Bizhub 421 duplex copies jam

[jeffreyclay]

One original in the doc feeder, ask for one duplexed copy...fine. Same for 2 copies but when you ask for 3 copies or more it will jam. It jams in 2 different ways depending on the original's orientation. Portrait original usually causes a jam at the fuser with 2 sheets feeding together. One sheet is about 3 inches ahead of the other. Side 2 (which is the first side to be printed is the side its creating) Landscape originals seem to cause a jam at the loop rollers with a new sheet of paper colliding with a sheet moving from the turnover.
I've flashed with latest firmware, verified all sensors in ADU and turnover paper path, pulled the fuser and examined it, all gates are on their pivot points and move freely, the flag above the fuser for the exit sensor was checked for position. I do know what else to look for. Has anyone seen something like this?

[hosman80]

i had that problem once and it got fixed when i replaced the duplex unit clutches cl7 and cl8

[suomi]

dirty

clean the duplex unit clutches

[dogsbody]

It was originally a 420/500 problem. They put too much grease on the ADU gears to keep them quiet and the grease gets into the clutches.
If you clean the clutches (this almost always works for me) clean every surface of the clutch not just the clutch plates, also clean any excess grease from the gears. If you replace the clutches make sure you remove the excess grease so you don't have to go back again.
Cheers.

[copytechman]

Same here, wash the clutches! Worked like a charm for me!

Regards!
A.