Questions related to 915 drain plug magnet loss

[930yyc]

My questions are;

- what kind of damage is likely to happen if the drain plugs are oriented wrong and the magnetic plug drops a piece?

- if it doesn't drop to the bottom or found during a flush is it at all likely to be crushed.

Background;

Now years prior; I did a transmission fluid change on my 915 ROW box with cooler, by the time it was done I realized I had the plugs swapped around. Magnetic on the side, non on the bottom.

DE coming right up I left it that way, this year I advise/remind my mechanic that I put the plugs in the wrong spot and to switch them around. Approximately 3000km has been driven since I put them in the wrong spot years ago, largely track.

The call comes in yesterday, the magnet is no longer present on the plug.


-Ivan

[Gunter]

If it's the centre pin magnet inside the plug, it's hard to picture it coming loose.
And since it's magnetic, it would attach itself to something and not just float around.

I would like to see a picture of this plug; it may well be just a regular one without a magnet.

BTW, I installed magnetic plugs top and bottom on the 915 plus magnetic plugs on the oil tank and the engine sump.

Why don't you order a few magnetic ones and install?

[930yyc]

Will find out today what the status is from the mechanic and post an update.

I will post a picture when the plugs change. Should there be one available, the old one won't be going back in.

I do remember distinctly taking a picture then of the plug (damned if I can find that .jpg now), cleaning the fuzz off the old plug, keeping the fuzz in a bag and noting I had the order wrong after I filled up the transmission.

Normally I would have done what Gunter suggested and put plugs in both spots (and ultimately noticed the missing magnet then) but the car was at the shop for other significant work already in prep for this season.

[fredmo1947]

This is interesting. In Wayne's book "101 Projects" one of the recommended upgrades while changing transmission fluid in a 915 tranny is to replace the check/fill plug (s) with a magnet type drain plug. Given your experience that may be ill advised.

[Zeke]

Originally Posted by fredmo1947

This is interesting. In Wayne's book "101 Projects" one of the recommended upgrades while changing transmission fluid in a 915 tranny is to replace the check/fill plug (s) with a magnet type drain plug. Given your experience that may be ill advised.

I don't know why he would recommend that. The plug is above the static level and gets washed during operation. The missing magnet is probably on the bottom somewhere. Go fish for it.

[SteveinTO]

I believe if you swap the plugs, the magnetic tip will be broken off the first time the gear stack is shifted so that a gear momentarily engages the magnet. I say momentary because it snaps off and lands somewhere, hopefully in the bottom of the transmission case. Next time you drain, fish around inside with your pinky. You might get lucky.

I know a guy that reasoned two magnets was twice as good as one, but that proved not to be the case. In the end, the pipe threads get worn by hambone mechanics installing the plugs with impact wrenches, eventually allowing the plug to protrude too deep into the case.

[Gunter]

I cannot believe what I am reading here.
Even if the little center magnet comes loose, it'll stick to the plug because the plug is steel?
You know? Magnet and steel? They stick!

The plug gets washed?
Yes, the oil sloshes around in the 915 and that's why the magnet holds on to the fine metal gunk you'll find on the magnet.
Same for the engine oil tank, the oil sloshes around but will not dislodge the magnetic residue.
Please!
As for the magnet being knocked off through shifting, wow!

The plugs in the 915 are NPT (National Pipe Thread) meaning: tapered.
Most people tighten them way too much to a point of almost cracking the case but the plug (Or the inside magnet) cannot reach any internal parts like gears etc.
And BTW, there is no room for an impact gun for the filler plug.

The internal-hex plug can be changed to an external-hex plug which makes it easier to remove.

Using 2 magnetic plugs in the 915 cannot do any harm.
And yes, I have found small amounts of magnetic gunk on the upper magnetic plug in the 915.

The plugs in the oil tank are straight Metric with seals (Crush washers).
I use magnetic plugs on the engine sump and the oil tank for good reason.

Still hoping for a picture of the "Missing-magnet-plug".

[Grady Clay]

Gunter is correct.

Using two magnets is better than one. For track use I even add large (40x28x26 mm) Alnico U-magnets bolted inside the case. If some piece of hardened steel comes loose or breaks, I want it on a magnet and not circulating through the other (expensive) bearings and gears.

During a race I lost a tooth off a 904 “E” 2nd gear. It landed on a magnet and nothing else was damaged.

This can be done on a street transmission. Simply put two steel bolts through the case near the shift pivot on a 901 or 915. Make the bolt heads smooth and flat to mate with the faces of the poles of a U-magnet. Bolt/clamp the magnet outside the transmission. During a service, remove the shift pivot, remove the magnet and clean the ends of the bolts of any debris.

These big magnets are far more powerful than anyone on a drain plug.

Best,
Grady

[SteveinTO]

I could be wrong, it wouldn't be the first time, but on the 915 in my '82 there is a gear in close proximity to the side fill hole. The non-magnetic side plug had been over tightened, as I can attest. I took a breaker bar and a three foot pipe to get it loose the first time. I replaced the plug with a "magnet plug" identical to the bottom plug. Torqued it down to something very reasonable.

The following year when I again changed the oil (this time requiring only a 1/2" ratchet), the magnetic tip was gone. Found it with a bent, telescoping magnet near the drain hole. It appears to have survived nicely at the bottom of the case and did not appear to have been ground up in the works. Lucky me!

As observed above, the magnet should stick to the steel plug, unless it gets whacked and tumbles down the aluminum case. I recall the plug definitely looked like the magnet had been broken off. The plug, now magnet-less, turns down almost flush with the outer surface of the transmission.

I applaud the double magnet concept, but still consider my experience a cautionary tale when dealing with 28 year old pipe threads in aluminum.