Need Help Troubleshooting my JD 762 Scraper

[J_Deere]

I have a 1980 John Deere 762 Scraper. It has been a great machine for precise grading. A couple of years ago it developed a problem with the elevator chain drive system. When the hydraulic oil gets warm the elevator chain looses power and operates really slow. When it first happened, I took it to my local JD Dealer and they changed out a few relief valves and $3,500 later they told me it was fixed. It worked good for a week and the problem came back. I called the dealer and they came out to the jobsite and checked pressures. They changed out anothe relief valve and it worked fine once more. The problem kept coming back and we have had the hydraulic system completely flushed and we swapped out a whole bunch of parts. No matter what we do the problem comes back. Does anybody have any experience with these scrapers? My local JD dealer really doesn't have the experience with these machines and I feel like I am paying them to learn about this scraper.

 

[Shaunrh]

I came across a similar problem on a 639D and every man and his dog had looked at it and said it was fixed.I pulled the hyd motor that drives the elevators and the cartridge was cracked and ready to fly apart.That would be the first place I would look.Hope you get it sorted out soon.

 

[J_Deere]

Shaunrh,

Thank you for the reply! I think that the elevator motor maybe the only thing that hasn't been replaced. Definately worth a look at this point!

This problem has been a real head scratcher!

 

[bigrus]

Elevator Woe's

When I purchased my 101F Wabco, the elevator reduction box was shot & in pieces so I had not much idea how fast the flytes should move. With box rebuilt the worksop manager told me the 'cartridge' looked ok but if loading begins to slow replace the cartridge (about $700 AuD) in 2006
Hope that helps. On Michigan/Clark elevator scrapers have a 'sunstrand' pump and that's the 'heart' of those machine, so check your pump too. Good luck

 

[DPete]

Does it have a 2 speed elevator? Don't know much about JD scrapers but I had a broken spring in the directional valve on one of my 623's Would have pulled my hair out if it were not for a knowlegeable shop foreman at the dealer. Cost me $30.00. If the pressures are good and the drive motor is healthy and the bypass valves are good I'd look into the control valve, could be as simple as a broken spring like I had. Puzzling why it works for a while though. No fun spending and not fixing, good luck

 

[Taylortractornu]

We had the same thing happen on our 762. We had a former JD mechanic come out and he couldnt figure it out. A friend of mine is a hydraulics guru and he told me that the Hydrostat pump and motor is a closed loop. He said the motor was probably bad. They dont filter the fluid between them just from the tank to the hydrastat. He told me to have both rebuilt. We pulled them and took them to a pump shop and had them rebuilt. Its been going on 2 years. The pump and motor is a sunstrand unit. If the motor is beyond repair a drive motor off a 715/ 815 IHC combine will work but the shafts have to be swapped. We had the problem after that thinking it was acting up one time but it was trash from the first wreck stopping the filter up. We changed the oil and filters 3 times and later just the filter. Part of our problem was the JD mechanic we hired first ddint know what was going on. He had been out there to test the pump pressures when the original motor got slow. Against my aadvice he put 2 quarters in the fitting to the elevator line o nthe pump saying he needed tp put backpressure on it. I tried to tell dad that was bad for the pump. He tried it and then pulled the line off and baoth quaters were gone. Im gladd he used quaters instead of a proper cap. he found one i nthe line at the end of a short hose. When we got back he said he had the other one. A year later I was pulling the motor off and found the other quarter. I was hot. We bsically paid the man 500 to mess our rig up. From now on I do my own mechanic work on it as JD or other Deere mechanics in the area down know the machine.

 

[bigrus]

Good help's is hard to find

We had the same thing happen on our 762. We had a former JD mechanic come out and he couldnt figure it out. A friend of mine is a hydraulics guru and he told me that the Hydrostat pump and motor is a closed loop. He said the motor was probably bad. They dont filter the fluid between them just from the tank to the hydrastat. He told me to have both rebuilt. We pulled them and took them to a pump shop and had them rebuilt. Its been going on 2 years. The pump and motor is a sunstrand unit. If the motor is beyond repair a drive motor off a 715/ 815 IHC combine will work but the shafts have to be swapped. We had the problem after that thinking it was acting up one time but it was trash from the first wreck stopping the filter up. We changed the oil and filters 3 times and later just the filter. Part of our problem was the JD mechanic we hired first ddint know what was going on. He had been out there to test the pump pressures when the original motor got slow. Against my aadvice he put 2 quarters in the fitting to the elevator line o nthe pump saying he needed tp put backpressure on it. I tried to tell dad that was bad for the pump. He tried it and then pulled the line off and baoth quaters were gone. Im gladd he used quaters instead of a proper cap. he found one i nthe line at the end of a short hose. When we got back he said he had the other one. A year later I was pulling the motor off and found the other quarter. I was hot. We bsically paid the man 500 to mess our rig up. From now on I do my own mechanic work on it as JD or other Deere mechanics in the area down know the machine.

Don't you just love "help" like that especially when you're paying for it
I just cured a fuel return line leak- fittings I was sold weren't JIC but metric, no wonder they wouldn't seal.

 

[Acivil]

I just bought a 762 A, we are having a problem blowing O-Rings on the Piston Plug on the bottom of the Hydraulic Pump. It seems to happen mainly when under a heavy load, but right now as wet as things are, ruts in the haul road are unavoidable. It is only this 1 plug, but Im wondering if anyone has had this experience?

 

[Taylortractornu]

Im not sure what pump the a has but tthe straight 762 has a 4 cubic inch OilGear pump. Its a rotary pump withthe plugs around it. Ours was rebuilt then blew seemed they took off too much reboring the pistons when being remanned at JD. It happened a few times the bore had split later we had the same thing happen 5 years later on the replacement 762 we have now. The bores were good but the check valves that the fluid feeds throug had hung causing it to over presure. Is it blowing out the oring and the thin teflon/plastic seal on the top of the plug to. Deere didnt have our pump or something so a local pump shop redid it for about 900.
Where are you located I can give you the name of our hydraulic repair shop we use. The name is Hydrauilc Equipment and its at Smithville MS
662 651 7229 . He rebuilt my hydrostat for the elevator and the motor on the elevator to for about 1200.

 

[Acivil]

Yeah, it's blowing both the O ring, and the Plastic Shield. Thought we had it fixed, but it did it again this morning. I think it must be something with that piston (or the check valve). Thanks for the info, I will post when we get it figured out.

 

[Acivil]

Bought a reman pump, installed it, filled the reservoir with AW46 rather than HyGard. :Banghead Hasn't been right since. Hydraulics will work fine for the first pass or two in the morning, then they get slower and slower until it is no longer operable. Talked with an ex-deere mechanic today, and turned up the pressure on the pump a bit and it worked better, but still not right. At one point my employees mentioned that the lock nut on the pressure adjuster was loose so I am wondering it adjusted itself out of pressure.... pretty lost at this point and ready to pull my hair out. ointhead Wondering if the wrong oil could possibly cause all of this trouble, or if I need to turn the pressure up more, or if it would be best to call someone who knows what the hell they're doing?!