I was able to repair the solenoid, for those of you who are familiar
with the construction you might be able to follow the repair as I try to
explain First the solenoids are basically two coils one high current
that draws the plunger in and the second a low current that holds the
plunger once in place. If you remove the protective boot covering over
the solenoid there is a plastic cap held in place by two small screws.
Once the screws are removed the cap can be lifted, under the cap are the
soldered connections that connect the coils to the breaker contacts. It
is similar to the points inside your distributor. During normal
operation when the high or pulling coil energizes it pulls the plunger
in to the solenoids bore, when the plunger bottoms out it strikes a
nylon pin located in the center of the bore. Upon striking the nylon pin
it pushed it backwards or to the rear of the unit. This backward
movement then pushes against the contact breaker causing it to open the
breaker gap. This is the switching mechanism that allows the pulling
coil to switch to the holding circuit. I hope this all makes sense for
it is my best explanation to how the solenoid works.. Buy measuring the
different contacts you can measure the individual coils to determine the
health of the solenoid. You should have readings on one coil of .44 ohms
and 11 ohms on the other coil. My measurements were as indicated.
Now to the repair; First of all I polished the plunger to remove burs
and potential drag. I then polished the bore of the solenoid. After
removing the plastic cap and exposing the contacts I noticed that the
nylon pin had become over heated and had melted. This melting diminishes
the ability of the pin to open the breaker gap once the plunger is
engaged. I carefully lifted the breaker contact using tweezers and
removed the nylon pin. Once removed my first thought was to make a new
pin by turning one on the lathe. However the pin is so thin it would
flex while turning. So I decide the only thing to do was to modify the
original pin. I was able to chuck the pin in the lathe exposing only the
end of the pin; I drilled the center and tapped the pin. I found a 6-32
nylon screw and threaded it into place. This provided the additional
length I needed to allow the plunger to open the breaker gap once
engaged. I reinserted the pin, I re-bent the contact back into the
correct shape and correct location. I then re-flowed all the solder
connections and measured the coils resistance. Reassembled the solenoid
and tested it using a 12v power supply. Electrical circuitry is not one
of my fortes so I enlisted the help oh one of our engineers. He assisted
me with all the necessary testing to insure the unit was working
correctly. Prior to installing the solenoid back to the overdrive I
applied a small amount of lithium grease to the plunger and the solenoid
bore.
The other mod; if you have ever replaced on of these you know that
access to the bottom screw is nearly impossible. The first time I tried
I spent two hours on my back under the car using a very long screwdriver
and flash light. Not this time, I located a scrape piece of octagon rod
about five inches long I turned down about a half inch and threaded it
to a 8-32 screw. I could then insert the rod into the bottom hole of the
solenoid and turned it into place using a < in socket.
Once the solenoid was installed I adjusted it according to the shop
manual making sure to have the correct gap between the adjusting nut and
the adjustable stop.
I connected the wiring and applied power to the unit, I repeated the
switching several time and it never failed. After engaging the unit many
more times decided a test drive was in order, so far so good.. I
hopefully prolonged the life of this solenoid for a while however I will
obtain a spare for the shelf.
Thanks Dave, Michael, Joe, Fred and Randall for all your input.
Ronnie
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