I've posted a number of times talking about how I seem to find a lot of items that were loose on my '61. That includes starter solenoid connections, engine-side clutch Z-bar bracket, pan bolts, water pump bolts, seat bolts, door handles, etc. Most times, that's not that big a deal, just tighten what seems to be loose but that changed just a minute ago.
After putting about 20 miles on the car after the 6 month long mini-overhaul I adjusted the rear brakes as best I could (separate post coming on that one) and then figured I'd double check the drain plug on the differential because it always seemed to have this drip hanging from the plug.
Put the large crescent wrench on it and was very surprised to feel it move so easily. I first thought 'great, it was just loose and I'll snug it up'. Well, a half turn led to another half turn and then it was obvious, it's not getting any tighter, it's just spinning in place. If some bozo overpowered the threads like this, I'm amazed I haven't seen more of a leak.

So, anyone else run into this before? What's the fix...short of pulling the third member and welding a nut in there?

UPDATE: I figured I might as well get it outta there and drain the diff. The old drain plug had the remnants of the housing threads on the three threads nearest the drain plug hex head. Once it was turned counterclockwise a few turns (oh, about three), it seemed to have a pretty good grip on the housing threads so I might be able to get away by using a new/thicker washer to keep the threads engaged and maybe a bit of sealer or teflon tape.
Now the $64 question...anyone happen to know how many threads there are in the housing for the drain plug?
Thanks,
Mike T.

 

Sometimes some auto parts stores have a selection of oversize, self tapping plugs. This will certainly work fine, but to me, it is NOT a preferred method.
I prefer 2 alternate methods. Both require welding.
First have a good welder weld a bead all the way around the hole threads then run a tap through the weld (I believe the thread size is 1/2in fine thread).
The other method, as you have already mentioned (which I have done to the 56) is to install the plug, then run the appropriate size nut down on the plug from inside-----------tight. Then, have the nut VERY securely tack welded inside the housing. Remove the plug then drill holes through 2-3 of the flats on the nut (these holes in the flats will allow the oil to drain down lower inside the housing).

Tom Parsons

 

Tom, once the 'very-gray' lubricant ran out of the drain hole I was able to look up into it and see that there are only maybe 4 or so threads cut into the housing and they are all screwed. I'm really surprised that the plug stayed in place like it did. I would have expected more than just a drip every so often. There's a receipt for the rear end work done in '04, kinda surprised to see so much 'gray' to the lube since I don't think the car saw that much racing since '04.
Once I got the old drain plug out of the hole and the upper threads on the plug seemed to take a slight bite, I am thinking there is a chance I could get by with some teflon tape but that will be a trial fit situation and if I don't get good thread engagement, that approach will get tossed.
Since I'm more concerned with just plugging the hole and not worried about maintaining the threads (at this point), an expandable plug similar to those rubber freeze plugs would do the trick, at least until I get to the point of stripping down the differential and then can fix it...or just replace it with a 12-bolt. Grand plans indeed, for now, I'm just looking for a way to adequately plug that half-inch hole.
Mike T.

 

Use a 1/2" single oversize oil pan plug and nylon washer. Problem solved. I would change that fluid though.

 

Hey Mike,
How about one of these??

http://www.sherco-auto.com/drainlpluggasket.htm

For less than two bucks, it looks like its worth a try. they have oversized, double oversized, and piggyback models.

Mike Coletta

 

Landshark - I definitely had no intention of putting that gray colored stuff back in there. Never have seen that color out of any posi differential I've ever worked on before. I expect that the gray color is from the posi clutches. Just something else to deal with when I do get around to pulling it all apart...later on that is.

MIke - Thanks for the link, that's what I'm looking for. I'm hoping to find them locally but if not, I'll order one up from them.

Thanks,
Mike T.

 

Must be the 'clean living' or just plain lucky (good luck for a change) because I found a local parts house that had the 'single oversize' and double oversize' replacement drain plugs for the 1/2-20 size plugs. The factory plug seemed to be about .493 wide at the crown of the threads and the single oversize was .520.
Cleaned out what was left of the threads in the housing and started the new single oversize with the thick fiber washer. Worked like a charm. Nice and tight without binding up and snugged up perfectly.
Since I hate leaks, I even added a smear of Loctite 545 to make sure.
Finally...success!
Thanks,
Mike T.

 

Those plugs are a common item. Every parts house I have ever dealt with stocks them. No luck involved.

If that fluid was light to medium grey, that sounds like water contamination. Posi clutches would not do that, I think.

 

Nope, the gray look to the lube was not moisture related. Just a guess that it's fallout from the posi clutches but it doesn't really matter as the diff made no strange sounds either before or after the change.
Sure wasn't bearing material or any other type of metallic shard.

As for the luck of finding a shop that had the oversize drain plugs 'on hand', it was 'luck' no doubt about it considering it was Sunday when I went looking for one and factor in the recent closure of so many parts shops in this area.