I need help figuring out what is wrong with my transmission on my 1998 mazda 626?

[James]

I have a 1998 mazda 626 4cylinder. Just recently, when i have been driving the car for a while, the o/d light in the dash starts blinking non-stop. I pull over and turn the car back off, and back on, but it still does it. Also it jerks between 10 and 20 mph. After leting the car sit for a little while and starting it back up, it stops blinking, and does not jerk anymore. I checked my fluid and noticed that it has a blackish sludge in it, or that could also be from accidentally scraping it on something. Last weekend, (before this all started) the fluid level seemed a little low, so i added about half a quart of fluid and a little bit of stop slip, that was supposed to help keep it running smoothly, then checked the fluid again and it looked like i had possibly overfilled it. I think this may have had something to do with it but i am not sure, as i do not know much about cars. Can anyone tell me what may be wrong with my transmission?

[Mr.T]

mess with the overdrive button (o/d) it may need to be cleaned out. The transmission is simply getting old. The jerk is from it switching gears, mine does it too. It is not a big deal. Change the fluid as soon as possible. Not many people change the fluid ever in a transmission. It should lessen the jerk of the gears. Hopefully you used the right kind of transmission fluid. They can tell you at Autozone. Since you said it jerked I am assuming it is automatic and in that case you should be using ATF Automatic Transmission Fluid. Manual transmission fluids can damage your vehicle.

Good luck!