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Discussion Starter · #1 ·
The rotor speed jumps up and down and we cannot combine until we fix it. The combine vibrates and the corn gets ground up. What is wrong and how do we fix it? We are going to ask the dealer today but any insight is appreciated. Is it a module or pump problem and how do you find it?Thanks.
 

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check the speed sensor on the front of the rotor.. I had a mounting bracket get loose and it caused the rotor speed to jump around.. the computor mod should be flashing a code check it.. the dealer will be able to tell u what the code means..
 

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Discussion Starter · #3 ·
We ordered a new sensor this morning hoping it is that but nothing looks amiss. We will try to install a new one when it arrives. It is a real pain to get at. We will need a contortionist to install the new one, hopefully tomorrow. At least it is something simple we can try. Thanks for at least a confirmation of a possible solution.
 

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yup I've replaced the rotor speed sensor a few times now on our 8780. Feeder housing all the way down, I use plastic tie to hold up belt flap and suck in the gut its tight. I had upgraded the sensor to standard two hole mount away from threaded cylinder because new one was 30% of cost but make sure u grind paint off the teeth if its still not working. Good Luck
 

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Discussion Starter · #6 ·
we finally got the new sensor installed but the only speed it registers is 580 when running or zero when it is stopped. The crazy speed surges up and down are gone and the speed changes as you adjust the rotor but you have to guess when you have the speed you want. We combined one round before it started snowing again so we are stopped again but we think we can keep going if the weather ever cooperates. Any idea how to correct the display? When we first tried it there was no display at the sensor setting that was recommended and had to lower it. Could it be too low now or is there another problem? Thanks
 

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I'm sure there is a computer mod that controls the constant speed system.. a 3''x7'' black box, I don't know where they are in a 8780.. ask your dealer he should know or will be able to find out.. the mod has a set of lights that give status and will show codes..
 

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Discussion Starter · #11 ·
The dealer put in a new power wire for the magnetic clutch because the voltage to the rotor sensor was too low for the sensor to work right. We were able to run the combine but other sensors are not working properly so we will need to figure out the mess when we get a chance. The fan sensor, air cleaner and hydraulic oil sensors are all not working right. There may be some we don't see yet. If it stays too warm and wet I will have to try and figure it out. We plan to try and check voltages and possibly added a ground wire or two but it is guessing at the moment. Anyone run into a similar problem? Thanks.
 

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Discussion Starter · #12 ·
We had the dealer out to try a second time and this time they bypassed something in the cab. The jumping up and down stopped but we were having trouble adjusting the machine speeds like fan or rotor speeds. We finally figured out that the bypass somehow causes a reverse current flow and to increase a speed we now turn the knobs down and to decrease the speed turn the knobs up. The hydraulic oil reservoir alarm still goes off occasionally but everything is working so we can live with that.
 

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Sounds like a problem I heard about on a 9790. They had the pump and motor apart changed the speed sensors checked the grounds but it was a electrical plug behind the engine that had a pin pulled back. Double check all the plugs is where I would start.
 

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Discussion Starter · #15 ·
We did need an alternator rebuild and that solved some of the sensor problems-ie low batteries - but not the hydraulic oil or the rotor. The new wire added after that did stabilize the rotor reading but the control works in reverse as noted above.
 
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