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 | keith rose
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2001-03-04 25017
Been looking for tractors for about 3 months now. Drove a 790 yesterday with 70 loader, I am concerned that the loader and the 3 pt hitch are lite on capacity.I am also worried that the dry brakes will be a higher maintenance item, Price was 14,500 with a 513 cutter. I also looked at a 990 with 430 loader and 613 cutter and ballist box. Price on that was 19,900. Any info or experience with the 790 or 990 is greatly appriciated.
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| Jim Reichard
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2001-03-04 25024
I have a JOHN DEERE 790 with the 70 loader. I under stand your concerns , I had to unload a old bridgeport mill that weighed over 2600lbs yesterday and had to lighten it up by removing the head and ram we got the weight down to just over 2000 lbs and we were lifting it off a 18" trailer the 70 loader actually picked it up about 1/2" and that was as far as the loader would go.I had to roll the bucket back to get more height and at that point all the hydraulics were going to the loader and I had no power steering. after I backed up it was a mad race to get it into the shop because it was starting to lower and would not raise we made it. And used the tractor to slide it in place. the next item to unload was a lathe that weighed near 1000 lbs we had to lift it from its top side which almost did not give me enough height to lift it off the trailer. But all in all it did do the job . I know the 70 loader is only rated at 1400 lbs at 18" but the bucket does have quiet a bite of roll force. I'm very pleased with the tractor it a little beast . I use to have a JOHN DEERE 950 which is near the 990 in size and lifting . and it was a great tractor but the 790 has proved to me its no sloutch and i'm sure the 990 is even a step better . I paid $18,000 FOR MY 790 WITH 70 loader and #7 backhoe with R 4 tire and 4wd last dec. I hope this helps in your decision.
JIM ....
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| keith rose
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2001-03-04 25026
Thanks for the feedback Jim. Sounds like the 770 is a pretty powerful machine. Factory specs. for the loader was only 715 lbs. but you proved that it is able to do much more then that. It seems for the price and the work you where able to preform that is a great machine for the money, thanks for the feedback.
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| Jim Reichard
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2001-03-04 25035
Yes Keith the 70 loader has a factor spec of 735lbs at full lift height, but can have 1450lbs at 18" and 1230lbs at 36" . and a breakout force (bucket)of 1915lbs acording to JD tech manual TM1593.
JIM ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley 
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2001-03-05 25040
Jim: Not to detract from the impressive 790 capability described. However, I don't think it's very likely the loader was robbing the PS. I imagine the 790 has a priority valve rather than a separate PS pump, but a priority valve works the other way. The PS would rob the loader. I suspect the very heavy steering encountered was simply the heavy load. I use heavy steering as a warning that I need more rear ballast. I think some of these manufacturer specs are as much about safety as physical capability. The ratings may be suitable for worst case conditions and operator skills, and the equipment may have quite a bit more physical capability. However, you may already know these issues. I'm writing mostly for novice owners. I know that the first thing I did when I got my tractor was to order a load of gravel and started redoing the drive. I now realize that I was merrily bouncing down the hill with full buckets of gravel, with no ballast, and at risk of tipping up on my nose. I didn't know about ballast or tractor tip-overs then. ....
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| Jim Reichard
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2001-03-05 25059
Tom . The 790 has 2 hydraulic pumps 1 dedicated to the Hydraulics and one for power steering .I talked to my dealer about what happened and he said that the P.s. pump would assist the main hydraulics in surge type situations and it could cause lose of power steering. I had plenty of counter weight , I had the backhoe and bucket that weighs 1300lbs mounted and. Both R4 tires are filled 750 lbs, and an exta 300 lbs of lead bars in the backhoe bucket with it extended out about 7 or 8 feet. The dealer said the same thing about safety weight # verses what the bucket will actually lift are very different. He also commented that the state highway repair crews use this tractor and loader and have brought them in for repair with the cylinders on the loader bent in the shape of a "J". I wonder what they were doing to do that . OUR TAX DOLLARS AT WORK!
THANXS
JIM
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2001-03-06 25075
Jim: Thanks for the note. It's always good to find out something about how another tractor works. The design sounds interesting, and is something I haven't heard before. I think I'll have to ponder the mechanics awhile before I get a sense of how the two pumps might work together. ....
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| Jim Reichard
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2001-03-06 25077
The 2 pumps are driven by a common shaft . 1 in front ,1 in back .about 8" apart its driven in the middle . 1 large feed line that "Y"s to both pumps supplies its oil. the hydraulics pump is slightly larger than the power steering. Acording to my Deere dealer says there is an internal spool in the common housing that senses pressure like a releif valve but backwards compensates for needed pressure. the 2 pumps together gives you around 10 gpm . and deere specs them seperate and together in there specs for that reason. He says its why deere has the most flow and lift in there class with out costing the customer a ton of money.
THANKS!
JIM ....
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 | Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York
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2001-03-06 25080
Jim you sound like a JD salesperson! Check your spec's and you will find out different. ....
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| JeffM
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2001-03-06 25087
Art, what do you think the right specs are? And what specifically of what Jim said do you disagree with? I respect your knowledge and opinions, but I know that you are definitely NOT a JD fan, so I would appreciate facts to refute Jim's assertions as opposed to just casting doubt with innuendo. Makes you sound like a salesman. :>) (Just teasing you now.) ....
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| Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York
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2001-03-06 25103
Jeff you are right I am bias. I don't need to go to far but a quick call to my neighboring JD dealer service department with the Question on a 790 being: my hydralics don't work but my power steering is way faster than it was what is going on? I was informed that there are two seperate pumps, totally seperate pumps that cannot be doing what I'm saying or infering as to one helping the other. So that leaves you with just 5.6 gpm. No feed lines from one to the other as indicated. Even Deere in there literature says two dedicated pumps. That is one company that I normally say to watch on boasting. Many times they advertize ALL NEW and it is only all new to them, the competition has had it for a several years or models. There efforts have brought many new designs and styles to farming thru the years but over the past 10 years in the farming end there marketing team gets them the most nods from this industry. ....
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| Jim Reichard
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2001-03-06 25105
ART the 2 different Hydraulics are driven by a common shaft as I have indicated ( Check you I.P.B). The John Deere person I talked to was a sales person but was the service manager prior to promotion to sales( He's the owners son)So some of what he was telling me may Very much be bunk ! But john deere does spec those pumps both seperate and together on just about every sales flyer that tells about the 790.As well as 4000 series. Check John deeres litho DKA56(00-06) and DKE984884(99-06) It shows Hydraulic pump 5.6 gallons steering 4.3 and total flow 9.9. Now I'm not saying your incorrect at all .I'm saying that is what I was told .I have been operating tractors and heavy equipment for 27 year s as well as repair and its the first time I had lift but no steering until I lower the mill and bucket about 10" so If the dealer was not telling me the truth than it does not explain why it happened that way? ANY IDEAS?
THANKS JIM ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2001-03-07 25135
Well gee! I'd like to use this as an opportunity to learn something--as opposed to who has what. I'm aware that some very fancy types of spooling valves are available. However, I'm still grasping for a mechanical concept to explain how something like this would work. I'm at the level thinking 'Well let's say the hydraulic system is open centred. Everything is at idle, and there's about 100 lbs. in the HP line.' So, a control valve is operated the centre closes and the HP line pressure starts building. If it's a light load, the cylinder moves, and the pressure doesn't build much. If it's a heavy load, the pressure continues to build until the cylinder moves or the relief valve opens. I imagine that there is a drop in line pressure immediately after the cylinder starts moving. What then? I don't know. I can't figure how a second pump operating in parallel comes into play. The trouble I'm having is that pressure & cylinder diameter determines lifting power while pump capacity determines speed. Pressure isn't the usual problem during a lift, because a pump will produce enough pressure to overcome the system relief valve, which ultimately limits lifting capacity. I guess a second pump would add to speed, if it started out at an equal pressure. Or, it could add power if it started out at a higher pressure. However, I go blank every time I start thinking about the feedback that would be required to coordinate two pumps with the requirements of a load as well as PS. There's light loads, heavy loads and idle; there's picking up, lifting and sustaining loads; there's dumping loads; and so on. I suppose that assuming that the PS steering pump is a closed centre variable displacement type simplifies things a bit, but the idea seems really complex. There's pretty obviously something here. I just wonder what it does exactly. ....
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 | Murf
Join Date: Dec 1999 Posts: 7249 Toronto Area, Ontario, Canada
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2001-03-07 25140
Tom, my 'northern' neighbour, if living so close to our nation's capital hasn't given you a chronic headache I think this level of deep thinking might yet do it. I think your confusion is best cleared up this way, I'm sure you are aware that, as in all forms of energy including electricity and fluid power (including your water well) there is an inverse proportion between quantity & pressure (i.e. volts to watts). In other words as you 'load up' the pump, pressure increases, but the volume drops. In order to overcome this, some systems run two pumps, sometimes each dedicated to certain tasks, such as one for power steering, and one for 3pth, sometimes they are in parallel. In the later case, the theory is that each pump bears it's share of the load, is 'loaded up' less and performs better. Clear as mud yet? Basically its the more units working less each theory. Hope it helped. Best of luck. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2001-03-08 25190
Hi Murf. Yep, 2.5 hours west of Ottawa and it's still too close. I prefer to think of my post as a thought process rather than confusion. However, I suppose that anybody who had to read it might prefer the term 'confusion.' At any rate, the thought process did enable me to come close to what you said without actually knowing how the thing worked. I pretty much decided that what you said is the only thing that would make much sense for such a design. However, I thought it was too much thinking for one post. I figured that if a gear hydraulic pump works like a well pump (more pressure = less flow), then switching in a second pump at a fairly high pressures would help maintain the lift speed. That wouldn't be too much of a trick with a spooling valve and two open centre pumps--just connect the PS pump to the hydraulic system and disconnect from the PS. Hydraulic gear pumps may work like well pumps, but I don't know about a piston type hydraulic pump. JD does use piston pumps in some of its farm tractors. If this is how the design works, I can see some value. However, several comments can be made. First, the design would help with the speed of lifting heavy loads, but wouldn't allow heavier loads to be lifted. Second, adding the two pump capacities together wouldn't be a realistic measure of the tractor's hydraulic capacity. I believe that hydraulic pumps are rated at PTO speed and in an open centre condition. The PS pump would come into play only when the hydraulic pump was already operating at fairly high pressure and reduced volume. In such a condition, both pumps would be operating at less than speced capacity. Only one pump would be employed with light loads and dumping operations. It is an interesting design though.
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