Caspro vs KYB vs Bilstein

V

vic marks

New member
Sep 5, 1999
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The KYB shocks are far superior to the Caspros. The caspro shocks look
larger and more rugged but they are not. The KYB shocks are a true gas
shock
the caspro are not. Its a toss up between the KYB and bilstein shocks.

Tom:

I would beg to differ with you on this. After a long discussion with Jim
Anstett a few years ago, I replaced my KYB's (which were about 5 years old)
with Caspros. I did it based on a Jim's experiences. As many of you
probably know, Jim has written a number of articles on his coach
experiences in GMCMM. He also wrote an article a few years ago on shocks.
He also has nearly 300,000 miles on his coach.

Jim ran with Bilsteins for a number of years but was plagued with the
problem of broken shocks. He went through 10 or more shocks over the years,
and although they have a lifetime guarantee, the hassle was significant
(especially when he broke two on a Mexico trip). He was especially
concerned when a shock broke on a friend's coach and went through the tire.

Jim switched to Caspro shocks about 4 years ago and has put on 40,000 plus
miles since then. After he switched, he felt that the coach handled far
better in winds and that it removed 70% of the rut wobble problem. This
experience seems to be in line with Glenn's description of how his coach
handles on the road since his front end was overhauled and new Caspro
shocks were installed. After I made the change, my coach handled remarkably
better on mountain roads but I also put on (non-Caspro) rear sway bars and
a heavy duty front bar, so I have no idea which change was most responsible
for the improvement.

The drawback to the Caspro shock is that it is far more expensive than the
KYB and it doesn't have the lifetime warranty's of the Bilstein. A coach
owner in Vancouver switched from Caspro to KYB after Chuck Stoddard refused
to replaced two of his shocks that leaked. As I understand it, Caspro is
extremely reluctant to replaced shock that go bad, which I think is a shame
given the cost. His thinking seems to be that it is a part that normally
wears out, much like a water pump or fan clutch. Does anybody know under
what situation the shocks will be replaced?

Jim would put the KYB's in second place after the Caspro shocks but he has
not personally used them on his coach.

I think that it's an impossible call to say that one make is better than
another. They all seem to have their good (and bad) points. I would
summarize them as follows:

KYB: Good value for the money
Bilstein: Expensive but lifetime warranty
Caspro: Expensive but appear to improve the handling

Vic Marks
Vancouver BC
75 transmode
 
Vic this subject has been thoroughly studied by Cinnabar engineering and
detailed in several different issues including the December 1998 issue of
the GMC motorhome news.

Bottom line KYBs and Bilsteins are true double acting gas shocks with life
time warranties...Caspros are not.

Relative to the shocks breaking. THEY WERE DESIGNED TO BREAK UNDER SEVERE
LOADS! Remember the GMC motorhomne shock absorbers also act as SUSPENSION
LIMITERS. When they are overstressed they break instead of breaking
something else in your suspension system. If someone is breaking shocks
either the mounts are not parallel or they are driving them to hard. In
either case its not the shocks fault.

Before I bought the KYBs I read everything I could find and am convinced
they are the best buy with excellent performance.

>
>The KYB shocks are far superior to the Caspros. The caspro shocks look
>larger and more rugged but they are not. The KYB shocks are a true gas
>shock
>the caspro are not. Its a toss up between the KYB and bilstein shocks.
>
>Tom:
>
>I would beg to differ with you on this. After a long discussion with Jim
>Anstett a few years ago, I replaced my KYB's (which were about 5 years old)
>with Caspros. I did it based on a Jim's experiences. As many of you
>probably know, Jim has written a number of articles on his coach
>experiences in GMCMM. He also wrote an article a few years ago on shocks.
>He also has nearly 300,000 miles on his coach.
>
>Jim ran with Bilsteins for a number of years but was plagued with the
>problem of broken shocks. He went through 10 or more shocks over the years,
>and although they have a lifetime guarantee, the hassle was significant
>(especially when he broke two on a Mexico trip). He was especially
>concerned when a shock broke on a friend's coach and went through the tire.
>
>Jim switched to Caspro shocks about 4 years ago and has put on 40,000 plus
>miles since then. After he switched, he felt that the coach handled far
>better in winds and that it removed 70% of the rut wobble problem. This
>experience seems to be in line with Glenn's description of how his coach
>handles on the road since his front end was overhauled and new Caspro
>shocks were installed. After I made the change, my coach handled remarkably
>better on mountain roads but I also put on (non-Caspro) rear sway bars and
>a heavy duty front bar, so I have no idea which change was most responsible
>for the improvement.
>
>The drawback to the Caspro shock is that it is far more expensive than the
>KYB and it doesn't have the lifetime warranty's of the Bilstein. A coach
>owner in Vancouver switched from Caspro to KYB after Chuck Stoddard refused
>to replaced two of his shocks that leaked. As I understand it, Caspro is
>extremely reluctant to replaced shock that go bad, which I think is a shame
>given the cost. His thinking seems to be that it is a part that normally
>wears out, much like a water pump or fan clutch. Does anybody know under
>what situation the shocks will be replaced?
>
>Jim would put the KYB's in second place after the Caspro shocks but he has
>not personally used them on his coach.
>
>I think that it's an impossible call to say that one make is better than
>another. They all seem to have their good (and bad) points. I would
>summarize them as follows:
>
>KYB: Good value for the money
>Bilstein: Expensive but lifetime warranty
>Caspro: Expensive but appear to improve the handling
>
>Vic Marks
>Vancouver BC
>75 transmode
>
>
>
>
 
Just a couple of comments on "whose is better"?
>
>KYB: Good value for the money
***Also A Lifetime Warranty, No?***

>Bilstein: Expensive but lifetime warranty
>Caspro: Expensive but appear to improve the handling

Question: How was this improvement in handling demonstrated?

I am not interested in debating the issue, I just need to know if this
improvement is based upon Jim Anstett's experience with Caspro's AND KYBs
or just Caspro shocks.

My KYBs have over 100k miles on them so if there is something better I
want to know for when they need to be replaced, but I tend to need hard
evidence.

David Lee Greenberg
200 MacFarlane Dr
Delray Beach, FL 33483-6829
www.gmcss.com/registry.htm
 
I still get a kick out of this every time I read it :). What a great way to
find out your shock mounts are slightly out of alignment or that you drive
your GMC too hard. I'm surprised weak shocks aren't sold as Shock Mount
Aligning and Aggressive Driver Warning tools. With free lifetime replacement,
you should be able to get the mounts pretty well aligned after only a couple
of sets :). I'm sure the aggressive drivers out there would start driving
more carefully after replacing the same shock a couple of times :). Anyone
can feel free to start up a business with this idea (no charge).

I can see the infomercials now. I apologize ahead of time for the following
"infomercial". I just can't resist. It is meant to be humorous and is not
intended as a slam of any product, person, or company. I marked it so that it
is easily skipped. Feel free to do just that.

- -----------------INFOMERCIAL BEGINS-------------------
This shock is no ordinary shock, Jim. It is the Shockomater 3000. It does
everything. It breaks to indicate poorly aligned mounts. It breaks to
indicate overly aggressive drivers. It even dampens road shock for a couple
of miles before breaking or failing Jim! Do you believe it? I don't see how
anyone can live without one of these tools. With the lifetime guarantee, you
pay only S&H to get a brand new Shockomater 3000 shipped right to your door
after yours fails or breaks with no questions asked. I know you all want to
know how much such a wonderful product must cost. You've seen them in stores
for a lot of money, and I'll tell you that some of those are built so strongly
they don't even do half the jobs done by the Shockomater 3000. Well, here on
the GMC Shopping Network, the Shockomater 3000 can be yours for the low low
price of $3,000. OK OK $2,0000
OK! If you act now, you can get a set of 6 of the Shockomater 3000s for just
12 easy payments of just $49.99. If you act within 30
minutes of seeing this, we'll even include a piece of paper with the
handwritten message, "We say that the Shockomater 3000 was designed
specifically for your ."
- -----------------INFOMERCIAL ENDS-------------------

Now back to our regularly scheduled message.

The shocks aren't doing a very good job of acting as "SUSPENSION LIMITERS" if
the break are they? Seems to me that if the suspension is counting on the
shock to limit its travel, some other parts could be broken/bent because the
shock is no longer there to do its job. It also seems to me that having a
broken shock clanking around can't be a good thing for any of the other
suspension parts or especially the tires (as someone mentioned a GMCer whose
broken shock punctured their tire).

Coming from the side of overbuilding things, I just find it difficult to
believe that anything automotive (especially suspension) is really "designed
to break". Breaking just doesn't seem to be a very predictable method of
failure to me. I would believe this if there was a "failure spot" of the
shock that was intentionally weakened precisely the same way on every shock,
but I don't believe that this is the case. It seems that this would be the
only way to get the shocks to fail at a consistent force level which seems to
be a requirement of "designing" to me. This just really seems like a way of
explaining a weak shock to me. Actually, if a shock were "designed to break"
properly in my mind, it would fail internally and stop dampening rather than
fail catastrophically and break.

One thing this whole topic has brought up is how long any of these shocks
actually last. I am beginning to think that most of the shocks we are using
stop dampening fairly quickly. How many people on the list have taken off
shocks that had a decent amount of mileage (>20,000 maybe?) that were still
good? Do the rears fail faster than the fronts, do the fronts fail faster
than the rears, or do they fail at roughly the same time? Maybe we can spot a
trend.

Zak

PS - I put no faith whatsoever in the C "article" mentioned. It was clearly,
at least to me, a response to the article in GMCMM the month (or so) before.
As I recall, unlike the GMCMM article which offered cutaway views and actual
measurements as supporting facts, the C article offered nothing other than
saying that the shocks were designed for the GMC and were not overpriced truck
shocks. The overpriced truck shocks remark was one of several that made it
overly clear to me that the article was just a response to the GMCMM article
and not a real article intending to objectively review GMC shock performance.
Don't believe my memory. Go back and read the GMCMM shock article. Then read
the C article and form your own opinions.

Vic this subject has been thoroughly studied by Cinnabar engineering and
detailed in several different issues including the December 1998 issue of
the GMC motorhome news.

Bottom line KYBs and Bilsteins are true double acting gas shocks with life
time warranties...Caspros are not.

Relative to the shocks breaking. THEY WERE DESIGNED TO BREAK UNDER SEVERE
LOADS! Remember the GMC motorhomne shock absorbers also act as SUSPENSION
LIMITERS. When they are overstressed they break instead of breaking
something else in your suspension system. If someone is breaking shocks
either the mounts are not parallel or they are driving them to hard. In
either case its not the shocks fault.

Before I bought the KYBs I read everything I could find and am convinced
they are the best buy with excellent performance.
 
This stuff about shock failure under extreme loads is as another person
said "silly". You don't have to pay big bucks to get a shock that will
fail under extreme use!

A shock is supposed to help damper\n the effects of the road on the
suspension, thus the term "dampener".

Unfortunately, the rear shocks are the limiters of the rear suspension. It
sounds nutty but that's the way the suspension works. The shocks do help
tire wear but I do not rely on my shocks for a smooth ride or to stiffen up
my ride.

Actually, I only had 5 shocks on the dumpster when I drove to the balloon
rally. I had subjected my baby to a 5 mile washboard road in the Ocala
Forest the week before and had ripped out one shock (my fault when I ran
30mph on that dirt road).

I had a great ride 30 hours to the rally and 30 back. The missing shock
made no difference, ask my co-pilot Nelson! We flew low through Texas at
85+ and stayed between the lines just fine.

I run Delco shocks, yea I know that may be a dirty word to many people, but
they are cheap and seem to last. And if they break, guess what? They have
the same lifetime warranty and I get a new one right away. The only reason
I did not put on the new one I got after I obliterated the other shock is I
had too much to do!

KYB shocks are great, I have never heard a disparaging word, Caspro shocks
have Chuck standing with two feet firmly planted to support his stuff and
Bilsteen are as close as UPS! For my $, I install Delco and tell everybody
to keep the receipt!

If you want a better ride, stop putting band aids on your suspension and
get a 4 air bag suspension and be done with it!

Contrasting views will probably follow and they will probably be noteworthy!

Jim Bounds
- -------------------------------
 
Dumpster is not a 4 bagger !!!

gene

>This stuff about shock failure under extreme loads is as another person
>said "silly". You don't have to pay big bucks to get a shock that will
>fail under extreme use!
>
>A shock is supposed to help damper\n the effects of the road on the
>suspension, thus the term "dampener".
>
>Unfortunately, the rear shocks are the limiters of the rear suspension. It
>sounds nutty but that's the way the suspension works. The shocks do help
>tire wear but I do not rely on my shocks for a smooth ride or to stiffen up
>my ride.
>
>Actually, I only had 5 shocks on the dumpster when I drove to the balloon
>rally. I had subjected my baby to a 5 mile washboard road in the Ocala
>Forest the week before and had ripped out one shock (my fault when I ran
>30mph on that dirt road).
>
>I had a great ride 30 hours to the rally and 30 back. The missing shock
>made no difference, ask my co-pilot Nelson! We flew low through Texas at
>85+ and stayed between the lines just fine.
>
>I run Delco shocks, yea I know that may be a dirty word to many people, but
>they are cheap and seem to last. And if they break, guess what? They have
>the same lifetime warranty and I get a new one right away. The only reason
>I did not put on the new one I got after I obliterated the other shock is I
>had too much to do!
>
>KYB shocks are great, I have never heard a disparaging word, Caspro shocks
>have Chuck standing with two feet firmly planted to support his stuff and
>Bilsteen are as close as UPS! For my $, I install Delco and tell everybody
>to keep the receipt!
>
>If you want a better ride, stop putting band aids on your suspension and
>get a 4 air bag suspension and be done with it!
>
>Contrasting views will probably follow and they will probably be noteworthy!
>
>Jim Bounds
>-------------------------------
>
>
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
 
Zak read what you said and hope that you are saying all of this with tongue
in cheek.

1. The GMC has no means to limit suspension travel other than the shock
absorber. Thats why it is absolutely imperative that you install the correct
shock designed for the GMC motorhome. Remember the rear shocks must be
reversed valved. How would a Delco shock work on the rear???? In addition
Bilstein shock absorbers for the GMC have built in extension limiters both
for compression and extension.

2. The GMC needs a double acting shock absorber to dampen both motions

3. What would you rather break the eye of the shock absorber (and get it
replaced under warranty free) or expensive almost irreplaceable suspension
components that you have to pay for? Wonder if those cracks in the A frames
around the ball joint might be from inferior shocks?

You forget all GMC owners are not as mechanically inclined as you are and
would not know if their suspension components are bent or not. If you break
several bilstein or KYB shock absorbers, than you have something out of
alignment......period! If you had diarrhea three days in a row would you
continue eating prunes??????? Than why in god would anyone keep installing
shock absorbers when they repeatedly break?

When I talked about driving hard I am talking about driving fast on rough
roads, dropping a wheel into a deep pot hole etc where it over stresses the
suspension.

Delco shocks are single action shocks and not suitable for the GMC
motorhome. Makes no sense to me, spend thousands of dollars in paint,
reupholstery etc, but scrimp $10 on a second rate shock. Where is the
logic????

fact is that double tube shocks like the delco and caspro start
deteriorating as soon as you take them from the box. Believe it or not!

>I still get a kick out of this every time I read it :). What a great way to
>find out your shock mounts are slightly out of alignment or that you drive
>your GMC too hard. I'm surprised weak shocks aren't sold as Shock Mount
>Aligning and Aggressive Driver Warning tools. With free lifetime replacement,
>you should be able to get the mounts pretty well aligned after only a couple
>of sets :). I'm sure the aggressive drivers out there would start driving
>more carefully after replacing the same shock a couple of times :). Anyone
>can feel free to start up a business with this idea (no charge).
>
>I can see the infomercials now. I apologize ahead of time for the following
>"infomercial". I just can't resist. It is meant to be humorous and is not
>intended as a slam of any product, person, or company. I marked it so that it
>is easily skipped. Feel free to do just that.
>
>-----------------INFOMERCIAL BEGINS-------------------
>This shock is no ordinary shock, Jim. It is the Shockomater 3000. It does
>everything. It breaks to indicate poorly aligned mounts. It breaks to
>indicate overly aggressive drivers. It even dampens road shock for a couple
>of miles before breaking or failing Jim! Do you believe it? I don't see how
>anyone can live without one of these tools. With the lifetime guarantee, you
>pay only S&H to get a brand new Shockomater 3000 shipped right to your door
>after yours fails or breaks with no questions asked. I know you all want to
>know how much such a wonderful product must cost. You've seen them in stores
>for a lot of money, and I'll tell you that some of those are built so strongly
>they don't even do half the jobs done by the Shockomater 3000. Well, here on
>the GMC Shopping Network, the Shockomater 3000 can be yours for the low low
>price of $3,000. OK OK $2,0000
>OK! If you act now, you can get a set of 6 of the Shockomater 3000s for just
>12 easy payments of just $49.99. If you act within 30
>minutes of seeing this, we'll even include a piece of paper with the
>handwritten message, "We say that the Shockomater 3000 was designed
>specifically for your ." ,what else, SHOCK>
>-----------------INFOMERCIAL ENDS-------------------
>
>Now back to our regularly scheduled message.
>
>
>The shocks aren't doing a very good job of acting as "SUSPENSION LIMITERS" if
>the break are they? Seems to me that if the suspension is counting on the
>shock to limit its travel, some other parts could be broken/bent because the
>shock is no longer there to do its job. It also seems to me that having a
>broken shock clanking around can't be a good thing for any of the other
>suspension parts or especially the tires (as someone mentioned a GMCer whose
>broken shock punctured their tire).
>
>Coming from the side of overbuilding things, I just find it difficult to
>believe that anything automotive (especially suspension) is really "designed
>to break". Breaking just doesn't seem to be a very predictable method of
>failure to me. I would believe this if there was a "failure spot" of the
>shock that was intentionally weakened precisely the same way on every shock,
>but I don't believe that this is the case. It seems that this would be the
>only way to get the shocks to fail at a consistent force level which seems to
>be a requirement of "designing" to me. This just really seems like a way of
>explaining a weak shock to me. Actually, if a shock were "designed to break"
>properly in my mind, it would fail internally and stop dampening rather than
>fail catastrophically and break.
>
>One thing this whole topic has brought up is how long any of these shocks
>actually last. I am beginning to think that most of the shocks we are using
>stop dampening fairly quickly. How many people on the list have taken off
>shocks that had a decent amount of mileage (>20,000 maybe?) that were still
>good? Do the rears fail faster than the fronts, do the fronts fail faster
>than the rears, or do they fail at roughly the same time? Maybe we can spot a
>trend.
>
>Zak
>
>PS - I put no faith whatsoever in the C "article" mentioned. It was clearly,
>at least to me, a response to the article in GMCMM the month (or so) before.
>As I recall, unlike the GMCMM article which offered cutaway views and actual
>measurements as supporting facts, the C article offered nothing other than
>saying that the shocks were designed for the GMC and were not overpriced truck
>shocks. The overpriced truck shocks remark was one of several that made it
>overly clear to me that the article was just a response to the GMCMM article
>and not a real article intending to objectively review GMC shock performance.
>Don't believe my memory. Go back and read the GMCMM shock article. Then read
>the C article and form your own opinions.
>
>
>

>Vic this subject has been thoroughly studied by Cinnabar engineering and
>detailed in several different issues including the December 1998 issue of
>the GMC motorhome news.
>
>Bottom line KYBs and Bilsteins are true double acting gas shocks with life
>time warranties...Caspros are not.
>
>Relative to the shocks breaking. THEY WERE DESIGNED TO BREAK UNDER SEVERE
>LOADS! Remember the GMC motorhomne shock absorbers also act as SUSPENSION
>LIMITERS. When they are overstressed they break instead of breaking
>something else in your suspension system. If someone is breaking shocks
>either the mounts are not parallel or they are driving them to hard. In
>either case its not the shocks fault.
>
>Before I bought the KYBs I read everything I could find and am convinced
>they are the best buy with excellent performance.
>
>
>
 
I ordered the KYB's. My Caspro's were trash. They had twenty thousand
miles on them and there was absolutely nothing left but a shaft of steel
with a very loose steel sleeve wrapped around it. I may be taking a risk by
purchasing a so called lesser shock but I got all six KYB's for nearly the
price of two Caspros. At that point they become almost disposable to me. I
can afford to carry spares and still be ahead. I find it very hard to
believe that the shock mount was designed to be the suspension stop. There
is no way that the Caspro shock nor any shock that I've seen, could
withstand that kind of repeated stress. If the shock really performs that
duty maybe a person should install a limiting strap for the desired off road
baja racing desired. When I get the shocks installed I'll follow up with my
experience. Even though I had two of the Caspro shocks fail (on the same
side rear.) I will admit the rest of the ride was really something. I hope
I haven't made a mistake and I'll be the first one to eat crow if I'm wrong.
As always, thanks to everyone for the input.

Mike
 
Emery,

Have you taken the shocks out to confirm they are good, or are you going by
ride quality? Just wondering. It seems that most of us don't notice that the
shocks are "dead" until we take them out or they break. The GMCs seem to ride
pretty well even with shocks that are totally dead, so it seems pretty easy to
miss the gradual deterioration of the shocks. From the messages I have read,
it seems like just about everyone that has taken out their shocks has found at
least one dead one. Maybe they are just the only ones writing in though.
Your 65,000 is pretty impressive. It would be nice to see some hard
information (ie shocks taken out and tested) of how long each brand of shock
typically lasts. When I say tested, it could just mean either yes it is still
dampening fairly smoothly when taken out and operated by hand or no it is
basically frozen or free and isn't dampening much at all when taken out and
operated by hand.

Did you fix anything in the back where the KYB broke, or has the Bilstein
lasted in the same conditions that the KYB broke in. How did the KYB fail (ie
eyelet broke, eyelet disconected from shock or rod but remained intact, rod
broke, mount broke)? Any idea why? I think it will be useful to get some
details to see if most of the shocks are breaking the same way.

Zak

>

My Bilstein's have about 65,000 miles on them and still going strong. My
last ones were KYB and I had a rear one break.

Emery Stora
77 Kingsley
Santa Fe, NM
 
Emory, a point that everyone seems to have overlooked. A gas shock behaves
totally different than a double tube shock, such as a caspro or delco. When
the KYB or Bilstein fails they lose their gas all at once since they are
under such high pressure. Take them off and if they still have resistance
they are good. Assuming they still are structurally sound of
course.Corvettes, ferrari, mercedes etc all come standard with Bilsteins.

>

>
>by
>
>ride quality? When I say tested, it could just mean either yes it is
>still
>
>dampening fairly smoothly when taken out and operated by hand or no it is
>
>basically frozen or free and isn't dampening much at all when taken out and
>
>operated by hand.>>>>
>
>ZAK -- When I put on the disk brakes on the four rear wheels last summer I
>was able to check the Bilstein shocks. They seemed like new. They were
>still so strong that I had a bit of a struggle compressing them by hand to
>get them back onto the mounting bolts. When I first installed them they were
>wired to keep them from extending. It was a lot easier to install the first
>time.
>
>The front ones were checked a year ago last Jan. when I replaced the ball
>joints on the front lower control arms. They also seemed in very good shape.
>
>
>
>eyelet broke, eyelet disconnected from shock or rod but remained intact, rod
>
>broke, mount broke)? Any idea why? >>>>
>
>The support bolt going to the GMC pivot arm was bent and the eyelet on the
>shock was cracked. They didn't seem to have a lot of pressure left in them
>and were relatively easy to compress or extend. I have no idea as to why the
>damage occurred.
>
>I had installed the KYBs in about 1984. I put on the Bilsteins in about
>1992 or 1993.
>
>Emery Stora
>77 Kingsley
>Santa Fe, NM
>
>
 
Emery,

Thanks for the information. Sounds like those Bilsteins might be worth the
extra money. I'm still a little leery of the other breakage reports, but you
definitely can't argue with >65,000 miles.

The KYB breakage info is very interesting. It sounds like the shock might
have temporarily jammed/froze to cause that type of damage. Since they were
dead, maybe the rod started rubbing on the inside and wore through something
or got sloppy enough to temporarily catch/jam on another internal part.

This information brings up some interesting things for us to consider. The
out of alignment mounts could be causing the shocks to fail which then allows
the shock to get sloppy and temporarily lock and then break. I'm assuming
that the shocks would be designed well enough so that they won't jam/catch
when hitting a bump (doesn't seem like jam in rebound would be as important or
cause as much damage) in a normal application even when worn out. Since our
rears are used in "reverse", however, they might jam/catch in that same
situation unless the rest of shock's design is also changed (more than just
the valving I would think). For such a low production application, I could
see changing the valving (pretty easy I would think), but I doubt if the rest
of the shock design would be worth changing. Of course, this would only be a
valid idea if most of the shocks are breaking on the rear of the GMCs. I
don't know if this is the case or not. Anyone have the cutaway views from the
GMCMM (or maybe better ones from somewhere else) to take a look and see if
this looks like the idea has any merit? Anyone else have any thoughts? Has
anyone ever found a "good" broken shock?

Thinking about this some more still leads me back to the shock design itself
causing the breakage. It might not, however, be a weak external design as I
had been thinking. Something internal must be going pretty seriously wrong
for a dead shock to lock enough to break itself and bend its mount. It seems
like proper bushings or other design precautions would keep the shock from
getting out of alignment enough to do this. Shock brands that aren't breaking
must have an internal design that prevents this situation from occurring. If
I remember correctly, the gas shocks had pretty small OD rods while the
non-gas shocks had much larger OD rods. The larger outer diameter rod could
give enough additional side load bearing surface at the bushings to prevent
the shock from getting sloppy as quickly due to unaligned mounts.

Lots of guessing on my part in this one,
Zak

ZAK -- When I put on the disk brakes on the four rear wheels last summer I
was able to check the Bilstein shocks. They seemed like new. They were
still so strong that I had a bit of a struggle compressing them by hand to
get them back onto the mounting bolts. When I first installed them they were
wired to keep them from extending. It was a lot easier to install the first
time.

The front ones were checked a year ago last Jan. when I replaced the ball
joints on the front lower control arms. They also seemed in very good shape.

The support bolt going to the GMC pivot arm was bent and the eyelet on the
shock was cracked. They didn't seem to have a lot of pressure left in them
and were relatively easy to compress or extend. I have no idea as to why the
damage occurred.

I had installed the KYBs in about 1984. I put on the Bilsteins in about
1992 or 1993.

Emery Stora
77 Kingsley
Santa Fe, NM
 
Rick,

My point was that the major forces the shock is taking are in the reverse
direction. IE the shock is extending when hitting a bump. I would think that
this is when most damage would occur. I would think that if a shock locked
temporarily during rebound, it wouldn't be nearly as much of a problem as if
it locked during jounce. The shock can damp both ways, but it really only has
to be designed to take spike forces in one direction for a normal application.
In our application, those spike forces are extending the shock. In a normal
application those spike forces are compressing the shock. The valving, as I
said, would be easy to change (especially since, as you said, the shocks are
already damping both ways anyway). The rest of the design might not be so
easy.

Zak

Zak,
PMFJI, but I've heard this theory before, and I thought I'd try and shoot
one more myth before bed. ;-) Ordinary, everyday shocks DO damp in BOTH
directions, just not equally. Standard OEM shocks are usually between 40/60
and 30/70 rated, meaning that (in the first case) they provide 40% of their
damping on jounce (wheel rising.) and 60% on rebound (wheel descending)
This allows the wheels to move upward easily when hitting a bump (for a soft
ride), but apply more damping on rebound to prevent excessive bouncing. High
performance rally or road-racing shocks usually are close to 50/50 (same
damping force on jounce and rebound.) Even the highly specialized front
shocks sold to drag racers, calibrated to let the front end rise quickly off
the line and then STAY high for maximum weight transfer to the rear wheels,
are rated 90/10 (90% jounce (to keep it up) and 10% rebound to let it rise
quickly off the line.) My point is that ALL of these shocks exert damping
force (convert motion to heat) in both directions, so that's nothing new.
True, our rear shocks work "backward" (extending on jounce and compressing on
rebound), and so will need reversed valving to work "right", but they're not
otherwise different from any other shock.
BTW, I'm not recommending Delco shocks (think I prefer something a little
fancier), but for those who claim they won't work on a GMC: What do you
think GM put on our coaches at the factory? If it is designed for the GMC,
and listed for the GMC, it'll work (some better than others.) As someone
said, "This isn't rocket science."
My .02.

Rick Staples
'75 Eleganza
Louisville, CO
 
Emery,

I still don't see it that way. When you hit a pothole/etc, the force is
almost totally instantaneous. When a force is an impact like that, it is much
more destructive because the entire force is put into the suspension over a
very short amount of time. On the rears of our GMC, this is a force that
makes the shocks extend. On most applications this would make the shock
compress. The rebound is going to happen much more slowly (relatively
speaking) and is therefore going to have much more time to dissipate the
force. If the shock jams in jounce, the entire force is sent directly to the
mounts as an impact. If the shock jams in rebound, not much is going to
happen. On the front, the wheel wouldn't come down, so the motorhome would
come down on it which would create a jounce condition again. On the rear, it
is a more complicated to think about since the air bag is involved that
connects the two wheels. It seems to me that any rebound forces on the rear
shocks would have to be provided by the airbags which would seem to be pretty
non-impact. There is nothing on the GMC that is going to push the wheels down
with an impact force like a pothole is going to push them up.

Zak

The only rebound force is going

>

Zak -- I have to disagree with you on this one. With the heavy weight of the
tire, wheel, brakes and suspension arm the GMC also needs support for the
"spike" forces when compressing the shock as well. There is a lot of
unsprung weight that must be taken care of by the shock. The upward movement
of the body and the downward movement of the control arm (such as a wheel
going into a pothole) would both extend the shock. But when the wheel comes
back out of a pothole or gravity pulls the body of the motorhome back down
there would be a lot of compressive force that need dampening from the
shocks. Its just a matter of what ratio the shock provides as Rick had posted
.

Emery Stora
77 Kingsley
Santa Fe, NM
 
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