Hi from Montreal, Qc!
I own two of the most hated cars on this show, a Renault Alliance and a Peugeot 505 V6.
On the 505, the transmission was shifting pretty roughly, it was knocking hard. I bought another 505 for spares that was shifting smootly. So this summer, I decided to spend 4 weekends on hard labor and I swapped the ZF automatic transmission from the rough car to the good one.
After all that job, I didn’t notice any real difference. So I guess it was the torque converter that I left on the engine?
Anyway, I decided that it will stay like that because I will rather take a bullet than drop this tranny again.
Now yesterday, it was -30?C outside, after 3 months of storage outside, just for fun, I tried to start it. It started right on! So I let it warm up for few minutes then went for a little ride.
Big surprise, it shifts very smootly now in cold weather…
So what’s wrong?
Wrong type of oil? I filled up with the one suggested in the owners manual!
Later, I will have another problem to solve, but this time with the Renault Alliance 
Thanks.
JF
'87 Peugeot 505 STX V6
'87 Renault Alliance DL
'70 Renault 16
'97 Volks Transporter T4 (Eurovan diesel).
You can probably count the number of current Peugeot 505 owners around here on the fingers of one elbow…have you posted this on a Peugeot forum?
You have one eclectic group of cars. I had a Renault 18i years ago ('81 perhaps) and that car had lots of issues. Not many in US have Peugeot experience, but mostly those that do it wasn’t good. To round out your collection you need a Range Rover, a Rover sedan, and any Citroen. You won’t drive them much, but you will have an interesting bunch of cars.
I’ve had three 505s. My 25 year old son came home from the hospital in one of them, a year old turbo Diesel. As I recall, none of them had enough power to shift anything like what I’d call harshly. To their credit, they got good fuel mileage, handled well, and still had a very soft ride. Parts availability and cost in middle America were always an issue.
I would not mess with any fluids not recommended by Peugeot.