JD 790 front end problems

[DWCox]

Made a major discovery today that helps explain some of the problems I have encountered:

The JD dealership I talked to indicated that I needed ca. 400 lbs of ballast with the 300 loader. As most of you indicated, that seemed awfully low. My box blade is 418lbs, so I thought that I was okay.

Wrong.

I should have looked it up myself, so it is ultimately my fault. I looked today and the 300 loader manual calls for a minimum of 617 lb. of 3-point hitch ballast in addition to fluid-filled rear tires. In other words, from day one, I have consistently been running 200 lbs. less rear ballast than is minimally required, and that was before boosting the hydraulic pressure!

What made me decide to double check the numbers was another dealership I called this morning out-of-state, which had one of the washers I needed for the repair. First thing out of his mouth was the question, "having trouble with the front end gears?" Next thing he said was, "you need more ballast in the rear." He likes to get about 1,000 lbs of rear ballast (which includes the filled tires) on the 790.

 

[RoyJackson]

Made a major discovery today that helps explain some of the problems I have encountered...

No doubt a lesson learned...but an expensive lesson! It takes a big man to admit a mistake. You proved you're a tough guy and can handle errors which we all make...some of us just don't admit them.

If there is a silver lining to this cloud, other 770/790/3005 owners will pay heed to this thread.

Good post, DW...I'm sure you won't have any other problems with the front end...once this one is squared away

 

[JDGreenGrass]

Decent...Glad you have discovered the ballast knowledge.

And Roy is right....I have a 770 with a JD Ballast Box. It is filled with concrete minus a few inches at the top. I honestly don't know how much it weighs and from time to time I would think to myself that it may be too much ballast weight.

After reading this thread I am confident that it is NOT too much weight.

And now we know why these little JD tractors are referred to as being "robust" or, allow me to use the word......Stout.!!

DW....Hope this has eased your worried mind. Now, get to work.

 

[AGGIE00]

This just seems nuts to me. A tractor should be engineered to handle its hp capacity without the need for a counterwieght. Planetery drive systems are very durable and what is found in all industrial construction equipment. I bought mfwd primarily for loader work and don't expect to have to add weight to the back to keep from damaging the tractor. I say buy a bigger tractor.

 

[AGGIE00]

So I looked at my manual and it requires 2400# of ballast for my loader. Never gave it any thought before now since all I have ever run is backhoes.

 

[RoyJackson]

This just seems nuts to me. A tractor should be engineered to handle its hp capacity without the need for a counterwieght. Planetery drive systems are very durable and what is found in all industrial construction equipment. I bought mfwd primarily for loader work and don't expect to have to add weight to the back to keep from damaging the tractor. I say buy a bigger tractor.

Well, bigger tractors require ballast too.
Since you mention industrial equipment...take a closer look next time. They have huge permanet counterweights built right into them (big thick castings). So do forklifts.
About the only difference is tractor counterweights (ballast) are removable and you can tailor the ballasting for the job at hand.

 

[AGGIE00]

Well, bigger tractors require ballast too.
Since you mention industrial equipment...take a closer look next time. They have huge permanet counterweights built right into them (big thick castings). So do forklifts.
About the only difference is tractor counterweights (ballast) are removable and you can tailor the ballasting for the job at hand.

I know that, but I always thought is was for capacity and not to keep from damaging axles. We run 420d IT backhoes all day in 4x4 with as heavy of load as it will carry and never a damaged axle, even at 10k hours.

 

[Tractor King]

You don't have enough weight...I added ballast to both tires about 500 lbs plus a weight box about 600 lbs plus....you need at least 1000 lbs to take the weight off the front end.

 

[Muxster]

When the 3005 revision of the 790 came out, some said the front end was stronger. I looked at the parts list for the 790 and compared it with the 3005 and indeed the gears have different part numbers. Everything else has the same part number. I wonder if the 3005 gears could be put in the 790 front end.

 

[RoyJackson]

When the 3005 revision of the 790 came out, some said the front end was stronger. I looked at the parts list for the 790 and compared it with the 3005 and indeed the gears have different part numbers. Everything else has the same part number. I wonder if the 3005 gears could be put in the 790 front end.

Print out both parts lists and compare, PN by PN...to see what else has changed. Also, just because the PN changed doesn't mean there's a stronger component.
There may also be bore diameter or other machining differences too.

This would be a good question for your dealer to take to Deere engineering to find out what changed and why...before you bought any parts.

 

[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.