PDP-11/44 gas struts

Alan Frisbie Flash688 at flying-disk.com
Thu Dec 30 14:39:29 CST 2021

On 12/25/21 3:37 PM, I wrote:

> I made a wild random guess and ordered two of the 30 pound struts,
> which should be delivered Wednesday (12/29/2021).  The 40 pound
> ones have a seven week lead time, and a pair of 50 pound ones seem
> way too high.  When they arrive, I'll let you know how well they work.

The 4138T55 30-pound struts arrived, and I have learned a few things:

1. The ball connector ends on the DEC struts have 5/16"-24 threads, but
the 4138T55 struts have 5/16"-18 threads.  Therefore, you need to swap
the ball ends.  This is actually the method that DEC recommends for
replacing the struts and is described on pages 5-5 to 5-7 of the
PDP-11/44 System User's Guide (EK-11024-UG, available on Bitsavers).

2. 30-pound struts are not strong enough.  They improved things a bit,
but it still takes a lot of effort to raise the box.  I have ordered a
pair of 50-pound struts and will post an update when they arrive (next

3. The 4138T55 struts from McMaster-Carr are made by Suspa, Inc. in
Grand Rapids, MI.  According to their design guide, the rod part of the
strut should be installed lower than the body.  This is the reverse of
how DEC installed them, which may be why they don't last.  When the new
struts arrive, I will see if they can physically be mounted that way
(I think they will), and will let you know.

I'm learning a lot about gas struts these days, as the ones on the cover
of my sand blast cabinet also failed after only a few months and the
seller (Eastwood.com) can't supply replacements.  Yet another learning
experience!  :-)

Alan Frisbie

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