[AMC-list] 1981 Spirit 6 cyl air intake trap door vacuum motor failed (more)

[gqrxzy8974@xxxxxxxx]

> If you can remove that diaphragm I'd suggest you try
> to replace it with a similar thickness of rubber.

I've thought of that, but it looks difficult because
the diaphragm isn't flat.

Without the case, just the diaphragm looks
approximately like:

              <top>

   +-+                    +-+
   | |                    | |
   | |                    | |
  -+ +------========------+ +-
                 |
     linkage to pull up trap door

 <---       about 2 inches       -->

That isn't to scale but gets you the idea of the fold.  It
will easily unfold to a cylinder (with a bit of taper like
a cone but close to a cylinder) somewhat like this:

              <top>
      |                   |
      +                   +
      |                   |
      |                   |
      +                   +
      |                   |
      +                   +
      |                   |
      |                   |
      +-----========------+
                 |
     linkage to pull up trap door

So it's easy to get to the folded areas, but it's
not flat.

The tear is around 1/8 an inch in size right on the
fold.  The tear looks in some ways like a puncture
as it's triangular (3 inside edges which match up)
and is very different to the other parts of the fold
area which just shows surface wear lines.  The rest
of the diaphragm looks fine.

> Also, you could check with one of the antique
> carburetor repair shops to see what rubber they
> use for rebuilding vacuum advances.  These are just
> suggestions.  I dont' have any experience with a

Good idea.  Google searchs for vacuum advance has
interesting information too (and some are rebulding
them).  They do seem to have flat diaphragms though.

> There is no source for replacements -- you can
> try your local Jeep dealer to see if they have any
> leftovers in their pipeline.  Part number for that
> piece is 8983501350.

Ah, a part number (none is visible on the one here).
Is this for the "TAC" (thermostatically controlled
air cleaner) vacuum motor or the "trap door" vacuum
motor, there are two...

> However, later parts books have a note that says
> you have to buy the whole air cleaner assembly
> (can no longer get just that piece).  May have to
> try to find a good used one at the pick-and-pulls
> (look at the 258-powered Jeep CJ's for starters).

It may get to that.  Hopefully I can fix or replace
the diaphragm.

> I've never tried to repair one -- don't really need
> it down here where its warm all the time.

And it's warm here in california too, however this is
the "trap door" vacuum motor which blocks off the
air intake when the engine isn't running so that
gas vapor can't get out the engine air intake.

The other vacuum motor on the air intake is the "TAC"
vacuum motor which selects outside vs heated air and
it passes a vacuum test (holds vacuum and moves).

This is a *California* 1981 AMC Spirit...

I'd guess that since it's warm here the "TAC" motor
has less wear/movement, while the trap door needs to
open each time the engine starts.

I'm going to try a repair/glue first.  I'm leaning
toward some silicone rather than the gorilla
(polyurethane).  I've dug out my decade old bottle
of gorilla glue and it's hard.  Cutting it open the
center was rubber stickly like but it's clear that
exposed to air/water vapor it gets hard not at all
like rubber.

Any suggestions on which silicone to use?

Permatex Ultra Black Silicone looks like black rubber
but it's msds says it's got lots of fillers.  I have
some Permatex blue RTV (#6BR) which might have less
fillers (cured looks almost clear). Oh, the msds
is very similar -- how can that be?

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