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As some of you know, I had an oil pan drain plug problem when I changed oil in November to give the 400 a long winter's nap. It turns out that the pan has had an oversize drain plug in it since I bought the car. I don't know what finally killed it but I only change oil once a year and the same mechanic always drains the oil and changes the filter. I dove under the tarp to recover the pan off the parts car but it is too rusty to trust. However the drain plug, which seems much smaller than the current one, had really good threads and was obviously smaller in length. Packard spotwelded a thick bung inside the oil pan and the body man at ther garage where I have oil changed says he can drill out the spotwelds on the bungs of both pans and install the good bung by rewelding it in the good pan. He said it would be about $30.00 which is much cheaper than installing a helicoil which was another alternative. The helicoil kit was $50.00 and I would have to purchase the required 41/64th drill bit separately. Dropping the pan is a PITA but I will be much happier with that fix. Sorry to be long-winded, but I wanted to explain the problem and the options in detail.

Welcome to the Forum Randy.

$30 sounds like a very fair price. Good to know those kind of options are still out there!

Welcome aboard Randy, and thanks for updating us on your problem.

It's interesting to know that the pan has a "bung" plate that is spot-welded in place, lending itself to a transplant. Yet, I suspect that it wouldn't be too hard to fab a new one if a donor wasn't available. Also, have you any thought about "sweating" some solder (after welding) to make the seam leak-proof or is that not necessary?

Helicoils have their place, but I suspect this will be a better fix in the long-run.

Don't worry about being long-winded in your posts, as this is the kind of good, detailed information that we need to archive for future reference. (A forum is about more than just one-on-one discussion.) Also, know that you can break your post into paragraphs as you would with any word processor, and this forum will handle it, without need for any special coding on your part.

Brian, the bung originally was just spotwelded in place. After examining the spare pan, it seems the sealing is done by tightening the copper or nylon washer snugly against the pan.
The hole in the pan just accomodates the 5/8-18 drain plug.
The plug that was in the 400 was an oversize one. I just want to get back to original. I will test it with water before I bolt it back up.
I wonder how long Packard initially allowed to install a new oil pan gasket? I don't have that manual although Kev may have posted it here.
A separate thought - I believe there is a bung in the transmission pan also. The drain plug there is also a 5/8-18.

If the plug from the parts car is rusted then the bung (tapping plate) from the parts car is not saveable either????

Check both tapping plates to be sure that they are not split near the bottom. Making a new tapping plate should not be too difficult or expensive if necessary.

Randy -

I understand about wanting to get back to original - had just wondered how that plate was sealed (if need be). My dad, who started turning wrenches prior to WWII, had told me that the gas tank fittings were soldered, and I thought it might be same for this sheet metal oil pan.

Quoting from the "1955-1956 Packard Flat Rate Manual"...

Oper. No.: 5-165
Oil Pan or Gasket - R & R
Includes : R & R Cross over, or side exhaust pipe, starter motor, flywheel lower cover, disconnect and lower steering linkage.
Suggested Time: 2.6

(end quote)

I'm curious to know how that compares to real world time?

BTW, the manual provided an additional 0.3, with pan removed, to R & R the oil pump assembly, and 0.4 to recondition the removed pump (i.e. - disassemble, clean, inspect, reassemble, and replace any necessary parts.

Yes, the Twin Ultra. pan used exactly the same drain plug and sealing washer as the V8 oil pan. I don't recall anything so substantial as a spot-welded plate in that application, but it's been over a decade since I had a pan off an Ultra.

Keith, As I said in my original post I am putting the bung from the rusty parts oil pan into my good pan which has a stripped bung. Good hint at checking bungs to make sure they are not split.

If you're bung's worn out, and you can't get a different one to work, try this:

B&M Trans plug kit



I've used these before on modern auto's, and they work great.

Thanks Eric but that wouldn't help the existing hole which could leak. Perhaps that B&M kit is for more modern tranny pans that don't have any drain plug. They want you to drill a 1/2 inch hole. I already have a 5/8 hole. We successfully removed the bung in the rusty pan. It was only spot-welded two places on the top side of the bung. When I drop the good pan, we will remove that bung and weld in the good one. I'm going to look at my spare tranny - bet it has the same bung.

I believe the trans pan does have the same plug. I also have a spare '56 trans pan, and can look at it when I get home.