[I]Hi there, I own a 1997 LS400 with just over 248,000 miles on it. earlier this spring I experienced a shuddering effect from the transmission ( not all the time.) when downshifting to a stop. ( during warm up) as of today, The car will upshift rapidly to O.D. ( or lock up) and triggers the check engine light storing code PO770. Also does the shudder on downshift. after light comes on ( limp in) trans seems normal.
Now I have done some looking around the web on this issue and have seen everything from a relatively simple repair to "light fuse and run away quick." I live in a small town in the middle of nowhere with two repair shops in town ( and one as afraid to do more than an oil change on the car) the other has worked on a lot of older and late model domestic transmissions so are willing to look at doing the repair if it is a straightforward one.
Now I am a disabled auto mechanic, I spun wrenches for 30 years before Muscular Dystrophy took me out of the game. I am 30 miles from a Toyota dealer so I can order parts from them and drop ship to my location. my research shows that my failure is quite possibly the LOCK UP CONTROL SOLENOID ASSY ( Lexus Part Number: 35280-50010). Am I on the right track?, if so does this require valve body removal? I have owned this car for just over a year now and it is the most forgiving vehicle to drive with my condition. ( I did buy a P.O.S Mercedes C class to haul my mother-outlaw er I mean in law to get groceries once a week because I got tired of subjecting the Lexus to 4 miles of goat path ( sorry goats) gravel roads).. So any info/help would be wonderful!!!! thank you in advance!!!!!!!! /I]

 

most shudder and clunks from the trans could be from the transmission mount itself which tends go at around the 100-120k mile mark. it's a very easy replacement though it does not point to the P0770 code. also a quick drain and fill can do wonders on a slipping trans. only use toyota type-IV auto trans fluid, and fill using the "hot" side of the dip stick after warming up.

 

Like timmy said I would check/change the fluid and if that does not work then I would swap the solenoid out. You have done some good research already so I commend you on that alone. Let us know what happens.