1968 Deville Posi Trac?

[Rosie68]

A lot of aftermarket parts have come out in the last year for the 60's Cadillacs. Wondering if Posi Trac is on of those options? I'm trying to accomplish this feat without a rear end swap, or well having to heavily modify a different rear end.

1968 Sedan Deville

[cadman56]

Many 68 Cadillacs came from the factory with Limited Slip differentials.  They are a bolt in.  If you are luck, you might even find one out of a limo which has a better gear if you are using an OD trans.

[Rosie68]

What exactly should I look for part # wise? any pictures available?

[savemy67]

Hello Kyle,

My '67 shop manual indicates that the letter G precedes the number code for the gear ratio on the '67 limited slip differentials.  The letter number combination can be found on the front face of the carrier assembly.  This location is somewhat obscured by the pinion flange, and possibly years of road grime.  "68 may be the same.  You should be able to find the info in a '68 shop manual.

Respectfully submitted,

Christopher Winter

[The Tassie Devil(le)]

I have a 1966 Controlled diff that came out of a SDV, but postage would be horrific.

Bruce.

[TJ Hopland]

I have never done a lot of research on the subject but I seem to recall that unlike most other brands and designs Cadillac didn't just 'drop in' either a standard or controlled assembly into the same housing.   Housings were different between them so you had to swap the entire axle assembly if you wanted to change your style?

[Rosie68]

Well I did manage to find what the seller is claiming to be a 68-69 locking diff. I do have a shop manual but its not close, I imagine it does not mention swapping out diffs between axle housings.

[DeVille68]

My 68 has a limited slip from the factory. Works pretty good. Had to replace the front seal and the seal of the housing.

There is a huge difference between 68-69 and 70-75. The first has a completely removable front section. So the complete differential can be removed. The latter has the more common "like chevy" style with the access cover on the rear. So it is more difficult to service because bearings and stuff remain in the axle housing. Although I think there are more parts available for the latter style.
I just know that there are absolutely no parts available for the 68-69 limited slip besides from seals and gaskets. There are no ring gears, clutches etc. The unit was build by eaton.

I would try to figure out if the later style 70-75 accepts aftermarket limited slip units.
Not sure what will be involved to swap a 70+ rear end into a 68-69 chassis...

Best regards,
Nicolas

[fishnjim]

If I were you, I'd have a conversation with a differential shop.   These guys do that for a living.   They'll know better what's available both used, interchange, and aftermarket.   Shops probably getting scarce out there right now.   
I also don't understand why your car doesn't have it?   I'd think it was pretty standard in those days for anything with HP/torque.
What problem are you trying to solve?   Modified?
"Positraction" is a "limited slip".

[cadillacmike68]

Someone will have to get a Wards book out to confirm, but limited slip was probably only a 10-15% installed option back then on Cadillacs.

[35-709]

Yes, back then it was a rarely ordered option at our dealership even in upstate New York, but we always ordered it on our demos and family cars.  Cadillac's term for it was "Controlled Differential".

[Rosie68]

If I were you, I'd have a conversation with a differential shop.   These guys do that for a living.   They'll know better what's available both used, interchange, and aftermarket.   Shops probably getting scarce out there right now.   
I also don't understand why your car doesn't have it?   I'd think it was pretty standard in those days for anything with HP/torque.
What problem are you trying to solve?   Modified?
"Positraction" is a "limited slip".

I've got a new motor going in Heads, intake, switch pitch conversion. I don't drive it like a knucklehead but when I get on the gas one tire spinning is just not cool.