790 HP Reduction By John Deere

F350Lawman · Oct 16, 2003

The part number for the shims is AM875169. I believe the is the number. There is another number on the package (20030213DY4), but I think the first one is the part number. You need to order two of these packages. It is an assorted pack of shims that you can put in to increase the relief pressure. I first used one package, but that didn't seem to increase it very much, so I used two full packages. This really did the trick. Before my loader was so weak that it wouldn't pick up a full bucket of sand. Now it is just right. I will attempt to get some pics to post on here soon.

Just got a call today, the dealer has my shims. I need photos and some instructions. Please /forums/images/graemlins/smirk.gif

Whiskey · Oct 16, 2003

Scott:

I'm waiting to see if your's blows up before I try.. /forums/images/graemlins/smirk.gif
keep me posted, and I'm going to try the front wheel swap this weekend like I read somewhere you did, I'll see if I can get through it with all my fingers intact.. /forums/images/graemlins/blush.gif

What did you have to give for the parts....and did the dealer give you a "and what do you need these for" question????

Whiskey

Mark_D · Oct 20, 2003

OK, I'm going to try and post a picture with this email. Flip up the seat on your tractor and this is what you will see. You will notice there are three caps. The one on the right is where you will add the shims. Be careful when removing the cap because there are a couple of parts from inside the cap that can fall down and get lost. The shims get added to the inside of the cap, so as to push all of the other parts down slightly more. I originally said to add two full packages, but don't do this. I put mine on a guage and the PSI was way too high. Get a guage, start with one full package, and then work up from there. Keep in mind that the factory setting is 2050 PSI. I have mine at 2500 now with a modest increase in power. (3500 works really good, but don't ask how I know). When putting the cap back on, if it seems difficult, then reach in the hole and pull out the rubber o-ring and slip it over the threads on the cap. I will thread right in then.

F350Lawman · Oct 20, 2003

What reading did you get with one pack and how much extra lift do you think you got??

If hypothetically I did this, I think I'd like the results. I am curious what my hypothetical pressure might be.

Having it run at 3500lbs. and not blow indicates the built in safety factor and makes me feel much better about running at perhaps 2300-2500 for example. I think the hoses are rated for 3000 so 3500 sounds EXTREME but 2500 seem like a good compromise.

Mark_D · Oct 20, 2003

I didn't measure it w/just one pack. I had both packs in when I saw the 3500 (actually a little more...the guage was a 3500 psi guage). My brother, who is a diesel mechanic, said that there was danger of cracking the pump at that pressure. We took out part of one of the packs and came up w/2500. Most of the difference was in the second pack. I would buy two packs (they are very cheap) and add them accordingly. The factory rated 2050 psi is just a safety measure that JD has built into these tractors so that no one turns one over. The frame on the loader as well as the hydraulics are capable of much more than this. I would actually feel comfortable at 3000 PSI....2500 is very well within the safety margin. There is a modest increase in lift capacity w/2500. My tractor would not even pick up a full bucket of sand before.

F350Lawman · Oct 20, 2003

I am happy with the one pack right now. If I had a guage I might be more "adventerous" /forums/images/graemlins/smirk.gif

thanks for the idea and advice.

glalonde · Oct 23, 2003

Being new to this, I would rather not do this blindly but instead rely on a gauge.
Where do you connect this gauge and are they expensive (or can you rent them ) ?

Mark_D · Oct 23, 2003

You just need a guage with a fitting that will fit into one of your FEL hookups. You could probably borrow one if you know a mechanic.

mountain_man · Oct 23, 2003

Mark - Thanks for posting the modification which I'm considering for my 2000 790 (well past warranty). What issues should I be aware of /forums/images/graemlins/confused.gif. I'm guessing the potential for a burst hose, but what about bending something or the effect on the hydraulic pump? Also what effect does it have on the 3ph? Any thoughts?

Mark_D · Oct 24, 2003

If you go with a modest modification (I would say under 3000 PSI) you should have no problems. As stated, before I checked mine with a guage, I was operating at a little over 3500 PSI. It worked great, but at that pressure there was a chance of damaging the pump. Keep in mind the setting from the factory is 2050 PSI. You probably have the 70 loader on yours...mine has the newer 419 loader. If you went to 2500 PSI, in my eyes you have absolutely nothing to lose, only some lift power to gain. I believe that the reason they are "turned down" so much from the factory is for liability reasons. The more lift you have, the more inherent is the risk of tipping the tractor over. I feel comfortable with this and I use counterweight when necessary, stay off of hills, and always keep the bucket low to the ground. Does that answer your question? I don't think your tractor would give you any problems.

Also, the 3PH lift will be increased as well. The relief is for the whole system. It's exactly what the tractor needs.

Mark

mountain_man · Oct 24, 2003

That's exactly what I was lookin' for. To me, the 70 loader seemed a little underpowered considering the "heft" of the frame, cylinders and the tractor. I'll give it a try. Thanks mucho!

scottbrrtt72 · Nov 17, 2003

Mark,

I recently purchased a log skidder attachment for my 3-point hitch. I was extremely disappointed when I tried lifting a log with my 790 and it wouldn’t budge. The specs on the 790 3-point hitch is 815 lbs. With the additional shims do you have an idea of what the 3-point hitch can lift at 2500 PSI? I would be very interested in finding that out. I also have the #7 backhoe with my machine. Would that added PSI affect the backhoe at all? I will try calling the dealer and get there suggestions on making this change. My machine is a 2001, so I am not worried about a warranty issue. When my 790 was at the dealer for service I had them test the lift capacity of the loader. It came in at 860lbs, which is above the specs for the 70 loader. I believe this was from the ground to a certain height. I know after a certain height you start loosing lift capacity. I started thinking I would have to buy a bigger machine, 4010 series. I really don’t want to do that since my 790 is paid off. Any information would be great.

F350Lawman · Nov 17, 2003

I have added the shim pack.

Well this is justa guess, but if our factory psi was 2100lbs and now it is 2500lbs., I would think it might be about a 20% increase in lift capacity? So maybe it is about 1000lbs at the 3 point. That would actually be 1000lbs -24" behind the ball ends.

I know my tractor really did not lift the front end by pushing the FEL down unless I used the curl function, now it lifts easy. I also now lift a rock to full height that I could only lift a couple if inches before the "modification".

Not really scientific, but capacity has increased with no ill effects thus far with the addition of one pack of shims.

1000lbs of 3 point hitch lift should skid a pretty BIG log, after all aren't you just lifting the end? Seems like a log much bigger than that could easily get away from you on any type of hill with such a light tractor.

With the modification I think you will find the tractor will lift anything that yuo would want to SAFELY lift and transport with a 790.

Not that I wasn't before but I am very pleased with the machine.

HalseyGreen · Nov 18, 2003

I was looking at my parts and service manual last night, from the parts manual there appears to be a seperate relief valve for the three point, and it listed a different part number for the shim pack for it. The three point is adjusted by shims under the cap to the left of the system relief valve. Not sure how the system valve reflects on the three point valve.

F350Lawman · Nov 18, 2003

I was looking at my parts and service manual last night, from the parts manual there appears to be a seperate relief valve for the three point(part #5), and it listed a different part number for the shim pack for it. The three point is adjusted by shims under the cap to the left of the system relief valve(#6). Not sure how the system valve reflects on the three point valve.

I see what you mean, the 3pt relief valve is the next biggest cap and is to the left of the system relief valve cap. from the drawing the shims are as easy to add as the system relief valve.

A couple of questions? Does the system relief valve pressure contol the entire system? Adding shims to the system relief valve as we have COULD still have raised the 3pt capacity IF the 3pt valve is set from the factory at a higher setting so that the sytem valve trips first. It is possible that JD has the system valve set as the limiting factor at 2100lbs and thet the 3pt is at a different, higher setting as a backup in case of a clog or defect etc??

I don't think any of us have tested the 3pt lift after the modification (no need for most of us). My gains were measured ny FEL lift. I have nothing thta would warrant adding the 3pt shims IF that were needed but the procedure would be equally simple and the part is $2.

I still have a feeling the system valve has an effect on the 3pt and thta the 3pt valve COULD be an additional safety built in to the system. If the 3pt defaults at he same or lower pressure than I am dead wrong and you need to add shims (parts # 7 &8 )right to the 3pt.

We could use the original posters help?

All I know is my tractor lifts itsef to full height easily with the FEL w/o using curl now. It would not do that before. My 3pt capacity is still unknown however.

Mark_D · Nov 27, 2003

I was told by the service department at my JD dealer that adding the shims would increase the relief pressure for the whole system, including the 3PH. I know the factory specs for the 3PH are somewhat low compared to other brands, but I have no complaints about the lift capacity of mine. It will lift a very large disk (actually too big to be using w/this tractor) as well as other heavy items. I was plowing w/it once and the plow caught on a root. I lifted the 3PH and it pulled down so much that the tractor gained extra traction. It would've killed the tractor had I not hit the clutch.....it has plenty of power.

The loader is a different story. I have the 419 loader which has even lower specs than the old 70 loader did. As I said before, two packs of shims made a big difference....then I looked at a guage and got scared. I took one pack out and that left the PSI at about 2500. The bucket will now lift what will fit in it.....

Magruder · Nov 29, 2003

I have to agree Rob, I have been happy w/ my 790. /forums/images/graemlins/grin.gif

nickgalyon · Oct 25, 2004

Thanks for posting the parts diagram. Several of the previously mentioned small parts got away as I pulled off the cap. The diagram and a magnet resolved that issue.

I ordered 2 packs of shims. The dealer only sent 1. He cautioned me about damage to the front wheel drive system from excessive loads in the bucket.

I installed the shims (4) that came in the package. Prior to installation the loader would not lift the front of the tractor off the ground, now it will.