Linkage for reverse in Merc 4.5

Folks, I recently picked up a 70s vintage mercury 4.5 longshaft in pretty decent shape. Great starting, solid, powerful motor, and I'm really happy with it.

The only problem is that it won't stay in reverse. Stays in forward with no problem, but to get the boat to back up I have to hold the shifter back in the reverse position, and it feels like it's slipping when I do that. I have a feeling it's the linkage.

Can somebody give me an idea of how to check and adjust the linkage in this motor? I picked up the Clymer manual and it's almost no help. I have a feeling this isn't a complicated repair, I just need a little guidance to get me started.

Can anybody give me some advice?

Thanks -Chris

Do you have the serial #? If so we could grab a parts schematic. In most cases there are a couple of springs that are supposed to hold your engine in gear. If the spring(s) have weakened they can allow the engine to slip. I suspect that you holding the gear shifter in place is allowing it just enough tension to keep it in reverse even though it's on the edge of slipping.

Thanks, Jake - I can get the serial number by Sunday (after I go up to the boat this weekend). Where are the springs you're talking about located? Up by the gear selector or down in the lower end? - Chris

Down in the lower unit, unfortunately.

On my 80's merc 4,5 this was also the case.
Turns out you have to move the shift lever to forward when you put the lowerunit back together after an impeller change.
If you don't then there isn't enough lever throw for reverse and you have to hold it back yourself.
The lowerunit shifts itself into forward when you pull down (disconect) the shiftrod.
So the usual neutral position of the lever then becomes forward and reverse neutral (if you just assemble the lower unit regardless).
This then means that reverse cannot be selected.
Quick fix:
1 remove lowerunit (just undo the two nuts either side)
2 shift lever into forward
3 then put back together (remember to lineup the cooling pipe and waterpump)

Thanks, Mr. Big. I'll try this as soon as I get up to the boat. Do I need to disconnect the linkage for the shift shaft when I lower the bottom end? I'm only asking because on the OMC 9.9 there's a pair of screws that connect the top part of the shift shaft with the bottom. Is it the same way on the merc? Or does it just seat itself when I take the bottom off and put it back on again?


If it works, super and easy! If not, I'll be back with the numbers Sunday and we'll go from there.

Thanks again to both of you - Chris

When the nuts are loose the linkage just slides apart. No screws to hold the linkage together. To get the driveshaft to line up when assembling just jiggle the flywheel a bit.
Haven't tried the Clymer manual, my Seloc one describes the process pretty well.
My engine is the belgium build version but it should be simmilar. I have attached a picture so you can check.
Good luck.

Big! Thanks! You were right! I couldn't get the thing to go in in forward, so I put both into neutral. Slid together and worked like a charm. Totally awesome.

Noticed my gear oil is chocolatey, though. Time to change the lube and then redo the seals in the off season.

Thanks again-

C