My 1955 Thunderbird has a Borg Warner T86 3 speed light duty overdrive transmission.  When I lock out the overdrive by pulling out the handle, the car runs fine.   When I push in the handle, the car seems to shift into OD OK, but the whole drive line clunks hard when I slow down to a stop.  It's a very hard clunk.  Not something to be ignored.   I can drive the car without OD, but I'm worried it will break something.