Hello All,

I would like to install a posi-trac rear-end in my 1969 Cutlass S. I currently have a limited slip that has been in it since I bought it and I believe since it was new.
I am curious as to what I should buy and what specifications I need to know and look for. I've assisted with the installation of a few posi-trac pinions and gears so I'm fine in terms of the actual installation. Also any of your experiences would be nice to here about.

 

So, ye want to upgrade from "limited slip" to "positraction"?

 

Is there a difference?

 

I am mostly interested in installing a slightly bigger gear ratio. The definition of Posi has changed/people use it in different ways. I currently have limited slip where as when one wheel spins the other then begins to spin to catch up, as opposed to all power being initially distributed evenly between both wheels.

 

 

Wow!.....let's clear this up. Do you have an OPEN carrier or not?


And if you want to change gears you do not want a BIGGER GEAR. You want a ratio change. Semantics can cause confusion. I suspect you want to go to a numerically larger (aka steeper) gear. eg if you have 3.08s now & you want to go to 3.91s.

 

*popcorn*

 

I do have an open carrier. I said I wanted to a bigger gear ratio, I should have said higher in reference to the ratio not the gear itself. I am unsure of what my ratio currently is but I want it closer to 4.00 than 3.00.
Thanks

 

Contact Monzaz or Brian Trick with the type of rear end you have (Type O or Type C or whatever it is) & the desired ratio you want to go with. They will set you up with a carrier, a gear set, a rebuild kit & all the bearings & races etc to have the differential rebuilt to your needs. Many of us on here have done this with great success. Note your gear ratio choices will be very limited if you have a Type O rear end due to a shortage of gear sets.


In the mean time go get dirty. Crawl under the car & take pictures & look for the axle code on the passenger axle tube. Or if you are feeling ambitious jack it up & pull the cover & drain it down & see what you have.

 

Thank you, ill keep him in mind!

 

"Positraction", "limited slip", and "anti-spin" are all marketing terms for the same thing.

Let's review. The base differential has nothing between the differential side gears. The tire with the lowest traction spins first, period. You can rotate one wheel with the other on the ground.



Posi/limited slip/anti-spin work by using friction clutches (either flat plates or cone type) between the side gears. These clutches slip during normal cornering, but hold under hard acceleration as the torque of acceleration causes the side gears to move sideways slightly and engage these clutches. If these clutches are in good shape, you will not be able to rotate one wheel if the other is on the ground.



Some newer cars and trucks (like my 99 Chevy) have an Eaton type limited slip which uses a centrifugal weight to engage the clutches. One wheel will spin until the differential RPMs are high enough to engage that centrifugal weight, at which point the clutches engage. As with non-posi, you can rotate one wheel if the other is on the ground.



Locker type differentials positively engage the two tires using a variety of mechanisms. The Detroit Locker and Trutrac style differentials use helical gears to allow relative motion on turns but lock up when needed.



An air locker uses a pneumatically driven piston to solidly lock the differential, acting like a spool. An external control allows the driver to engage and disengage at will. There is an electromagnet version of this system also.



Finally, there's a spool that is simply a solid metal hub that eliminates the differential gears and drives both axles at the same time. This works fine for drag racing and off road, but it is not a good idea for street use if you plan to turn corners, especially in the wet. A "mini spool" is a toothed piece of metal that bolts in between the side gears of a normal differential, locking them like a real spool. Again, not recommended for street use.



The only form of "limited slip" that acts as you decribe is the centrifugal Eaton style, which is definitely not factory installed or available for a 1969 Olds. Either you have a non-posi axle or a badly worn anti-spin.

 

Thank you, very informative, Rear-ends have never been my forte.

 

Just to clarify Joe's instructions about how to test for a limited-slip rear end by spinning one wheel while the other's on the ground:

The transmission must be in neutral (and, of course, the front wheel's chocked). With one rear wheel on the ground, spin (by hand) the one in the air. If it turns (and so does the driveshaft), you have an open (not limited-slip) rear end -- or you have a limited-slip but the clutches are completely worn out. If you can't spin the wheel in the air, it's because you do have a limited-slip and the clutches are "locking" that wheel to the one stuck on the ground.

By the way, you say you are unsure of your current ratio. You need to be sure, because it'll help you pick your next gears. How can you know how much you want to change without knowing where you are now? The current ratio also determines whether or not you will need a new carrier for your new gears, as different gear sets require different carriers.

 

In addition to the above, if you have an O-Type 12 bolt rear (which was fairly standard on '68-'70 Cutlasses), then the available gear ratios are very limited.

 

I am impressed with Joe's diagrams!!! In living colour as well.

 

If your 69 Cutlass was built in Canada,it would have come from the factory with a 12-bolt Chevy rearend.The top of your cowl tag would read MADE IN CANADA,if it is.
All of 69 Cutlass/442's built anywhere in the US,would have come from the factory with a 12-bolt O-axle.There are currently NO aftermarket gears available for the O-axle at this time,and the original used GM gears are scarce.
If you have a 12-bolt Chevy,you can get a wide variety of gear ratios & parts.
Chances are,your car has the typical 2:56 or 2:78 gears(2:73 if Chevy).
Let's find out where your car was built first,then we'll go from there.

 

You impress easily.

Google Images is your friend.

 

What happened there? I thought there were a couple companies besides Richmond Gear making them.

I'm guessing this means the value of the gears I have has gone up significantly.

 

Richmond was bought out by Motive awhile back. When that happened,they stopped making the O-axle gears. There has been talk about production starting again,but the dates keep changing as time passes by.
Yes,that makes anything used or available has gone up in value. The posi units are not the problem. Just the gear availability.

 

Hey ya'll I hate to act a noob here but I think, 99% sure my 1966 Cutty 12 bolt is an O Type.
I have saved a link or two on this 12 bolt with a 8.25 12 bolt carrier, right?

Anyone has a link or two to parts and gear sets. Because I am gonne be dabbling here soon.

 

No Type O rear ends were installed in factory cars until 1967. If you have a Type O it is not original to the car.


The carrier is 8.5" & uses 10 bolts not 12 (although the cover uses 12).


And lastly it is a Cutlass not a Cutty.

 

My car was built in the 4th week of July 1966....so I was told it was an O but I will have to get under it and jot down some codes. I'll chime it and let ya'll know.



Yeah this is the first time I used that Cutty term so, it's out LOL....I think

BTW my cover IS 12 bolts...looks like every GM 12 bolt I have ever seen from the outside so hell I dont know what I have.

 

I just had a funny thought (funny in my head anyway). So the worthless 2.56 gear sets I have are now 2x worthless.
Well, at least my Richmond 3.90, GM 3.42 and 3.23 gear sets have increased in value.

 

If any of those become available,I will put them to use.

 

I was thinking Yukon had some gears for the O type 12 bolt. I may be mistaken
Steve

 

For whom ever is looking I can do a 66 10 bolt 3:23 posi (limited slip)

Direct email is lemoldsnut@aol.com

 

I'll keep that in mind. The Richmonds are in a box (I think they are new, never used) but the other sets are still installed in complete rearends.