I have heard that cars with a true-posi traction differential have problems on the street. I have heard that taking corners is a pain, and the posi will not last long when driven on the highway.

Myth or Fact? I want to put an Auburn / Eaton Posi In my "new" junkyard 10-bolt to make it stronger(?) and of course to make it a posi.

 

I think it matters cause its not always locked til it slips I think.

 

If you use the GM posi additive with a good brand oil, you should be fine. The way to wear out a posi is to run different height tires, or different brands, or letting one get low on air for a long time, otherwise you should not have any premature problems with a posi.

 

I'm just going off what probuilt said. I do have a Power Trax limited slip unit in my Fbird and it can pop when taking corners too fast. If you change your gear oil often and with high quality stuff like M1 it will also help the posi last longer. The posi tends to generate alot more heat and break down the oil faster. I cahange my gear oil at least once a year, twice a year when I was driving out of town for service calls.

 

<b>I do have a Power Trax limited slip unit in my Fbird and it can pop when taking corners too fast. </b>

I know limited slip is good. Im questioning the "true Positraction Differentials" Like auburn or Eaton's Posi or Spools....

My main thing is street driving so I guess I would be happier with a limited slip then?

 

Positraction is limited slip.

 

whoa, now your freaking me out. I though the auburn / eaton style spools did NOT allow for slippage?

 

That's right, spools don't allow for slippage.

I don't know where you're getting the term "true Positraction Differential" from. "Positraction" is GM's trademark for their limited slip differentials.

 

Spools are for Drag Racing only, because they lock the axles together. Useless & dangerous on the street, where one wheel needs to spin faster than the other in a turn.

A full spool replaces the whole carrier (limited or open).
A mini spool goes inside a gutted carrier (Only seen mini's for open carriers).

Auburns are a cone type posi/limited, & a Eaton is a clutch disk type posi/limited.
I know that Auburn does make spools, but don't confuse them with a carrier, weather open or limited.

There’s two types (for discussion) rear ends for the street; Limited & Open. (Spools- read above or order your new axle now, cause they are not going to last long)

Each manufacture patented there own name for limited slip. In are case GM patented there version of the limited slip "Posi-Traction".

Hope this helps a little,

Ron

 

Alright.....

A "Spool" and a "Posi/Posi Traction" and a "Locker" are THREE different things.

A Spool is a device that does not differentiate. Both axles turn the same same rate at the same time. With the axles installed into a common spline, the inside tire will not be allowed to turn a smaller radius, and you will drag the inside tire around corners (and most likely break parts while driving it on the street). Bottom line= NO slippage

A Posi or Posi traction (dubed by GM in the 60's when the Eaton differential was first designed and used) is a device that can differentiate, but uses a friction medium to to apply power to both drive wheels. An Eaton uses a friction plate or "Disc" and is spring loaded. An Auburn uses a forcing cone design and is also spring loaded. These two designs will allow the inside tire to turn the smaller turning radius, saving you from tire wear and driveline breakage. The Eaton IS tuneable and re-buildable, where-as the Auburn is neither. The Eaton is also substantially stronger IMO. With a Posi you must run a friction modifier with the standard differential oil, it stops the "chattering" from the friction plates rubbing together. Bottom line= controlled slippage.

Now as for a locker, well it is kinda like both the two above with some exceptions. Under a loaded condition, accleration or decceleration, the axles are mechanically "locked" together like as in a Spool. Then under an unloaded or float condition, it mechanically will unlock and allow the axles to turn at different rates (to "differentiate"). The most common are found in trucks and are known as a "Detroit" locker, a "Lockrite" and their new version the "No-spin or No-slip". Bottom line= They clunk and bang when they 'reset' from driving around a corner and load the side gears, but when loaded no slippage.

Street.....................a posi.
Strip........................a posi or a locker. The question will be, "Will it be driven daily or on the street?"
Drag race only........a locker or a spool.

 

A locker is drag race only, obviously never ridden in a powertrax equipped car. It's far from a detroit locker--you have to listen close to hear it click. "Does a posi die when Daily Driven?" Yes eventually, but it will last a long time if you keep the fluid changed and use the correct additive.

 

So, as far as the limited slip type "posi's" go, an Eaton would be the best (cost effective?) choice for the street?

So whats the problem with my 9-bolt then, both tires spin together for about 2 feet then only the right spins... I guess the "friction disc" thing is worn out? Easier to just throw a new one of those in and goto a different gear? I know 9-bolt parts are expensive but Putting a posi / gear / strengthening a 10-bolt would probably be just as expensive?
What kind of posi is in the 9-bolt, and is it reliable / worth the money?

if not, I should buy a 10-bolt from a junkyard and build it up a little with say, and eaton?

And Will ANY Of these 2 rear ends (10 / 9 bolt) hold up to a transbrake / slick launch? I dont plan on doing it, but you never know in the future...

 

As soon as you said "Trans Brake" the answer changes. NO.

But unless you burn the cash and step up to a 12 bolt or 9", the only reason I would get a 7.5-7.6" 10 bolt is due to the fact that 9 bolt parts are going to be rare in the near future. At least the 10 bolt has a future life, so parts availability shouldnt be a problem. And yeah, I would do an Eaton, USGEARS and maybe some housing mods......but only if you dont say trans brake.

Some Cat on the site has info on 9-bolts, www.9bolt.com but as you will see you are limited to a depleating supply of parts.

 

Guess what 'chacane67', I saw an outfit that does 8.5" 10bolts in Canada, that fits up to 3rd gens. I don't remember the link, but there was a thread that had it a couple of weeks ago.

If this isn't the perfect compromise; the strength to hold up to 2nd gen big bodies, and I'm sure is much cheaper than the 2 grand 12bolts & 9".

Ron

 

Hey ya know what? I'd run an 8.5 10 bolt. It has the same pinion shaft diameter as a 12 bolt and uses the same bearings. And to think it is only 0.25" smaller in ring diameter. So....IMO an 8.5 is just about as strong as a 12 bolt. I would be interested in finding that web site, as it would be a great alternative for the big dollar 12 bolt and 9"!!!!

 

I found it !!!

http://www.amazingmechanical.com/rearend.htm

I've never got around to getting a price on the units, and haft there website dosn't work. (At least on my end?)

But there's lots of 8.5 out there, so it shouldn't be to jacked up on the price. (I have a 8.5 on my '81)

Ron

 

Very cool...........

 

Hey I know that guy, that's Ian!!! The last time I talked to him he was working on that project, I guess he's finally got it done.

 

It LOOKS good but I cannot find prices or availability or ANYTHING besides how GOOD it is. Somone clue a poor thirdgenner in?

 

You'd have to call or e-mail to find out I guess. It's a small shop, but the guy knows his stuff.

 

Yes he certainly does. I emailed him and he emailed me back.

The total cost (minus shipping) is $2100 it comes with the torque arm he said. Im sure its a great rear end, but for $2100 I would rather have a 9".