05 TL, between 40 and 50 mph, when the converter is locked up, I get this very light shuddering. Over 50 it's fine, that seems to be the magic number when the converter is fully locked. under 50, it does it's little rpm jump deal(jumps up and down 3-400 rpms), that's when it shudders. It will stop if I give it more gas or let off completely. My tranny guy thinks it's the converter, I just had it serviced this morning, and it still does it. We serviced it with the honda fluid, now I see alot of guys going to type-f. Any suggestions as to what this could be and if type-f would fix it?

 

You may want to try to narrow it down to the torque converter for sure. It seems like the harsh reverse along with TC shudder usually means the end of life for the trans.

You can shift it manually and see if you can get it to repeat the problem in more than one gear which would point toward the torque converter clutch (TCC). Im not saying you're wrong but it's easy to get the TC lockup confused with a gear shift which the manual mode will eliminate.

Regardless I suggest the type F fluid, it will only help but for how long, who knows. You might want to try a cheap no name brand just to see. I'm going to buy a service manual soon so I can pinpoint these problems but I believe there's a linear solenoid that controls TCC lockup. Also, the 4th gear pressure switch has an influence in TCC lockup.

How did the drain plug and fluid look?

 

I did not see the plug or fluid, but my transmission guy said it was not out of the ordinary. He has serviced this car before, and knows it fairly well. It has done it in 4th gear before, but rarely. By 4th gear I mean around my subdivision, cruising at 30 mph it's in 4th gear. Pardon my lack of knowledge here, but are you saying the TCC has something to do with every gear? I thought that once in high gear, only then will the converter "lock up". I'm thinking based on your statement, that I maybe wrong. Maybe this could be a fluid pressure switch problem?

 

I know it can lock in 3rd, 4th, and 5th. I've heard 2nd also but not verified. I'm used to older cars that lock the converter based on speed and load and usually only in high gear but the TL will do it in nearly every gear to increase efficiency. I'll look it up to verify which gears it locks in for sure.

 

Yeah, all my experience has been with much older cars. Took it out this morning and drove it around shifting manually, it didn't shudder at all. Now I'm very confused....

 

i thought torque converters only engaged between 0-.5 MPH, stopping the wheels would normally stop the engine which is when the torque converters comes in, converts all the torque from engine and lets the engine spin freely as your wheels are stopped, if torque converter fails, ur engine will stall everytime you come to a complete stop or shifting from Neutral to Drive.

 

You've got it partially right. It's the fluid coupling between the engine and trans, has the same purpose as the clutch in a manual.

It freewheels at idle and gets more efficient with more throttle and rpm. By design it always has "slip" meaning the engine rpm will always be higher than the transmission input shaft rpm when you're on the throttle. A good racing convertor like the one in my turbo car only has about 1% slip at full throttle. An OEM convertor like in the TL will have 10% or more slip at full throttle. There's even more slip at part throttle which reduces mpg and power transfer and shows up as heat in the transmission. To counter this, most cars built since the '90s have a clutch inside the convertor that locks up under the right conditions to give it 100% coupling just like in a manual and as a side effect it drastically lowers trans temps.

If the clutch inside the convertor fails to unlock, the car can stall when coming to a stop, this has happened to me many times in my older car when the TCC solenoid fails and gets stuck on. Otherwise, when a convertor fails, the car usually won't go anywhere as if it's in neutral. If the stator fails the car will be incredibly sluggish especially off the start.

 

To update-
I have replaced tranny fluid with redline racing atf, have not replaced switches yet, but the shuddering has gone away. I'm still going to replace the switches, but it seems to run fine now.