B-421 Duplex jams on landscape. Portrait does fine

[Pocavon]

Hi, everyone
I have a B421 that jams when duplexing landscape orientation only about every 30 copies or so. Its frustrating because I have to run so many to get the malfunction. From tray 1 portrait duplex , I can run as many as 120 copies. But running landscape, I can hear the paper "crackling" then it jams . I have checked the paper path guides and baffles, replace the feed, sep and pickup rollers. I'm thinking next to replace the ADU clutches but I dont see how its able to feed portrait if they were bad. I'm also looking at the drum claws and the Trasfer/sep unit. Anyone ever had this before?

[Downunder]

Yes, change both ADU Clutches.

[mo0651]

I would agree that I find it hard to think the duplex clutches are bad if you get that many copies between failure. Does the lead edge of copies shift at all?? I think we have had more issues with the registration clutches than with duplex!! I would watch thru the vents on the duplex as it runs, paper should stop at the same spot every time.