JD 790 front end problems

[Tractor Pilot]

The previous owner of my JD770 had to repair the front gears around the 500 hour mark just before I bought it. He claimed that a snap ring had come loose in the front hub which destroyed both front gears. But after reading this thread, I wonder if he didn't just overstress the front gears by operating the tractor in 4wd on a slope with a full bucket of heavy material. He also didn't own a ballast box; didn't have rear wheel weights, and/or didn't have the rear tires filled. At best, he had an implement on the 3-point.

One of the first things I did after I bought the tractor was to fill the rear tires. I could definitely feel the difference with an extra 320lbs. Since I almost always have an implement of the 3-point, I would love to add weights to the rear tires too, but they are really expensive. But with the cost and hassle of fixing the front gears, I may just get them. My model 70 loader operator's manual recommends using a ballast box, rear wheel weights, AND fluid-filled rear tires. That is probably around 1200-1300 lbs total weight in the rear (the manual doesn't give an exact minimum rear ballast weight needed). It is possible there may be no amount of rear ballast that can protect the front gears on these tractors under all circumstances.

Bruce

 

[godaddy]

Just finished rebuilding the front end on my 01 790. Not all gears had to be replaced but $1340 worth. More ballast on back and selective 4x4 use for me in the future.

 

[grsthegreat]

na..that isn't it. My old JD870 had the front end seize up on me after about 1000 hours or so. I had filled tires, and do not over stress my tractors.​

I was told by the JD mechanic that repaired it that this is a flaw with the yanmar design, and they have repaired alot of them over the years. Only one side seized up, so i had him go and look at the other side while he was at it. turned out that that side was ready to fall apart also. some cheap snap ring. the repair consisted of new gears and a drilled pin to hold nut in place (if i remember correctly). Was a $1,800 repair when all said and done.​

 

[Tractor Pilot]

I was chatting with the JD guy down at the dealership yesterday and he said, in his experience, that one of the major reasons that they had fixed several of the front gears on these tractors over the years was because people happened to lift the front tires off the ground in 4WD while doing loader work. And if the front tires were spinning really fast when the front end of the tractor came back down then something had to give - and it was usually the front gears. That was his explanation. Makes sense. And for those that increase their hydraulic pressure by shimming have to be even more alert to the possibility of raising the front end off the ground while using the loader in 4WD.

Bruce

 

[MaxxB]

Hi everyone! I'm thiiiis close to buying a used 790 with 300 hours on it. Sparing the rest of the details, is there any good way to check the condition of the front end without a detailed inspection? My thoughts were to get into a low gear in 4 wheel drive and make some tight radius turns.....slow of course

Thanks...this could happen as soon as tomorrow, so anything you've got would be great!

 

[godaddy]

When mine was going out it would make a clunking noise when i would be backing up mainly in 4x4, until it was very close to going out. Then it would make it not in 4x4 also. Shortly after that, it went out. U could drain the front diff oil to see what comes out in the oil and run a small magnet up in the pumpkin housing drain plug also. About $20 to replace the gear oil. Probably not an issue with so little hrs.

 

[Tractor Pilot]

Just got my JD ballast box (24"x20"x18") today for my JD770.

 

[polishrookie]

Old thread, I know. Found it looking for answers for my Dad. Bought a 790 with 200 hours. It has filled tires and the John Deere backhoe on back. He was going in reverse with dirt in his bucket and blew out the gears in both sides of the axel. It was in his lawn so he was in 4wd as to not tear things up. Plain and simple, it is just not beefy enough. So even if the gears are new and not damaged, heaven help you if you want to actually use your machine. He replaced his previous Deere 650 that gave him years of good service. Now he is finding out he has a larger machine but can only do the work his smaller tractor used to do without fear of breaking it. What a sad waste of money. I told him to trade it in.