Re: 1988 40 hp johnson outboard lower unit
Welcome to iboats.
Get an OEM manual(NOT Seloc, Clymers or anything on CD) a factory manual, it covers only your engine from top to bottom and has a great trouble shooting guide.
They can be had here at iboats or on Ebay if you are tight for money.
There are 6 bolts in the lower unit, 4 obvious, 1 on the trim tab and 1 under it.
You will need to DISCONNECT the battery(!) and then take the starter off to get to the shift rod bolt which is under the carbs, 11mm(I think)-1/4 drive ratchet with a long extension, take this out before you drop the lower or you may bend the shift rod, be carefull not to turn it once it is out or you will mess up the shifting.