Bathtub cold stem valve leaks after replacement, a month later. Washer keeps failing. Any suggestions on why?

[LodgeC]

I've replaced hot and cold stem valve with Danco 11B-1H/C (this fitted old one style) and it came with the seats, washers and o-rings). And I also replaced the diverter. Hot stem and diverter are still working fine even a year later.

I've had to constantly replace the washer in that cold stem due to it constantly failing, for over like a year now it seems. I've even replaced the 1/8" washer with a 1/4" neoprene heavy duty one (thickness rating) to see if that washer lasts longer. That washer lasts for around 4 months before leaking again. I've reseated the seat a few times to assure it was seated right. Teflon taped threads. Used another brand new stem, with washer. Used different screws for washer. Tighten down back nut (behind o-ring); don't know what the nut called.

The old valve stem lasted for decades, before it even started failing. So, it's definitely a frustrating situation to install a new one and it can't last that long.

What's some possible solutions on what could be going on?

 

[Rocknroj]

Since you have no replies, I offer my $.02..

Wrong part perhaps? You should probably identify the make of the valve that you are trying to repair to get any help. And of course leak meaning what, not shutting off, leaking from the stem??? I have heard new stands for 'never ever worked'.. maybe specs not quite matching the old part. I gave up trying to fix old valves long ago and instead put the effort into replacement with a better and more serviceable product..