vibration/shudder at 70 - possible alternatives (other than wheel balance?)

[amalventano@sc.rr.com (Allyn)]

hmm, ok, so we got the height issue taken care of, there goes my cv theory.
patrick, i know you mentioned your rear toe was perfect with the ehims
removed, how about the toe?

new theory:
shudder gets worse under acceleration due to weight transfer onto rear
misaligned wheels.
now to figure out why it modulates at ~1 hz
Al

----- Original Message -----
From: "Eric S" <scirocco81@vwmail.net>
To: "Patrick Bureau" <txrocco@sbcglobal.net>; "Rhett Farnum"
<rocco_crossing@hotmail.com>; <amalventano@sc.rr.com>;
<scirocco-l@scirocco.org>
Sent: Monday, April 21, 2003 11:24 PM
Subject: Re: vibration/shudder at 70 - possible alternatives (other than
wheel balance?)


> Let me chime in with a "me too" on this.  The mk2 has done this since I
got it, and it bugs the crap outta me.
>
> And, patrick, I *just* put new a-arms with poly bushings in....no
difference.
>
> Its done it with 13s with 175/70s and now with 15s with 205/50s, it
already has new shocks, I was going to change the rear wheel bearings next
and get a *true* 4-wheel alignment (shim the rear backing plates).  I have
new half-shafts that I thought about trying...but now from hearing from you
guys that it made no difference, for some reason, I think its coming from
the rear....don't ask me why, just a gut feeling.  I will let you all know
how it goes with the 4 wheel alignment.
>
> --
> Eric
> Northglenn, CO
>
> 79 VW Iltis
> 81 Scirocco S (*TDI* swap and complete restoration in holding pattern)
> 81 Rabbit Truck LX Diesel (Waiting for BAE Turbo Install)
> 83 Scirocco Wolfsburg
> 91 Cabriolet (2.0 Crossflow 8v swap and mechanical rebuild in progress)
>
>
> --- Patrick Bureau <txrocco@sbcglobal.net> wrote:
> >Nope it did this with spider wv 13" , with Konig;s
> >15x7 with new rubber, and still doing it with
> >speedline 14" with new rubber as well...
> >
> >it is not a tire/rim related issue I am pretty sure of
> >it, Oh yeah add change bearings, cv joint, shocks and
> >springs, ball joint and tied rods...
> >
> >I am thinking that it could be the sway bar bushings
> >or the a-arms bushings that need to be changed (small
> >bumps would cause because of deterioration of the
> >bushing a "loose" vibration....
> >
> >I have the same problem on the prowler and I will know
> >soon anought as I change the bushings for poly's on
> >a-arms, and new sway bar bushings (oem)...
> >
> >
> >
> >--- Rhett Farnum <rocco_crossing@hotmail.com> wrote:
> >> HOw about flat spots? I have at least one tire with
> >> a flat spot on my Cut'
> >> and she likes to shake between 76-80mph. Just a
> >> thought.
> >>
> >>
> >>
> >> Peace Out,
> >> Rhett
> >> Rocco_crossing
> >> '83 Rocco (autocross ready, tune up, harness bar,
> >> rear wheel bearings, and
> >> finally I may get to makeing it look better!!)
> >>
> >>
> >>
> >>
> >>
> >> >From: "Allyn" <amalventano@sc.rr.com>
> >> >To: "scirocco list" <scirocco-l@scirocco.org>
> >> >Subject: vibration/shudder at 70 - possible
> >> alternatives (other than wheel
> >> >balance?)
> >> >Date: Mon, 21 Apr 2003 20:28:24 -0400
> >> >
> >> >ok, the rieger has had the same shudder at 70ish
> >> for the longest time.
> >> >
> >> >things changed:
> >> >a-arms, bushings (all), bearings (all), half shafts
> >> (replaced with a
> >> >questionable set), engine/tranny, engine mounts,
> >> and a totally different
> >> >set
> >> >of wheels. not to mention rotors and hubs (i think
> >> this covers just about
> >> >every moving part).
> >> >
> >> >...and yet i still get the shudder...
> >> >
> >> >exact symptoms:
> >> >
> >> >- 0 vibration felt in wheel, even with the shudder
> >> at its worst.
> >> >- alignment is close enough such that it couldnt
> >> cause a problem like this
> >> >- shudder is not constant, the vibration is
> >> consistent with wheel rotation
> >> >at 70 mph, but it comes/goes at a 1 second cycle
> >> (kinda like its amplitude
> >> >modulated).
> >> >- shudder seems proportional to throttle
> >> application. the other day i did
> >> >several runs on the highway, coasting from 90-60 in
> >> neutral, and the
> >> >shudder
> >> >seemed to go away. shudder returns when holding
> >> speed at 70, and gets worse
> >> >under acceleration.
> >> >- feels like an out of balance wheel, but i've also
> >> felt the same feeling
> >> >when i had a bad inner cv (however the bad inner cv
> >> had a constant
> >> >vibration).
> >> >- also seems like bad inner cv in that its almost a
> >> side-to-side vibration,
> >> >felt in the floor under the center console.
> >> >
> >> >possibilities:
> >> >1. other set of half shafts (rebuilds from
> >> potterman) had the exact same
> >> >problem with the inner cv.
> >> >2. frame/engine is misaligned such that one of the
> >> half shafts is at its
> >> >compressed limit when installed / car on ground.
> >> possibly forcing tranny
> >> >over as it rotates, causing the vibration.
> >> >3. both sets of wheels/tires have had the exact
> >> same imbalance, after being
> >> >balanced several times between both sets
> >> (doubtfull).
> >> >
> >> >suggestions???
> >> >
> >> >(thx in advance for info)
> >> >Al
> >> >
> >> >
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