Hey all. As some of you may remember, I rebuilt my second LS400 trans a couple of years ago. I've got about 12,000 miles on it now and am experiencing an issue. The torque converter seems to be draining back into the case overnight. What this does is overfill the trans sump and causes the fluid to find the easiest path out and on to the ground. That point on my unit right now is the throttle cable. I'm leaking quite a bit overnight. It's extremely annoying. The fluid is about 2" above the max HOT mark on the dipstick when checked cold with the engine off. If you pull the dipstick out and start the car it burps fluid out of the dipstick tube. This is our primary vehicle until I get out and replace the evaporator core on our diesel Jetta so it's a bit frustrating to say the least.

I always thought that some of the fluid was supposed to drain back from the converter but apparently not. For fluid to drain out of the converter air must be able to leak in. This can mainly happen around the pump bushing that the converter neck goes through in the pump. I'm going to have to pull the unit again and pull the pump and inspect everything in there. I'm not aware if there is anything in the valve body to look at with regards to this issue. The converter was a new rebuild from a shop that has a guy that has been building converters for 35 years. That doesn't mean that something can't be wrong with it though. We'll see. I was first going to just replace the throttle cable o-ring but that isn't the primary concern.

I'm wondering if anyone else has experienced drain-back in their trans of if I'm going to find something worn in my unit when I get it back apart.

 

I'd like to bump this thread. I'm still having this issue. I haven't experimented with fixed for it but I'm about to at least replace the throttle cable o-ring. But, I don't think the torque converter should be draining back this badly.

I have to wonder if I should remove the trans and at least pull the pump and check the fit of the pump pushing to the converter. I'm also not sure if there is a check valve or something somewhere in the valve body that is supposed to hold the fluid up in the converter.

I can't park the car anywhere over a few nights without a 6" puddle underneath.

 

I don't have near as much knowledge of this stuff as you do, and I do see you're in Florida, but ... would strategically parking on a hill (do they have those there?) or sloping driveway solve the overnight leaking problem?

 

My general understanding is that fluid flow is from the pump, through the pressure regulation system and then to the torque converter. I would think that if the converter is draining back into the sump, it's draining back through the pressure regulation system; either a valve or solenoid.

 

Hi All. I did a drain and fill on my 1998 LS400 and found that 4 quarts came out. It had been standing for a few weeks with front wheels in the air a bit waiting for a cambelt change to be finished.
I was told that this was normal amount when allowed to sit like that. Normally I get 2 quarts at the most through a drain and fill that I normally do when changing engine oil. Have had no oil leak problems.

 

Without pulling the transmission back apart, it's going to be hard to figure out. My guess would be the oil seal that fits into the pump, that slides over the input shaft, is worn. Especially if it wasn't replaced during the rebuild.

I feel like Paulo57509 is on the right track. That's a somewhat common issue with many old American vehicles. The issue I'm running into is that I'm not seeing any check valve or regulator between the pump and converter for the A650e. Every one I find is valve body related, which in theory shouldn't cause your issue

Did you fill the converter before installation? How many quarts of fluid was added after reinstallation of the transmission?
Could it be possible that you bought the car and a previous owner installed the wrong trans dipstick and it's causing you to overfill?

 

I thought it could be overfilled too.

The OP doesn't state which transmission he's working on (or swearing at).

FWIW, the A650E; there's a solenoid that modulates line pressure in the valve body (Shift Solenoid SLT). I haven't yet come across a fluid flow schematic for an A650E, but there's a caged check ball and spring between the valve body and the transmission case. I don't know what the function of this check ball is.

 

I needed to fill 5.1L (5.4qt) of Toyota T-IV when I dropped the pan. The job needed totally 4 days+, because I was out of my house for 3 days right after I dropped the pan. I found that there came down drips next to next from the pump and it must be the drain back from the torque converter. The interval between the drip to drip or should I say the frequency was almost unchanged for more than 3 days and the total amount of drips was 2.6L. The reason why 5.1L is that 2L(from the drain bolt hole) + 0.5L( remaining in the pan) + total amount of drips 2.6L. They say that the drain and fill needs 2qt but when you wait longer, you get more than 2qt.

This much of ATF was still coming down on 4th day and the cardboard set under the AT was quite wet.

 

i spent an hour looking for schematics last night. I couldn't find anything..

 

The attachment shows the general location of that caged check ball but it's anyone's guess as to what fluid circuit it's in or it's function. I don't even know if this is the check ball.

I tried looking for a fluid schematic like the second attachment but no dice. I wonder if Toyota has separate manuals for transmissions?

It has also been my experience with automatics that they will continue to slowly drain until they reach some equilibrium point. The more I think about it, the OP might just have a bad seal.

 

Sorry fellas, you're right. I didn't list at least the year of the car. It's a 1996. Aisin A340E.