PSA- check your power steering pump filter

E28 technical advice asked and given! Troubleshooting, modifications and more.
tn535i
Posts: 5418
Joined: Jul 14, 2006 1:30 PM
Location: Middle Tennessee

Re: PSA- check your power steering pump filter

Post by tn535i »

If I had a new filter I could measure permeability and optically measure pore size at work. I doubt this media is fine enough for sophisticated pore size measurements we can do. Perhaps I can clean up the newish one from my M6 and do this. Anyway, that would tell me(us) what size SS wire mesh to use to just wind a filter of several layers of mesh. Then you could silver solder or epoxy the start and ends and you would have a lifetime clean-able re-usable filter. More expensive, but given the way things are becoming with our cars probably a good approach.

I would be curious to look at a really nasty one under the SEM or scope and see just what size junk it collects? Although I suspect the ones that bellow have their resin system failing. The color tells me it's phenolic but I'm not sure if the fibers are cellulose or glass or a combination. And there are variations on phenolic. Many manufacturers have stopped using the old variations with more free phenol and formaldehyde and use a newer type. The new stuff gets softer with temperature and moisture, meaning, newly made filters might be not nearly as robust as the old stuff. So another vote for wire screen filters.
Mike W.
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Joined: Feb 12, 2006 1:00 PM
Location: Covid 19 Life during Wartime

Re: PSA- check your power steering pump filter

Post by Mike W. »

The distorted filters suggest there is a problem with at least some of them in time, but I changed mine because the P/S pump was whining more and more in the AM and it was worse with a new filter than with what I think was the original filter at 300K. Color was different but shape was the same. Of course it turned out the bolts on the pump being loose was the problem with the pump cavitating, not the filter, but a new filter made it worse. YMMV.
tn535i
Posts: 5418
Joined: Jul 14, 2006 1:30 PM
Location: Middle Tennessee

Re: PSA- check your power steering pump filter

Post by tn535i »

Old resins were dark brown and the newer types tend to be more yellow/brown. That is what I think I'm seeing in the pictures of parts. As with any filter lots of variables in the manufacture and would not surprise me if things transitioned from somewhere they way they used to do it, to a newer process and supplier. When that happens the porosity and such of the media itself may have changed. It's a legacy part BMW no longer cares about.

There are still people who make such phenolic fiber tubes. http://rmfiltration.com/
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