Date: Tue, 29 May 2007 21:48:03 -0600
Reply-To: Richard A Jones <jones@COLORADO.EDU>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Richard A Jones <jones@COLORADO.EDU>
Subject: Re: Syncro propshaft vibration mystery
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My request for help with my propshaft vibration was answered by
lots of emails from over a dozen different people. I want to
thank all of you; all of the replies were valuable, either with
suggestions, information I had forgotten, or to point out how
I had not clearly described some things--or the error of my ways.
Rather than reply to each one, I'm going to summarize and clarify
and describe what I have learned so far.
Some pointed out the problems of rebuilding stock VW propshafts;
I neglected to state that both my "known good" ones are slip-
yoke style, one from Storm at A-1 (2005) and the other from
GoWesty (2007). Suggestions that frequently problems were
with wheels and tires made me review but conclude (so far, still)
that those are not the source of my problem.
I wasn't clear when I wrote by engine/tranny pointed "down"
6 degrees (actually 5.5 after remeasuring) and my front diff
pointed "down" 2.5 degrees. These angles are measured from the
(imaginery) line connecting the two--not horizontal. This
is partly what makes the site
http://www.vibratesoftware.com/html_help/html/Diagnosis/Propshaft/Propshaft_Angles.htm#Information
or http://tinyurl.com/36bdt4
confusing--the use of the inclinometer and comparing everything to
horizontal. My alignment tool, since it mounts flush on the flanges,
is comparing the difference to the line between flanges, not horizontal.
That is, that is what is very easy to measure.
I also was not understanding the beta angles at
http://www.baileymorris.co.uk/technical5.asp
thinking that the U joints split the difference and that was
why beta-1 equaled beta-2. NOT! That is why the "working angles"
have to be nearly equal! Not that beta-1 equals beta-2, but that
beta-1 MUST equal beta-2. So those who questioned my six degee
drop really made me think this through.
Then I put the passenger side up on blocks and ran it in 4th
gear at idle(!) I could feel the vibration but could not see
any one thing out of balance--but the propshaft made noises that
didn't sound like anything I wanted to hear.
I took the propshaft out, rechecked the angles with my alignment
tool and pondered over everything--including Jorick's latest post
sharing his success. It is pretty clear that my 5.5 degrees and
2.5 degrees conflict and I have to bring them closer together.
Since my front diff is shimmed "UP" I can remove the washers and
that will increase the 2.5 some. Somehow I have to work with
the tranny mounts and motor mounts to decrease the drop from 5.5.
There have been a couple of suggestions about this, but if anyone
has specifically altered these, I would love to hear exactly what
you did.
Meanwhile, another measurment: I measured from the ground to
the bottom of my tranny flange and to the bottom of my front diff
flange. The difference is 2-1/4"--the tranny flange is that much
lower. If anyone has measured, or would measure, this difference,
I'd love to know the numbers. I think my difference is another
side of my 5.5 degree droop.
Can't work on Syncros all the time. Trail Ridge Road opened last
Friday, so we drove up there, 12,000+':
http://jones.colorado.edu/jones/TrailRidge.jpg
Again, thanks to all who have helped so far.
Richard
Boulder
