Cherokee Strut Lower Strut Seal Replacement Report

Well, did my first seal swap on the 140 on all 3 legs. Took me and the
wrench about 5 hours total. Completely slimy, dirty job. Remember, I
worked in my father's body shop as a younger man, so I am no stranger to
being filthy. This was worse. Being dirty WITH oil/grease involved is
way worse than just being dirty from sanding dust and dirt. Completely
forgot to take pictures. Sorry about that.

To start, you need new seals, scrapers, etc. I bought the complete seal
"kits" from Chief Aircraft. You get a nice bag o' parts for each leg.
What seemed a shame was, these kits were for a "complete" rebuild. They
also included seals for several different models of Cherokee. Since a
bottom rebuild only used 2 or 3 of the 7 or 8 seals in the kit, you had
lots of extra parts. I just gave them to the wrench for his stock. I
also bought new valves. The seal kit has the new crush rings for the
valves (seemed odd that the valves did not come with new rings). The
wrench advised that these puppies don't seal correctly every time. And
the crush seal is a one time deal. So, if one does not seal and you have
used your one and only crush ring, you may be walking home. His advice
was that, if they ain't leaking, leave them alone. Generally, the cores
contain all the necessary sealing stuff. So, if they leak, a new core
will usually seal em' up. I agreed to leave them alone.

Working at the mechanic's place with the entire plane up on jacks is way
easier than trying to do them one at a time (with the other 2 legs on
the ground).

Once the 3 legs were relieved of air and oil, they are "freed" from the
beast by disconnecting one of the torque links. On the mains, I chose to
disconnect the bottom link that incorporates the brake line bracket.
That way, all you would deal with is the strut tube itself as the links
would be left mounted to the bird. Also, if you disconnect the middle or
top link, you have to undo the bottom link anyway to free the brake line
and caliper. I also disconnected the nose gear lower link.

Getting the snap rings out on the mains are a REAL wrestling match. The
snap rings are not of the type with the eyelets, rather they are the
kind with the ends bent (almost) 90 degrees. Once you have a grip on the
ends and squeeze, it is a real bear to work them out. They are pretty
"robust". There is a spacer ring above the snap ring that is split. If
you find the end and work it a bit the spacer will "spring" closed
slightly and remove easily.

The nose gear snap ring is of the eyelet type, but the original (circa
1974) rubber scraper is right in the way of compressing the ring and
removing it. For the nose, once the snap ring is removed, the gear
fork/tube drops out with an inner assembly that holds all the seals.
Conversely, on the mains, you work upside down getting out the various
scrapers and seals.

Installing the main seals, scrapers, spacers, and snap rings back in are
a lot easier than taking them all out. The nose gear has the main "quad"
seal stuffed in the groove along with a leather "backup" seal. Install
the leather one first with the smooth side facing the quad seal, and
then the quad seal. Any other order won't work. The service manual does
not mention any of this. The nose scraper rubber needs to be cut to
size. CUT IT 3/8 inch TOO LONG. I did and it JUST FIT. Another little
tidbit the service manual fails to mention. By the way, the new design
of the scraper ring makes it so that it does NOT interfere with getting
at the snap ring. Made it a lot easier to get the nose snap ring back in.

Once the struts are all together you push a hose onto the air valve stem
(valve core removed) with the other end in a can of fresh 5606. Raise
the strut slowly with an official, FAA approved, calibrated, 8 foot long
2 X 4. lower slowly to draw in fluid (you may have to slap or lightly
fist the tire to get it to drop). Compress and extend about 6 or 7 times
or until the last 3 or 4 inches on compression shows no air in the hose.
Remove from the fluid/hose and let it drop completely before filling
with air. The object is to fill the strut completely with fluid when it
is completely compressed.

Replace the valve cores. You can use a nitrogen bottle, strut pump, or
little 12v compressor that can do at least 200 psi to refill the beasts
on a Cherokee. The mains take about 190 psi unloaded and the nose takes
about 120 psi or so. Some have strong opinions about using air. Mine
have been riding on air for 12 years. The bores and strut legs showed
absolutely no corrosion. But, we did not take the top end apart. So, the
nitrogen fanatics may have the last laugh some day.

Taking the beast over to the runway at the wrench's place involves going
across his bumpy grass and up onto the pavement. The runway also has
some "personality" at his airpark. So, the newly rebuilt legs got a good
initial workout. What a remarkable difference when the struts actually
move up and down rather than sticking and transferring the bumps into
the airframe! It was also cool to see a distinct ring of oil where the
strut would bottom as the scrapers and seals actually did what they were
supposed to do (namely, scrape and seal).

So, how was the "experience"?
I usually prefer to perform all service work on the beast myself at my
wrench's place under his watchful eye. But, this is one job I would have
probably turned over to the local boys. I used to do a lot of work on my
own cars too. But, with age, I have come to appreciate the local
mechanics to do exhaust, suspension, and coolant related repairs because
I have no desire to do that nasty work. Strut seal replacement appears
to fall into that category. Unless the mechanics wanted to charge more
than about 2 hours labor for each leg, it just did not seem worth it to
do it yourself.

Good Luck,
Mike