Re: Difference between 55 & 56 rear end assemblies

Posted by BH On 2013/11/13 12:25:46

Never had a problem with the axle shafts in any of the three running 56s that I have. Seems to me, from the available factory evidence, that Packard was pretty aggressive about weeding out the early shafts that failed (Dana/Spicer's fault, not theirs). Of those three cars, only my Carib has Twin-Traction, but I've never tested it, let alone opened up the case to inspect it.

My dad had no troubles with either the shafts or the TT diff in his 56 Exec over the nearly 75,000 miles he put on the car, which he purchased brand-new. I'm reluctant to add that one evening at the local watering hole after work (and a few beverages), he even threw a chain around the snout of the axle housing and towed a dump truck far enough for the driver to dump the clutch to get it started.

Meanwhile, the term Power-Lock is merely a trademarked name applied by the supplier to a variety of limited-slip differential designs used over decades - marketing hype. The name has nothing to do with quality or durability.

When the TT gives up the ghost, you're pretty much SOL if you have any hopes of retaining that feature. IIRC, there are three versions of the TT diff between 1956 and 1958. While cases are interchangeable between 57/58 axle housing, I don't think so for 56 - at least not with Senior cars. New parts specific to that particular edition haven't been available from the supplier in years. I know of a Carib across the line in OH was restored over 20 years ago; the owner told me that only help the supplier offered was to replace TT diff with a standard one. I suspect that NOS parts are practically unobtainable, and I wouldn't wanna play Russian Roulette with a used one. Yet, I have heard of some owners having the cross-pins welded to the diff case to get by.

I never heard of any major problems with the 55 and earlier axles built by Packard. I only ever owned one 55 (some 20 years ago), and I never got around to restoring it. It had just over 58K on the clock when I bought it, but looked more like 158K.

However, I see no real benefit of swapping a 55 axle assembly for a 56 unit WRT to the purposes for which these cars were intended. Mind you, I have no interest in rodding or racing these cars. I can put the time and money to better use on other aspects of the car.