The transmission was making a little noise and a few people were telling me that I might be able to fix it by changing out the fluid. Even though the noise sounded to me like a bad pilot bearing there was no reason to not change out the oil on a 150,000 mile car since I had no idea if it had ever been done before.


I always ran expensive Redline synthetic transmission fluid in my Miatas but people were recommending that I use Synchromesh fluid in the Geo. I found the fluid at Napa for $7 a quart (the tranny holds about 2.5 quarts):



ALWAYS remove the fill plug first when changing out transmission fluid. If you drain the fluid first and cannot refill the tranny you are screwed. The fill valve was really tight and I ended up stripping out the 3/8" square drive on the plug. This is when the excitement started and turned a simple 30 minute job into a 6 hour nightmare. After stripping the plug I decided that I could remove it by welding a bolt in the square hole. It was a good idea on paper but welding a dirty/oily fill plug while laying back and dropping red hot slag on yourself made the job really tough. Also, my welding helmet was dead (I use a solar powered electric helmet) so I did the old "close your eyes" method. After 30 minutes of burning myself, setting the newspaper on fire that I had under the car to catch the drips, and accidentally welding the bolt on the transmission (I had to use a dremel with a cutting wheel to cut threw the weld) I had the fill plug out:



Yes, it gets worse! Once the fill plug was out I decided that I would clean up the really bad weld a bit to make it a little stronger. Remember when I said my welding helmet was broken? Well, I accidentally moved my hand when trying to put a better weld on and got some weld on the threads. Now I was in trouble. My make-shift fill plug was ruined so I headed off to the parts store to get a new one. After two hours, four 4 parts stores and a hardware store, I had come to the realization that you could not purchase a new fill plug anywhere. So, I went back to the house and looked for a die to recut the threads. Nope, I didn't have anything in that size. I decided to bite the bullet and start filing away the weld to make new threads on the plug. File a little, get under the car to see where the threads were catching, and then get back up and file some more. Two hours later and I had the threads just about right:



I removed the drain plug and drained out the old fluid. It really didn't look too bad but who really knows if it was ever changed out. The drain plug had a lot of goop on it:



I cleaned off the sludge and found a little metal in there but I think that is pretty standard find. So, did it fix the transmission noise? Nope, but it was still a job that needed to be done: