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Discussion Starter · #1 ·
Hi,


It seems that, unfortunately, our JD 7800 will need to have the differential and/or gearbox repaired. We were in the middle of changing the hydraulic-transmission oil and everything was going well until we removed the oil line on the front left side of the differential case. As seen in this picture:
We found metal parts in the oil - smaller pieces have come out together with the drained oil, while "T" looking part and few others were kinda stuck near the drain hole, so we were able to reach them and remove them with a magnet:
We bough this tractor around 3 years ago and we changed the oil and filters at that time. The tractor haven't even reached the 1500 hours yet (as written in the manual for the transmission oil change) but we decided to change it this year, since we are servicing the tractor and changing other fluids anyway.

We had some strange problems with transmission oil pressure in 2019 but changing the transmission oil pressure sensor appeared to have fixed them. Other than that, the tractor seemed to be working fine, all the gears, differential, PTO worked, we did not notice any weird noises or transmission behavior. The previous owner also told us that he did not have any problems with it. The hourmeter on the instrumental panel shows ~11,000 hours.

Anyway, the local John Deere dealer won't be able to come until the next week. Maybe someone have seen something similar and knows what part could have broken? The "T" metal part is somewhere around 4 cm in length. All the bits are hard and do not bend at all.

I've checked through the whole John Deere Parts Catalog for 7800 Powerquad with MFWD online and I did not manage to find anything that could resemble these metal parts.
 

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Agree! Go to a dealer and compare with cone bearings used in the rear differential and on the rear axle shafts.
 
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Discussion Starter · #4 · (Edited)
Thanks for the replies, guys, I appreciate it.

Yeah, I can now clearly see that it is a bearing cone, I don't understand how I managed to overlook it while looking through the parts catalog.

Well, seems like this will be a big and expensive job, and I doubt that we will have enough time and skill to do it ourselves.
 

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I think you managed to avoid a catastrophic breakdown. Tapered roller bearings are usually on heavy shafts so likely transmission output or axle. Besides the labor, getting all the metal debris out is critical. Get several of the hydraulic filters. That's what protects the hydraulic pump. If the debris gets into the hydraulic system, you'll have the devil of a time cleaning it. Think of all the cylinders, fittings, and valves it can hide in.
 

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There is another possibility here. This could be leftover debris from a previous failure that wasn't thoroughly cleaned up. With 11,000 hours on the clock, it is certainly possible. Did you remove the screen when you changed the oil less than 1500 hours ago? If so, was there any debris found then? That suction screen tends to pull debris to it, but it can take a while to get there depending on where it was lodged at. I can't imagine a bearing cage coming apart like that until the bearing is in very poor condition and it should be making noise. I would hate to see you spend a lot of money on a search for a problem that may not exist. How much history do you know on the tractor? How long did previous owner have it? Can you tell if tractor has been apart previously? Look for chipped paint on bolt heads of final drives and transmission attaching bolts. Paint inconsistent at gasket joints, etc. Can you post pictures of the rest of debris you found? You have to do what makes you feel comfortable, but if the worst of what I found in my tractor with 11,000 hours was what you have pictured, I wouldn't spend many hours disassembling a tractor with no symptoms to maybe find nothing. I would send an oil sample out for testing and put clean oil and filters back in it an run it for 50- 100 hours and then cut open a filter and see what's in it and then if suspicious, drain oil and check sump screen again. All the while running it of course keep a close ear on it for any suspicious noises.

These are my thoughts after 40+ years of working on other peoples tractors. I have spent a lot of hours and cost customers a lot of money trying to find problems that don't exist. WIth that said, you definitely could have a real problem and I don't want to persuade you to delay a repair that could conceivably cost you more for waiting. I am just saying what I would do in your situation unless the other debris you found would change my mind or results from an oil scan proves a major issue.
 

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Discussion Starter · #7 ·
So, an update. Our 7800 has been at the JD dealer since last week, and I'm relieved to say that jd110 was absolutely spot on - these metal parts were leftovers from a previous failure/repair. It seems that it was the differential that needed to be repaired sometime in the past, and whoever did it, somehow forgot to do a proper cleanup.

All the parts in rear axle and differential are in good condition. We did not have any major problems with transmission, but since the whole rear end of the tractor is disassembled anyway, we might as well have it thoroughly checked and replace some parts if needed. We also plan to change the brake discs, while we're at it.

Thanks guys for taking your time to reply to this thread.
 
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