What is the reason for the left front shock mount failures on 90's buses?

[David Brady]

I lived in the Bay Area for 11 years. I know of what you speak. True,
if you are lifting the tires off the ground; i.e., complete front end unload
and shock hyper extension, well neither the shock nor the mounts
are going to last very long under those conditions. The shock is
designed to hold 8500 lb under full extension. Lifting the front wheels
off the ground with the HWH jacks and the air dumped results in the
axle being suspended by the fully extended shock; this scenario is
easily within the 8500lb limit. Add air to the airbags and you're
easily loading the shocks to 13000lb. Take in to account the angle
of the shock and the loads are even higher. "Get air" while driving
down an undulating highway... the shocks and mounts are likely to
survive even a couple of oscillations. If this is truly happening, then
you need to install straps or chains or something else to limit
suspension travel cause the shock/mounts aren't even close to
being strong enough.

David Brady
'02 LXi, NC

-----Original Message-----

From: Pete Masterson

Sent: Mar 10, 2009 1:50 PM

To: WanderlodgeForum@yahoogroups.com

Subject: Re: [WanderlodgeForum] Re: What is the reason for the left front shock mount failures on 90's buses?

Since the failure is at the TOP of the mounting plate, it seems like its the EXTENSION of the shock, not the compression that's the problem. I invite you to drive the Nimitz (I-880) from Oakland to San Jose -- you will hit _many_ road undulations that will fully extend your shocks, no matter how carefully you watch for the bad spots. Even at 55 (the official speed limit for 3 axle vehicles) you'll get full extension on some of the undulations. The road passes over clay bay fill and subsides, expands, and contracts with the seasons. (I -hate- to pass over that area -- but it's unavoidable if I'm going south to the coast...)

Pete Masterson

'95 Blue Bird Wanderlodge WBDA 42 (For Sale)

<http://www.aeonix.biz/BBforsale.html>

El Sobrante CA

"aeonix1@mac.com"

On Mar 10, 2009, at 9:14 AM, david brady wrote:

And BB knew all along.

The shock could "just fit" with the air dumped. But when
owners drop their birds off the jacks, the front goes
crashing down, the bump stops compress, and the shock
mounts take a huge impulse. It's a good theory.

The rough road scenario doesn't fit for me. You'll never
find a road rough enough that will cause the air springs
to bottom on their rubber bump stops. The air springs
are enormously progressive. At full compression
they can support something like 4G's. That's equivalent
to dropping the bus in free fall from 15 feet (give or take).

David
'02 LXi, NC

timvasqz wrote:

Dave this kinda supports your "shock stroke too long theory" if BB moved the mount farther away from the other mount.
pot holes are violent at 70 mph. if you ever see a slomotion of a PU truck hitting them the entire truck frame twists. In the bus there is no twist so the only place the equall reaction force is felt is in the suspension (and tile grout)
Greg of Tim&Greg
--- In"WanderlodgeForum%40yahoogroups.com", david brady"dmb993@..."wrote:
>
> Eric,
>
> There's been a whole lot of discussion on this Forum
> relative to the shock mount failure. You may want to
> search the archives for "shock mount".
>
> David Brady
> '02 LXi, NC
>
> Eric Perplies wrote:
> >
> > When I discovered my front left shock absorber mount had failed just
> > before the Q rally in 08' I thought my experience was unique.
> > Evidently it was not. There seems to have been several similar
> > failures on 90's vintage buses. All of them appear to have occurred on
> > the left front shock mount. It might be both interesting as well as
> > useful for all of us that have experienced the failure as well as
> > other interested parties to discuss what had caused the failures. If
> > there is a design flaw we know we are on our own, of course. Right now
> > it continues not to be clear to me what caused the problem.
> >
> > I realize that some of you have already discussed your failure. I do
> > hope you can participate in what may be on line troubleshooting. Let
> > me start out by discussing my failure.
> >
> > Just before the Q rally in 08' the left front shock absorber mount on
> > my coach failed. The whole piece of metal on the frame of my bus was
> > pulled away from the frame, leaving the shock mount still connected to
> > the chunk of metal that was pulled away from the frame. CCW in
> > Riverside repaired the problem. They had extensive discussions with
> > the engineers at Ft. Valley. I will tell you that CCW was less that
> > fully communicative with me about what they discussed in their
> > multiple phone calls to Ft. Valley. Always say they "discussed the
> > problem and solution."
> >
> > The fix was to weld a 1/2" plate to the area ripped out of my frame
> > and re-weld the still good shock mount back in position. (Caution:
> > what I am about to say is unreliable It looked to me as though the
> > repair shock mount was re-welded back in position just slightly lower
> > than it may have originally been located. When I asked CCW about the
> > location of the mount they said something like: "We put it back in
> > where it should have been." Never saying that they relocated it.
> >
> > When I strongly suspect that the failure occurred on my bus is when I
> > traveled a poorly maintained road (US 30) between Chicago and Ft.
> > Wayne, IN. While along that roadway my bus developed a "squeak" coming
> > from what I thought was the right front of my bus. I could not see
> > anything wrong with the underside of the coach. I did not look at the
> > left upper shock mount. I was looking for at problem on the right side
> > of my coach. I took my coach to a big rig shop in Ft Wayne that did
> > among other things, front end work. They said everything looked fine.
> > On my trip from Ft. Wayne to Las Vegas I did a lot of inspections,
> > greasing and spraying of lubricate on the front right of the coach. I
> > even removed the Steer Safe. By the time I got to Sante Fe the noise
> > had stopped. When I went to put my Steer Safe back on in Las Vegas,
> > just before the 08 Q rally, I discovered the failed shock mount on the
> > left side of the coach.
> >
> > (By the way, sorry for the long post.) The question still remains in
> > my mind: What caused the failure. I have been on many bad road in my
> > life with this coach. The road I was on when the "squeak" started was
> > bad but not ridiculously bad. I would hate to think that every time I
> > might ride a bad road that I may be replacing a shock mount.
> >
> > Eric Perplies
> > 96' 42' WBWL
> >