Packard Forum Index » V-8 (1955-56)

450352 vs 6480887 High Speed Governor Body
The latter has a pin about 20 thou longer than the former. This keeps the valve farther off the body. When possible, the latter should be used with the 56th style Governor valve to reduce the chance of the valve sticking. The parts are identified by casting number.

470091 vs. 6470250 Rear Housing Assembly
The parts are identified by casting number yet the castings are the same. Instead, the only difference is the spider (the bushing support piece). The 55th type has four holes in pairs. The 56th type has four holes spaced evenly. The part was redesigned for greater strength, but they are interchangeable in practice.

All Seals (not including gaskets)
The 1956 type were improved design over the 1955 type. Irrelevant now.

High Range Clutch, Input Shaft, Converter, Etc.
The 56th input shafts had a finer spline than the ones previous. Anything that is engaged into the input shaft has a different part number for 56 and may be correspondingly identified irrespective of other differences that may exist.

465754 vs. 6480734 Oil Cooler
The 55th type has a seam running down the center of the cooler. The 56th type the seam is on one side, much like a sardine can. The 56th type has better cooling performance. While not necessarily helpful for a 55th, it is recommended to use on a 56th car or 55th Caribbean to dissipate the converter heat more effectively.

470049 vs. G137406 Oil Cooler Line Adapter To Case
The former has a smaller orifice than the latter. The former part itself is obsolete as there is no need to restrict the oil flow to maintain pressure in the converter. It can simply be modified by drilling the hole oversize to match the diameter of the other hole.

440845 vs. 470143 Oil Pan
The 56th type has one less hole than the 55th type. This is most easily identified by the fact that when looking at the pan from the underside, the 55th type will have one reinforcing strip at the front of the pan while the 56th type will have a reinforcing strip both at the front and back edge of the pan. It is important to note that all of the Packard pans have the filler tube fitting at the right of the front side of the pan (looking at the pan right side up). If the fitting is on the front of the right side of the pan, then it is for a Hash car. See Hash vs. Packard Differences. In other words, the drain plug and the filler tube connection are on adjacent sides on a Packard pan, but are on opposite sides for a Hash pan.

458950 vs. 6484046 High Range Clutch Assembly
The 56th type is shorter than the 55th type. If the transmission body endplay is outside the range of selectable spacer washer, exchange one for the other. All which have a "0" stamped opposite the check valve are 56th type, but most are unlabeled. See SB 346. This is not to be confused with the "0" that is stamped into the ring gear as all ring gears are the same. The units may be easily compared using a dial indicator as shown. The 55th will indicate approx. 0.060" thicker than the 56th. Or using a caliper and gauge block the 55th distance is approx. 4.471".

421073 vs. 6470245 High Range Steel Clutch Disk
The 56th type have more clearance between the disk and the body than the 55th type. Irrelevant.

450552, 450553, 470172, 6484614, 470219 Converter Rear Thrust Washer
See explanation here:packardinfo.com/xoops/html/modules/newbb ... 6809&post_id=288698#forumpost288698

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Here are some high-speed governors. The one on the left is the 55th type that has the 450352 body without the pin. The middle is the same 450352 part number except it has a pin installed making it the early 56th type. The right is the 6480887 type making it the late 56.

The valves are shown clearly. In particular, left one has the 55th spool valve as shown in the manual while the middle and right use the 56th type.

The springs are also slightly different. The left spring has one more coil than the right two springs. See the photo whereby rotating the springs to line up the spring coils at the bottom of the spring, it is obvious that the left one has one more turn throughout its length. The right one shown is the 56th type which was the same for both governors. The wire diameter is also different but only very slightly; the 56th type is 36 thick while the 55th type is 34 thick. Therefore, the 56th spring is also slightly stiffer.

Therefore, to determine a 55th or 56th type governor, the 56th type must use the 56th type spool valve and a body with a pin to hold the spool valve off the end of the governor and the 56th type spring which has the one fewer turn.

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Is that the 5588 version or the everything else version?

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Does Packard define an "early 56th type"? I haven't come across that definition. Or could someone have just added a pin to a 450362 body?

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The 55th is also wound with a different pitch. If you compress them to the same length, how different is the pressure?

You can't tell from the pictures, do the valve lengths differ from spring seat to end and are the bore depths different?

As far as I'm aware, I don't have a convertible version of anything. Once I get a 55 convertible transmission, I will have to make some measurements of the respective parts for reference.

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Yes, Packard added the pin to the 450362 body. As mentioned in my first post, if you measure the two types, you will find that they are exactly the same in all respects aside from the casting number. I believe Packard used up their remaining stock of 55th types and installed the pin, and only when they needed more did they change the casting number. On a pair that I measured earlier, the pin length was slightly different but it's probably not important and could have simply been some assembly error or one of the pins getting shifted slightly out of position for some reason in the past. It could have also simply been a revision at the same time that they updated the casting number.

If you compare the design of the 55th and 56th governor valves, it's clear that you have to use the pin type body with the 56th valve and the body without the pin with the 55th type; it absolutely won't work the other way. A 55th valve and a 56th body would compress the spring far too much, whereas a 56th valve in a 55th body would not want to move off of the end of the bore since there is no area under the valve for the fluid to push it out.

My assumption is actually that Packard considered all of the ones with the pin to be the updated part number, it's just that it wouldn't be obvious nowadays by looking at the casting number. The early 56th nomenclature is my own wording.

For your last question, yes, the spring constants and the uncompressed lengths as installed are different but I did not measure them. I have a chart somewhere that simply shows the governor pressure at a given speed for the 55th and 56th types, which is really all that one would care about, so it's not data that I particularly need to collect.

450887, 470096, 470097 Case Breather
55th is larger and a 90-degree fitting, with I believe a 1/4" pipe. 56th is a straight fitting on a 1/8" pipe street 90.

458296, 458295 Standard vs. Hycar gaskets
See here.

470178, 6489039 Brake Band
See here.

450076, 6470244 LRB Actuator
The 56th type has a geometry with greater mechanical advantage for the piston, than the 55th type.

458950, 6484046 HRC Housing, 450249, 6470337 HRC Hub
See "High Range Clutch Assembly" and/or "High Range Clutch, Input Shaft, Converter, Etc." earlier.

450245, 6480641 HRC Fiber Washer
See "High Range Clutch, Input Shaft, Converter, Etc." earlier.

Control Assembly and Component Parts
See the service manual (don't forget the 56th addendum!) and letters which describe the various changes, e.g.:
56th Valve Body Separator Plate
55th Direct Shift Valve Spring
55th Caribbean Changes
55th vs. 56th Rear Upper Valve Body
Valving Kits (i.e. Changes from 54GS or 55th to 56th)

450405 Pump Check Valve (In Valve Body)
These are sometimes found with a hole drilled in them. This is a field modification. A "hole" type is only necessary to install to act as a check valve for the rear pump circuit. If one is installed for the front pump circuit, then the rear pump will work excessively when driving at highway or direct drive speeds.

470010, 470221, 6479085, 6479086 Converter Assembly
The 55th to 56th assemblies have a number of differences. Since the converters should only be serviced as an assembly, and many of the differences are obvious, only some will be discussed.

- There are a number of differences between 55th and 56th converters, however the four assembly part numbers are mainly from the differences in pump used. The 55th except 5588, and 56th sedans, used a pump that gave a lower stall speed and less torque multiplication than the 5588 or even higher 56th 2-door cars, which had a 3.25:1 stall speed pump. The different part number between the converters with the standard pump between 55th and 56th is due to the remainder of the changes.

- See also "High Range Clutch, Input Shaft, Converter, Etc." earlier.

450481, 450482, 450483, 450484, 450485, 450490, 450674, 6470320, 6470321, 6470322, 6470323, 6470324, 6470325, 6470326 First Turbine Thrust or Spacer Washer
The thicknesses are per the parts book, but the 55th is a proper bronze thrust washer with a groove on each side, as the first turbine rides on it. The 56th is merely a spacer as the first turbine thrust is taken by the needle bearing in the nose of the converter.

470080, 6489368, 6489210 Front Oil Pump
470079, 6470302, 6489211 Front Oil Pump Housing
Looking at the front of the pump (remember, the front is the flat side), you will see a metal plate held on with two Phillips screws. If the screws remain, then you will see either 13 or 14 holes. (If the screws are removed, then 15 or 16 holes, respectively). The 56th is the 13 (15) hole type, while the 55th is the 14 (16) hole type. The specific difference is that, holding the pump so that the notch in the large center hole of the plate is up, there will be a hole at the top of the plate on the 55th pumps, which is absent on the 56th. See image.

The bushing is also different. The bushing has two slots in it. Considering from the center of each slot, there will be a 90-degree angle between the slots on a 55th. The 56th is a 135-degree angle. See image.

As the rotor thickness and number of teeth are shared between some 55th and 56th designs, you cannot check the year of a pump using those characteristics.

450335, 6480750 Parking Pawl Stop Pin
The 55th has a groove while the 56th is plain. The groove type is prone to breaking.

470082, 6480965 Manual Valve Lever Stop
The 56th is L shaped and generally satisfactory on a 56th. The 55th is straight with a slot and is basically garbage. Technically I think the 56th can be used on a 55th but it's not advisable. Instead, Ross uses a new type of stop which bolts to the valve body directly, as of mid-2024. I will use them as well.

TODO: 3.510, 3.518, 3.53, 3.5415, 3.551, 3.6483, 3.6495, 3.6497, 3.654, 3.667, 3.680

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