JD 790 front end problems

[Phineas7]

This may in fact prove to be one of the very reasons why JD purposely dropped the pressure on a pump and lines which are clearly designed to operate safely beyond their default setting. Their concern may have been the front 4x4 planetary gears (as per the previous comparable model failing when not having sufficient counterweight). This is beginning to make a lot more sense.

I hope you're wrong about this. IMO that would be very underhanded of JD. Setting the pressure significantly below the PUBLISHED spec to hide a design flaw that should have been fixed during the redesign in the next model.

I can say I have used the rip out of my FEL and 4wd in the past 3 years without issues. I typically use 48" frontier BB as a counter weight and often hang 2 - 70lb weights toward the back of it. One thing to consider 600lb of BB / weight with a center of gravity 6 ft behind the rear axle does more than an 800lb concrete balast with a center of gravity 4 ft behind the rear axle. After reading this, I may rig up a way to hang 4 70lb weights, sideways, along the back of the BB! FWIW, I have the tires loaded too.

Like the OP, I can't really use a bigger tractor, the 790 get's into some amazingly tight and steep spaces on my wooded property. I need it's shortness and low CG.

 

[DWCox]

I hope you're wrong about this. IMO that would be very underhanded of JD. Setting the pressure significantly below the PUBLISHED spec to hide a design flaw that should have been fixed during the redesign in the next model.

I can say I have used the rip out of my FEL and 4wd in the past 3 years without issues. I typically use 48" frontier BB as a counter weight and often hang 2 - 70lb weights toward the back of it. One thing to consider 600lb of BB / weight with a center of gravity 6 ft behind the rear axle does more than an 800lb concrete balast with a center of gravity 4 ft behind the rear axle. After reading this, I may rig up a way to hang 4 70lb weights, sideways, along the back of the BB! FWIW, I have the tires loaded too.

Like the OP, I can't really use a bigger tractor, the 790 get's into some amazingly tight and steep spaces on my wooded property. I need it's shortness and low CG.

I am right there with you Phineas. Great sized tractor, bullet-proof engine and other systems, and nimble as can be. I really do not want to upgrade, even if cash flow was a non-issue.

Also, now that I think about it further, I am not really sure I can afford to drop the hydraulic pressure (it is perfect now at 2400psi), as default break-out force was terribly insufficient. I was not trying to be trendy in making the change, it was a matter of getting done what needed to be done.

Based on the responses I am getting here, as well as the recommendation of the JD tech., I think I will just get considerably more weight over the rear end of this tractor AND continue to be very conscious of using 4x4 wisely.

Any ideas on maximizing cheap weight over box blades? Is Sackrete (sp?) in five gallon pails the way to go? Other?

Either way I will give it one solid season of use (and I use it plenty on our five acre homestead) and report back.

 

[foggy1111]

I am right there with you Phineas. Great sized tractor, bullet-proof engine and other systems, and nimble as can be. I really do not want to upgrade, even if cash flow was a non-issue.

Also, now that I think about it further, I am not really sure I can afford to drop the hydraulic pressure (it is perfect now at 2400psi), as default break-out force was terribly insufficient. I was not be trendy in making the change, it was a matter of getting done what needed to be done.

Based on the responses I am getting here, as well as the recommendation of the JD tech., I think I will just get considerably more weight over the rear end of this tractor AND continue to be very conscious of using 4x4 wisely.

Any ideas on maximizing cheap weight over box blades? Is Sackrete (sp?) in five gallon pails the way to go? Other?

Either way I will give it one solid season of use (and I use it plenty on our five acre homestead) and report back.[/QU

Do you have fluid in your rear tires? That adds about 400 lbs and adds to the stability on hills, etc as well as ballast for fel work without hanging it on the 3 point. I hang 4 suitcase wieghts (70 lbs ea) on my box blade for extra weight.

 

[DWCox]

Yep, back tires have been filled from day one.

Suitcase weights make best sense, but as I understand it they can be very pricey, no?

 

[foggy1111]

Yep...they are pricey when purchased new....but they last forever. I have had a few for a long time now....and have used them for a few different tasks. Lately they found a place on my box blade. Somehow I have accumulated eight suitcase weights of about 3 different sizes / makes. :laughing: At farm auctions they sell for 1/2 or less than the new price.

 

[Phineas7]

Yep, back tires have been filled from day one.

Suitcase weights make best sense, but as I understand it they can be very pricey, no?

My dealer stocks some no-name brand weight. A 70lb costs less than a 40 lb jd, and yes, even with that they are expensive. I have 4 because that's as many as I can fit accross the front. I want to say the last two I got were about $80 each. The previous 2 were less than $50, but that was about 2 years earlier. Not sure why the price jumped so much.

I know what you mean about the break-out strength, it is aggravating even with the pressure bumped up, but at least it can be done if you work the front end a bit.

 

[JDGreenGrass]

I think Ag tires would help your cause.

Or, as Roy said....chains.

I don't like hearing these things.

Good luck with your projects and repairs.

 

[RoyJackson]

This may in fact prove to be one of the very reasons why JD purposely dropped the pressure on a pump and lines which are clearly designed to operate safely beyond their default setting. Their concern may have been the front 4x4 planetary gears (as per the previous comparable model failing when not having sufficient counterweight). This is beginning to make a lot more sense.

I don't think Deere lowered any pressures in the system. The 790 is an old, old design...dating back at least to the 1980's. The 670 and 770 tractors were direct predecessors and the hydraulics were about the same. Although Deere probably could have increased the pressure, it's actually a pretty good fit for a 2200 lb tractor.
Also, the 790, being a "value" tractor cut into the sales of the 4200 and 4210 (which had about the same engine HP and a little less PTO HP), so Deere had no incentive to increase the specs (which would have probably cut more into the 4200 and possibly the 4300 sales).

 

[Barely Smokin']

I've got 293 very rough hours on my 790. I've used the FEL to transport 160 tons of gravel on steep, uneven terrain, all in 4WD, with a BB ballast. This, of course, includes repeatedly driving into piles of gravel and reversing with a full bucket.

I have loaded a zillion pallets (ok, 120?) of landscape stone and recycled brick that have been loaded so precisely that the FEL will pick them up 4 feet but no higher...just enough to load them on a trailer. This is with shims.

I have used the FEL to excavate two roads @ 100 feet each on a 30 degree slope...rock, tree stumps and all, plus two garden terraces on hill sides. I excavated a 60 x 60 building site with the BB and the FEL in some of the hardest clay you'll ever see, where the deep end of the excavation was 36" and tapered to 0 feet 60 feet later.

Every time it snows, I plow 6 miles of road in 4WD and a front-mounted snow blade.

So far, no issues with the front end. On the one hand, I'm a maintenance freak. On the other, I expect my 790 to earn its keep. On the other hand, what's up with your tractor that's not up with mine?

Thanks for the heads up!

 

[DWCox]

I don't think Deere lowered any pressures in the system. The 790 is an old, old design...dating back at least to the 1980's. The 670 and 770 tractors were direct predecessors and the hydraulics were about the same. Although Deere probably could have increased the pressure, it's actually a pretty good fit for a 2200 lb tractor.
Also, the 790, being a "value" tractor cut into the sales of the 4200 and 4210 (which had about the same engine HP and a little less PTO HP), so Deere had no incentive to increase the specs (which would have probably cut more into the 4200 and possibly the 4300 sales).

Yea, you are correct. Technically, JD did not reduce the pressure. They simply never brought it up to higher levels that the same pump and hoses are rated for in other applications. My hunch (and that is all it is) was that since they knew their later designs were going to be beefier in the front end (a point demonstrated in loader capacity and breakout), there would be no point in retooling an older design like the 790. As far as I am concerned with JD, no fault, no foul.

At this point I assume complete responsibility for the problem. I am meticulous about maintenance, but I grew up on farms and I make a tractor work--hard--evidently too hard. The JD tech looked at the gears and said meshing patterns are fine--they are stress failures. My applications are also somewhat unique with a lot of reverse motion backing up a slope with a full bucket. This thread has given me some good ideas about what I can do to perhaps minimize or offset the problem.

Again, I will add more weight to the back, be a bit more careful (though I thought I was being after the last time), and give it a year and see what happens.