Date:         Wed, 23 May 2007 21:10:09 -0500
Reply-To:     Matt Roberds <mattroberds@COX.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Matt Roberds <mattroberds@COX.NET>
Subject:      Re: Syncro propshaft vibration mystery
Comments: cc: Richard A Jones <jones@COLORADO.EDU>
In-Reply-To:  <20070524011209.TNOM2832.eastrmmtai109.cox.net@eastrmimpi05.cox.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed

> From:    Richard A Jones <jones@COLORADO.EDU>
> Date:    Wed, 23 May 2007 12:57:58 -0600
>
> I need help finding the source of a vibration in my '87 Syncro.
> [...] Removal of the propshaft eliminates the vibration.

Is there a big chunk of mud or goo stuck to the propshaft or one of the
drive axles somewhere?  OK, OK, you've been under the van enough by now
that you probably would have seen it, but you never know.  (Step One of
the "engine turns over but won't start" in Muir is "Is there gas in the
tank?")

This may not be possible in a Syncro, but I know that on mostly older
American rear-wheel-drive cars, it is possible to clock/index the
driveshaft with respect to the differential flange and/or the
transmission output flange.  In other words, if there is a flange with
four bolts, you can bolt up the driveshaft to the flange in any of four
ways by rotating the flange.  This is sometimes done to fix vibrations
in the driveshaft.  The usual procedure is something like: clock the
driveshaft 180 degrees and go drive; if the problem is gone or livable,
you're good; if it didn't improve much or got worse, clock it 90 degrees
and try again; then clock it another 180 degrees if that didn't work.

You may be able to have the propshaft balanced off of the van just to
eliminate it from the equation.  In most big cities, there is a shop or
two that does nothing but CV axles, driveshafts, propshafts, etc and
they can probably do the balancing.  A 4x4 shop might also be able to do
it.

A DIY option might be to get ahold of some of those flat metal weights
that the tire shops use to balance fancy rims, where people don't want
the usual lead weights clipped over the lip of the rim.  Then experiment
with those weights and maybe some duct tape to see if you can balance
out the propshaft yourself.  This will require a _lot_ of driving,
stopping, fiddling, driving some more, etc.

Matt Roberds