On my trip to Monroe City, MO.. about 40 miles outside of Joplin my speedo went full peg and then dropped to not registering any speed or distance.. and as I looked at it yesterday saw I was missing a screw from the face plate.. (not sure that is directly linked or not) ... haven't tested speedo yet to see if it or the drive unit toasted/crapped out.. but just sending feelers out.. speedo for 81 interstate..... 79-81 would fit.. possibly one with about 56k miles... that way it won't be too far off from my original..