You know what the problem and cause is. There's a fluid leak. What you don't know is you're turning a minor problem into a really serious and expensive one by continuing to drive it like that. There's two or more clutch packs, and each one uses transmission fluid under high pressure to apply those clutches. Each clutch pack has about half a dozen plates, alternating a steel plate with a fiber plate. All of the wear takes place on those plates during the fraction of a second while they are engaging and disengaging. No wear takes place once they're solidly locked up. That's why they can last 100,000 miles or more.
When the transmission fluid level is low, air gets sucked up by the pump, and since air can be compressed, not enough pressure can be built up to firmly hold those clutch plates together. When they slip, you feel or hear the engine speed up but the car doesn't pick up speed. That slipping in the clutch plates builds up a lot of heat real fast and will tear the material off the fiber plates. Overheated transmission fluid will turn dark or black, and it will lose its lubricating properties. You'll smell that on the dip stick. Once that damage is done, it's just a matter of how many miles or how many minutes will the car continue to move before you're sitting on the side of the road.
You've already done a lot of damage by trying to drive the car this way. First have the leak diagnosed and repaired, then they will fill the fluid and test-drive the car. You may have no further problems for a while, but a lot of wear has already taken place. If the transmission continues to slip, it's because there isn't enough fiber material left on the plates to allow for solid engagement. The internal filter does a pretty good job of trapping dirt, but if a piece of a fiber plate breaks off and is able to circulate with the fluid, it can tear up a rubber seal in those clutch packs. That would cause still more inability for those clutches to lock up, so more slipping and more wear will take place very quickly. If a chunk of clutch plate material gets stuck in a shift valve, the transmission may fail to shift to the next gear or it could shift at the wrong time.
In the worst case, the transmission will need to be rebuilt. At the mileage you listed, you're at that point already, depending on how much highway driving you do, but driving with a slipping transmission is going to insure a rebuild is needed.
Sunday, January 12th, 2014 AT 5:02 PM