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Does transmission actually lock up in cars? What happens when moving?

If the transmission is completely out of oil and say it overheats…I’m guessing the gears inside it warp and the entire assembly locks up.

What happens if the vehicle is moving at 60mph when this happens?

(Specifically, this is about the trans in 2000 corolla 4-spd auto)

This is one of the most misunderstood areas. If a transmission loses all its oil it won’t function at all. All gears will be like neutral. The servos won’t operate the clutches or bands, the torque converter won’t couple if its empty. The car won’t drive at all.

I’ve seen people claim they’ve driven their cars after they had their transmission serviced and the tech forgot to refill it. That’s impossible.

When the transmission is a quart or two low it will warn you by intermittently slipping, especially going around corners or up steep hills. Usually just adding fluid will correct this with no damage if you catch it right away.

Edit - Now if it were a manual transmission that would be entirely different. It would suffer severe damage.

Ah ok.

So, the damage is from the trans missing a couple of quarts of oil (there is not enough oil for cooling).

Say the trans has a massive leak and all the fluid leaks out at once…there is no damage right? Because it didn’t have enough time to build up heat.

When it is low on fluid and it slips, the clutches can be burned fairly quickly requiring an overhaul.

The main function of the oil is to operate the hydraulics and provide lubrication. If you had a massive leak and all the oil leaked out at once the transmission would, in effect, shut itself down due to lack of oil pressure to operate the hydraulics and all you could do is coast to the side of the road. There would likely be no damage if you shut the engine down right away.

As for running it a couple of quarts low, it would depend on how long you ran it that way once the slipping symptoms appeared and how severe the symptoms were. Judging by the photo you submitted in your previous thread the fluid looks bright pink. That’s a good sign that no damage occurred. If the fluid were overheated the fluid would be brown and have an acrid odor. Slipping clutches are what burn the fluid. I suspect you caught in time.

A modern, electronically-controlled transmission will also crank the line pressure up to the highest it can to prevent clutch damage if a problem is detected. This will result in harsher than normal shifts, so you will notice something is not right. Also, if a severe problem is detected, the transmission will typically default to 2nd gear and stay there, another indication that a problem exists. Usually if an automatic is very low on fluid, it just won’t move at all.

What happens when a transmission seizes at 60? It’s not pretty. Usually the driven wheel(s) will lock up like slamming on the brakes, which can result in a loss of control.

Got a couple of more questions.

  1. If low transmission fluid doesn’t cause the transmission seize…what then causes it?
  2. What happens if the transmission is over-filled (say by a couple of quarts)?

I’d rather have a FWD trans seize than a RWD for the same reason brakes are supposed to lock the fronts first. If the rears lock you have no directional stability (if you steer you spin), if the fronts lock at least you slide in a straight line.

  1. Without fairly intimate knowledge of the specific transmission design, it is hard to say what would cause it to seize. @MY 2 CENTS is right about the likely things that happen. It shouldn’t seize, but if it does, it could be many things like debris in the trans getting between gear teeth. Usually a fatal problem.
  2. Over-filled fluid; The fluid will foam and shoot out the filler tube or vent tube making a mess. It can cause foaming which will act a lot like low fluid - slipping, loss of shifting, dropping to neutral.

xaml, how long were you driving this car low on transmission fluid (miles?) and how low was it? Rocketman

Not sure how long, but when the problem happened, about 2 weeks. There was no fluid whatsoever on the dipstick. Strangely, the transmission shifted smoothly. The problem only happened after a sharp corner (and only for 1-2 seconds).

Anyways, after adding about 1.8 quarters, the level is back to normal and the problem is gone.

Good, I hope you’re OK. Good luck! Rocketman

Just want to point out that just because there is no fluid on the dipstick doesn’t mean there is no fluid in the transmission. There can be several quarts in there below the dipstick and throughout the transmission.

“The problem only happened after a sharp corner (and only for 1-2 seconds).”

You didn’t sense the trans was seizing did you? I’m assuming it slipped for those few seconds (car slowed, engine revved up). I’ve never heard of an auto trans seizing in a moving car. I guess it might happen if the solenoids go wonky and try to put the trans into two gears at once.

After taking a corner and coming to a dead stop fast, the engine would be stuck around 1200rpm (like the torque convertor was connected and not disengaging even though the car was stopped). After a couple of seconds, there would be a “thud” and I can feel the torque convertor disconnect from the engine and the RPMs go back down to 650rpm (normal).

On some corners, the engine would suddenly start revving up like it was confused. I guess that is what is called “slipping”.

You only have to be down a quart or so before the fluid won’t show on the dipstick. So you could still have reasonably normal trans operation when its that low. It’ll hold what, 10-12 quarts?

I’m not saying it doesn’t happen but I’m not going to worry about a transmission locking up on the highway. In over a million miles, a number of transmission failures, and on high mileage vehicles, I have never experienced it myself. This, seems to me, would be truly catastrophic failure with parts laying on the road I think.

Edit: Sorry 2 cents, didn’t see your comment. There is also a solenoid that locks and unlocks the torque converter that could be sticking. Usually felt when coming to a stop and feels like a standard transmission with the clutch not disengaged. Used to be pretty common on well used GMs. About a $300 or so fix since the trans has to come partly out to get at it.

IIRC, Honda had to recall their automatic transmissions because they had a lubrication problem with one of its gears, which could result in the gear welding itself to the shaft by friction and locking the transmission while driving.
@xaml, I think you got it the other way around. A torque converter that stays locked would have the engine stopping with the car rather than revving high. This is more likely an engine control issue.