Packard Forum Index » V-8 (1955-56)

BH & Randy: I need your help. A friend of mine in Williamsport purchased a two 1956 Packards. The cars are Packard 400 and a Patrician, along with the cars have some several extra parts including two rear end assemblies.

My question is as follows how do you identify the limited slip rear from a conventional Packard rear end?


John F. Shireman

Like all limited slip rears, jack up the back, put it in neutral, and spin a tire. If the other one goes the same direction, it's a limited slip. If it turns opposite, it's a conventional open rear.

John, are you talking about Willamport Pa. If you are that kind of close to home for me. I wonder if we know the same guy. Do the cars in the pics look familiar?

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John -

Rear axles for the 56th Series were of an all-new design that was supplied by Dana/Spicer. The rear axle was smartly designed with interchangeability in mind; that is, the only difference between a conventional rear axle and a Twin Traction unit is the differential carrier.

Yet, implementation of the Twin Traction (aka - "Power Lock") differential in production was delayed several times. An STB seems to indicate that cars with T-T units did not begin reaching dealers until sometime in February 1956. In fact, it was so late in coming that servicing the Twin Traction differential isn't covered in the 56th Series supplement to the shop manual, but only in the April 1956 edition of the Service Counselor.

So, there probably weren't a lot of Packards built with that option - certainly none with early/low serial numbers in the 56th Series run.

A couple of things make identification tough. While the factory installed a tell-tale tag on T-T units, I have to wonder how many of those got tossed over the years (during an axle drain and refill). Then, for a variety of reasons, I've heard that some Packards with Twin Traction were converted to conventional diff. On the other hand, while it's hard to say if many people shelled out the $$$ to have a conventional rear axle converted to T-T, but it is possible.

While I've done Turbo's test with later designs of limited-slip differentials, I'm not sure how valid that test is with the T-T units. The production order for my Carib shows it was built this option (code PL), but I have never tested it and am so backed up with work that I won't be able get out to offsite storage until late this fall. My dad's Exec had it, but the car is sitting in a field, which doesn't lend itself to testing. I believe Randy Berger's Carib was built with T-T as well, but while he told me it has the tag IDing it as a Twin Traction unit, the rear wheels spin in opposite directions when he when spins one by hand.

The definitive way to check is by pulling the rear axle cover and examining the differential carrier. A Twin Traction unit will have TWO pinion pins, which have "cammed" ends - each resting in a V-groove in the carrier (which serves as a ramp to engage the clutch pack). This is illustrated in the Service Counsleor article.

Or -- you could put your left foot on the brake, put it in low, wind it up and floor the, "exhiliarator," when you release the brake --- Oh! Oh! Excuse me. A little regression took me there for a second ---- but you could tell from the tire marks during acceleration and the whisper marks when you let off the throttle.

While we are on drivetrain: i discovered that the rear u-joint companion flange bolt pattern of a 1985 Jag w/automatic is extremely close to that of the 56 Executive prop shaft Detroit joint bolt pattern. It is only about 1/64 inch off.
Perhaps useless information but something to keep in mind for future retro fit projects.