Re: 5KCST Harmonic vibration-help

[Don Hoefer <hoefer@jaxom.eng.pko.dec.com>]

Chad,

> My '87 5k Tq recently had both 
> motor mounts replaced but none of the exhaust was moved in doing this
> repair. Everything seemed fine and then about a week later I noticed that
> at exactly 1800 rpm, there is a harmonic vibration that came about.

I don't know how many models this applies to, but my Bentley says that
the exhaust supports must be tightened when the system is hot.  Other-
wise a rumbling sound may be produced.  These systems have rubber
hangers on the rear (so no adjustment there) and are hard mounted with
a bracket on the transmission (tighten here).  Changing the engine
mounts would change the position of the engine.  Were the engine
mounts tightened when the engine was idling?  If not, the position of
the engine could be a little "off".

Don Hoefer
'82 Coupe