There isn't a transmission capacity the only thing you go by is the amount of gears it has.
The Mercury Sable transmission has a fluid capacity of 12 quarts. You can use any SAE certified automatic transmission fluid.
The 1991 Mercury Topaz has a fuel tank capacity of around 13.5 gallons.
Dexron 3 will do just fine.
Possibly. Look at the model # on each transmission. If they are the same, then they are interchangeable.
Mercury Topaz was created in 1983.
The 1993 Mercury manual transmission linkage will have adjustment nuts on each end of the linkage. Turning the adjustment nuts will move the linkage back in forth.
4.1 Qt.s
On your 1989 MERCURY TOPAZ, the BACK-UP LIGHT SWITCH is: UNDER HOOD, DRIVER SIDE, LOWER ENGINE AREA, MOUNTED ON TOP OF TRANSMISSION
On my 1993 Topaz, the transmission fluid dipstick is on the right side of the engine, near the front, just to the left of the battery. It looks a lot like the oil dipstick, but, when you pull it out, the writing on the dipstick clearly mentions that the fluid level should be checked when the engine is hot and idling, and that a certain type of Mercury automatic transmission fluid should be used to refill.
Low on fluid, dirty filter, worn clutches.
A 1991 mercury topaz has drum brakes on the rear wheels.
Big job. You have a choice, remove the whole engine with the transmission, or just the transmission. Either way you have to be equipped with the right tools. Best is to find someone to do the job for you. It will cost.