John Deere 840 stuck on full throttle

[John Deere Johnny]

I have a John Deere 840 diesel electric start tractor and it is stuck on full throttle (1250 rpm) irregardless of hand or foot throttle position, I have to shut it off with the decompression lever. I removed the injection pump cover and the rack is stuck but not from rust, it is oily and clean. I cannot move it by hand. I am just wondering how to get it unstuck without removing injection pumps?

 

[buickanddeere]

Do all the linkages move ?

 

[used red MN]

Hello JD Johnny, welcome to YT! Did you possibly mean to type 830. I may be wrong but I don’t think many other JD tractors had “decompression” levers besides the two cylinder diesels. That leads me to believe you meant you have an 830 two cylinder built between 58 and 61. You can use the edit feature to make corrections, but there is a 24 hour time limit on that. Edit button shows on the bottom on a PC. On a phone click the 3 dots to the right of Report at the bottom left. Sorry, I can’t help you with your problem. It may be helpful to others to know what you were doing with the tractor before this happened. Usually these things happen when a tractor has set a while.

 

[wore out]

Hello JD Johnny, welcome to YT! Did you possibly mean to type 830. I may be wrong but I don’t think many other JD tractors had “decompression” levers besides the two cylinder diesels. That leads me to believe you meant you have an 830 two cylinder built between 58 and 61. You can use the edit feature to make corrections, but there is a 24 hour time limit on that. Edit button shows on the bottom on a PC. On a phone click the 3 dots to the right of Report at the bottom left. Sorry, I can’t help you with your problem. It may be helpful to others to know what you were doing with the tractor before this happened. Usually these things happen when a tractor has set a while.

It's certainly POSSIBLE he has an "840".

 

[used red MN]

wo, Roger that Thanks!

 

[Dieseltech]

One or BOTH plungers are stuck which will keep the rack from moving. Pumps need taken apart VERY CAREFULLY if there's any chance they can be used again.

 

[John Deere Johnny]

Hello JD Johnny, welcome to YT! Did you possibly mean to type 830. I may be wrong but I don’t think many other JD tractors had “decompression” levers besides the two cylinder diesels. That leads me to believe you meant you have an 830 two cylinder built between 58 and 61. You can use the edit feature to make corrections, but there is a 24 hour time limit on that. Edit button shows on the bottom on a PC. On a phone click the 3 dots to the right of Report at the bottom left. Sorry, I can’t help you with your problem. It may be helpful to others to know what you were doing with the tractor before this happened. Usually these things happen when a tractor has set a while.

I actually have an 840 like the picture except it is not restored but has decent paint and good tires and it is hooked to a Hancock paddle scraper. The fuel injection system would be basically identical to an 830. When we used the tractor and scraper 5 or 6 years ago it ran fine, but it sat for several years and I started it back up and it went to full throttle and stayed there, that was about 2 or 3 years ago. So yes it has sat.

 

[John Deere Johnny]

One or BOTH plungers are stuck which will keep the rack from moving. Pumps need taken apart VERY CAREFULLY if there's any chance they can be used again.

Thank you for your reply, that is what I will have to do with it. Can a person get new pumps or would I have to purchase used ones?

 

[WeirdDeere]

Thank you for your reply, that is what I will have to do with it. Can a person get new pumps or would I have to purchase used ones?

They can generally be rebuilt. They require specialized equipment to setup that most modern diesel shops probably don't have. I've never had it done but heard lots of good things about Garry Power at https://hendrichfarmtractors.com/

Do you actually have an 840? I'd love to hear more about it. I'm trying to make a list of surviving 840s

Brandon

 

[Dieseltech]

They can generally be rebuilt. They require specialized equipment to setup that most modern diesel shops probably don't have. I've never had it done but heard lots of good things about Garry Power at https://hendrichfarmtractors.com/

Do you actually have an 840? I'd love to hear more about it. I'm trying to make a list of surviving 840s

Brandon

I have one of the old Woodring and Wise two cylinder test stands some JD shops used to have. Not fancy but it works.

 

[buickanddeere]

It is
Maybe possible that with some careful wiggling. The racks can be worked back and firth by hand until they free up .

 

[Dieseltech]

It is
Maybe possible that with some careful wiggling. The racks can be worked back and firth by hand until they free up .

Not likely, rack won't move because the PLUNGERS are stuck in one or both pumps. Rack moves the gear/sleeves to control plunger rotation to increase/decrease plunger effective fuel delivery stroke. When just one plunger is stuck on ANY make/model inline pump the rack won't move.

 

[WeirdDeere]

I have one of the old Woodring and Wise two cylinder test stands some JD shops used to have. Not fancy but it works.

Awesome. Simple is better!

 

[John Deere Johnny]

They can generally be rebuilt. They require specialized equipment to setup that most modern diesel shops probably don't have. I've never had it done but heard lots of good things about Garry Power at https://hendrichfarmtractors.com/

Do you actually have an 840? I'd love to hear more about it. I'm trying to make a list of surviving 840s

Brandon

Hi, thanks for your reply. Yes, I actually do have an 840 tractor, serial number 8400550. It is factory electric start and is hooked up to a Hancock scraper. It burns some oil, but we did a full service the last time it ran. It has 8.25-20 truck tires in front and 23.1-26 rear tires, all the tires are in pretty good shape. It is overall decent shape and not beat up and not much rust and it has decent paint. It also has a float-ride seat and 25 hours on a new tach that my Dad installed when we got it almost 25 years ago, so I do not know the original hours. That is about all I can say without sending a picture, which I can do.