Anyone notice the brushes on K machines are lasting about 6000 hours. The originally installed brushes lasted a lot longer. My machines are 2003 vintage.

Yes, I think this is correct, also if they do make it to 8000 hours alot of times you have to replace the pump head. They to are not what they use to be.

The brushes that are installed by the Dunkermotern factory are much longer, 30 to 40 %, than the replacement brsuhes that you get from Fresenius. So the original deair brushes will last the 8000 hours, but the replacements probably will not. So after the first replacement the 8000 hour time is no longer a valid number. Also, if you have to turn up the DAC value above 180 to get the -24 then you are running the motor faster and you will get less brush wear because of it. On the new pump heads with the large sheet metal locking device they use a red Locktite sealer to hold the settings. Once you break that seal whatever setting you had when you did the cal will not hold unless you apply some kind of sealer like calking or quick setting epoxy. That may be why you think that the pump heads are bad. Fresenius has never supplied the longer brushes and the only reason that I can think of for that is maybe they are afraid someone might still try to use the longer brush in an old motor (pre 1998?) that required the short brush. The old motors had the composition brush plate and the new ones have the ceramic plate. Also, and I have no facts here to back this up, but my opinoion ios that they use a long hard brush in the flow motors out of the factory, not a soft brush. Between that and the lower speed of the flow motor that is why those brsuhes last so long. As to pump head reliability, they are much more reliable now than they used to be. The old heads had metal gears in them, the new ones have nylon, and they last longer.

Nice response Ktech. Thanks for the info, was wondering why the factory motors where lasting longer then the brush replaced motor.