Packard Forum Index » V-8 (1955-56)

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IIRC there are significant changes in the internal passage.

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The late Steve Williams and I spent an afternoon comparing and measuring the two pumps side-by-side and concluded there was no practical way to make a first generation pump into a second generation pump. It would be wonderful to be proven wrong, but the two modifications described above wouldn't seem to work without the change in the casting. This is why there was a new casting and a part number assigned and not just the simple field fix the two changes mentioned would have been.

thnx, jack vines

Thanks for helping me identify a "second generation" oil pump; that pump with the plugged relief valve is the one that is in my spare engine, Utica #D6478 which is bit earlier than TSB 56-20 indicates but of course it could have been changed later.

Any help with my other prior questions? Was the second generation pump really superior, and if so, how? I do have one rebuilt by Bob Aller and my 90,300 mile 56 Carib which has great oil pressure and never any tappet noise has the "opium pipe" field fix. If the newer pump was really all that superior, I might make the change.

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Unless the gears are changed in some significant way (diameter, tooth root volume, etc., there would be no actual difference in pumping capacity, which is the REAL issue.

Anyone ever compare the two side-by-side?

Craig

<p>I have two 1956 oil pumps casting number 6492430. Both have been modified on the bottom plate (not by me) and the vacuum pump removed.</p>
<img src="http://www.OriginalHO.com/Packard_56_374/1956_6492430_Mod1.JPG">1956 Mod 1<br>
<img src="http://www.OriginalHO.com/Packard_56_374/1956_6492430_Mod2.JPG">1956 Mod 2<br>
<img src="http://www.OriginalHO.com/Packard_56_374/1956_6492430_stockGears.JPG">
<h3>1956 Stock gears. Note the tight fit between the gear teeth in the center. The tighter the fit, the LESS room for oil!</h3>
<img src="http://www.OriginalHO.com/Packard_56_374/GearComparison_Packard_vs_PontiacHV.JPG">

<h2>Packard vs Pontiac High Volume</h2>
<h3>Note the Pontiac has fewer teeth and square cut roots, both mean HIGH VOLUME. I do not have an Olds HV to show right now, but it is basically the same as the Pontiac.</h3>

I think that Packard's "re-engineering" of the oil pump requiring a new casting was a <b>WASTE OF EFFORT.</b> They should have known better and used high volume gears, per what at least Pontiac and Olds (maybe others) did less than a decade later, e.g., 1959-62 Pontiac 389/421 Super Duty.

Craig

Owen.
The late 56 plugged pump is only slightly better than the early pump. The plug in the late 56 pump eleminates SMALL amounts of air that can be drawn at that point in the early pump whre the PR port is not plugged.

The problem with BOTH pumps is that the input shaft wears PREMATURELY AND WEARS the PUMP bore that the input shaft spins in. Air is sucked at the worn clearence that occurs between the input shaft and the pump as well as at the pressure relief valve port if it is not plugged. However, based on my experiments the amount of air sucked at the PR valve port is minimal.

As a side note: Too fully understand this one must come to grips with the fact that the pressure relief circuit of each, all, and every Packard factory V8 oil pump is ALWAYS subjected to the SUCTION SIDE OF THE PUMP. This is also true of nearly ALL other oil pumps among all manufactureres going back into the 30's. At NO TIME nor at NO point does oil leave the pump when the pressure relkief valve opens. If the pump is an early pump with the hash pipe campaign then oil is sucked UP THE HASH PIPE and INTO the pump. NOT out of it. NOT down the hash pipe.


Let me put it another way:
As originaly designed by PMCC:
Once oil enters the pump it can leave from ONE place, EXACTLY ONE place, and ONLY one place. That one place is out thru the mounting flange where it is supposed to go. There is also an extremely tiny amount of oil exuded at the shaft to keep it lubricated.

One disclaimer: The vacuum pump requires a VERY SMALL amount of oil that is supplied from the oil pump. That is the only exception. Oil Pumps without the vacuum pump will adhere to my above explanation.

FURTHERMORE:

Both Packard pumps, early and late 56, lack an oil goove that is needed from the PRESSURE side of the pump to the shaft bore. This oil groove is needed. It is so simple that i made one in my pump with just a die grinder and a small stone. There is NOTHING precision about it.

OD writes:
"If the newer pump was really all that superior, I might make the change."

The late 56 plugged pump is not significantly superior. Prefered but not superior. Both pumps are relatively weak for reasons i've stated above.

THAT'S why i changed to the Olds conversion kit that Craig offers. The OLDS pump is NEW (as in NEW). There is NOTHING rebuilt about the Olds pump and it is HEAVY DUTY with a LOWER shaft bushing in the bottom. The Olds pump is available from discount chains for about $60 as of 3 years ago.

Also beware:
I had minor trouble mounting the late 56 plugged pump to my earlier Executive that originaly had the early pump. One of the mounting flange holes in the late 56 pump had to be elongated about .020 - .040 inch. Otherwise the bolt would not start into the rear main cap.

Also, the Hash pump, from the factory, has a LOWER plate support. No vac pump. The upper neck of the hash pump is shorter tha nthe Packard pump and thus less input shaft bearing surface. I have a Hash pump in my posession.

According to what i have been told by others, this was necessary because the Hash chassis and suspension clearence was a problem, thus an oil pan difference thus the pump needed to be shorter.