I have a 2002 john deere 790 that has 450hrs. Recently I've been doing a lot of digging with the front bucket. Yesterday I was driving down a hill in 4wd with a load of dirt in the bucket. I went over a bump and heard a crack come from around the left front tire. I stopped and saw oil leaking from around the left front hub. I took it out of 4wd and dumped the dirt then tried to drive it back to the garage but i kept hearing a crack about every 2 ft or so I drove so I stopped and left it there because I didn't want to do any further damage. Any idea what is wrong and how I fix it?
jd 790 front axle leaking oil
- Thread starter dms
- Start date
Do a search on "790 front axle" and you will find what you need. Sold mine two years ago without any problems. But from what I've seen on here they are not meant for heavy bucket loads, especially in reverse. Good luck in your fix
I think the damage is done. I hate working outside so I would drive it. Keep searching. I remember threads with details of the rebuild and pics. Don't think its that bad to do. I feel for you. Shouldn't happen
I can't find any threads with any details of rebuilds or pics so far. Links? So I decided to drive it up to the garage. It made a horrible snapping sound coming from the front end every 5-10ft and the left front tire twitched every time I heard the sound. I took both tires off and drained both axle oil bolts. There was a lot of metal shards in both sides. Not to sure what to do next. I guess i'm going to have to take it all apart or take it to the dealer.
Heres where its leaking
Some pieces of metal that came out in the oil
Here's a link to a video of the terrible sound it makes
0721112022.mp4 video by rerider150 - Photobucket
Heres where its leaking
Some pieces of metal that came out in the oil
Here's a link to a video of the terrible sound it makes
0721112022.mp4 video by rerider150 - Photobucket
Tractor Pilot
Silver Member
dms,
Sorry to read about your front gears. I have a JD770 and the previous owner had to have the front gears fixed too around the 500 hour mark just before I bought it. He claimed a snap ring came loose in the front axle and broke two of the front gears. However, it is more common to overstress the front gears on these tractors when using the loader in 4wd on a slope without adequate ballast on the rear (i.e. filled rear tires; ballast box or heavy implement on the 3-point; and possibly wheel weights), especially when moving in reverse. If it wasn't for these forums, I wouldn't even know about this.
How big was that bump you hit? What rear ballast were you using? Maybe after you take it apart you will find that it was a snap ring that came loose for you too when you hit that bump.
Bruce
Sorry to read about your front gears. I have a JD770 and the previous owner had to have the front gears fixed too around the 500 hour mark just before I bought it. He claimed a snap ring came loose in the front axle and broke two of the front gears. However, it is more common to overstress the front gears on these tractors when using the loader in 4wd on a slope without adequate ballast on the rear (i.e. filled rear tires; ballast box or heavy implement on the 3-point; and possibly wheel weights), especially when moving in reverse. If it wasn't for these forums, I wouldn't even know about this.
How big was that bump you hit? What rear ballast were you using? Maybe after you take it apart you will find that it was a snap ring that came loose for you too when you hit that bump.
Bruce
I had a York rake on the 3point hitch which only weighs around 150 lbs I think. I was carrying about half a bucket of clay. It wasn't a very steep hill that I was driving down. I drove over a rounded bump about 8 inches tall in 1st gear high. Then I heard the snap and the oil immediately started to leak out. I think backing out of the hole I was digging with a full bucket of dirt in 4wd may have put a lot of stress on the front gears.
Tractor Pilot
Silver Member
dms,
It sounds like a combination of too fast a speed, heavy load in the bucket, inadequate rear ballast, 4wd, slope, and a bump broke your front gears (i.e. the perfect storm).
When I bought my JD770, I filled the rear tires and always have an implement on the back when I use the loader. And I don't use the loader in 4wd unless absolutely necessary. If I do need the 4wd, I make sure I have at least 500lbs on the 3-point to take the strain off the front end.
A few weeks ago I was using the loader in 4wd (I forgot it was in 4wd! - Oops!). I had a full bucket of loose dirt and was driving slowly on level ground. I hit a small pot hole in the field and I heard a slight metallic bang from somewhere around my front end. I looked down and noticed the tractor was in 4wd and my heart sank. So I stopped the tractor and checked the front end. It seemed fine. So I jacked up the tractor and checked the 4wd. Again, to my relief, everything was fine. I suspect the slight metallic bang sound was just the front end swiviling when I hit the pot hole and coming into contact with the metal frame. The moral of the story is that the situation of broken front gears can happen to any of us even when we are trying to be careful but overlooking simple things like not noticing the tractor was left in 4wd.
Hang in there, dms. It will just take some time and money and your JD790 will be back to work (I'll take a broken tractor over a broken body anyday!). It really is a great little tractor, but has to be used very, very carefully when using the loader in 4wd. Keep us posted.
Bruce
It sounds like a combination of too fast a speed, heavy load in the bucket, inadequate rear ballast, 4wd, slope, and a bump broke your front gears (i.e. the perfect storm).
When I bought my JD770, I filled the rear tires and always have an implement on the back when I use the loader. And I don't use the loader in 4wd unless absolutely necessary. If I do need the 4wd, I make sure I have at least 500lbs on the 3-point to take the strain off the front end.
A few weeks ago I was using the loader in 4wd (I forgot it was in 4wd! - Oops!). I had a full bucket of loose dirt and was driving slowly on level ground. I hit a small pot hole in the field and I heard a slight metallic bang from somewhere around my front end. I looked down and noticed the tractor was in 4wd and my heart sank. So I stopped the tractor and checked the front end. It seemed fine. So I jacked up the tractor and checked the 4wd. Again, to my relief, everything was fine. I suspect the slight metallic bang sound was just the front end swiviling when I hit the pot hole and coming into contact with the metal frame. The moral of the story is that the situation of broken front gears can happen to any of us even when we are trying to be careful but overlooking simple things like not noticing the tractor was left in 4wd.
Hang in there, dms. It will just take some time and money and your JD790 will be back to work (I'll take a broken tractor over a broken body anyday!). It really is a great little tractor, but has to be used very, very carefully when using the loader in 4wd. Keep us posted.
Bruce
Last edited: