I've got a '85 Mercruiser 3.7l 170.

In the last two trips, I've had trouble out on the water shifting from
forward-neutral-reverse and vice versa. There really isn't a neutral,
which makes docking a challenge, you can imagine.

There's a good bit of resistence at the remote control where I fight it in
and out of gear... the resistence may grow as the engine warms (or I may
just tire).

After the first time, I ran it on muffs in the yard for more than an hour
and the problem seemed to go away, which prompted me to go out the second
time. So maybe there's something to the added pressure on the prop, I
dunno.

I figure the problem is either electrical (shift interrupt switch) or
mechanical (shift cables, levers, etc.). I'm inclined to attempt to debug
the electrical portion before taking it to a mechanic. I read in my
Clymer's manual about the shift interrupt switch and saw a wiring diagram
of it, but for the life of me, I can't find it when I'm looking down on
the engine.

Does anyone have a helpful photo or advice?

The fact that the engine doesn't stall says that the lower cable isn't
causing the stiffness. The switch might be bad. It could also be the forward
cable, but that usually goes bad gradually. Two cables go to a pivot block
that is mounted to the side of the exhaust manifold You will see a micro
switch just below where the cables connect. Tripping the switch should stall
the engine. If it doesn't stall the engine you probably have a interrupter
switch or wiring problem. If it does you probably have an adjustment or
forward shift cable problem.
JIMinFL

"Fred" wrote in message
news
I've got a '85 Mercruiser 3.7l 170.

In the last two trips, I've had trouble out on the water shifting from
forward-neutral-reverse and vice versa. There really isn't a neutral,
which makes docking a challenge, you can imagine.

There's a good bit of resistence at the remote control where I fight it in
and out of gear... the resistence may grow as the engine warms (or I may
just tire).

After the first time, I ran it on muffs in the yard for more than an hour
and the problem seemed to go away, which prompted me to go out the second
time. So maybe there's something to the added pressure on the prop, I
dunno.

I figure the problem is either electrical (shift interrupt switch) or
mechanical (shift cables, levers, etc.). I'm inclined to attempt to debug
the electrical portion before taking it to a mechanic. I read in my
Clymer's manual about the shift interrupt switch and saw a wiring diagram
of it, but for the life of me, I can't find it when I'm looking down on
the engine.

Does anyone have a helpful photo or advice?

There is a piece of metal that pivots where the shift cable from the control
box attaches and also the cable to the lower unit attaches as well as the
linkage to the carb. This is where the shift interrupter is located. It is
a common leaf spring micro switch. It temporarily kills the engine during
shifting to release the pressure on the gears.

Usually the best solution is to replace both of the cables and the shift
cable bellows. The parts are not excessively expensive but you need a
special tool to install the threaded end on the lower unit end, or you can
make one by splitting a 3/16 slit in a deep socket so you can slip the cable
into the socket.

You did not state, but I'm presuming you have a Merk.

Don Dando


"Fred" wrote in message
news
I've got a '85 Mercruiser 3.7l 170.

In the last two trips, I've had trouble out on the water shifting from
forward-neutral-reverse and vice versa. There really isn't a neutral,
which makes docking a challenge, you can imagine.

There's a good bit of resistence at the remote control where I fight it in
and out of gear... the resistence may grow as the engine warms (or I may
just tire).

After the first time, I ran it on muffs in the yard for more than an hour
and the problem seemed to go away, which prompted me to go out the second
time. So maybe there's something to the added pressure on the prop, I
dunno.

I figure the problem is either electrical (shift interrupt switch) or
mechanical (shift cables, levers, etc.). I'm inclined to attempt to debug
the electrical portion before taking it to a mechanic. I read in my
Clymer's manual about the shift interrupt switch and saw a wiring diagram
of it, but for the life of me, I can't find it when I'm looking down on
the engine.

Does anyone have a helpful photo or advice?

On Wed, 05 Oct 2005 01:50:38 +0000, JIMinFL wrote:

The fact that the engine doesn't stall says that the lower cable isn't
causing the stiffness. The switch might be bad. It could also be the forward
cable, but that usually goes bad gradually. Two cables go to a pivot block
that is mounted to the side of the exhaust manifold You will see a micro
switch just below where the cables connect. Tripping the switch should stall
the engine. If it doesn't stall the engine you probably have a interrupter
switch or wiring problem. If it does you probably have an adjustment or
forward shift cable problem.
JIMinFL

"Fred" wrote in message
news
I've got a '85 Mercruiser 3.7l 170.

In the last two trips, I've had trouble out on the water shifting from
forward-neutral-reverse and vice versa. There really isn't a neutral,
which makes docking a challenge, you can imagine.

There's a good bit of resistence at the remote control where I fight it in
and out of gear... the resistence may grow as the engine warms (or I may
just tire).

After the first time, I ran it on muffs in the yard for more than an hour
and the problem seemed to go away, which prompted me to go out the second
time. So maybe there's something to the added pressure on the prop, I
dunno.

I figure the problem is either electrical (shift interrupt switch) or
mechanical (shift cables, levers, etc.). I'm inclined to attempt to debug
the electrical portion before taking it to a mechanic. I read in my
Clymer's manual about the shift interrupt switch and saw a wiring diagram
of it, but for the life of me, I can't find it when I'm looking down on
the engine.

Does anyone have a helpful photo or advice?


Great, I found it. I started it up this morning and let it run long
enough to warm up. In the neutral shifter position, the leaf spring is
not compressed; I can detect continuity across the poles of the switch.

I triggered the switch by hand and nothing happened... no engine stall.
While the leaf was compressed, I checked the continuity again and
(assuming continuity in neutral is normal) expected to see that it was
broken, but it wasn't. So maybe the switch is bad?

After watching it more closely (which sure was easier not having to be in
two places at once), I don't fully understand how the switch is supposed
to function. I understand that it's supposed to kill the engine
momentarily to ease shifting. What I don't understand from watching the
operation is that when the shifter is in full forward or full neutral, the
leaf spring on the switch is still fully compressed. Maybe my base
assumption of there should be continuity at the neutral position is wrong?

enough to warm up. In the neutral shifter position, the leaf spring is
not compressed; I can detect continuity across the poles of the switch.

I triggered the switch by hand and nothing happened... no engine stall.
While the leaf was compressed, I checked the continuity again and
(assuming continuity in neutral is normal) expected to see that it was
broken, but it wasn't. So maybe the switch is bad?


I wasn't detecting continuity correctly. I was measuring across the two
screws in the switch body which at second thought are probably mounting
screws. I measured again from the wires extending from the switch after
removing them from the terminal block. I have no continuity when the
leaf/switch is in the open position; I have continuity when the leaf is
compressed. This is true whether the engine is running or not. So, I'd
conclude that the switch itself is working although I don't get the engine
stall. My wiring diagram says the white/green wire runs to a connection
on the distributor and the black wire runs to the starter slave solenoid.
I'm going to check those connections now.

On Wed, 05 Oct 2005 14:27:59 +0000, Fred wrote:


conclude that the switch itself is working although I don't get the engine
stall. My wiring diagram says the white/green wire runs to a connection
on the distributor and the black wire runs to the starter slave solenoid.
I'm going to check those connections now.

I fixed it. There was a broken connection at the distibutor. Thanks for
all the help!