Combines 7720 vibration

did ya check the cylinder bars. might have a brokin bar. we had a vibrations when the main pully on the cylinder had a peice broke out of it. somthing must be out of balence

First check for dirt clinging to the undersides of cylinder bars--this builds up unevenly. If you have chrome plated cylinder bars, you'll sometimes get uneven wear on them due to chrome chipping and this can be on 2 or 3 adjacent bars. If all that looks OK, suggest you back off drive belts on the shoe, fan and rear beater until you've isolated the problem. The center bushings on the shoe actuator arms, if worn, can mimic an out of balance cylinder pretty readily.

look at the inside of the drive belt under the seat.Sometimes a chunk can come out and cause a problem.

Check the primary couter shaft. These can bend if the combine gets slugged and is started again under full power. Had this problem with a 4420

I have never heard of that happening. I would have thought the belts and slip clutches would slip before you would bend the primary countershaft. I bet that bent shaft was a job to fix!

It could be a bad primary countershaft bearing causing the vibration.

If you have a straw chopper on this machine I would consider that too. They can be out of balance bad and shake the crap out of the whole machine.