Gearbox woes, Merc 90 4str. yr 2000

[alystra]

Just about to set off from the mooring the other day, checked engine, forwards ok, reverse a bit stiff and not engaging properly. Back to neutral, ok.. Shift to forward, ok. Try reverse, not engaging. Back to neutral now can't shift into fwd or reverse. There were no unusual noises.

Boat now ashore. I've checked the remote control and cables and they're ok, the linkage to the shift shaft seems ok. The gear change is locked solid in neutral. I can't see a reason why the upper shift shaft (rotating) should have suddenly seized, so guess the problem is in the gearbox.

Anybody got any ideas as to what might have gone wrong? Do the symptoms point to something specific (apart from the obvious, that it's broken)?

I'm just about to take off the lower unit. I've got the Clymer manual. Is it feasable to attempt to disassemble the gearbox following that manual, or should I leave it to experts?

Very frustrated in this beautiful weather.

Luckily, the Yacht Centre here has just become Merc (well, Mariner really) dealers, so I could take it along to them when I get stuck.

[9D280]

You have disconnected at the engine to check it's not stiff / knackered cables or remotes?

[alystra]

Originally Posted by 9D280

You have disconnected at the engine to check it's not stiff / knackered cables or remotes?

Yes, did that. Also opened up the remote control to see if any wires were trapped or control cable connections ok. The control and cables are as smooth as silk.

Took the lower unit off today. That should free up the linkage I thought - but it didn't . Couldn't push by hand so fiddled with the roller thingy, connected controls and it's as smooth as silk again... mostly. Something is jamming it intermittently and it's not easy to see what it is, though I heard it click free once. Main suspect is the spring clips that fix the cable to the linkage catching somewhere. It's jammed right now and I've left it like that until tomorrow.

So, may not be the gearbox, phew! though some good has come out of this as the lube oil was quite milky (changed before the season) so I may need to replace some oil seals. I'll have a look at it all tomorrow.

[matt h]

sounds like it the section underneath the power head that has seized, very common on those engines, really no amount of wd40 will losen it, its a plastic or something like that thimble sized cotton reel that supports the shaft as it goes through the cowling.
take the gear cable off and try to move the gear selector arm with the gear box off

[alystra]

Well, sussed one problem, I think. A friend had stood on the cables while tending the rope for a bit of impromptu barefoot water skiing (failed), and they weren't leading properly. This put an upwards pull on the linkage causing it to jam occasionally. Just moving the cables sorted this.

Sadly, the gearbox is stuck in forward gear now. The shift shaft on the box will not go into reverse, but will find neutral, though it reverts back to forward as soon as I turn the drive shaft. Something's obviously not right, just wish I knew what it was. Trouble is, I don't really understand these gearboxes.

Today I tried to get the bearing carrier out with no success (10 years old and never been removed). Have given it to the yacht centre, should get a report tomorrow. Guess this is going to cost close to a grand by the time I'm finished - judging by the prices on the Mercury Parts web site.