1978 Bass boat, mercruiser 140 shifting problem

[RandyJ]

This boat goes into gear and shifts fine from sitting still position. When in forward shifting seems to be binding. I can put pressure on the control and it will jump from forward to reverse or reverse to forward and is very difficult to get in neutral while under power at idle speed.

 

[frank246]

Re: 1978 Bass boat, mercruiser 140 shifting problem

You already gave the answer..it is binding, the lower shift cable is.
Good luck!

 

[RandyJ]

Re: 1978 Bass boat, mercruiser 140 shifting problem

Thanks for the reply and I hate to question it... but how could it be the shift cable binding when it shifts fine until the boat is under power and in gear? Seems to me that something is causing it to be difficult for the cable to move the shift rod... i.e. the cable seems to be working fine. Guess I just don't understand....

 

[frank246]

Re: 1978 Bass boat, mercruiser 140 shifting problem

Thanks for the reply and I hate to question it... but how could it be the shift cable binding when it shifts fine until the boat is under power and in gear? Seems to me that something is causing it to be difficult for the cable to move the shift rod... i.e. the cable seems to be working fine. Guess I just don't understand....

thats why!

The interrupter switch should be adjusted to stall the ignition for a split second while shifting out of gear so the shift clutch can dis-engage without the force of the engine trying to turn the prop under water.
(Like pushing the clutch pedal to shift in a car.)
A bad lower shift cable can activate the interrupter switch when not needed or..for to long.
In your case it does dis-engage but without the help of the engine stall on the right moment (or not at all) By the cable stress from you pulling or pushing on the handle it skips into the oposide gear.

Good luck!

 

[RandyJ]

Re: 1978 Bass boat, mercruiser 140 shifting problem

hmmm.... if old 140's have shift interrupter switches I'm not aware of it. I know they have neutral safety switches. Most old 140's I've run into have them disconnected...

 

[Bt Doctur]

Re: 1978 Bass boat, mercruiser 140 shifting problem

they were disconnected because the motor kept shutting off, they are necessary for proper shifting.
http://www.boatfix.com/merc/Servmanl/6/6C1R3.PDF

 

[achris]

Re: 1978 Bass boat, mercruiser 140 shifting problem

Shift interrupt switch disconnected, that's causing hard shifting out of gear, will still go in easy enough. The switch was probably disconnected because the lower shift cable is binding and causing the engine to stall when going into or out of gear.

Have a look in the Adults Only section of this forum and you'll see a 'Theory of Operations' for the shift interrupt switch...

Replace the cable, then reconnect and adjust the switch.... Yes, your old 140 has (or should have) a switch....

Chris........

Edit: Just looked, the 'Theory of Ops' has gone.... Hey, Don, where'd it go?

 

[RandyJ]

Re: 1978 Bass boat, mercruiser 140 shifting problem

I don't doubt anything posted here. I've run into lots of rigged boats simply fixed to make is them run. I haven't had this boat long. The idle speed had been raised because it would not stay running when shifted to idle so the idle speed was raised too high and would not allow shifting out of forward or reverse easily. Lowered idle speed and problem disappeared. Adjusted valves, cleaned out carburetor and it runs fine now.... but still have a problem with it running about 3 miles then acts like it is running out of gas. Now suspecting a problem in venting of gas tank....

 

[achris]

Re: 1978 Bass boat, mercruiser 140 shifting problem

Found it.... Look HERE.

Chris......

 

[RandyJ]

Re: 1978 Bass boat, mercruiser 140 shifting problem

for sure, you guys diagnosed the problem correctly and educated me on shift interrupt switches. This is the one that was on the boat... thank goodness I happened to have 3 or 4 more in my junk pile. I'd say this old one got broke when the motor got pulled and resulted in lots of odd problems.... and that's probably why I ended up with the boat at a very reasonable price...