A750F transmission acting weird? Overfill it!

[Brickyard]

I'm on my second transmission. I am confident the first broke after filling ATF to specification in accordance with factory service manual. Second transmission had symptoms of first transmission until I added an extra 1.5 quarts of ATF WS.

Do you drive a 2003-2005 Limited V8 4WD? Does your T4R jerk forward when you hard brake, or from a rolling stop? Have you had the ATF flushed or refilled for any reason? Have you ruled out driveshaft clunk because you're confident your problem is transmission related? Do you have an A750F sealed transmission? Another quart or two of ATF WS MIGHT fix it...

 

[nevada]

that sounds a lot like the driveshaft clunk.

I don't think intentionally overfilling the transmission is a good idea...

 

[Morphyne]

I'm on my second transmission. I am confident the first broke after filling ATF to specification in accordance with factory service manual. Second transmission had symptoms of first transmission until I added an extra 1.5 quarts of ATF WS.

Does your T4R jerk forward when you hard brake, or from a rolling stop? Another quart or two of Transmission fluid might fix it!

No offense but taking transmission tricks from a guy who is on his 2nd one isn't likely gonna fly. Plus I heard that the worst thing you can do is overfill your transmission.

 

[duffdog]

No offense but taking transmission tricks from a guy who is on his 2nd one isn't likely gonna fly. Plus I heard that the worst thing you can do is overfill your transmission.

Ive heard that too, but I'm not sure exactly what it causes. Lockup converter problems maybe? Anyone know?

 

[The Yin]

Limited knowledge

I'm not sure what over filling can do, but I know I've had a very odd experience with over filling motor oil on a pressure washer.

Not sure if it's common for other situations, but when the oil was over filled, the pull start would lock up and snatch back from me. The harder I pulled, it seemed the motor pulled back with equal or greater force. After we drained the oil to it's proper level, it started up fine.

Not 100% sure if the oil was the cause, but it was a new experience for me.

 

[Brickyard]

No offense taken to any of the comments, after all, it seems absurd, especially if you would not personally mess with such complicated systems like the engine and transmission. Two years ago, I hydrolocked my original engine and threw a connecting rod, while punching a whole in the engine block. I had to replace the engine myself, filled ATF per FSM in my original transmission, and everything was fine until a year later. In that year, I contributed the forward jerking to "driveshaft clunk," until one day, a clunk became a whirling noise and the 4Runner would not move forward. After removing my transmission, and upon closer examination, I realized that my "driveshaft clunk" was purely transmission related. One photo is of shaft spline coupling, connecting transmission shaft to transfer case, and the other photo is the worn shaft on my original transmission.

Upon installing the donor transmission, and filling ATF per FSM, the symptoms remained. A few weeks ago I decided to take the chance and add more ATF. If anything seemed weird, like CEL's and transmission lights in the cabin, or driving was off, I would have removed the extra ATF. Instead, it appears to have fixed my "driveshaft clunk." As hard as it is to say, I suspect the FSM is misleading, and would have the DIYer put too little ATF back into the transmission.

If you have messed with your ATF for whatever reason, remedied the "driveshaft clunk," and problems still exist, you might be suffering from low transmission fluid. I believe these photos are the result of low transmission fluid, which was initially mistaken as driveshaft clunk. One quart of fluid may have been the difference.

BTW, I also heard overfilling a transmission was bad, but took the chance, and so far its paying off with a smoother ride, and peace of mind.

It's possible that the A750F sealed transmissions were "overfilled" from the factory.

 

[m85476585]

I assume it's worn because the spline coupling broke, so the transmission shaft spun in the coupling. That's the whirling without moving. I guess if it was slamming into gear then maybe the shock broke it. It can do that if it's low on fluid.

Are you sure you filled the fluid correctly the first two times? It sounds like you are confident you did, but just checking? You're supposed to check the level with it hot, and the FSM gives a range of temperature (with risk of severe burns from the exhaust while you are checking the level). It takes about 10-15 minutes of idling in park to get there (or a short drive). If you open the level check plug with it cold a lot of fluid will drain out, at least a quart.

Maybe you got air in there somewhere, but after 10-15 minutes of idling it should work its way out. Did you cycle through all the gears after filling it up? (I don't think it will actually go into 3-5 while parked, but I think it worked OK for me.)

Mine clunks pretty bad if I manually downshift to 3rd going down a mountain pass, but otherwise it's smooth. The clunk when stopping is back, so it's time to grease the driveshaft again and see if that and the downshift clunk go away.

 

[Brickyard]

I assume it's worn because the spline coupling broke, so the transmission shaft spun in the coupling. That's the whirling without moving. I guess if it was slamming into gear then maybe the shock broke it. It can do that if it's low on fluid.

Are you sure you filled the fluid correctly the first two times? It sounds like you are confident you did, but just checking? You're supposed to check the level with it hot, and the FSM gives a range of temperature (with risk of severe burns from the exhaust while you are checking the level). It takes about 10-15 minutes of idling in park to get there (or a short drive). If you open the level check plug with it cold a lot of fluid will drain out, at least a quart.

Maybe you got air in there somewhere, but after 10-15 minutes of idling it should work its way out. Did you cycle through all the gears after filling it up? (I don't think it will actually go into 3-5 while parked, but I think it worked OK for me.)

Mine clunks pretty bad if I manually downshift to 3rd going down a mountain pass, but otherwise it's smooth. The clunk when stopping is back, so it's time to grease the driveshaft again and see if that and the downshift clunk go away.

After breaking the first transmission, I was sure it was because I had missed a step in the procedures. Myself and two others followed the FSM to a T during the second transmission install, and I was quite disappointed when the symptoms remained. All I could think of was "I am going to need a third transmission in a year or less." Its a good feeling knowing, if I ever I have to slam on my brakes again, my transmission wont die. It's also nice thinking about it less and less after every day. Hopefully one day, I won't even consider it.

 

[Alphadoofa]

I need this part!!!

Any chance you can get me a part number for the spline coupling? I have one that looks just like yours and need one that doesn't!!

No offense taken to any of the comments, after all, it seems absurd, especially if you would not personally mess with such complicated systems like the engine and transmission. Two years ago, I hydrolocked my original engine and threw a connecting rod, while punching a whole in the engine block. I had to replace the engine myself, filled ATF per FSM in my original transmission, and everything was fine until a year later. In that year, I contributed the forward jerking to "driveshaft clunk," until one day, a clunk became a whirling noise and the 4Runner would not move forward. After removing my transmission, and upon closer examination, I realized that my "driveshaft clunk" was purely transmission related. One photo is of shaft spline coupling, connecting transmission shaft to transfer case, and the other photo is the worn shaft on my original transmission.

Upon installing the donor transmission, and filling ATF per FSM, the symptoms remained. A few weeks ago I decided to take the chance and add more ATF. If anything seemed weird, like CEL's and transmission lights in the cabin, or driving was off, I would have removed the extra ATF. Instead, it appears to have fixed my "driveshaft clunk." As hard as it is to say, I suspect the FSM is misleading, and would have the DIYer put too little ATF back into the transmission.

If you have messed with your ATF for whatever reason, remedied the "driveshaft clunk," and problems still exist, you might be suffering from low transmission fluid. I believe these photos are the result of low transmission fluid, which was initially mistaken as driveshaft clunk. One quart of fluid may have been the difference.

BTW, I also heard overfilling a transmission was bad, but took the chance, and so far its paying off with a smoother ride, and peace of mind.

It's possible that the A750F sealed transmissions were "overfilled" from the factory.

 

[AuSeeker]

Any chance you can get me a part number for the spline coupling? I have one that looks just like yours and need one that doesn't!!

I just looked at Brickyard's profile and he hasn't been on the forum for over a year so you most likely will not get an answer from him.