Re: Mystery Rattle

["Jay Mackro" <jmackro@domain.elided>]

Stacy Gary had asked:

> I have a mystery rattle around the catalytic convertor at certain rpm's,
> like
> around 2500-3500, and especially when I step hard on the gas. I'm
> assuming my
> 78 Spider has a catalytic convertor--it could be something else, though,

As others have suggested, it could be the cat itself, or it could be the
heat shield above it.  However, another alternative is the sheetmetal
heat shield that is tack welded to the down pipe between the cast
iron exhaust manifold and the cat.  I have a '77 spider, and its downpipe
has such a shield - what purpose the thing serves is beyond me!  This
is the style of exhaust where the cast iron manifold is one piece, and
has a 4 bolt flange.  While the exhaust tubing lasts virtually forever 
(at least out here in the salt-free zone), the shield is made of lighter 
gauge metal, and the spot welds will fatigue with time.  If you remove 
the down pipe, you may find that the heatshield (which surrounds the 
two tubes, with about 1/8" clearance) is cracked, some of the welds are
busted, and as such is prone to rattling.  20 minutes work with a
hacksaw and chisel removed the heatshield from my front exhaust
section, and cured an annoying buzzing rattle that sounded a lot like
what you describe.

Regards - Jay Mackro, San Juan Capistrano, Calif.

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