Mixet valve issue

[Bones66]

Mixet shower valve was dripping & stiff to operate. I picked up a cartridge at my local plumbing supply and jumped in. All good until I was checking everything before turning on the water. When I turn the water control knob off and just when the control knob feels like it’s beginning to bottom out the hot/cold knob turns. At that point it seems the water control knob is bottomed out on the white plastic outer part of the cartridge instead of the seat thus it begins to just turn the H/C knob around & around. The reverse happens when you open the water control valve full open. I’ve called plumbers, visited plumbers supply shops and call good ole boys that just seem to be able to fix things. Everyone is stumped.
Sorry if my description is a bit confusing.

 

[hj]

BE sure the stem is in the fully open position before you install the cartridge. Must no be very good supply stores OR "good ole boys", it is a very easy faucet to service.

 

[Sponsor]

 

[Bones66]

I did do the the install with the valve open. Maybe I misstated my post about the plumbers & supply houses etc. They were aware of the mixet valve however they had no idea what might cause my problem. Everything went very easy during the install. When it didn’t work as it’s supposed to I suspected a faulty cartridge but it’s so simple I thought what can go wrong? There are 2 brass washers and 1 thicker plastic washers on this cartridge. The thicker plastic washer is slightly tapered but 1 of the flat brass washers fit on each side of the plastic washer thus the taper has no purpose that I could see. Although I only installed it with the taper facing the direction it was in the original packaging and the way the gentleman at the help desk said it was supposed to go. Maybe my explanation is not very good. I tried to upload an 8 second video but it was too large.
I went back to the plumbing supply house today 38 miles each direction got another off shelf but could find no external differences. I’m going to order one online and see if another valve corrects my problem. Thanks