Shock mount failure

[David Brady]

Dan,

Additional stress is only created if you lift a tire off the ground via
the jacks and the suspension is still aired up. Of course, under
most circumstances, the height control valve should dump air,
but this takes time and in the meantime the air spring is fighting
against the shock and shock mount.

David Brady
'02 LXi, NC

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

From: Dan Williams

Sent: Mar 10, 2009 3:30 PM

To: WanderlodgeForum@yahoogroups.com

Subject: RE: [WanderlodgeForum] Re: Shock mount failure

Pete, I may be getting in on this
late, but how does lowering the leveling jacks with the
suspension still aired up put stress on the front shocks and mounts?

Dan Williams, 88WB38, Jackson, MS

---

From: WanderlodgeForum@yahoogroups.com
[mailto:WanderlodgeForum@yahoogroups.com] On
Behalf Of Pete Masterson

Sent: Tuesday, March 10, 2009
12:20 PM

To:
WanderlodgeForum@yahoogroups.com

Subject: Re: [WanderlodgeForum]
Re: Shock mount failure

There is
a sub-frame that holds the shock mount, air bag, and other parts of the front
end. It's a piece that's about 24 to 30 inches long. That piece comes from
Ridewell. (Although Ridewell might claim that Blue Bird provided the
specification.)The speculation is that the Ridewell piece is not
thick enough (or otherwise not sufficiently strong) to take the constant
hammering.

Awhile back on one or the other WL lists, someone reported that
lowering the leveling jacks with the suspension still aired up puts an
unusually large stress on the front shocks and mounts. That may start the
weakening process. However, I know that it was rare for me to forget to dump
the suspension before I leveled the coach.

Before the complete failure of my shock mount, I'd noticed a 'popping'
noise in the front end when encountering theporpoisingmovement that
occurs after passing over one of the multitude of ground subsidence undulations
that are frequently found on the freeways, especially in the SF Bay Area where
the highways are frequently built on fill (near the bay) or unstable clay soils
(nearly everywhere else in the area). Later I realized that the noise was cause
by the flexing of the split (and eventually broken) piece of the Ridewell
sub-assembly. (The acoustics caused it to sound like it came from the opposite
side.)

Pete Masterson

'95 Blue Bird Wanderlodge WBDA 42 (For Sale)

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

El Sobrante CA

"aeonix1@mac.com"

On Mar 9, 2009, at 7:40 PM, Don Bradner wrote:

Did your tear look at all like mine (mine looks almost exactly like
Pete's)? Presumption is that the slamming downward when the wheel bottoms into
a pothole or similar is the issue. Countless slams, and the metal gives way.
Note that it is not the frame, but rather the steel mounted to the frame - that
steel is a part of the axle assembly and was presumably not welded by BB.



The repair done on mine comes close to matching the original assembly, making
it possible/likely that sometime in the next 20 years it will fail again. I'm
going to try to remember to stick a camera in there for photos every few months
(more often to begin with!) that it is driven.



On 3/10/2009 at 2:22 AM Eric Perplies wrote:

My front left shock mount broke just before the Q rally in 08.
CCW in

Riverside
fixed mine shortly after the Q rally. On my coach the shock

mount ripped out a chunk of metal on the frame. A piece of steel
about

1/2" x 8" x 6" was welded onto my frame. A hole
was drilled in it to

accommodate the brake air line. The original shock mount with it's
three

gussets were removed from the broken out piece. That original
shock mount

was then welded back onto the 1/2" plate mentioned above.

The welds made during the repair were VERY thorough. There was an

indication that the original BB welds may not have been as through as
they

could have been. (One side of one of the gussets had not been
welded onto

the frame.) That having been said this could not be the reason
for the

failure. After all the frame on my coach had a section ripped out
of it.

The shock mount itself did not fail.

A far more interesting question is: What causes the failures on
the shock

mounts?

[Pete Masterson]

If I understand correctly, that raises the front of the coach. If the air bags are inflated, it can put 13,000 lbs pressure on the shock mount (from the air pressure in the bag) with the maximum pressure achieved if the front tires are lifted completely off the ground (as sometimes is the case).

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 12:30 PM, Dan Williams wrote:

Pete, I may be getting in on this late, but how doeslowering the leveling jacks with the suspension still aired up put stress on the front shocks and mounts?

Dan Williams, 88WB38, Jackson, MS

---

From:"WanderlodgeForum@yahoogroups.com"["WanderlodgeForum@yahoogroups.com"]On Behalf OfPete Masterson
Sent:Tuesday, March 10, 2009 12:20 PM
To:"WanderlodgeForum@yahoogroups.com"
Subject:Re: [WanderlodgeForum] Re: Shock mount failure

There is a sub-frame that holds the shock mount, air bag, and other parts of the front end. It's a piece that's about 24 to 30 inches long. That piece comes from Ridewell. (Although Ridewell might claim that Blue Bird provided the specification.)The speculation is that the Ridewell piece is not thick enough (or otherwise not sufficiently strong) to take the constant hammering.

Awhile back on one or the other WL lists, someone reported that lowering the leveling jacks with the suspension still aired up puts an unusually large stress on the front shocks and mounts. That may start the weakening process. However, I know that it was rare for me to forget to dump the suspension before I leveled the coach.

Before the complete failure of my shock mount, I'd noticed a 'popping' noise in the front end when encountering theporpoisingmovement that occurs after passing over one of the multitude of ground subsidence undulations that are frequently found on the freeways, especially in the SF Bay Area where the highways are frequently built on fill (near the bay) or unstable clay soils (nearly everywhere else in the area). Later I realized that the noise was cause by the flexing of the split (and eventually broken) piece of the Ridewell sub-assembly. (The acoustics caused it to sound like it came from the opposite side.)

Pete Masterson

'95 Blue Bird Wanderlodge WBDA 42 (ForSale)

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

El Sobrante CA

"aeonix1@mac.com"

On Mar 9, 2009, at 7:40 PM, Don Bradner wrote:

Did your tear look at all like mine (mine looks almost exactly like Pete's)? Presumption is that the slamming downward when the wheel bottoms into a pothole or similar is the issue. Countless slams, and the metal gives way. Note that it is not the frame, but rather the steel mounted to the frame - that steel is a part of the axle assembly and was presumably not welded by BB.

The repair done on mine comes close to matching the original assembly, making it possible/likely that sometime in the next 20 years it will fail again. I'm going to try to remember to stick a camera in there for photos every few months (more often to begin with!) that it is driven.

On 3/10/2009 at 2:22 AM Eric Perplies wrote:

My front left shock mount broke just before the Q rally in 08. CCW in

Riversidefixed mine shortly after the Q rally. On my coach the shock

mount ripped out a chunk of metal on the frame. A piece of steel about

1/2" x 8" x 6" was welded onto my frame. A hole was drilled in it to

accommodate the brake air line. The original shock mount with it's three

gussets were removed from the broken out piece. That original shock mount

was then welded back onto the 1/2" plate mentioned above.

The welds made during the repair were VERY thorough. There was an

indication that the original BB welds may not have been as through as they

could have been. (One side of one of the gussets had not been welded onto

the frame.) That having been said this could not be the reason for the

failure. After all the frame on my coach had a section ripped out of it.

The shock mount itself did not fail.

A far more interesting question is: What causes the failures on the shock

mounts?

[Kurt Horvath]

I also believe that the stress cracking comes from extension not compression of
the suspension. When my coach was lifted up on the front end the broken piece
pulled away when lowered it you could barely see the fracture lines on the
mounts. I just basically reseated itself in it's original position. I doubt that
anything we could do intentionally would cause such a fracture. Air in or out of
the airbags lifted with the jacks or not. A constant pressure of 13000 LB is not
the same as 13000lb rebounding and extending at 60 MPH. Perhaps dropping the
jacks on empty airbags could do it, when it hits bottom it hits hard, real hard.

Kurt Horvath
95 PT 42
10AC



--- In WanderlodgeForum@yahoogroups.com, Pete Masterson wrote:
>
> If I understand correctly, that raises the front of the coach. If the
> air bags are inflated, it can put 13,000 lbs pressure on the shock
> mount (from the air pressure in the bag) with the maximum pressure
> achieved if the front tires are lifted completely off the ground (as
> sometimes is the case).
>
> Pete Masterson
> '95 Blue Bird Wanderlodge WBDA 42 (For Sale)
> <http://www.aeonix.biz/BBforsale.html>
> El Sobrante CA
> aeonix1@...
>
>
>
>
> On Mar 10, 2009, at 12:30 PM, Dan Williams wrote:
>
> > Pete, I may be getting in on this late, but how does lowering the
> > leveling jacks with the suspension still aired up put stress on the
> > front shocks and mounts?
> > Dan Williams, 88WB38, Jackson, MS
> >
> > From: WanderlodgeForum@yahoogroups.com
[mailto:WanderlodgeForum@yahoogroups.com
> > ] On Behalf Of Pete Masterson
> > Sent: Tuesday, March 10, 2009 12:20 PM
> > To: WanderlodgeForum@yahoogroups.com
> > Subject: Re: [WanderlodgeForum] Re: Shock mount failure
> >
> > There is a sub-frame that holds the shock mount, air bag, and other
> > parts of the front end. It's a piece that's about 24 to 30 inches
> > long. That piece comes from Ridewell. (Although Ridewell might claim
> > that Blue Bird provided the specification.) The speculation is that
> > the Ridewell piece is not thick enough (or otherwise not
> > sufficiently strong) to take the constant hammering.
> >
> >
> > Awhile back on one or the other WL lists, someone reported that
> > lowering the leveling jacks with the suspension still aired up puts
> > an unusually large stress on the front shocks and mounts. That may
> > start the weakening process. However, I know that it was rare for me
> > to forget to dump the suspension before I leveled the coach.
> >
> > Before the complete failure of my shock mount, I'd noticed a
> > 'popping' noise in the front end when encountering the porpoising
> > movement that occurs after passing over one of the multitude of
> > ground subsidence undulations that are frequently found on the
> > freeways, especially in the SF Bay Area where the highways are
> > frequently built on fill (near the bay) or unstable clay soils
> > (nearly everywhere else in the area). Later I realized that the
> > noise was cause by the flexing of the split (and eventually broken)
> > piece of the Ridewell sub-assembly. (The acoustics caused it to
> > sound like it came from the opposite side.)
> >
> > Pete Masterson
> > '95 Blue Bird Wanderlodge WBDA 42 (For Sale)
> > <http://www.aeonix.biz/BBforsale.html>
> > El Sobrante CA
> > aeonix1@...
> >
> >
> >
> > On Mar 9, 2009, at 7:40 PM, Don Bradner wrote:
> >
> >
> > Did your tear look at all like mine (mine looks almost exactly like
> > Pete's)? Presumption is that the slamming downward when the wheel
> > bottoms into a pothole or similar is the issue. Countless slams, and
> > the metal gives way. Note that it is not the frame, but rather the
> > steel mounted to the frame - that steel is a part of the axle
> > assembly and was presumably not welded by BB.
> >
> > The repair done on mine comes close to matching the original
> > assembly, making it possible/likely that sometime in the next 20
> > years it will fail again. I'm going to try to remember to stick a
> > camera in there for photos every few months (more often to begin
> > with!) that it is driven.
> >
> > On 3/10/2009 at 2:22 AM Eric Perplies wrote:
> >
> >
> > My front left shock mount broke just before the Q rally in 08. CCW in
> >> Riverside fixed mine shortly after the Q rally. On my coach the
> >> shock
> >> mount ripped out a chunk of metal on the frame. A piece of steel
> >> about
> >> 1/2" x 8" x 6" was welded onto my frame. A hole was drilled in it to
> >> accommodate the brake air line. The original shock mount with it's
> >> three
> >> gussets were removed from the broken out piece. That original
> >> shock mount
> >> was then welded back onto the 1/2" plate mentioned above.
> >>
> >> The welds made during the repair were VERY thorough. There was an
> >> indication that the original BB welds may not have been as through
> >> as they
> >> could have been. (One side of one of the gussets had not been
> >> welded onto
> >> the frame.) That having been said this could not be the reason for
> >> the
> >> failure. After all the frame on my coach had a section ripped out
> >> of it.
> >> The shock mount itself did not fail.
> >>
> >> A far more interesting question is: What causes the failures on
> >> the shock
> >> mounts?
> >
> >
> >
> >
> >
>

[Don Bradner]

The primary jolt I hear/feel is when the wheel drops into a pothole. There are a
lot of potholes in the US, and I feel like I've hit 80% of 'em!

Dropping into a pothole at the full pressure of the airbag puts all of the force
in the extension direction.

Each of the breaks documented so far tear *down*, never up.

Don Bradner
90 PT40 "Blue Thunder"
My location: http://www.bbirdmaps.com/user2.cfm?user=1

On 3/10/2009 at 7:30 PM david brady wrote:

>If the tires stay on the ground, not "getting air" on the Nimitz
>in Ca, the max shock force is 4000lb (according to Justin at
>Koni), and all of that force occurs under rebound; i.e, the Koni
>shocks provide no, or negligible, compression dampening.
>IOW's all the forces are in the extension direction. That's not
>to say that the initial damage hadn't occurred under compression.
>It's just that for it to occur under compression something weird
>has to happen, like shocks that are too long, or dumping the
>HWH jacks w/o air in the bags. Once the initial damage
>has occurred, then normal shock loads add to the metal fatigue
>and the ultimate failure.

[david brady]

If the tires stay on the ground, not "getting air" on the Nimitz

in Ca, the max shock force is 4000lb (according to Justin at

Koni), and all of that force occurs under rebound; i.e, the Koni

shocks provide no, or negligible, compression dampening.

IOW's all the forces are in the extension direction. That's not

to say that the initial damage hadn't occurred under compression.

It's just that for it to occur under compression something weird

has to happen, like shocks that are too long, or dumping the

HWH jacks w/o air in the bags. Once the initial damage

has occurred, then normal shock loads add to the metal fatigue

and the ultimate failure.



Kurt Horvath wrote:

I also believe that the stress cracking comes from extension not
compression of the suspension. When my coach was lifted up on the front
end the broken piece pulled away when lowered it you could barely see
the fracture lines on the mounts. I just basically reseated itself in
it's original position. I doubt that anything we could do intentionally
would cause such a fracture. Air in or out of the airbags lifted with
the jacks or not. A constant pressure of 13000 LB is not the same as
13000lb rebounding and extending at 60 MPH. Perhaps dropping the jacks
on empty airbags could do it, when it hits bottom it hits hard, real
hard.



Kurt Horvath

95 PT 42

10AC



--- In "WanderlodgeForum%40yahoogroups.com",
Pete Masterson > wrote:

>

> If I understand correctly, that raises the front of the coach. If
the

> air bags are inflated, it can put 13,000 lbs pressure on the shock


> mount (from the air pressure in the bag) with the maximum pressure


> achieved if the front tires are lifted completely off the ground
(as

> sometimes is the case).

>

> Pete Masterson

> '95 Blue Bird Wanderlodge WBDA 42 (For Sale)

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

> El Sobrante CA

> aeonix1@...

>

>

>

>

> On Mar 10, 2009, at 12:30 PM, Dan Williams wrote:

>

> > Pete, I may be getting in on this late, but how does lowering
the

> > leveling jacks with the suspension still aired up put stress
on the

> > front shocks and mounts?

> > Dan Williams, 88WB38, Jackson, MS

> >

> > From: "WanderlodgeForum%40yahoogroups.com"
[mailto:"WanderlodgeForum%40yahoogroups.com"


> > ] On Behalf Of Pete Masterson

> > Sent: Tuesday, March 10, 2009 12:20 PM

> > To: "WanderlodgeForum%40yahoogroups.com"

> > Subject: Re: [WanderlodgeForum] Re: Shock mount failure

> >

> > There is a sub-frame that holds the shock mount, air bag, and
other

> > parts of the front end. It's a piece that's about 24 to 30
inches

> > long. That piece comes from Ridewell. (Although Ridewell
might claim

> > that Blue Bird provided the specification.) The
speculation is that

> > the Ridewell piece is not thick enough (or otherwise not

> > sufficiently strong) to take the constant hammering.

> >

> >

> > Awhile back on one or the other WL lists, someone reported
that

> > lowering the leveling jacks with the suspension still aired
up puts

> > an unusually large stress on the front shocks and mounts.
That may

> > start the weakening process. However, I know that it was rare
for me

> > to forget to dump the suspension before I leveled the coach.

> >

> > Before the complete failure of my shock mount, I'd noticed a

> > 'popping' noise in the front end when encountering the
porpoising

> > movement that occurs after passing over one of the multitude
of

> > ground subsidence undulations that are frequently found on
the

> > freeways, especially in the SF Bay Area where the highways
are

> > frequently built on fill (near the bay) or unstable clay
soils

> > (nearly everywhere else in the area). Later I realized that
the

> > noise was cause by the flexing of the split (and eventually
broken)

> > piece of the Ridewell sub-assembly. (The acoustics caused it
to

> > sound like it came from the opposite side.)

> >

> > Pete Masterson

> > '95 Blue Bird Wanderlodge WBDA 42 (For Sale)

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

> > El Sobrante CA

> > aeonix1@...

> >

> >

> >

> > On Mar 9, 2009, at 7:40 PM, Don Bradner wrote:

> >

> >

> > Did your tear look at all like mine (mine looks almost
exactly like

> > Pete's)? Presumption is that the slamming downward when the
wheel

> > bottoms into a pothole or similar is the issue. Countless
slams, and

> > the metal gives way. Note that it is not the frame, but
rather the

> > steel mounted to the frame - that steel is a part of the axle


> > assembly and was presumably not welded by BB.

> >

> > The repair done on mine comes close to matching the original

> > assembly, making it possible/likely that sometime in the next
20

> > years it will fail again. I'm going to try to remember to
stick a

> > camera in there for photos every few months (more often to
begin

> > with!) that it is driven.

> >

> > On 3/10/2009 at 2:22 AM Eric Perplies wrote:

> >

> >

> > My front left shock mount broke just before the Q rally in
08. CCW in

> >> Riverside fixed mine shortly after the Q rally. On my
coach the

> >> shock

> >> mount ripped out a chunk of metal on the frame. A piece
of steel

> >> about

> >> 1/2" x 8" x 6" was welded onto my frame. A hole was
drilled in it to

> >> accommodate the brake air line. The original shock mount
with it's

> >> three

> >> gussets were removed from the broken out piece. That
original

> >> shock mount

> >> was then welded back onto the 1/2" plate mentioned above.

> >>

> >> The welds made during the repair were VERY thorough.
There was an

> >> indication that the original BB welds may not have been
as through

> >> as they

> >> could have been. (One side of one of the gussets had not
been

> >> welded onto

> >> the frame.) That having been said this could not be the
reason for

> >> the

> >> failure. After all the frame on my coach had a section
ripped out

> >> of it.

> >> The shock mount itself did not fail.

> >>

> >> A far more interesting question is: What causes the
failures on

> >> the shock

> >> mounts?

> >

> >

> >

> >

> >

>

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