New to me JD 790D LC

Howdy!

Been away from the forum for a while, bought a quarter section of raw land recently and just got a 790D to clear etc with.

She's a project but overall in decent shape, it's a very basic machine (no electronics) which I like!!

I'm wondering if anyone out there has a wiring diagram?

Going to buy a service manual eventually but just need to get the wiring sorted for now.

If anyone is interested in some pics just let me know and I'll take some.

Thanks!

Ran the old girl for a couple days piling and burning and found every issue with the machine, spent a couple days last week cleaning and washing while it was above freezing, now the"fun" begins..

I was at a shop in town buying a VHF radio for my pickup, he happened to have testing/service manuals and sold them to me for a great price! If anyone needs any info for a 790d or 892d Just send me a PM.

The issues I'll be dealing with...

Swing drive pinion seal tore up.
After draining 5gal of gear oil from the grease pit I found and retrieved pieces of what looked to be a mangled snap ring... Pulled the swing drive yesterday, sure enough the snap ring is missing off the pinion and it tore the seal when it got chewed up... Going to pull it down and reseal drive and motor.

Other issues I'll be tackling shortly..

Head gasket leaking coolant externally, famous 6466... New gasket/head bolts and elbow grease will cure this.

Otherwise the engine starts and runs great with no other issues.

Dumped all the fluids and replacing all filters.

Need to replace a few hoses then will be setting all the pressures and synchronising the pump regulators.

Will be repacking cylinders as need be, the fella I bought the manuals from just so happens to have a cylinder bench! Wish I would have met him sooner!!

Anyway that's pretty much the scoop, I'll take some pics so everyone can enjoy.

ALWAYS nice to here a success story.. when things go your way..!!!
Have fun & keep us posted.. BTW> whats all that white stuff?? Its 80* here in South Carolina..
I was out in the yard for 2 hrs this morning & got sun burnt.. Lol

thepumpguysc said:

ALWAYS nice to here a success story.. when things go your way..!!!
Have fun & keep us posted.. BTW> whats all that white stuff?? Its 80* here in South Carolina..
I was out in the yard for 2 hrs this morning & got sun burnt.. Lol

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I know what you mean, getting sun burnt in South Georgia in the winter, there just is something not right about that.

GregsHD, nice machine, hope it serves you well...

Thanks guys.

The only time I've had a sunburn in winter was from the reflection off the snow!

Been pretty mild this winter, had a couple weeks of -30c but no big deal!
Last week was +10c now it's hovering around freezing during the day.

Pulled the swing drive down as far as I'll go, I've heard it can take over 100tons to push the pinion out and the biggest press in town is good for about 80ton...
Bearings are in nice shape so no reason.

Here's the motor dangling and recovered debris.

Forgot the seal pic, there was still a piece of the snap ring jammed in the seal when I took the retainer off, everything looks great otherwise!

Good deal! Have fun!

I've got a 590D on my property right now...for an old beater, it sure is a nice machine to run! Gotta love old simple stuff.

Made some headway over the last few weeks.

Managed to drain 260l of hydraulic oil out of the system, took 280l of fresh zinc free ISO46 to fill her up, I don't have access to a filter cart so I filled the system through the return filter.

Swing drive turned out nice, worst part was slopping in 3/4 of a pail of sticky open gear grease into the belly of the beast whilst the ol' lady rotated the house for me.

Only a few hydraulic leaks left, worst is the LH pilot valve making a mess in the cab, also it must have broken or worn springs, it doesn't center itself which confuses the whole system, need to get it in the sweet spot to track straight, same for the auto idle to work. I may just replace the valve with a good used..

Head gasket is next on the list with the couple hydraulic leaks. Also need to do some welding on the thumb and some bushings in the Q/C.

Should be good enough for my projects after that!

I've got about 40ac to stump and rake, 20ish huge "slash" piles to pull apart and salvage logs for firewood etc. (The logging outfit hid lots of good wood, they wouldn't even burn the way they piled them anyway!!) Some roads to build, a 30+ac hay field to create, and a nice little gravel deposit to develop.

If the old girl survives all that (knock on wood) I may sell it to recover some of the investment, I got the machine for $12600 delivered and so far about $2k in parts/oils, I think I'm doing alright so far, I figure its a $20-25k machine once all the repairs are complete with 2 heavy duty buckets and a rake?

It appears to be an old road builder, heavy shop made steel gaurding, rock gaurds, idler stiffeners, top roller supports, and seen some boom breaking abuse in its day. Perfect ranch machine! Haha!

I'll take some action pics once I get going, It's break up right now can't do much until the ground dries up a bit.

Greg

Made some headway on the ol' hoe, stopped more leaks, repaired and loomed the wiring, welded assorted cracks, rebushed the Q/A and thumb, head gasket quit leaking externally so I just did the exh manifold gaskets for now. Cleaned out the cooling system and changed out the rest of the oils.

Put about 60hrs on it over the last two weeks and she's running sweet, need to repack the boom cylinders next and replace one sprocket ( p/o replaced one and included the other new sprocket with the machine)

Here's a couple pics showing the amount of salvageable wood in these "slash" piles, close to half each pile are solid short logs!

I found a PDF 6466 service manual, it explains all the different head bolts used etc. When I do it I'll be installing the *special* torque to yield bolts.

But for now I ain't fixing what's not broke!!

Hi GregHD! I've also just purchased a 790D and was wondering if you could share any pdf you may have on this machine ? Thanks -Chris

mathatech said:

Hi GregHD! I've also just purchased a 790D and was wondering if you could share any pdf you may have on this machine ? Thanks -Chris

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I sent you a PM.

Greg

Hi Greg
Just bought a 790D and the electrical is a mess and does not work, if you have any wiring diagrams that would be great, just started using it to clean up some land, found 2 other issues I need to fix, the boom cylinders both leak till they get warm and the hydraulic oil cooler is not getting any flow, any thoughts or suggestion would be welcome.
Thanks John

Hey John,

I've got a complete fold out wiring diagram/schematic, I can take pics of certain sections of it if you need. Here's some pics of several individual. diagrams.


Sounds like you either have a severely restricted hyd cooler or a problem with either the cooler bypass valve or the cooler restriction valve.

Rest of the pics. Hopefully they're not too blurry!

GregsHD said:

Hey John,

I've got a complete fold out wiring diagram/schematic, I can take pics of certain sections of it if you need. Here's some pics of several individual. diagrams.
View attachment 207990 View attachment 207979 View attachment 207980 View attachment 207981

Sounds like you either have a severely restricted hyd cooler or a problem with either the cooler bypass valve or the cooler restriction valve.

Click to expand...

Thanks Greg
Had a look at your wiring diagram, but does not look right, I have a 25 to 12 volt converter in mine, I see you have a thumb on yours, is there an extra spool on the hydraulics or did you have to add one?will wait for a warmer day before I trace out the hydraulic line and see if I can see where it is plugged. I had no heat at all on the cooler lines and tank was very warm, so has to be a complete blockage.
Thianks again for the help
John

The wiring diagrams match mine other than the alternator as mine has a Delco rather than Motorola. The 24v-12v converter is an add on for in cab accessories, radios etc, It may have been added to the later wiring diagrams? These are from Jan/88.

What problems do you have electrically?

Yes the main control valve has an aux spool, would need a pilot control valve and circuit relief valve cartridges to make use of it.

Greg