Hi there! I'm new to the forum.
So I have a trek road bike which is about 8/9 years old with shimano 105 front and rear derailleurs.
My problem is with the rear. I removed it from the frame recently for cleaning and removed the pulley wheels also.
Now when I try to tune the gears, when the chain is on the small chain ring and on the smaller cogs of the cassette, the derailleur curls upwards and starts jumping (as in the chain doesnt pass smoothly through the 2 pulley wheels).
One important point is that while re-inserting the top pulley wheel, I had to install it without the two metal washers since the screw seemed to not have enough thread. The three parts simply didnt fit. Maybe this is another reason for the instability