Question re: JD 790 with #7 JD backhoe--

[sixdogs]

I have a JD 790 with JD backhoe--TLB-- that I bought last winter. It has 100 hours on it and works like a dream. I have had a number of tractors over the years but this is the sweetest little tractor I have ever owned.
This is a "sleeper" piece of equipment in that it does far more work than one would suspect. The 790 is near perfect and the #7 backhoe has to be one of the handiest backhoes around.
I have been moving some 12 ft cedars--northern white--and they move pretty easy so I have been letting the tractor idle at 1300 RPM while doing this. It's easier to control the boom at the lower RPM and i am less likely to damage the trees this way.
I do hear some minor squeals I believe to be pump cavitation since I am running at such a slow RPM. Is this OK? Am I hurting anything?
I would post a photo but they all look alike. If anyone wants one I will.

 

[RobS]

It is a nice combo, isn't it? I just love my 790/7! I'd say the squeal is normal but I try not to keep the load on when I hear it. It's probably the relief valve, not cavitation.

And hey, we always like pictures!

 

[Ken Cunningham]

The owners manual for my 1070 has a low and high rpm range listed for normal operation of the tractor. If yours has this info then I would not run under that low rpm range. Im not at the house right now to look at it, but im pretty sure its more than 1300 rpm as the low range.

Its my understanding that running at low rpm is bad for the injectors, but im no expert. Maybe someone with more experience on this could chime in?

 

[gordon21]

Are you sure the squeal is from the hydraulic system? Could it be a lack of grease somewhere? I ran my #7 hoe at about 1500RPM 90% of the time. Only when it was straining to move something did I bump the RPM up to 2600 to get the extra power. It sure is quieter at 1500rpm, especially with earmuffs on.

Try 1500 rpm and see if that solves the problem and double check for grease at the bottom of the main boom itself and the two side cylinders.

 

[sixdogs]

No, it's not grease--I'm the king of proper greasing stuff. As the prior post mentions, it probably is the relief valve straining when I work it too hard. I'll bump up to 1500 RPM or more. I do love what this tractor-loader-backhoe will do. Thank you.

 

[RobS]

If it is your relief valve, you will probably still encounter it even at higher rpms. It's just doing it's job of protecting the rest of the system when the cylinders get overloaded. Just don't hold the pressure on too long when you do hear it.

I just remembered (my hoe has been off all winter now). There is a swing crossover relief valve seperate from the main tractor hydraulics. It's down in the vicinity of the swing cylinders. I hear that one a lot. Just changing swing directions will pop it off for a quick squeal as there is a lot of momentum in the swing.

 

[sixdogs]

Rob S

That's the slight squeal I hear. Sounds like no big deal so I will keep moving trees and having a wonderful time. What a great T-L-B combination. I love it.