My new to me 7120 makes a "thump, thump" sound when the rotor stops at about 40 rpm. The rotor also makes the "thump, thump" sound and shakes the combine when you first engage the seperator. No other noticeable problems.
The slow down thump is a brake in the gearbox engaging. It first grabs about 40 rpm, then grabs again to bring it to a complete stop. Once the rotor is stopped, it seems to let go completely as you can then rotate it by hand.
Not sure what exactly is going thump thump when you start the mechanism, but that's normal as well. Probably something to do with the hydraulic motor starting the rotor spinning, then the clutch engaging to add geared power. All my machines have always done that.
I accidentally engaged the mechanism at full throttle once while trying to deslug. The rotor didn't do anything of course, but the rest of the system had quite a shock. Don't recommend that! I'd have thought the computer would have prevented the system from even trying (seems happy to complain that I'm in road mode, for example!).
I always wait a second or two after engaging separator before throttling up. Allows the rotor to be sped up with out doing the thump shift thump thing without a bunch of torque on the system. Not sure if it actually matters but it sounds easier on the machine.
Just as a caution, if your running high rotor speeds, it takes a while for the rotor to actually stop spinning and the brake to apply. So don't go peeling rotor sheilds off and sticking your hand in anyting until your sure it has all stopped rotating. A good visual check you can do is see if the shaft fom PTO to Rotor gear box is spinning or not. If it's not moving the rotor isn't either. Or simply wait for the brake to apply, you'll hear it standing beside the machine.
This is all normal. First year with new to me 8120. Looking at rb this fall noticed and asked friend/recently retired case salesman about it. 2 different clutches engage during start up. You will notice rotor speed picks up at same time you hear both thumps. Also when disengaging you will notice rotor speed slows up slowly then you hear thump at 40 rpm and it goes from 40 rpm to stop. How it's designed. Said he's been asked that too many times to count
At the header school they explained how it worked but also every now and then go into the calibration screen and do a rotor calibration. It calibrates the clutches. Mine was pretty abrupt sounding till I did that and now the thumps are smoother. Not a bad design I spose beats trying to start that big heavy rotor in one Big Bang.
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