Packard Forum Index » V-8 (1955-56)

I have had my 56 trans rebuilt by friend Ron and am installing it to the engine. The installation torque specs in the shop manual raises a question.
a. The manual states that the ten 7/16-14 bolts that bolt the converter housing to the transmission case should be tightened to 55-60 ft-lbs.
b. Then the manual further states that the 7/16-14 bolts that bolt the converter housing to the engine should be tightened to 25-30 ft-lbs.
The torque specified at (a) seems excessive and we double checked the manual at the time because Ron thought that was a heavy torque for the aluminum case.
The torque specified at (b) seems light given the spec at (a).
It dawned on me that the manual was written in 1955 when the transmission case was cast-iron. I don't see any changes made allowing for the new aluminum case used in 1956.
Can anyone offer some insight? I've checked and there are no modified specs for 1956 that I can see. I've checked my own manual and the one posted on this site and see no modifications for 1956. Am I wrong or did Packard forget to document new torque specs and what should they be?
All opinions welcome.

There is a STANDARD bolt and nut torque specifications chart available on the I'net as well as as in many handbooks and manuals. They give different specs depending on materials used such as Al or cast iron or steel. I don't have one handy right now.

If u check a standard chart u'll find the answer.

I did a quick google and found
engineershandbook.com/Tables/torque3.htm

Do a google search and check several sites.

if u have a spare trans laying around check the torque on the bolts.

Standard tables of torque ranges for different thread size and grades of bolts, while useful, don't always provide the correct answer for a particular application. For example, engine main bearing bolts are generally capable of higher torque and thus clamping force that what the manufacturer recommends they be tightened to. Another other factor which comes into play is an appropriate clamping force without distortion of the fit. That said, sorry Randy I don't have an answer. Checking an old transmission installation would be a reasonable idea if you knew that it hadn't been dissassembled since it left the factory. Fifty or 60 ft-lbs sounds like a lot to me for a 7/16 NC fastener going into cast aluminum.

Randy -

That would explain why I've found a few pulled threads on the Twin Ultra on my first '56 Patrician.

Unfortunately, I found no reference to revised torque specs for the alumimum Twin Ultra in any of my materials - including those available here at P'Info.

Does anyone know of a vehicle with a transmission that has a similar case construction and is bolted up to a cast-iron engine? If so, find a shop manual, check the specs. Properly researched and backed up with hands-on trial, someone could make a nice piece for the Articles section about this.

A quick search in the I'net shows that most Aluminum trans to engine torque specs are in the 35# range, and most Aluminum to Aluminum specs are around 25#.
If you were really worried, you could use the 35# and 25# settings and either use a thread sealer or drill and safety wire the bolts.
HTH,
John

John, that sounds much more reasonable than the published specs in the manual. for your input.

morbark.com/Service/belttorque.pdf
If you look at the bottom of the site in the notes it says to reduce values in alloy by 30% and increase the depth of engagement

Al, I appreciate your response. After talking it over with Ron, I am going to leave the internal bolts (55-60) alone and torque the trans to engine bolts 35 ft-lbs. If I ever have need to disassemble the tranny or any other 56 Twin-Ultra I will torque those bolts 35 ft-lbs when reassembling. The 55 converter housing is aluminum also. That is the reason for the light torque spec vs the 55-60 spec. 1954 and back (excluding gear-start) is cast iron.
Thank all of you who contributed your opinion. It is appreciated.