# John Deere 720D Issues



## ArcticKnyght (Sep 23, 2021)

New to the forum and hoping someone can give me some ideas to troubleshoot our 720D.

The father in law passed away just before the pandemic started and we're just now giving all the tractors a once over before they go to auction. The 720D has been finicky. We know this tractor ran before he passed, and while we've had pretty good luck prepping the rest of the fleet so far no joy on the 720D.

When we started working on it, we pretty much had a giant brick. So far we've replaced the stale fuel, the battery, replaced some corroded electrical connections and finally got the pup motor to fire and run consistently. But we still can't get the main engine to engage. We've cleaned the fuel lines, verified that it's pumping fuel while the pup is engaged, bled the lines, but we've still go no joy on it catching and running.

Any ideas?


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## pogobill (Jan 31, 2012)

Welcome to the forum. Sorry about your Father-in-law. I personally can't help you, but there are plenty of folks here that I'm sure will help you trouble shoot your way to success.


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## unsquidly (Jul 13, 2021)

If it has a pony motor starter then it has the 6.2L 2 cyl diesel in it.....You say that you can't get the main engine to engage, are you saying that the pony motor will not engage and even turn the main engine over, or the main engine will not fire? Two totally different problems and starting points to trouble shoot.....


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## ArcticKnyght (Sep 23, 2021)

Sorry about that, late night and stepped on my tongue a bit. Yes, the main engine turns over but does not fire.


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## Tx Jim (Jul 28, 2020)

Welcome to the TF
My condolences on the loss of your Father in law. Do you understand that the diesel flow to inj pump is controlled by throttle & throttle lever needs to be advanced to 1/2 travel after engine crankshaft has been rotated several revolutions. Are you moving decompression pedal down so crankshaft will rotate faster while attempting to start then after several revolutions push throttle to 1/2 way & remove foot from decompression pedal. Pistons moving back & forth in cylinders creates heat inside combustion area which aids in igniting fuel. Have you bleed any air from fuel system that might be present from RH side of engine & fuel filters mounting base?


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## Tx Jim (Jul 28, 2020)

Fuel bleeding instructions from 720D operators manual which can be downloaded for free from JD site shown below.





Search for Equipment Publications - Technical Information Store







techpubs.deere.com


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## Tx Jim (Jul 28, 2020)

unsquidly said:


> If it has a pony motor starter then it has the 6.2L 2 cyl diesel in it.....


Actually a 720 diesel will have 6.2L engine if it has pony starter engine or electric 24V starter


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## ArcticKnyght (Sep 23, 2021)

Thank you for the suggestions.

While this tractor is new to me, I do have the benefit of decades of experience from my father in laws old farming partner. He's pretty well versed in this particular model. We've got the starting sequence down pat and he's already cleaned all the lines and bled them.

Our current theory is that the transfer pump isn't creating enough pressure to crack open the injectors. So seeing if we can track down some pressure gauges to check that out.

It also doesn't help that the guys prepping for the auction either split up or disposed of the extensive technical library that was collected over the decades on the entire tractor fleet.


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## Tx Jim (Jul 28, 2020)

Transfer fuel pump supplies fuel to inj pump but transfer pump has no affect on high pressure created by inj pump. Have you considered attempting to tow start the 720?


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## ArcticKnyght (Sep 23, 2021)

Tow start isn't really an option. The 720 has a hydraulic bucket attachment on it that we can't remove or lock in the up position without the engine running. Only other tractor capable of maybe towing it around they literally shattered the steering in yesterday. (look for my other post, I need help identifying what went boom).

Turning over the engine doesn't seem to be a problem, the pup does a good job of spinning everything but we're still missing something, and at the moment our guess is something in the fuel system.


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## Tx Jim (Jul 28, 2020)

Towing with a FEL bucket down is only a minor problem. Route chain under the bucket & bucket will raise off ground as soon as chain is pulled on. When bleeding fuel system did you get "air bubble free" from all 3 bleed screw locations???

I can't locate your reference to the "boom"!


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## ArcticKnyght (Sep 23, 2021)

Once we have something big enough running again, we might give the tow start idea a try.

Yes, the bleed was air bubble free, but we might give it another go before we end up having to call a tech in.

The "boom" was the shattered steering on our Model AR. Model AR Steering Problems


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## Tx Jim (Jul 28, 2020)

Air free fuel from all 3 bleeding locations???


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## ArcticKnyght (Sep 23, 2021)

Yes. I've got an experienced hand at these tractors helping out with the work. But even he's at a loss. So before we pay to have a tech come poke around, we'll double check to make sure everything is bled properly.


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## unsquidly (Jul 13, 2021)

Tx Jim said:


> Actually a 720 diesel will have 6.2L engine if it has pony starter engine or electric 24V starter



That is what I said.....If it has a pony motor then it is a 6.2L diesel......Not sure why you felt the need to add this post.....


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## unsquidly (Jul 13, 2021)

ArcticKnyght said:


> Thank you for the suggestions.
> 
> While this tractor is new to me, I do have the benefit of decades of experience from my father in laws old farming partner. He's pretty well versed in this particular model. We've got the starting sequence down pat and he's already cleaned all the lines and bled them.
> 
> ...



Have you tried taking a spray bottle with diesel fuel, removing the air filter and mist diesel directly into the air intake while trying to start it with the pony motor? Do not use ether or any type of starting fluid for this.


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## Tx Jim (Jul 28, 2020)

unsquidly said:


> That is what I said.....If it has a pony motor then it is a 6.2L diesel......Not sure why you felt the need to add this post.....


Well I didn't in my old age exactly comprehend what you stated. I fail to determine anything wrong with my stating a 6.2L diesel could have 2 different methods of starting.


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## unsquidly (Jul 13, 2021)

Tx Jim said:


> Well I didn't in my old age exactly comprehend what you stated. I fail to determine anything wrong with my stating a 6.2L diesel could have 2 different methods of starting.



Sorry, bro......I guess I took what you said the wrong way and reacted when I probably should not have.....How about we virtually shake hands, smile and put this behind us?


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## ArcticKnyght (Sep 23, 2021)

Winner, winner, @Tx Jim . We have a running 720. Rebled everything by the numbers and made sure to just let it run until we were sure it was air free. The third bleed screw ran air free for a good min and then literally blew a diesel bubble, belched and farted a couple of times and ran air free again. Buttoned it back up and after a couple good cycles to warm up, she fired up. Let everything warm up and she's running pretty decent.

Mechanically seems to be running good. Played with the hydraulics a bit, they seem a bit jerky and they keep kicking out, but ran out of daylight to play with it, so that'll be Wednesday issue and then hopefully onto the next one, while sourcing parts for the AR.


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## unsquidly (Jul 13, 2021)

ArcticKnyght said:


> Winner, winner, @Tx Jim . We have a running 720. Rebled everything by the numbers and made sure to just let it run until we were sure it was air free. The third bleed screw ran air free for a good min and then literally blew a diesel bubble, belched and farted a couple of times and ran air free again. Buttoned it back up and after a couple good cycles to warm up, she fired up. Let everything warm up and she's running pretty decent.
> 
> Mechanically seems to be running good. Played with the hydraulics a bit, they seem a bit jerky and they keep kicking out, but ran out of daylight to play with it, so that'll be Wednesday issue and then hopefully onto the next one, while sourcing parts for the AR.



Nice......Another happy customer of the Tractor Forum......LOL To me, posts like this are great to see and one of the reasons that I am happy that forums like this one exist and proud to be a part of it. This is a fine example of how the world would be a much better place if people would just put everything else aside and help thy brother out in a time of need. A man came in here going through a rough time in life and folks that didn't even know him stepped up to help him out.....This should make all of us here happy and proud....


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## Tx Jim (Jul 28, 2020)

unsquidly said:


> Sorry, bro......I guess I took what you said the wrong way and reacted when I probably should not have.....How about we virtually shake hands, smile and put this behind us?


That's fine with me because I didn't intend to create any ripples on the pond but just provide correct information about the tractor..


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## Tx Jim (Jul 28, 2020)

1 - 20 of 20 Posts


ArcticKnyght said:


> Winner, winner, @Tx Jim . We have a running 720. Rebled everything by the numbers and made sure to just let it run until we were sure it was air free. The third bleed screw ran air free for a good min and then literally blew a diesel bubble, belched and farted a couple of times and ran air free again. Buttoned it back up and after a couple good cycles to warm up, she fired up. Let everything warm up and she's running pretty decent.


I'm glad I could assist you in getting the old 2 cyl diesel operating. I wish you luck on locating parts for the AR steering housing. I've owned a JD BO for 50 yrs.


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## ArcticKnyght (Sep 23, 2021)

OK, well now I know I'm just missing something. Swung by last night and played with the hydraulics, made some adjustments, was happy with how they were working and cycling. Decided it was time to pull it around for a wash, threw it in gear pushed the clutch in and .... nothing. Tried the other gears and I'm not getting anything. Course than I ran out of daylight before I got too far into it. Does this model have a disconnect for the transmission? I flipped thru the info I have and haven't found anything and hadn't seen anything super obvious on the tractor itself. Any ideas? I've got all day tomorrow, but I was hoping to move on to the next one.


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## Tx Jim (Jul 28, 2020)

IIRC those trans have a 3 speed trans with an overdrive creating 6 speeds forward. I think gearshift can slip out of mechanism that shifts overdrive leaving trans in neutral in all gear selections. If what I stated is correct I think trans shift toower with gearshift lever has to be raised in order to put gearshift back inn correct location in shift mechanism. 

Maybe someone more familiar with that model will chime in.


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## ArcticKnyght (Sep 23, 2021)

I have to say thank you to everyone who contributed to my posts over the last month. It allowed me to troubleshoot, fix and track down parts for all the tractors we were working on. With your help, we were able to get everything prepped and running prior to the viewing for the auction. For those of you who are interested, you can check out the auction here: Pidhirney Estate Auction

@Tx Jim, you were once again correct. Was able to open up the shifter and found that when they pulled the 720 out of the tractor shed they had pulled it out of gear and the shifter separated from the overdrive linkage essentially leaving it in neutral between the high and low gears. After some fiddling came to the realization that the 720 shifts best when it's running and a little spin in the clutch helps everything mesh.

Thank you!


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## Tx Jim (Jul 28, 2020)

You're welcome. I hope your auction ends well.
Jim


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