This weekend I
changed transmission oil in my '90GT 5 Speed.
When I pulled the magnetic drain plug out, there was a piece of metal, looking like a piece of spring steel hanging on the magnet.
See the attached picture. My transmission has never given any problems, runs fine and shifts smooth.
Does anyone have knowledge about the internals of the 5 speed? I looked through the manual but none of the pictures shows anything that looks like it.
I wonder if it is a piece of a shift lock spring. The car has about 87,000 miles on the odometer
Look on page 34-10 of the workshop manual, part 5 "leaf spring".
The pawl prevents you going from 1 to R. The pawl is held in place by gravity and the spring, so with a broken spring it still works.
If you tried to change from 1 to R just as you went over a bump which caused the pawl to jump up, you could possibly overcome it. The worst thing that would happen is that the gears (syncro on a later box) would grind.
As others have said, the piece is one of the two springs that help center the shift lever. On the later five-speeds, the lever is firmly spring-loaded from the first/reverse slot toward the 2nd/3rd slot, and lightly spring loaded from the 4th/5th slot toward the 2nd/3rd slot. This gives a much more positive feel to the shifting, making it less likely that you will select the wrong gear. The car is driveable without the spring, and the spring is virtually the last piece to be removed from the case, so repair is only possible with complete disassembly. The broken spring can fall into the gears and cause major damage, but fortunately, that is very rare.
By the way - many owners don't realize that reverse is synchronized on the later cars. While I certainly don't recommend it, you can shift into reverse while doing 20 mph forward with no grinding - BTDT!