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Re: [GMCnet] New airbags [message #136564 is a reply to message #136562] |
Fri, 29 July 2011 11:03 |
Dennis S
Messages: 3046 Registered: November 2005
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Mark or anyone else who may have one,
Do you still have the end of the airbag that held the fill valve? If you have no need, I have a good bag that I keep here for a spare/loaner -- but it is missing the fill valve.
Happy to pay shipping.
Dennis
Dennis Sexton
73 GMC
Germantown, TN 38138-2066
USA
-----Original Message-----
From: Mark Grueninger <markgrue@hotmail.com>
To: gmclist <gmclist@temp.gmcnet.org>
Sent: Fri, Jul 29, 2011 10:54 am
Subject: Re: [GMCnet] New airbags
The shocks are on my TO DO list not at the top but close. I like the quality
f the bilstiens we use on our dirt late model stock car so I will probably go
ith them. Different animal I know but I would think the quality is still
here. I will see. I see Jimk has them so I will more then likely get them
rom him. I intend to get some adjustable links for the rear ride height and
ee what i can do with the front torsion bars to get the ride height in line.
ave 1 more camping trip in august then will start working on it. I think you
re really close with the rear height numbers. Thats about what i figured.
hanks for your input I appreciate it.
Mark
obert Mueller wrote on Fri, 29 July 2011 09:41
Mark,
The ride height for the rear is specified as 11 11/16" +/- 1/4" from the
ground to the top of the oval slot in the frame (MM X-7525 Page 3-34 Fig 70
Checking Vehicle Ride Height.)
From memory: the frame is 6" tall and the slot is about 3/4" "high."
Here's the ride height math for your GMC:
8 3/4" = Ground to bottom of frame
3 " = Distance from bottom of frame to middle of adjustment slot
3/8" = Distance from middle to the top of the slot (3/4" divided by 1/2)
12 1/8 = Ride height
If I've got all my figures right I agree that you're a bit too high. This is
what I thought when I saw in your pictures that the bag mounting flanges on
the bogie arms were not parallel but a bit spread apart at ride height. It
has been noted on the GMCnet that at the correct ride height you can draw a
straight line from the rear wheel spindle center to middle wheel spindle
center, it will intersect the center of the bogie pins; and the bag mounting
flanges will be parallel.
You note below that you need to drop your ride height by about 3/4" that
would result in a ride height setting of about 11 5/8" which is within spec.
BTW having the rear a bit low will increase caster (marginally) and improve
handling.
On to the shock absorbers; I suspect that the shocks you have on the rear of
your GMC are for a car or truck and not a GMC.
I reviewed the presentation that Manny Trovao made at the first GMC
Convention I attended (Santa Rosa 2008) and noted the following:
Quote:
Shock absorbers work on the principle of fluid displacement on both the
compression and extension cycle. A typical car or light truck will have more
resistance during its extension cycle then its compression cycle. The
compression cycle controls the motion of a vehicle's unsprung weight, while
extension controls the heavier sprung weight.
On our motorhomes, the front shock has more resistance on the compression
cycle than on the extension cycle. On the rear, it's the opposite, it has
more resistance on the extension cycle than on the compression cycle.
Unquote
A bit further along in the presentation he has photos of shocks that have
been cutaway to show their innards. They are AC-Delco, Caspro, KYB, and
Bilstein.
Under the picture of the AC-Delco shock he states:
Quote
This is the original AC/Delco that came with the Motorhome. It's a twin tube
design. Inner tube chamber. It is no longer made
Unquote
If you are a member of GMCMI you can click on the link below; log in and
review the whole presentation:
http://www.gmcmi.com/mem-bers/TechHandouts/GMC_Shocks.pdf
I have only been a GMC owner and GMCnet member for four years and to date I
have never heard anyone note that they had "new looking" AC-Delco shocks on
their GMC. AFAIK the only shocks currently available for the GMC are made by
KYB or Bilstein.
In discovered all of this because when I drove The Blue Streak from Mudgee
(country NSW) back to Sydney and it was all over the road. During my
research on how to fix it I discovered there was a bunch of stuff wrong with
the front end and on the rear end the shocks that a PO had installed were
from a car.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
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ark Grueninger 76 Palm Beach
almeyer IL
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Dennis S
73 Painted Desert 230
Memphis TN Metro
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Re: [GMCnet] New airbags [message #136587 is a reply to message #136550] |
Fri, 29 July 2011 12:38 |
fred v
Messages: 999 Registered: April 2006 Location: pensacola, fl.
Karma: 0
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[quote Rob Mueller wrote:
I reviewed the presentation that Manny Trovao made at the first GMC
Convention I attended (Santa Rosa 2008) and noted the following:
Quote:
Shock absorbers work on the principle of fluid displacement on both the
compression and extension cycle. A typical car or light truck will have more
resistance during its extension cycle then its compression cycle. The
compression cycle controls the motion of a vehicle's unsprung weight, while
extension controls the heavier sprung weight.
On our motorhomes, the front shock has more resistance on the compression
cycle than on the extension cycle. On the rear, it's the opposite, it has
more resistance on the extension cycle than on the compression cycle.
Unquote
[/quote]
isn't the "typical car or light truck" statement backwards. all cars resist compression more and extension less so the wheel will drop quicker to recontact the road. the motorhome statement is correct.
hope i didn't get this backwards myself.
Fred V
'77 Royale RB 455
P'cola, Fl
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Re: [GMCnet] New airbags [message #136629 is a reply to message #136585] |
Fri, 29 July 2011 20:14 |
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USAussie
Messages: 15912 Registered: July 2007 Location: Sydney, Australia
Karma: 6
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Matt,
Jawohl!
I zink zat is beecaus zeh not making zem in Deutchland not no more!
I zink zey are beink made in Khina!
Und ve all know vat zat means!
Regards,
Rob "ze USAussie Kraut" M.
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: Matt Colie
Mark,
I too was once a Bilstien brother.. (Now referred to as bilgetein.) Not
only have they gotten really nasty and hard to deal with at warranty time,
but the warranties seem to be very common for GMC. Before you buy, talk to
JimK about this.
Matt
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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Re: [GMCnet] New airbags [message #136653 is a reply to message #136629] |
Fri, 29 July 2011 22:41 |
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Rob,
How many brain cells did you loose on that one?
Ve haups yüse gout zom leff.
Byron
-----Original Message-----
From: Rob Mueller <robmueller@iinet.net.au>
Reply-To: <gmclist@temp.gmcnet.org>
Date: Sat, 30 Jul 2011 11:14:16 +1000
To: <gmclist@temp.gmcnet.org>
Subject: Re: [GMCnet] New airbags
>Matt,
>
>Jawohl!
>
>I zink zat is beecaus zeh not making zem in Deutchland not no more!
>
>I zink zey are beink made in Khina!
>
>Und ve all know vat zat means!
>
>Regards,
>Rob "ze USAussie Kraut" M.
>Sydney, Australia
>AUS '75 Avion-The Blue Streak TZE365V100428
>USA '75 Avion-Double Trouble TZE365V100426
>
>
>-----Original Message-----
>From: Matt Colie
>
>Mark,
>
>I too was once a Bilstien brother.. (Now referred to as bilgetein.) Not
>only have they gotten really nasty and hard to deal with at warranty time,
>but the warranties seem to be very common for GMC. Before you buy, talk
>to
>JimK about this.
>
>Matt
>
>
>_______________________________________________
>GMCnet mailing list
>Unsubscribe or Change List Options:
>http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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--
Byron Songer
Full-timing to enjoy the USA
Former owner but still an admirer
GMC paint schemes at -
http://www.songerconsulting.net
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Re: New airbags [message #136662 is a reply to message #136547] |
Sat, 30 July 2011 01:25 |
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mike miller
Messages: 3576 Registered: February 2004 Location: Hillsboro, Oregon
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lilmyk wrote on Fri, 29 July 2011 07:34 | One option for eliminating the possibility of over extending the shocks is to use "shock straps" ...
...
Hopefully, the internal bump stop of the airbag and the brackets will eliminate the shocks from being over compressed. ...
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The shocks work backwards to what you are saying...
The internal bump stop in the bag should protect the shock from over extension. (ie: straps would not help.)
GMC rear shocks get damaged by to much COMPRESSION, normally from jacking without letting the air pressure out of the bag. It causes the seals to leak oil. The Bilstein shocks on my '78 seem to be more susceptible to this problem than the KYB's on my other two coaches.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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Re: New airbags [message #136986 is a reply to message #136214] |
Mon, 01 August 2011 02:33 |
spiffycar
Messages: 133 Registered: May 2010 Location: Brook Park ,Ohio
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mgrue wrote on Wed, 27 July 2011 07:08 | I finished installing my new airbags and I am very satisfied with the results. They are 9.2 inches in diameter so use about half the pressure of the originals. Ride is about the same but the compressor is not working nearly as hard to produce 60 psi instead of 125. They have enough travel to raise and lower the coach to the limits of the shock travel. Let me know what you think.
http://www.gmcmhphotos.com/photos/showphoto.php?photo=39889&nocache=1
Mark
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Nice job! Its always good to see people trying new ideas.
Just a thought to add to it.....
I would consider setting the cutoff for the compressor at around 85-90psi and installing a regulator on the tank output to the power level valves. That way you would have some reserve to fill those big bags if you need to raise the coach in a hurry. You can then also add a valve with an unregulated output for an air-hose for filling your tires as well.
Paul W L
76 Daytona Beach! ( EX-Palm Beach )
Cleveland,OH
& Current Card Carrying Pull A Part VIP Member
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Re: New airbags [message #137863 is a reply to message #136986] |
Sun, 07 August 2011 10:16 |
C Boyd
Messages: 2629 Registered: April 2006
Karma: 18
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Mark[/quote]
Nice job! Its always good to see people trying new ideas.
Just a thought to add to it.....
I would consider setting the cutoff for the compressor at around 85-90psi and installing a regulator on the tank output to the power level valves. That way you would have some reserve to fill those big bags if you need to raise the coach in a hurry. You can then also add a valve with an unregulated output for an air-hose for filling your tires as well.
[/quote]
Sir: the only way to raise the coach faster is with more air volume to the bag, ie larger storage tank and supply line. The level control valve controls the air pressure in the bag. If it takes 80lb to get level it cuts the air off at level so there is only 80lb in the bag even if there is 125 in the storage tank.
C. Boyd
76 Crestmont
East Tennessee
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Re: [GMCnet] New airbags [message #138399 is a reply to message #136474] |
Thu, 11 August 2011 04:53 |
Donovan-formerly Jase386
Messages: 139 Registered: January 2009 Location: Greenville SC
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On the shorter bags like this thread is about and the ones southland is selling you cant store the Coach deflated. There isnt enough clearance between the 'back' of the blind screw and the piston. you have a tiny point the size of a pencil eraser supporting half the coach and pinches the airbag. Ask Zeb or I how we know....
Donovan, Greenville SC
1975 Eleganza II
81,500 miles
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Re: [GMCnet] New airbags [message #138798 is a reply to message #136250] |
Fri, 12 August 2011 23:38 |
Bob de Kruyff
Messages: 4260 Registered: January 2004 Location: Chandler, AZ
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Ken Henderson wrote on Wed, 27 July 2011 08:01 | Mark,
Looks like a great mod. Have enough road time with it enough to
comment on the change in ride/stability characteristics? I'd expect
more "floating" and rolling with so much lower pressure. That might
create more need for rear sway bars, which I don't like with the OEM
bags because of the leveling problems the heavy ones create.
Ken H.
On Wed, Jul 27, 2011 at 7:08 AM, Mark Grueninger wrote:
>
>
> I finished installing my new airbags and I am very satisfied with the results. They are 9.2 inches in diameter so use about half the pressure of the originals. Ride is about the same but the compressor is not working nearly as hard to produce 60 psi instead of 125. They have enough travel to raise and lower the coach to the limits of the shock travel. Let me know what you think.
>
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=39889&nocache=1
>
> Mark
> -
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Ken, unless the geometry of the suspension is changed, the ride rate should not change--it takes so much force to get the coach to the correct trim no matter what combination of area or pressure you use--again, assuming the bag is in the same place with the same lever arm relationship,
Bob de Kruyff
78 Eleganza
Chandler, AZ
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Re: [GMCnet] New airbags [message #138804 is a reply to message #138798] |
Sat, 13 August 2011 00:26 |
Ken Henderson
Messages: 8726 Registered: March 2004 Location: Americus, GA
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Well, yeah, that does make sense:
X psi * Y sq.in = Y psi * X sq.in. = Z lbf
Ken H.
On Sat, Aug 13, 2011 at 12:38 AM, Bob de Kruyff <NEXT2POOL@aol.com> wrote:
>
>
> Ken Henderson wrote on Wed, 27 July 2011 08:01
> > Mark,
> >
> > Looks like a great mod. Have enough road time with it enough to
> > comment on the change in ride/stability characteristics? I'd expect
> > more "floating" and rolling with so much lower pressure. That
>
> Ken, unless the geometry of the suspension is changed, the ride rate should
> not change--it takes so much force to get the coach to the correct trim no
> matter what combination of area or pressure you use--again, assuming the bag
> is in the same place with the same lever arm relationship,
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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Re: [GMCnet] New airbags [message #138849 is a reply to message #138798] |
Sat, 13 August 2011 09:49 |
winter
Messages: 247 Registered: September 2007 Location: MPLS MN
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[/quote]
Ken, unless the geometry of the suspension is changed, the ride rate should not change--it takes so much force to get the coach to the correct trim no matter what combination of area or pressure you use--again, assuming the bag is in the same place with the same lever arm relationship,[/quote]
That may be true in a static condition, but the spring rate of the bags could be different. A higher spring rate could make the coach feel more stable
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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Re: [GMCnet] New airbags [message #138910 is a reply to message #138849] |
Sat, 13 August 2011 16:32 |
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Matt Colie
Messages: 8547 Registered: March 2007 Location: S.E. Michigan
Karma: 7
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winter wrote on Sat, 13 August 2011 10:49 |
Quote: |
Ken, unless the geometry of the suspension is changed, the ride rate should not change--it takes so much force to get the coach to the correct trim no matter what combination of area or pressure you use--again, assuming the bag is in the same place with the same lever arm relationship,
| That may be true in a static condition, but the spring rate of the bags could be different. A higher spring rate could make the coach feel more stable
|
Jerrod,
While your concern about spring rate is valid, I will submit that the design with a rolling piston even if only at one end has got to be closer to the OE spring rate than any with the squashed balloon types that are most often used. (Change in volume per unit travel is very different between the two designs.) This type is one rolling piston, at about half the pressure for the same force. My person grab and go engineering judgment would say it has to be about as close as we can get with any off-the-shelf parts available. The fact that it retains the capability to "walk over" variations in road surface is, I believe, going to be one of its biggest assets.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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Re: [GMCnet] New airbags [message #139094 is a reply to message #138910] |
Sun, 14 August 2011 14:02 |
winter
Messages: 247 Registered: September 2007 Location: MPLS MN
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mcolie wrote on Sat, 13 August 2011 16:32 |
winter wrote on Sat, 13 August 2011 10:49 |
Quote: |
Ken, unless the geometry of the suspension is changed, the ride rate should not change--it takes so much force to get the coach to the correct trim no matter what combination of area or pressure you use--again, assuming the bag is in the same place with the same lever arm relationship,
| That may be true in a static condition, but the spring rate of the bags could be different. A higher spring rate could make the coach feel more stable
|
Jerrod,
While your concern about spring rate is valid, I will submit that the design with a rolling piston even if only at one end has got to be closer to the OE spring rate than any with the squashed balloon types that are most often used. (Change in volume per unit travel is very different between the two designs.) This type is one rolling piston, at about half the pressure for the same force. My person grab and go engineering judgment would say it has to be about as close as we can get with any off-the-shelf parts available. The fact that it retains the capability to "walk over" variations in road surface is, I believe, going to be one of its biggest assets.
Matt
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I'm in agreement on keeping the system simple and retaining its original function with off the shelf parts. The bottom stops are also a very nice addition to the GM design.
I often wondered if a higher spring rate, or a non linear rate, would yield a more stable ride with less porposing (if thats a word). I would imagine that most of the comfort of the GM design lays in a small amount of deflection of the bags. It would be interesting to measure the bag length while driving down the road.
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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Re: [GMCnet] New airbags [message #139172 is a reply to message #139094] |
Sun, 14 August 2011 20:16 |
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Matt Colie
Messages: 8547 Registered: March 2007 Location: S.E. Michigan
Karma: 7
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winter wrote on Sun, 14 August 2011 15:02 |
mcolie wrote on Sat, 13 August 2011 16:32 |
winter wrote on Sat, 13 August 2011 10:49 |
Quote: |
Ken, unless the geometry of the suspension is changed, the ride rate should not change--it takes so much force to get the coach to the correct trim no matter what combination of area or pressure you use--again, assuming the bag is in the same place with the same lever arm relationship,
| That may be true in a static condition, but the spring rate of the bags could be different. A higher spring rate could make the coach feel more stable
| Jerrod,
While your concern about spring rate is valid, I will submit that the design with a rolling piston even if only at one end has got to be closer to the OE spring rate than any with the squashed balloon types that are most often used. (Change in volume per unit travel is very different between the two designs.) This type is one rolling piston, at about half the pressure for the same force. My person grab and go engineering judgment would say it has to be about as close as we can get with any off-the-shelf parts available. The fact that it retains the capability to "walk over" variations in road surface is, I believe, going to be one of its biggest assets.
Matt
| I'm in agreement on keeping the system simple and retaining its original function with off the shelf parts. The bottom stops are also a very nice addition to the GM design.
I often wondered if a higher spring rate, or a non linear rate, would yield a more stable ride with less porposing (if thats a word). I would imagine that most of the comfort of the GM design lays in a small amount of deflection of the bags. It would be interesting to measure the bag length while driving down the road.
| Jerrod,
You are close, the spelling is porpoising.
You also seem to be stuck with a misconception. The smoothness of the ride is largely a result of a low spring rate coupled with very large suspension travel. If you are having porpoising issues, then you shock absorbers (which really are not, they are supposed to be motion dampers) and not doing their part.
In Short - The wheels can move a lot without the body moving very much.
While this makes a smooth ride, it unfortunately allows a lot of body roll (people call it sway, but it is not - sway is another axis). The four bag systems have a higher spring rate and less travel which leads some people to like the handling better. That is a matter of preference.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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