posi or not posi, that is the question - Team Camaro Tech
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post #1 of 22 (permalink) Old Jan 15th, 01, 10:10 AM Thread Starter
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The rear under my 67 is not the original. it is a ten bolt and what I assumed was non posi. I have had thcar up and turned one wheel noting that the oposite side also rotated but opposite. I thought this was a fairly definitive way to tell if it was posi or not. This AM, I stopped to run a local quarter stretch we used to run in high school. When I turned around and came back by the start, TWO big long black sets of tracks were left which hsd nice s shape and ended together. Aside from the beauty of this I wondered if I might have positraction after all. Any ideas?

Oh, by the way with the shifter in drive, it ran 13-14 sec. Speedo is off, so I don't know what MPH was. Of course this is just an estimated distance between two signs very close to a quarter mile apart so is's moot anyway. It felt good.

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post #2 of 22 (permalink) Old Jan 15th, 01, 10:20 AM
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Sounds like posi to me, if both wheels were spinning, and you verified the rubber marks. That's good enough proof for me! KZ

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post #3 of 22 (permalink) Old Jan 15th, 01, 01:20 PM
 
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If you turn a wheel and the other turns the opposite direction...its an open, or a very USED up posi. 99% sure its an open. There were very few cars with 8.2 Eaton Posis back in the day, and if you find out you do have one in there, it takes the same rebuild parts the 12 bolt does and the unit in question is quite rare and worth some moola.

Two tire marks doesnt mean a thing, except for a car the is balanced left to right and the weight distribution is equal to both tires.
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post #4 of 22 (permalink) Old Jan 15th, 01, 01:46 PM
 
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Sounds like a Posi to me too. If not, it's very tight and is in very good shape!
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post #5 of 22 (permalink) Old Jan 15th, 01, 02:01 PM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by backfire:

Oh, by the way with the shifter in drive, it ran 13-14 sec. Speedo is off, so I don't know what MPH was. Of course this is just an estimated distance between two signs very close to a quarter mile apart so is's moot anyway. It felt good.

<HR></BLOCKQUOTE>

It always feels good!

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post #6 of 22 (permalink) Old Jan 15th, 01, 02:59 PM Thread Starter
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Thanks for the input guys. Chacane67--how would verify the if this is a "rare" 8.2 Eaton posi? I believe the numbers on the rear are the following PA 10200(on axle), 389485 and GM18 on the forward side of the differential housing. I posted this before in the numbers forum but got mixed info. Maybe this will help to post again.

Thanks
Lance
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post #7 of 22 (permalink) Old Jan 15th, 01, 03:39 PM
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PA is a '67 3.08 single trac 10 bolt rear. If the tires spin in the opposite directions, then you don't have a posi, and the code says so also. They are very rare. I've only seen 3 in over 15 yrs. of messing with old cars.

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post #8 of 22 (permalink) Old Jan 15th, 01, 04:21 PM
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The only true way to tell is to jack up the car and pull off the rear cover. You can then tell if it is an open or posi. If you don't know the visible difference just get one of your Chevy repair manuals or get a Haynes repair manual for about 10 bucks and it will have a detailed drawing of the different rear units used. If you have that info then you will know for sure. It would most likely be a good idea to change the rear oil since you don't know how long it has been in there. Good luck!



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post #9 of 22 (permalink) Old Jan 15th, 01, 04:22 PM
 
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Forget about rear-end code numbers. In 30+ years who knows whats still inside it? The only way to be sure is to simply pull the back plate off and look inside. It's easy, doesn't take long (you should be able to take it off, re-install and fill with lube in under an hour), is cheap (one gasket and a few pints of lube). Also if you have an engine with enough torque to really break them loose, it will spin both tires consistantly. I had a "68 Camaro a couple years ago with a 383 built for low-end torque, car had a 2:73 gear 10-bolt non-posi that I had in it just to keep driving while I built up a good 12-bolt. This car would smoke both tires and lay heavy black rubber for 52 feet EVERY time I would nail it! It even had ladder bars. How-ever, 2nd gear bog was horrid!
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post #10 of 22 (permalink) Old Jan 15th, 01, 05:56 PM
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B-Boy said it.
Also the spring pack can be tough to re install and if someone had it out, they might have left it out.
I did that once on my cousins V8 Vega.

The 10 bolt posi that came in my 67 used to be very tight and used to squeal the stock tires when turning tight in a parking lot. I could even feel it grab going around long curves.

If this was common, someone might have taken the preload springs out to cure that problem.

Take a look in there!
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post #11 of 22 (permalink) Old Jan 15th, 01, 07:30 PM
 
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At this point, pull the cover. If not to only verify an open or posi, but to get a general 'looksee' on how the parts are doing. If you can catch signs of wear on certain parts it can and will save you money in the long run. If it all looks good, put some fresh oil in it. NOT STA-LUBE. A good quality oil.

I personally run 140 wt. in most of my clients vechicles, and in some I even run an ISO9000, 250 wt. diff fluid. Also I would not reccomend the RedLine diff fluids, reason being is that they are RACING fluids that are meant to be changed each race. I've seen a-lot of cooked diffs over the years just from oil selection.

Drive sideways-

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post #12 of 22 (permalink) Old Jan 15th, 01, 07:42 PM Thread Starter
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Forgive my ignorance, but what will I be looking for with the cover off? What makes the posi look diferent than the open differential?

Thanks
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post #13 of 22 (permalink) Old Jan 15th, 01, 08:34 PM
 
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Sounds like a limited slip differential to me. If you burn out with limited slip diff., both of your tires will spin if you are starting straight. but say you are making a turn or you are on a bumpy road the tire with the less weight will lose traction. There is an easy way to tell a LSD from posi. All you have to do is find a place where there are no other cars around and put the car in 1st gear. Turn the wheel completely to either the left or the right, it doesnt really matter. If you have a LSD only one of your tires will spin. Say you turn the wheel left, when you burn out with the wheel turned left the right rear wheel should spin because that tire is getting most to all of the power because of more of the weight being on the other tire. Then again it all depends on the roads and the conditions.
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post #14 of 22 (permalink) Old Jan 15th, 01, 08:39 PM
 
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Oops- sorry,

The above is not completely true, a limited slip when loose will act the same as an open. That is one of the nice things an Eaton has to offer, it is tuneable.
I know with the open I had back in the day, if you trun left and nail it, it will spin both tires. When turning right, it would eaisly take off 5000 miles of tread wear on the right rear, and at times cause severe wheel hop. This may happen with a worn out 30 plus year old limited slip differential.
The 12 bolt I have now with a limited slip is tight by set-up, it drags the inside tire while at low speeds in a shopping center, spins both in a stright line or you can throw the rear end around in a corner by a tap of the throttle.

When you look at the 'carrier' (the thing the ring gear bolts to), with an open it looks very simple. Four gears and a cross shaft.
With a Eaton, as soon as you look at it you should have a spring pack stuffed into it (two plates, with four springs preloading the side gears), and when looking at the case you will be able to see steel clutches in between the side gears and the case itself.
Also, some people know how to set these up without the pre-load spring pack in them, so it might not be there, but you will be able to see the clutch pack eaiser.

Count the teeth on the ring and pinion. Write it down, you can figure out the ratio by dividing the the numbers.....this will at least tell you which series you have. As I said before, it will be worth some moola, and depending on what ratio, depends on the moola.

I hangout with a bunch of land speed record cats, and all of them want a 2 series. So let me know.

You might be able to swap part for part and get a three series, which is more useful to you than a 2 series, and maybe even pocket some moola for yourself.

Tom

[This message has been edited by chacane67 (edited 01-15-2001).]

[This message has been edited by chacane67 (edited 01-15-2001).]
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post #15 of 22 (permalink) Old Jan 15th, 01, 10:08 PM
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Hey Jason, a posi track is gm's version of a limited slip...actually, limited slip is just a concept really..it has exactly the same function as a sure-grip, trac-loc, gov-loc, saf-t-trac, no-spin, etc...each manufacturer has their own name for it, but the function is the same...power is distributed to both rear wheels but still retain the differential action.

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