Mercury 40, 50, 60, 70 HP Drive Shaft Compatibility 1977 and 1989 Models

[rustnrot]

I have two lower units. One a 1977 on the left and a 1989 on the right. The 1989 has a short shaft and the 1977 is long shaft. The 1977 is off a 70 HP 3 cyl but would also be the lower unit for 3 cylinders and 4 cylinders of many years. The 1989 is on the right and is off a 60 HP 3 cylinder but again used on many 3 and 4 cylinders of many years.

1. Assuming the drive shafts are the same length, will the later model lower unit bolt over to an earlier model engine and vice versa? It sure seems so.

2. Will the short drive shaft from the 1989 work in the 1977 lower unit? The part numbers are different -- but has anyone actually installed a later model drive shaft into an earlier lower unit? The various bearings, etc are the same part numbers that go with it, however the lower water pump housing is different due to a different bottom seal.