucks we ever played with. 90% were 3.73s. Also, you're right - you'll need a different carrier for the 3.42s and the ability to set pinion depth, etc. if you decide to do it yourself.

[raycow]

A rear end swap will cost less than putting new gears in your present housing. Any 65-70 1/2 ton coil spring rear will be a bolt-in. 71-72 will work too, but they are 5 lug. These rears were available with gears down to 3.07, so you just have to keep looking. You can determine the ratio close enough just by counting.

Jack one rear wheel off the ground, put the transmission in neutral, and the parking brake off. Put matching marks on the pinion yoke and differential housing. Turn the wheel exactly TWO revolutions and count how many times the driveshaft turns, estimating any fractional turn as closely as possible. That number is your axle ratio.

If the wheel is difficult or impossible to turn, you may have posi. In that case, jack both rear wheels off the ground and turn either of them only ONE revolution. Count the driveshaft turns the same way as for an open rear.

Ray

[JJchamp48]

Since I've never messed with a rear end, this would be my 'guinea pig'. I have no doubt I could figure it out, but not sure now is the right time, maybe on my next truck.
Anyhow, I have a chance to get 3.42 gear set cheap, but need to know for sure it will work. Is the carrier the only thing I would need besides gears?
Also, is the carrier the pumpkin that I see under the truck or is it inside? From the books, I thought it was the outer hsg (pumpkin), then the posi unit inside, so just wanted to make sure which part carrier referred to.
Thanks,
Vickie

[JJchamp48]

I have nice 6 lugs that I would like to keep if possible, hence swapping rears sounds limited. Also if it is not Posi, will that make a difference on switching gears?

[68custom396]

The carrier will have to be changed if your wanting a 342 gear. Posi or not will not make a difference if the gears will work for you. You will need to know if you have a 12 or 10 bolt rear end and if you have 30 or 33 spline axels if you do buy a carrier to fit those gears. The carrier is inside the housing. The part your seeing when you look under the truck
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[Jacfourteen]

3.42 sounds about right for what you want. The carrier is the large section inside the housing that the ring gear attaches to and the axles slide into. As far as changing gears yourself its kind of iffy, there are people that say they had good success and there are others (like me) that run into BIG problems later. I have swapped many engines, trannies, rebuilt a few engines, etc and I figured I could handle swapping gears on a 94 ranger I used to have. Long story short, it worked great after the swap.....for 2 days, after that it wouldn't move. I pulled it apart and the carrier was sheared of at each bearing, so the carier was now in 3 peices. I ended up finding a junkyard rear with the ratio I wanted for $125 and swapped the whole thing in and it ran great the rest of the time I had the truck. Not trying to scare you, just trying to let you know to do your research before jumping in. Good luck with everything.

[JJchamp48]

Ok, I've got a 12 bolt rear. Not sure on splines, will check out. Out of curiosity, where is the difference in the carrier, is it larger on 4:11 or some other difference?

I didn't know this rear would be as much a pain, but I want it ready when engine is put in. Can't think of anything more aggravating than having a truck I can't drive.
The 350 that was in it only made it 100 miles at 50mph. Not sure if engine had issues beforehand or not.
Anyhoo, I want it right and if I just need the carrier, that's what I'll go with. Just got the 3.42 gears so will hunt for carrier.

Thanks,
Vickie

[JJchamp48]

Anyone in central VA area who knows how to do this, send me a price.
I want it done right tho, it takes same labor to install new parts or old, so I would want anything replaced that needs to be. My dad has been an outboard mechanic for 50 years and I learned that many years ago. I've
seen too many people try to save money by not replacing something only to have to pay labor again to do what they should have done to begin with.

I have family in Tidewater area, daughter is in college in Johnson City, TN and I go to races in NC, so any of these areas are ok too. I travel these areas every month just about.

Thanks,
Vickie

[Jacfourteen]

Originally Posted by JJchamp48

Anyone in central VA area who knows how to do this, send me a price.

Sorry I can't help by recommending someone, but I when you find someone you might want to ask them if they mind you watching/giving them a hand so that you can gain some firsthand knowledge so you might be able to do it yourself the next time around. Next time I need a gear change this is what I plan to do so I see what is involved. My other advice is that if you need to find a new carrier you might want to find one that is posi or a locker, otherwise you will prolly end up wanting one later. Once again good luck and I hope you find someone who is willing to teach you a little about the process.

[raycow]

Originally Posted by JJchamp48

Out of curiosity, where is the difference in the carrier, is it larger on 4:11 or some other difference?

The part that the ring gear bolts to is actually called a differential case by GM. This may be causing some confusion if you are looking for parts.

The difference between 3.42-down and 3.73-up is the location of the flange that the ring gear attaches to. As the gear ratio gets numerically higher, the pinion has to get smaller, because the ring gears are all the same diameter. To accommodate this, the flange on the 3.73-up case is closer to the pinion centerline. This is done so the ring gear doesn't get excessively thick and heavy.

The difference in flange location will be quite evident when you have the two cases side by side.

Ray