John Deere tractor burning up throttle cable
 

Hey guys I have a problem I need help with . Last year I bought a JD X740 diesel garden tractor . It was used with a little over 1000 hours on it . Used it all year with no issues .

But near the end of the year the throttle was getting harder to use . Visual inspection showed the plastic/vinyl coated steel cable was melted in a few spots . Apparently the melted goo seeps into the cable and causes a restriction .

I bought a new cable last month and installed it . Worked perfect for one week then seized up . Yep outer cable cover melted again 😩 . The cable from the factory is routed from the console , past the radiator and then along the air filter inlet tube ending at the diesel throttle linkage.

So it really doesn't travel anywhere that gets hot . So I am thinking I have a ground issue or exposed wire backfeeding current . But it lights up glow plugs fine , starts easily and all gauges and lights work .

A very quick visual inspection and tugging on the battery ground cable showed nothing . I will have to pop off the hood so I can clean and do a better visual . What else could it be ? Or what else should I look for ? I have purchased another throttle cable but don't want to install until I find the cause of this issue .

I'd try these folks and other dedicated forums. I use them and TractorByNet for my MF's and Kubota's

You have a very interesting problem!

https://www.mytractorforum.com/forums/john-deere-forum.12/

Yeah I also posted on my tractor forum and weekend freedom machines . But there are a lot of smart folks on this forum . Hopefully between the 3 forums I get a resolution to the problem .

All good. I have never had the issue you described. Odd.

Pictures? You could try pulling the wire out of the cable and coating with SuperLube.

It could be a bad ground. If the intended ground points have too much resistance current is forced to take the next best route, which may be your throttle cable. A quick and easy diagnosis is to run a wire parallel to the throttle cable and see if it still gets hot.

I came to say ground as well. You have current going up the cable and cooking it. I would remove the cable (electrically) and work backwards. Should be very clear where the issue is. Then, replace the cable!

I think it will be an "aha" moment when you see it.

Can't pull the cable out , it has z bends on both ends to connect to the throttle lever and linkage at the engine .

To my knowledge there are two ground cables . One obviously goes from negative battery terminal to a ground point on the engine . The 2nd cable goes from left engine mount to the same engine ground point . The 2nd cable is an uninsulated braided style . I will closely inspect both cables and the connections . I may proactively replace the battery cable as it could be corroded internally within the insulation . Not much $$$ to do so .

Electrical/ground seems odd, especially if existing grounds are intact. I will guess you could loosen up the throttle cable clamp(s) and/or disconnect and see if the engine will fire up? Maybe a No Start with the cable unbolted would seem to indicate an incorrect ground via the cable/clamps. If that happens, I'd refit the correct ground(s). If she otherwise starts/stops okay with the cable loose, seems unlikely it's getting electrically hot...

That said, a throttle cable is lousy conductor, and it has been my experience an unintended conductor would get REALLY sparky/cherry red hot otherwise, e.g., smoke/spark/flames, not just melty cable jacket. Maybe when you replaced the cable it got routed incorrectly, and is either electrically arcing somewhere intermittently, or is now incorrectly near a warm/hot spot on the engine.

With luck, the MTF guys will have some hands-on with your same model and can give some insight; I used to hang out there professionally during my time with Honda (trivia: Honda used to sell a 22hp diesel tractor here in the USA) and they are as solid a crew as you'll find here. Wait. That didn't come out right. ( :D ).

Too bad you are not closer to Houston.

My father in law did not make it past Sixth Grade, but he can do math in his head that makes my eyeballs hurt and fix anything with a motor

The cable I installed was routed exactly the same way as the one it replaced . I am assuming ( maybe incorrectly ) that the one I replaced was routed correctly . If it wasn't then I repeated the error .

Only two spots that the cable touches metal . It touches the radiator and the engine end is mounted to a metal bracket . Everything else it touches is plastic .

Obviously there is engine heat under the hood . But the cable is on the opposite side of the exhaust . And there is lots of airflow from the radiator cooling fan . Lastly I have to think mother deere engineers had it all figured out .

You have mentioned the cable routing by the radiator. Is it possible there are some hot spots due to flow restrictions in one area or another? Aging plastic or changing grades of plastic over time might increase the materials susceptibility to break down with higher temperatures.
Just guessing. I think at the least I would be adding insulating wrap until I knew why this problem occurred.
One other WAG :do you have an exhaust leak? I have seen a truck with an exhaust leak melt the air brake lines about a foot away and come to a screeching halt on the highway.
Best
Les

^^^ The exhaust is on the other side of the engine .

Same problem shows up on 914s when ground goes bad. First thing is throttle/clutch cable start to carry partial starter load plastic melts and seize.

I’ve had good luck with various groups on Facebook regarding my JD tractor.

I had the same problem years ago with an MGB It was a bad ground

I agree with it probably being a ground issue but at the same time I can’t imagine the cable laying on a 200 degree radiator is improving the situation.

I agree this is not ideal and will really study to see if there is an alternate way to route the cable . It's very tight and the location of the hand throttle is so close to the radiator I am not sure I can change it .

It was suggested to insulate the cable where it crosses over the radiator . I will definitely see if I can do that .

You can still force lube in there with air. But you have to find the problem first, obviously. If it is current it will not show up in a random spot. I would think at a the hardest bend.

But running the thing by hand while metering the disconnected cable end to ground will tell you all you need. Be careful what meter you use and what setting. I'd start with t 12v probe light first to make sure you're not seeing more than 10 amps. I fried a meter not thinking when I crossed more than it could handle.

Apparently it's not the same thing as the amp meter in the dash.