1977 75HP gear shift adjustment

Over the Easter long weekend I spent a lot of time in the boat, and started to notice a new issue.

The issue is - shifting the boat into forward gear often results in it taking off - not with a great deal of speed but certainly more than it should have. Normally it shifts into gear at idle but now the revs climb slightly before it engages. This causes a bit of a sudden take off, which can be embarrassing if you're not expecting it.

I also struggle to keep it in gear when trying to move slowly, eg. docking. It slips out at low revs.
Getting it to pop back into neutral often (but not always) requires pulling the throttle in the reverse direction, too (further back than beyond neutral).

The final thing that's happening is, when the boat is coming onto the plane after a hole shot and the load decreases slightly on the motor, the gear seems to slip (I presume this is the dog clutch slipping). This only happens at WOT, if I use slightly less throttle this doesn't seem to occur.

I expect I need to adjust the throw in the gear cable to fix the selection (idle) issue, the keeping it in gear and the grabbing neutral issue. Note that the reverse direction has no problem.
Is there a specific procedure for these motors to follow for this? I searched but didn't find anything specific to the Chrysler, so not sure if that means there's no particular method or that nobody has ever asked it before!

Is fixing the first 3 issues also likely to resolve the slipping as it comes onto the plane? I thought I'd read at some point that a poorly adjusted gear select cable could result in a slipping dog clutch.

Re: 1977 75HP gear shift adjustment



The dog clutch is a positive engagement device. It is not like an automobile clutch designed to slip. If it does come out of engagement under load, you will hear a heavy thud which may repeat often, depending upon the degree of wear the dogs have.

Now, you should have a large silver quick connect on the engine end of the throttle cable. This is spring loaded and the center should protrude about 3/16 to 1/4 inch at neutral. This allows shifting into gear before the throttle starts to advance.



As far as adjusting cables, there is very little adjustment available to the shift cable. The quick connect can be screwed onto or of the threaded end of the cable. Better to adjust shift linkage using the two nuts under the bottom carb. Pulling the shift linkage up will increase reverse throw and pushing it down increases forward. You adjust (in your case downward) until there is positive engagement in forward yet neutral makes no noise. Since the back of the dogs are ramped, if when in gear you turn the prop the correct way, if adjusted too loose, the prop will click as the dogs ride over each other. When adjusted correctly, the prop will lock up when you turn it in either direction.

Now, Chrysler control boxes and cables have a lot of slop in them It is very common to need to pull back slightly toward reverse in order to hit neutral from forward gear. This is minimal with correctly adjusted linkage but is still something you may need to live with.

Re: 1977 75HP gear shift adjustment

Thanks so much Frank. I'll check it out this weekend and see if I can get it set right.

Frank Acampora said:

Now, Chrysler control boxes and cables have a lot of slop in them It is very common to need to pull back slightly toward reverse in order to hit neutral from forward gear. This is minimal with correctly adjusted linkage but is still something you may need to live with.

Click to expand...

This is true - when it was all working fine, I was having to pull back a little to get it to pop to neutral. I'm now having to pull back quite a lot.

There is definitely a heavy thud when the dog clutch slips - but it only ever happens once (though when it does I normally back off the throttle a little, and ease it back on - not sure if that contributes). I guess I'm going to need to look at getting that fixed up in the near future, though!

Re: 1977 75HP gear shift adjustment

Here's what I found

The bottom adjustment nut on the linkage to the lower unit had come loose. The bottom nut had worked its way down the linkage, and there was about 10mm of play in the linkage before it contacted the nut. The neutral position was resting against the top nut (nyloc nut) which is why reverse was fine, but engaging forward had to move the cable quite a bit before the linkage would hit the nut, and further still to engage the gear.

So - after working out what was happening, I adjusted the bottom nut up to meet the plate and push it back against the top nut (which I left as is). Effectively, according to your instructions Frank, I decreased the forward throw so the gear engaged earlier.

Gave it a test run on the muffs, running it in gear for only a few seconds, and it behaves as expected again. Next thing is an on water test - will try that this afternoon!

Re: 1977 75HP gear shift adjustment

Alright - just got back from an on the water test. Everything is working properly again - and no slipping gears when coming onto the plane, though I'd like to try it again with another person and a load of fishing gear in the boat. I had to go on my own!