C-4 Transmission Drain Plug

Here is a small project that almost anyone can do and will greatly ease the maintenance of any automatic transmission. It is the installation of a drain plug on the transmission pan. All it took was for me to change the oil and filter once to realize that the addition of a drain plug would make the job far easier and cleaner.

Here is the pan without any drain at all:


There are bolt on drain kits kits available that only require a hole to be drilled, but since I had access to a welder, I made my own kit. I used a 1/2"-20 nut, and a plug off an old oil pan, The gasket is available at any parts store:


I decided to add the plug at the left front side of the pan so that the plug would not be in the way if it were on the bottom. A 9/16" hole was drilled first:


The paint around the hole was cleaned off with a wire wheel on a bench grinder in preparation for welding:


The nut was then clamped into position over the hole:


I used a MIG welder to weld the nut to the pan. The plug was installed, and the pan was filled with water to check for any leaks, fortunately there were none:


A little paint, and it is done. This was an easy to do project that cost nothing, and will greatly add to the ease of maintenance on the vehicle:

Nice! I will be doing that one when I get around to a transmission project on my car.

Thanks for that. You saved me $100 on a new pan!

cool, Ive received a few transmission with home made drains just never got around to doing it. Ive seen them on the bottom as well.

Don't put one on the bottom. If you car is lowered and you go over high man hole cover or if there is something in the road, you could shear it right off. I've seen it before.

Originally Posted by dablack

Don't put one on the bottom. If you car is lowered and you go over high man hole cover or if there is something in the road, you could shear it right off. I've seen it before.

hi
i got my 1970 mach 1, 3spd..... could not figure out why there was no drain hole.
great answer--- i thought it was a stupid idea by ford but i guss tha why i don't build cars....
thanks,molly

Originally Posted by Cupcake65

Here is a small project that almost anyone can do and will greatly ease the maintenance of any automatic transmission. It is the installation of a drain plug on the transmission pan. All it took was for me to change the oil and filter once to realize that the addition of a drain plug would make the job far easier and cleaner.

Here is the pan without any drain at all:


There are bolt on drain kits kits available that only require a hole to be drilled, but since I had access to a welder, I made my own kit. I used a 1/2"-20 nut, and a plug off an old oil pan, The gasket is available at any parts store:


I decided to add the plug at the left front side of the pan so that the plug would not be in the way if it were on the bottom. A 9/16" hole was drilled first:


The paint around the hole was cleaned off with a wire wheel on a bench grinder in preparation for welding:


The nut was then clamped into position over the hole:


I used a MIG welder to weld the nut to the pan. The plug was installed, and the pan was filled with water to check for any leaks, fortunately there were none:


A little paint, and it is done. This was an easy to do project that cost nothing, and will greatly add to the ease of maintenance on the vehicle:

HI

GREAT PIECE OF WORK...... I'VE GOT A 3SPD ON THE FLOOR IN MY MACH 1. DO YOU THINK THIS COULD WORK ON MY 3SPD MANUAL TRANS, REPEAT MANUAL NPT AUTO????
REALLY NEED HELP! EMAIL ME AT
hereford2@webtv.net. my posts arn't
gettin thru for some reason.

molly

HI

NOT SURE MY POSTS ARE GETTING THRU. IF YOU GOT THIS ALREADY IGNORE IT.
DO YOU THINK THIS MIGHT WORK ONMY MACH1 1970 3SPD MANUAL TRANS?

THANKS,MOLLY
EMAIL hereford2@webtv.net

Molly,

Unfortunately your 3 speed manual transmission does not have a removable pan like the automatic shown above.

Your transmission case is cast iron and could possible be tapped without adding additional support if it is cast thick enough. The problem with tapping it in this way is that the case may not be thick enough. Also metal shavings could be introduced to the inside during the process. This could bad so the transmission would need to be first dissembled to do the work.

If the case is not thick enough, then some type of additional support would be necessary. Unfortunately, it is not easy to weld to cast iron. It tends to crack when not cooled properly so it would require the professional services. Again, the transmission would need to be disassembled to do this.

For these reasons I feel that is probably not practical in your case to add a drain plug to that transmission.

By the way, have you looked at the underside of your transmission to see if it already has a drain plug? I haven't had a 3 speed in my hands for years but I do know that many (but not all) of the 4 speed transmissions available in the Mustang have a drain plug from the factory.