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Old 16-01-2016, 03:25   #1
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Gear change cable heating up and melting

Recently my gear change cable (as opposed to the throttle cable) parted and slipped out of its plastic bedding to which it was anchored. I replaced the cable however the plastic bedding was partly damaged therefor i clamped the cable to the hull (steel hull) next to where the plastic housing is positioned. To do so i used the same type clamp which connects the cable to the gear box lever on the engine side. The cable worked fine until i started the engine and used the anchor windless. Once the anchor was up the throttle lever wouldn't budge. I checked the cable and it was boiling hot, yet nothing else in the engine room was. I can only guess that somehow i made a connection from the engine, through the cable, and by connecting the metal cable to the steel hull i must have created a circuit, or something similar. Any ideas.
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Old 16-01-2016, 03:34   #2
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Re: Gear change cable heating up and melting

Grounding problems???
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Old 16-01-2016, 04:05   #3
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Re: Gear change cable heating up and melting

must be
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Old 16-01-2016, 15:56   #4
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Re: Gear change cable heating up and melting

Test it with a multimeter...bet you've got a ground fault...the fun part will be figuring out where.
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Old 16-01-2016, 16:29   #5
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Re: Gear change cable heating up and melting

There shouldn't be any power going through a shift cable. Do you have a neutral safety switch? It would seem that somewhere a positive wire has abraded or something and is making contact with either the outer sheathing of the shift cable, or possibly the inner cable itself, and, as you say, when you clamped it to the boat you completed a circuit. The cable is most likely ruined, usually there is a plastic inner liner that has probably melted. Test is with a meter to see if the cable is hot (electrically), if so, find out why, fix the electrical problem and replace the cable.
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Old 16-01-2016, 20:50   #6
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Re: Gear change cable heating up and melting

Check that the alternator has a heavy wire from its NEG to the battery NEG and not dependent on the engine block for connection. Ideally on a metal hull the alternator and starter should both have NEG connections that are isolated from their cases.
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Old 16-01-2016, 21:02   #7
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Re: Gear change cable heating up and melting

I suspect a ground problem or some other electrical issue. This probably caused the initial failure.
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Old 17-01-2016, 09:25   #8
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Re: Gear change cable heating up and melting

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Originally Posted by Nicholson58 View Post
I suspect a ground problem or some other electrical issue. This probably caused the initial failure.
My thoughts as well. If the negative connection on the engine is broken then the cable has become the new current path for the alternator and possibly starter.
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Old 17-01-2016, 09:55   #9
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Re: Gear change cable heating up and melting

Definitely check your alternator negative cable. Mine was stacked with several other terminals and a cable clamp where it was attached to the block, and had heated up and developed a resistive connection which reduced alternator output to near zero (and heated the clamp to where it melted through the insulation on a hot wire!).

I learned of a commercial two-way radio installation in a truck where the engine ground strap failed open. Cranking the starter put all the return current through the negative lead of the radio, to the shield of the antenna cable which grounded at the antenna mount on the cab roof. Apparently the cable heated sufficiently to ignite the headliner... and the owner broke an arm throwing himself out of the flaming cab.

Good grounds are your friends.
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Old 17-01-2016, 09:57   #10
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Re: Gear change cable heating up and melting

... oh, and insulate the shift cable where it's clamped, just for good measure. No good can come of current flowing there, and there may be some, even with a good ground.
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Old 20-01-2016, 21:11   #11
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Re: Gear change cable heating up and melting

Keep in mind the Anchor Winch electrics may also have been damaged in the process, or even caused the problem.
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Old 21-01-2016, 01:40   #12
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Re: Gear change cable heating up and melting

It obvious your shift cable functioned as a ground strap. Insulate the cable. Maybe mount a block of plastic or wood to the hull and the cable to that.
Since you have a metal hull, some bozo in the past may have decided he didn't need 2 wire system on some or all of the wiring. I think the most likely problem is either the winch or starter motors. But it could be the output from the alternator.
I would go thru all the dc wiring to make sure all items are on a 2 wire system and nothing is using the hull as a negative return. Using a metal hull for ground can also eat up your zincs.
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