Hey guys,
I got an 8.5" rear out of a '76 nova for my '67 camaro, i pulled out the freeway gears and open carrier, blasted it, painted it, and now am looking to rebuild it. I want to go to the junkyard to find a posi unit, as well as gears. Where should i look first? I couldnt find any good answers in search. What should i avoid, what's weak, etc... I'll be running about 425 hp through it, dont want something that'll grenade. Running the stock 28 spline nova axles as well...

Edit: looking for 4:10 gears :thumbsup:
any help would be great
olly

The easiest place to find posi units is in the 70-81 Camaros. I find that the mid-80's 4-wheel drive trucks are a good source for gears. The front axles have 8.5" ring and pinions and are lightly used. 3.73's are more common in the trucks than the Camaros, 4.10's are rare.

All Trans Am's have posi rear ends. The 1970-81's have the 8.5's. the older you find, the more likely you'll find 3.23 or 3.55's.If you can find a 79-81 Z-28, most of them came with 3.73's.

you won't find a 3.55 in any 10 bolt posi. 3.55 was 12 bolt only. Camaro Z28's typically had 3.42's if it was an auto and 3.73 if it was a 4 speed. Finding a used posi unit should be fairly simple...Monte Carlo's, Impala's, Camaro's, etc. Finding the 4.10 gears in junkyard might be a taller order. Consider new.

If you don't know how to tell the condition of a posi unit, have it checked (and possibly new clutches installed) before you go through the hassle of installing it.

i am doing the same thing.what is a fair price for a used posi,assuming it needs new clutches?

Also, you can look at full size mid 80's station wagons (Chevrolet/Pontiac/Oldsmobile/Buicks) that will have posi's in them, and should have 3.73:1 gears. I have checked several wagons and they almost always have posi's in them. Usually they are not picked over either.

I don't know what the steepest gear ratio was that was available for the 8.5's in those years but I would have to guess that the full size wagons have them!

I have 3.73 gears in my 1979 Camaro now. I was thinking about going to 4.10's. Would you recommend going to 4.10's or stick with the 3.73's, or do you recommend another? I plan to run this car at the strip on occasion, but for the most part, it will be a weekend driver. I am not worried about fuel mileage at all. The car currently has a mildly built up 305 with a TH350, but I am going to be putting a built up 327 into this car and I plan to run NOS. Thanks...Steve

I have 3.73 gears in my 1979 Camaro now. I was thinking about going to 4.10's. Would you recommend going to 4.10's or stick with the 3.73's, or do you recommend another? I plan to run this car at the strip on occasion, but for the most part, it will be a weekend driver. I am not worried about fuel mileage at all. The car currently has a mildly built up 305 with a TH350, but I am going to be putting a built up 327 into this car and I plan to run NOS. Thanks...Steve


I doubt you would see a huge difference between the two and if it's more of a street car, 4.10's are a bit steep.

I hear that 4:10's can be found on later model trucks. I know the carriers for those are 30 spline axles, which won't do, but the gears will work (up till 93 or something)... I'll pull lots of covers and see what i can find, maybe post what i find here. I've got a double overdrive T56 with a .5 6th gear, which makes 4:10's work well on the freeway.

.......ALSO, steve.. if you're planning on running nitrous when you drag race it, the 3:73's will be great because your engine will now have the torque to handle the slightly taller gear. Don't swap, IMO...
thanks for replies
olly

Loon in the front of 3/4 ton 4X4 trucks for the 4.10 gears. Don't use the differential from a truck because they have the Governor Lock differential. This is no good for a high performance street car. Your best bet for a posi is a new Eaton. It is much stronger than the old Traction Lock that GM used in these rear ends, and you won't have to pay $100 for a new set of clutches, or get dirty crawling under a car to remove it.

I know to stay away from Gov-Lok's.. they're the posi with the strange clutch things around them.. but ther'es gotta be a posi that can take a beating somewhere that i can simply pull. I'll later buy a Detroit True-Trac (the one with helical gear driven posi, out of my budget right now) Anyone had good luck identifying a good used posi that's held well?
olly

mgt999,Pontiac had 3.55's as an optional reared in the Firebird/ T/A's. These cars never came with 12 bolts, they only came with 8.5" 10 bolts and all T/A's had posi. By the way, If you find a 67-69 Firebird rear end, they were 8.2 10 blots with bolt in axles, were stronger that the Chevy axle, and 3.55's were pretty common. How can you use the geas out of a front axle 4x4? Aren't they pitched opposite so they can run backwards? Putting them in the rearend would put the load on the 'weak side' of the gear.

i believe it's just a rear rolled over backwards, so that the pinion is on the upper side of the ring gear on the front axle. I'll check it out, but im pretty sure that's how it works. the transfer case would just spin the driveshaft in the correct direction. Am i wrong? anyone?

The 3.55 was not an OEM gear ratio in any of the 8.5 10 bolt rear ends, not even the TA. It was a standard ratio in the 8.2 Chevy and 8.2 BOP 10 bolt rear ends. The 8.5 got the 3.42 gears.

Most of the 8.5 10 bolt limited slip differentials (posi) were the Traction Lock, which is all right, but not the strongest posi ever built. There were a few that got a version of the Eaton posi, but these are rare. What you will find in a Camaro or TA will be the Traction Lock. It will hold up to most street abuse.

The 4X4 GM trucks used the Dana 44 in the front through the mid '70s, then they got the 8.5 corporate 10 bolt, which takes the very same gears, differentials and other internal parts as the 8.5 that was used in all of the GM cars. The front axle in the 4X4 was turned upside down so that it would run backwards. It does not run on the coast side of the teeth. It runs on the drive side, just like it would if it were turned right side up and installed in the rear.