1977 233HP breaking circuit breaker intermittently when shifting into neutral

[jarbones]

I have a 1977 Fiberform 2400 Bahama with a Ford 351, 233HP Mercruiser mc1 pre-alpha that keeps breaking the 40 amp circuit breaker when shifting into neutral normally when I am trying to dock it. Very frustrating as I have to lift engine cover and reset the breaker that sits on the engine attached to the wiring harness. I don't think it has anything to do with the shift interrupter switch as that would just stall the engine but not break the circuit breaker. We have checked all wires that and made sure all connections were good. Any help would be appreciated. Here is serial number of engine 4619136. Thanks in advance for any advice. I am thinking that a switch has gone bad or there is a ground issue.

 

[achris]

Do you still have the original MerControl control box? If you have a newer control box, and it's got the an ignition safety switch (as well as the neutral switch) then the wiring might be rubbing on something inn the control box as you pull out of gear.

One test worth doing is to see if it does it when run on the flushers (muffs). If it does, it's nothing to do with the shift interrupt, as that should never be tripped when running on muffs...

Do you have a wiring diagram?

Chris...

 

[jarbones]

Hi Chris, I don't know if it is a Mercontrol box or a newer one. It has a single lever with the button to the back for engaging start up while cold. Here are photos of shifter control front and back. I don't have a wiring diagram per se but have found one online. Boat is in water now but we did start it with the muffs prior to putting in, but didn't do a lot of shifts.Will the shift interrupt potentially trip the circuit breaker? Another person told me that 99.9% of the time it is the inner shift cable to drive. Do you think he meant intermediate shift cable to drive? How many shift cables to drive is there? Will shift cable problems trip breaker? I was under impression that there are 2 shift cables, a lower and a upper. Thanks for your help Chris, I most certainly appreciate you and this forum.

 

[achris]

Ok, That is a Morse shifter, not Mercruiser. Never the less, it's unlikely to be the problem.

Read up HERE to see how the shift system works. There are 2 cables, the lower shift cable runs from the shift plate to the drive, the remote shift cable from the controls to the shift plate. The shift interrupt switch shouldn't be tripping the breaker, but I'm wondering if you maybe have more than 1 problem. Maybe the shift cable is causing the stall, then the breaker is tripping for some other reason...

If you can photograph your instrument panel, I can give you a diagram for that too. (or if you know whether you have an ammeter or voltmeter, and if it has a warning light..)

Wiring diagrams for you.

 

[jarbones]

My mechanic friend did an adjustment to the lower shift cable. which we thought would fix the problem. It seemed to work for awhile but shifting out of gear was more difficult. Then when we were docking it, it stalled and tripped the breaker again. It will restart immediately but I am at a total loss of what is causing the breaker to break. I will get you photo of gauge cluster.

 

[jarbones]

Any advice on how to troubleshoot this problem? Other than this problem, everything seems to work just fine.

 

[achris]

My mechanic friend did an adjustment to the lower shift cable. which we thought would fix the problem. It seemed to work for awhile but shifting out of gear was more difficult. ...

That sounds like his 'adjustment' was to disconnect the shift interrupt switch....

Did you test it on the flushers (boat on trailer)?

Chris..

 

[jarbones]

No, the shift interrupt switch was not disconnected, he was just trying to see if it was out of adjustment by some chance. We had the engine out last summer to replace the coupler and thought that maybe when the engine was re-installed, that we may have got the lower shift cable out of adjustment. We haven't taken boat out of water to run on flushers (muffs) yet. I don't think it is the shift interrupt switch as that wouldn't trip the circuit breaker. The breaker trips almost exclusively while docking and more specifically while attempting to enter slip after coming in from cruising and at the first attempt to put in neutral to coast into or slow down to enter slip, the breaker trips while taking out of gear. We immediately reset the breaker and it starts immediately. Just weird.

 

[achris]

Try this. Disconnect the lower shift cable from the shift plate and lock it in the neutral position. Run the engine and select forward gear on the control. (Obviously it will stay in neutral), start turning the steering wheel and moving the throttle/gear lever as if you were coming into the dock.... If that shows nothing, go and manually trip the shift interrupt switch (pull the lever one way or the other)... The engine should stall out, but not pop the breaker. Now try tripping the switch the other way.... Anything?

 

[Bt Doctur]

Just wondering if you have the interrupter hooked up to the + side of the coil instead of the negative side of the dist. The shift interrupter switch should not trip
the circuit breaker ,it should only cause the motor to stumble coming out of gear. If the motor is stalling coming out of gear ,then suspect a damaged lower cable .

 

[jarbones]

Thanks will try the above and let you know.

 

[jarbones]

Hi Chris, if it is the lower shift cable, do I just need the inner cable which I believe is part #[FONT=Helvetica neue, Helvetica, Verdana, sans-serif] 41951A1 or do I need the complete shift cable kit which I believe are part #'s [/FONT]

19543T2, 865436A02? Also, are lower shift cable and intermediate shift cable interchangeable names for the same part?​

 

[jarbones]

This gets so confusing, Now I have found another part # 865436A03 which has the same cable as 865436A02 but has what appear to be gaskets, seals, o-rings and bellows. I am assuming the outdrive has to come off to replace the lower shift cable thereby necessitating A03 kit over the A02 kit. I am not sure which one to get. Please advise and thank you so much for your effort. It is truly appreciated.

 

[achris]

This is how the system is laid out.

As there is only 2 shift cables, there can not be an 'intermediate' shift cable. Lower shift cable, Remote control shift cable; those are the only 2 options.

The shaft marked 'shift shaft' is actually 3 parts; upper, intermediate and lower.

If you need to replace the lower shift cable, you can only buy it in kit form, either with or without a new shift cable bellows.

With bellows: -865436A03
Without bellows: -865436A02

As you will be removing everything else, may I suggest you do the shift bellows at the same time... especially if it's any more than about 10 years old. And you can't buy just the inner or outer, if you need to replace, you need to replace the whole thing. The other thing to check, while you have it all apart, is the upper shift shaft bushing (and seal) in the exhaust cavity of the bell-housing. If it's still the old type, replace it with the new (part# 23-805041A2).

HTH,

Chris........

 

[jarbones]

Thanks Chris, you know a lot of about this stuff and for that I am truly grateful. Talk soon.

 

[jarbones]

So today we took boat out. We disconnected shift cable and attempted to mimic the docking scenario and everything worked fine. We activated the shift assist as requested and it stalled the motor but did not trip the breaker. Took it out and it was still tripping breaker after we connected the shift cable back up. We think it must be the shift cable but we still have no idea why the breaker is trippi

 

[achris]

Well, that just doesn't make any sense at all... I'll have a think about it and if anything occurs to me I'll be back...

 

[jarbones]

My inclination from a logic point of view as I am not a mechanic, would be that it is not a stalling situation due to the shift interrupter switch but something that is tripping the circuit breaker at the same time that the shift interrupter should be activated, if that makes sense. We have no loose connections that we are aware of so we don't think it is a dead short. The reason that I make this assumption is because you and another mechanic have both said that the shift interrupter should in no sense be tripping the circuit breaker whether the switch is bad. We have also replaced the circuit breaker to no avail. Unless we have 2 bad circuit breakers. We are stumped. Thanks though. Hopefully you come up with some more ideas as we don't want to start throwing parts at the problem only to find out it isn't the parts, thereby wasting money.

 

[achris]

... we don't want to start throwing parts at the problem only to find out it isn't the parts, thereby wasting money.

Agreed...

I hope you can bear with me... I'd like to go back to basics.

So, what we have is...
1977 Ford V8, 351 with a 2 bbl carb and a Prestolite or Mercury Marine distributor. Does it still have points? Also would like you to check and confirm a few things. Please confirm original coil (check the primary resistance, should be around 1Ω), and there should be a resistance wire between the coil + and the electric choke supply wire. That wire needs to measure around 1.9Ω. See if you can get a Fluke meter to make these measurements.

Now, here's a test I think may help isolate.
You need to be in clear water. Travel in gear at about 1000revs, then quickly pull the lever back to neutral. This should pull the drive out of gear, but NOT trip the interrupt switch (no load on the prop to hold the undercut on the dogs in)... Do that a few times and see if you get a stall and breaker trip... If you don't, move to the next test..

Again in clear water. just at idle, in gear, have someone manually move the lever that trips the shift interrupt switch in the same direction as it's moved when you pull out of forward gear. That raises another question. Does it only trip the breaker when coming out of one gear? (either forward or reverse) Or is it either? Now, when your assistant pushes the lever to stall the engine, have him/her hold it in that position, don't release it. Trip the breaker?

Let us know how you go...

One last thing. You were going to get me a photo of the instrument panel...

Chris.......
Just had a look at a drawing of your shift plate and I believe the lever will need to be pushed away from the remote control shift cable to simulate coming out of forward gear.

 

[jarbones]

Yes it still has points and condenser but we are thinking of converting to electronic ignition. We will run these tests and get back to you. I have forgotten about the instrument cluster photo. Will upload when I can and thanks.