Hello, I am back again about the torque converter lockup issue. I will review the history of the tranny. The tranny in my 98 LeSabre stopped dead ( I guess about three years back). After investigation it was determined that the front pump; well the only pump I guess in these transmissions, wasn't working. (Later on removal I found that the splines in the input shaft had stripped; a common problem on these early trans) With the number of miles on the trans, I knew that I would either be rebuilding the trans or replacing it. Looking at the cost of a rebuilt tranny had be almost passing out. Therefore, I decided I would risk a used trans if I could find a low mileage one. Luck was with me, I found one that only had 29 K miles on it; a Sunday driver that ended up being totalled in a crash. I had the tranny shipped from a big salvage yard in Oregon; some on here may know of the place. The fluid that was in the pan looked like new fluid so I was confident about the transmission. I am not sure how long the trans sat before I took ownership of it. I installed the tranny in the car using the torque converter that came with the used trans, and at first the lower shifts were a bit harsh but over time the shifting really improved. I got a trans-go shift kit for the trans but haven't installed; I haven't been able to free up the shed to be able to get the car in. However, I don't want to do anything until I can get the issue of the torque converter lockup determined; if I have to pull the trans again; and I may pull the trans and engine as a unit this time, I will do the shift kit then.

Now to the history of the torque converter lockup history. About three months after installing the tranny, the torque converter lockup issue started. At first it was very infrequent and I thought that it would stop; I let my short extended warranty run out on me which was stupid of me. However, the issue continued and has continued. The good thing is that it doesn't kill the engine but it shutters as you pull off. Oh, I forgot to add that I replaced all the electric solenoids in the trans with new Delco Remy including the pressure plate thingy. I figured the lockup shift valve was sticking since the torque converter would not always stay in lockup. I got some seafoam transmedic and put it in the fluid and after a short time my torque converter issue stopped, the torque converter lockup would release as it is suppose to do. I drove it for a full year and never once did the torque converter fail to release. I thought all was good. Then, it started happening again. I decided to try the seafoam additive again (no, I didn't change the fluid). Again, after a short time, the torque converter lockup issue went away and I again drove the car for a year or more without any torque converter lockup issues. Now it has returned.

OK, I will pause here and explain how I get the torque converter clutch to release. I found out that if I stop the car as soon as I notice the torque converter lockup is still engaged; such as stopping at a light and pulling off (or I see the check engine light come on); if I stop the car, turn off the engine, wait a short while, start the car, put it in reverse, the torque converter clutch will release. Once I do this, the torque converter lockup will work perfectly the rest of the time I am driving the car. Sometimes if I let it sit for a long period, such as visiting family, I may see the issue again; but often not until the next day I drive the car.

I also noticed a few areas where usually if the torque converter clutch is going to stick on, it will. One is a place about six miles from my house where I have to slow down and make a turn up a side road that is up a hill. Now the trans fluid is at the proper level (actually it is a bit high but not significantly too high; I know about possible foaming of the fluid in some trannys if the fluid is too high). Now here is something that has me quite puzzled. I have had the torque converter to lock up pulling out of my driveway. I will have come home with the torque converter lockup working properly to my knowledge. I will back up my driveway and backup into the turn-around area, put the car in drive and and drive the short distance (maybe 100 feet) to the main road and then stop. Then I pull out; a slight upgrade, and will feel the car shutter a bit. Sure enough the torque converter clutch is stuck on. How could the converter lockup clutch be engaged when I have been driving the car in my driveway at such a slow speed? I thought the lock-up doesn't occur until you are at a certain highway speed.

I am really hoping that someone on here can help me determine what to do here. I am wondering if it could be the converter itself that is the source of the problem. I do think if I have to pull the tranny that I will replace the converter; I would think that maybe pulling off at the light with the lockup clutch engage is doing some harm there. Maybe the senior techs on here can let me know. I sure would like to solve this issue even if it means pulling the tranny. I do have the old valve body from the old trans; it would have ~230K miles on the valves and the pump although I could swap out the pump gear and vanes from the current trans.

To me this sounds like an internal hydraulic leak of some sort. Maybe this directly involves the valve body. Maybe not.

This is an issue that insists on recurring even after the magic fluid treatment cures it repeatedly. This tells me that there is something internal that is only being stop-gapped by the magic fluid treatment.

I couldn't find "Seafoam Transmedic", but found a different product of theirs dedicated to transmissions. Is this the actual name of the stuff you used? If not then what is the actual name?

My concern here is that the treatment you used swells seals. If that'* the case, there is no predicting the results.

Thinking about this a bit further, I don't know the history of this transmission other than the mileage you were advised of and the anecdote that it was treated nicely in its previous life. I very often hear of used parts that are from low mileage cars and were previously treated nicely. I never hear of used parts that are from high mileage cars and were previously treated badly. This makes me suspicious that it is possible that stories are being told about these parts that are inaccurate, and possibly that some places will clean something up (including changing fluids) to make it look the part. I'm not accusing etc., however, if you didn't personally see that car with grandma driving it, then later see that transmission getting pulled out of its smashed corpse, you have no way of knowing for sure.

Regardless of the above possibility, I also don't know the nature of the accident. Perhaps the transmission was damaged in the accident. A sudden stop or bad jolt can cause all kinds of issues.

The salvage yard in Oregon is a huge one. They provide photos of the vehicle the parts come out of (yes, they could be lying) as well as the VIN number of the vehicle and they show the mileage from the dash of the car.

Seafoam trans tune; claim it does not swell seals etc. I used it because I thought the valve might be sticking. https://seafoamworks.com/product/tra...uid-treatment/

I still don't know why the torque converter would lock up driving it in reverse up my drive, turn around, drive forward at low speed, turn out of my drive onto the road going slow gaining speed and then feeling the shutter as it shifts out of first into second telling me the dang converter is locked up and then the check engine light coming on. Could the computer be at fault here? Could the computer be telling the converter to lock up when it shouldn't? Maybe the next time I drive the car I will back down the driveway so that I start out without the reverse, turn around, shift into drive, forward. I need to hook the laptop up to the data port and see if I can figure out how to record the trans data.

I just assumed it was a Sunday driver; I don't know many 1998 Buick LeSabre with 29K miles on them; I think I did look up the VIN number at the time but not sure when the car was crashed; it messed up the front end and often with older cars, even a minor crash will total the car by insurance; which is what I meant; not total as in extensive damage but wrote off by the insurance company.

I'm not sure what going on w/ reverse but definitely Scan the transmission for codes and post back what is found.
In my case I used the Seafoam trans tune which helped to remove the gum & varnish from the valve body,
I later then found the dreaded P1811 code = time to install the 4T-65E transgo shift kit & clean up the accumulator bores etc.
Also use Dexron VI (6) trans fluid.
https://www.gmforum.com/buick-172/sh...-307429/page2/

That'* cool. Can you post the name? I'm sure lots of folks here would love to know about this place.

Okay that'* what I was hoping.

Personally, with what I know of it so far, I suspect a hydraulic leak inside somewhere. Not sure of the nature of the accident the car was in, but if the wheels were suddenly and/or violently stopped, weird things can happen. All it takes is a small incident of a hydraulic pressure surge when the wheels are suddenly locked (during the wreck) to push a path between hydraulic circuits. If the vehicle had the converter locked when the accident happened then the damage would be worse.

I doubt it. The computer wouldn't change its mind about such things. It would do the same thing all the time.

This might help, but I suspect whatever you read off of it will tell us stuff we already know.

Makes sense. Yes, it is probably only worth a few grand even with the low miles, but the front end damage and lack of parts would quickly put it over the edge for totaling it.

I agree with CathedralCub and Soft Ride. It sounds like a fluid pressure issue. But it'* really important to know what codes have set. DTC P0742 is torque converter won't unlock. this sounds like what you have. but there is a slight chance a wiring problem can cause this too.
I'll try to explain. besides the TCC PWM (pulse width modulation) and and pressure control solenoid which you said you changed, you also have a TFP release switch (trans fluid pressure manual valve position switch, sorry,that'* what the manual calls it) in the trans, mounted onto the valve body. this has a TCC release switch in it. I'm not really sure how it all works together, but this valve is controlled by fluid pressure. this switch is normally closed (grounded). the computer looks at this switch to see whether it'* open or closed. when the TCC is released, fluid pressure opens the switch, which opens the TCC switch by pressure. if the switch fails to open the computer sets a code, if it'* code P0742, the computer commands THE TCC ON AT MAX VALUE. don't ask me why.
so you see, a bad PWM solenoid could cause this, or a bad TFP, or , and here'* the electrical part, a short to ground on the TFP circuit could cause this. also, when you shut the car off, the computer command to lock the converter goes away, that'* why when you pull over and shut the engine off and then start it again the problem is gone. it'* really hard to say what the cause is over the internet and especially without codes and with it being intermittent.
here'* a link to a video on troubleshooting the electrical part. copy and paste it into your browser.
and here'* a pic of the circuit.



this a very complicated problem. let us know what you find and good luck.

FYI the manual I referenced is for a 2003 buick Park Ave with the 4T65E. don't know if any changes were made between 98 and 03

I am back. Weather has been sort of nasty here. I drove the vehicle on Feb 14; which was a cold day here. I usually don't allow the car to sit and warm up before driving. I drove approximately 10 miles and it the lockup issue. It happened at a place that it often does happen; I have to slow down an incline, then make a sharp right turn up a hill. I dread when I have to take that road because I know it is going to do the lockup issue. I stopped, turn the engine off, waited a few seconds, started, put in reverse, and it was free and did not do the stuck on lockup for the rest of the trip; about 18 miles. However, the car did do it on the return trip; the car had sat for about six hours in very cold temperatures. I do wonder if it is related to cold. If it is losing pressure; usually that happens when clearances increase with heat.

I checked the code today and it is PO742; a stored code as I did the trick of stopping, engine off etc. and it unstuck and was good to go for my return trip home of about 18 miles. I haven't driven the car since the 14th as I work from home and only drive the car for personal trips. I find it strange that it will do the stuck on thing once; and then will not have any issues for the rest of my trip; I would think it would do it more often if some failure is happening. I have thought of replacing the computer; I did try cleaning the connectors at both the computer and the transmission. However, if a computer issue why would it act the way it does; a failure that tends to repeat at the same points; such as pulling out of my driveway and going up a slight incline. Driving 10 miles and making a turn up a side road uphill. It is really strange that it repeats at times at the same areas although I have had it to also do it at other areas in my trips. The pulling out of my driveway is really strange because when I back up, turn around, and start off, the car does not feel like it is in lockup; however, that could be because the drive is fairly level and I just can't detect it. The car doesn't die on me but it will stumble/jerk if it is locked on and I pull off at a stop.

The rub is that you can't remove the side cover; there isn't room to pull it off. The tranny or tranny/engine has to be pulled. I replaced the tranny by splitting the engine cradle the last time but I am not sure about doing that again.

You can't take out the strut/knuckle and get at it?