Hi All,

After disassembling my Muncie M20 today, I found a donut shaped magnet glued to the inside bottom of the case, in the vicinity of the lower drain plug boss. Did GM originally put this there, or did someone add it? Should I re-install it?(It came loose)
If so, what kind of adhesive should I use?

Thanks for any help.

Jeff

If it were me I wouldn't want anything in there that could even possibly come loose and get in the gears. Could be disaster. Not so sure it would do anything anyway since the oil really churns in a tranny. tom

I doubt it was stock maybe someone can help on that point but people use them so the magnet collects any metal particles from going into curculation. When the engine or tranny works it will have peices of metal that just wear off. I'm not sure bout the pan you have but if there is a drain plug you can get a new plug that has a magnet on it. don't think they cost much.

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That's probably what they were doing, catching some loose particles.I know that DZ(Tom) puts a magnetized drain plug in to do the same purpose on his cases.Maybe he will give you a little insight on where to attach the existing one, or pick up a magnetized one for your case.I would say you could probably clean the area well, and attach it to the case if you want with a high quality 2 part epoxy.Cleaning is the key, or it will break loose again.I would try the drain plug idea first though.

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Jeff,
All Muncies ever built had a drain plug boss. But it was not until 1970 that all Muncies got the drain plug (magnetic) installed (except for 66-69 M-22s). I have no clue why the earlier Muncies did not get the boss drilled and tapped for a drain plug. The previous 4spds, the T-10, always had a drain plug. In the Muncies without a drain plug, as you have discovered, there was a donut magnet glued in the bottom of the case to pull metal particles away from the gears and suck metal out of the oil to the bottom of the case. By my way of thinking this is one of the scariest and dumbest things I have ever seen. If the magnet comes unglued and gets into the spinning gears, ------------ well use your imagination. Also, the metal attracted to the magnet has no way of being removed (or the old oil) from the transmission.
On every Muncie I build, I drill, tap and install a magnetic drain plug for these reasons and I also have a large collection of donut magnets in my tool box. GET THAT THING OUT OF THERE!
Because the Muncie case is aluminum, it is easy to install a magnetic drain plug. You just need to drill the boss in the center and tap it with a 1/2in pipe thread tap. Be sure to install a MAGNETIC drain plug.

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Tom Parsons

Tom,

Where can I find a magnetic drain plug. The one's I found at my local parts store are not magnetic.

By the way, The donut magnet is history. Like you said, can you imagine what would happen if it ever came loose!!

Thanks,

Jeff

I just recently picked up about 9 cases, several had the magnetic dounut in the bottom. I have seen these before, the biggest complaint I have is it is impossible to get all the crude off when you rebuild the trans. I never saw one un-bond itself from the case, even when they blow the counter gear apart. But I agree with Tom, take it out and put in a magnetic plug.

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Wally
Gold #67
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Jeff,
The magnetic drain plug is a common AC/Delco part and probably is available from parts stores like NAPA. But if you have no luck finding one, the GM Part number is 3930923. Very probably there is a Chev or GM dealer in your area that has one in inventory. ALL GM parts depts are on computor, go to your Chev parts dept and have them check all the local dealers, or order one. This same plug was also used in the Super T-10.

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Tom Parsons