Long Term Effects 790 Hydraulics?

[DWCox]

Does anyone have any long term (ca. 2+ years) report on increasing the hydraulic pressure via shims to 2500 psi? In frequent applications I could use any extra lift, but I have so far been hesitant out of concern that it could degrade the life of the pump.

What would be even better is if anyone had information which would indicate that the 790's hydraulic pumps are still within manufacturers specs. at 2500 psi.

 

[jdbower]

Increasing the hydro pressure on any tractor isn't exactly proprietary information, Deere intentionally made the pressure what it is. Increasing it could cause excess wear on the pumps, cause seals the leak or burst, using the increased pressure to lift too much with the FEL can snap an axle or create a dangerous loading situation. Or increasing the pressure could simply reduce the lifespan of the tractor a little (if at all) because Deere stuff tends to be overbuilt anyway. Either way it goes without saying that you'll probably want to wait until the warranty is up before making the change.

If you're willing to undertake the responsibility of upping the pressure and you understand the potential issues, go for it. If you're not sure you may want to hold off. My 2520 has more than enough power for most of my needs today so I probably wouldn't bother since I'd rather keep the tractor for a few more years than have a little more lifting power, but I did put a supercharger in my truck knowing full well that I may end up with drivetrain issues because of it.

 

[DWCox]

Thanks for the response. After researching all the previous posts I could find on this issue, all those concerns and warnings seem to have been covered at one point or another.

What I am wondering is if sufficient time has passed for those who have increased the the pressure on the 790 to finally weigh in on the question: has there been any pump/seals or other problems?

As you and others have mentioned, JD sometimes overbuilds. But likewise sometimes a manufacturer may reduce capability for reasons other than the physical limitations of the system (viz., marketing newer but similar models with more capacity, concerns about the overall geometry of the tractor [the 790 does seem to have a high center of gravity], etc.).

If I find evidence which indicates that the 790's relatively weak hydraulic capacity falls into this latter category, I would not hesitate to increase it. If I cannot find evidence, I will err on the side of caution, as I am very happy with everything else about this tractor and wish for it to last a good, long time.

I am not just bored and tinkering on my tractor though; I really could use the increase in numerous practical ways.

 

[AKfish]

Does anyone have any long term (ca. 2+ years) report on increasing the hydraulic pressure via shims to 2500 psi? In frequent applications I could use any extra lift, but I have so far been hesitant out of concern that it could degrade the life of the pump.

What would be even better is if anyone had information which would indicate that the 790's hydraulic pumps are still within manufacturers specs. at 2500 psi.

The JD Technical Repair manual lists the hydraulic specs for the 790. Or a quick call to your dealer (shop mechanic.. better) and they could look it up for you.

AKfish

 

[Phineas7]

Actually, I thought the written spec was 2500#, they just never came set to that.

2500# seems to be a pretty standard pressure, what varies is the GPM of differnet tractors.

Also consider that your not going to hit the max pressure unless you put that much load on it, or run a cylinder all the way to the end, which is probably hardest on the system. Because all of a sudden the fluid has nowhere to go. You've probably noticed how the sytem kind of bucks and loads until the relief valve has time to open. This delay makes engine RPM a contributing factor even though it doesn't affect pressure, it does affect the pressure spike while the relief valve opens. IMHO, how you use the hydraulic will have a much larger affect on issues than years or hours, so it will be hard to come up with any real statistics from the relatively small sample of 790 owners around here. The vast majority of my loader work is done around the 1200 rpm range, everthing is slow and smooth. I generally don't snatch the control around causing abrupt movement of the loader and things like that, so I really expect the difference in lifespan to be un-mesureable. But, even if it is, the improved user experience is worth it. I did a fairly large digging project last year and still only put about 50 hours on the tractor.

 

[200%Dave]

I keep reading about "re-shimming" the hydraulics on a John Deere 790. What's involved in doing this ?


Thanks,

 

[Willl]

What's involved in doing this ?

Welcome Dave.

I believe this PDF I un-shamelessly stole from here will explain it all.

 

[200%Dave]

Great !

Thanks for your help.


--200%Dave

 

[YesDeere]

Willl Is that a John Deere part number on that pdf?

 

[Willl]

Yes, JD parts says AM875169 is a good shim number.

 

[Tractor Pilot]

Has anybody increased the hydraulic pressure with shims on the JD770 tractor? What were the results? Seems that many have done this successfully on the JD790 - so why not also on the JD770 since these two tractors are so similiar?

I am considering doing this mod. Right now I am gathering all the pieces to make my pressure guage. My tractor has the model 70 loader.

Thanks,
Bruce

 

[foggy1111]

I had a 790 with a #70 loader, and one set of shims increased the pressure to about 2300 lbs IIRC. After operating as such, I felt I did not need more lift in the loader nor the three point....so I left well enough alone. Prolly never really needed to shim anything....as I could lift full 54" bucket-loads of dirt and about any size pine tree I needed.

So.....I question needing more lift than JD supplies as standard. Maybe its just easier to break stuff? Those tractors are well-balanced units. :thumbsup: But.....I think I read that some "770 guys" had shimmed too. If you shim....use a gauge, and stay under 2500# pressure and you should be golden.

 

[Tractor Pilot]

foggy1111,

I was also thinking about increasing the hydraulic pressure to only 2300psi instead of 2500psi. Why push it? Based on my current needs, I probably don't need the extra 300psi, but I want to increase it a bit because of the general principle that it is just not very manly to have a tractor that is hydraulically derated.

Did you notice any improvements in the loader and 3 point by increasing the system pressure 300psi? I am more interested in increasing breakout performance than lift capacity.

Bruce

 

[godaddy]

I just shimmed my 790 with 1 pck and got a tad over 2300. Not that much difference in the loader but, a nice difference in the 3 point. That is why I did mine.

 

[kebo]

I jacked mine all the way up to 2500psi. No problems in about year and a half, let's hope it stays that way!

 

[RoyJackson]

I jacked mine all the way up to 2500psi. No problems in about year and a half, let's hope it stays that way!

Same here...but I ran the machine for around 3 years.
It's an easy and worthwhile modification as long as one doesn't go overboard with the shimming.

BTW, when you pull the cap off to install the shims, there are some pieces that will come out (due to spring pressure) when the cap is removed. Be careful not to lose anything and re-install them in the correct order.
I strongly suggest you do this in a garage or building with a concrete floor and sweep the floor before you begin (just in case).
You have been warned!

 

[NickTaylor]

Interesting thread. I recently bought a 98 770. Where can I learn more about this mod? Is there a kit out there somewhere?

 

[Tractor Pilot]

Nick,

Do a search on the forums for increasing the hydraulic pressure by adding shims on the JD790 and you will find several detailed threads on the subject. The info on the JD790 will be applicable to your JD770.

Bruce

 

[foggy1111]

foggy1111,

I was also thinking about increasing the hydraulic pressure to only 2300psi instead of 2500psi. Why push it? Based on my current needs, I probably don't need the extra 300psi, but I want to increase it a bit because of the general principle that it is just not very manly to have a tractor that is hydraulically derated.

Did you notice any improvements in the loader and 3 point by increasing the system pressure 300psi? I am more interested in increasing breakout performance than lift capacity.

Bruce

If my memory serves (which is questionable)......I think I could note some improvement in the capacity.....and as stated, I think I noticed more in the 3 point ability to lift my weighted disc. I did not have much experience in operating the tractor before shimming....as I performed this shimming quite soon after purchasing the tractor. I always had pretty good loader performance.

The 790 and 70 loader was a nicely balanced machine IMO. If I could not pick it up.....I probably needed to cut it in half or take two loads. (that's my story and I'm sticking to it )

 

[ptwohig]

Does anyone have any long term (ca. 2+ years) report on increasing the hydraulic pressure via shims to 2500 psi? In frequent applications I could use any extra lift, but I have so far been hesitant out of concern that it could degrade the life of the pump.

What would be even better is if anyone had information which would indicate that the 790's hydraulic pumps are still within manufacturers specs. at 2500 psi.

Well I was goofing around and over shimmed my front end loader. The results, I blew a 10 dollar lip seal that rides on the input shaft of the pump. It took me about an hour to pull the pump and change out the seal. I re shimmed it using the proper technique with no problems. The moral to the story is the lip seal is the weak link and will blow long before any hose or cylinder if they are in decent shape.