[GMCnet] Affect on alignment of rear ride height set too high
Gary Bovee
Thanks,
Gary Bovee
1978 Royale by Coachman
Red Bluff, CA
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D C *Mac* Macdonald
IIRC, it reduces the caster in the front suspension,
thereby leading to less stability, "wandering", etc.
A possible "cure" for the butt-dragging appearance
might be body-mount pads that were slightly tapered
and progressively thicker as they proceed front to
rear. I suspect they would have to end up about an
inch thick at the rear to get rid of the alligator
tail-dragging look. Probably not cost efficient with
the juice not being worth the squeeze!
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~~ k2gkk @ hotmail dot com ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
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~ www.gmcmhphotos.com/okclb ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
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*--OO---[]---O-*
A.
k2gkk wrote on Mon, 06 February 2012 11:00
> ...A possible "cure" for the butt-dragging appearance might be body-mount pads that were slightly tapered and progressively thicker as they proceed front to rear....
If the front pads are 1/4" thick, the rear ones would have to be 1-11/16" to take care of all of the difference.
--
'73 23' CanyonLands
UA (Upper Alabama)
James Hupy
accept the FACTORY RECOMMENDED ride height. The GMC Motorhome is not really
happy suspension, steering and tire wear wise if you stray very far from
the OEM specs. But, that having been said, America is the land of the free
and home of the brave, and you are free to choose to alter your suspension
ride height so it pleases your sense of "what looks right to you". If your
coach handles poorly as a result, but it looks "cool", and you are willing
to trade off driveability for style, feel free to do so. Up here in the
Pacific Northwest, we have something called the Columbia River Gorge, kind
of a natural wind channel from east to west. It has a multilane limited
access freeway that runs along the river. It is a supreme test of the GMC
handling when the wind blows through there. If you have any deficiencies in
your suspension and steering, it will serve you well to pay a good deal of
attention to ride height, particularly in the rear. If you are high at all,
the wind will blow the coach from lane to lane if it is severe enough. They
occasionally will post extreme wind warning signs there. Sometimes, the
chassis engineers screw up and get one right. The GMC really does respond
to small changes in suspension height and alignment.
Jim Hupy
Salem, OR
78 GMC Royale 403
Hal Kading
If one were to "fix" the butt low appearance of the GMC by using progressively thicker rubber pad cushions, I'd suggest using the stock thickness pads and making up the variable thickness with metal shims. The thicker rubber pads would compress more than the thinner ones.
Hal Kading 77 Kingsley 455 Las Cruces NM
Rob Mueller
I reckon that the engineers that designed the GMC set it up tail low with a tolerance in the ride height front and rear of +/- 1/4"
for a sound engineering reason; they have a propensity for that! ;-)
I sure wish "we" could have spoken to one of them and asked them what it was!
Regards,
Rob M.
-----Original Message-----
From: James Hupy
I have always wondered at the resistance of some in the GMC community to
accept the FACTORY RECOMMENDED ride height. The GMC Motorhome is not really
happy suspension, steering and tire wear wise if you stray very far from
the OEM specs. But, that having been said, America is the land of the free
and home of the brave, and you are free to choose to alter your suspension
ride height so it pleases your sense of "what looks right to you". If your
coach handles poorly as a result, but it looks "cool", and you are willing
to trade off driveability for style, feel free to do so. Up here in the
Pacific Northwest, we have something called the Columbia River Gorge, kind
of a natural wind channel from east to west. It has a multilane limited
access freeway that runs along the river. It is a supreme test of the GMC
handling when the wind blows through there. If you have any deficiencies in
your suspension and steering, it will serve you well to pay a good deal of
attention to ride height, particularly in the rear. If you are high at all,
the wind will blow the coach from lane to lane if it is severe enough. They
occasionally will post extreme wind warning signs there. Sometimes, the
chassis engineers screw up and get one right. The GMC really does respond
to small changes in suspension height and alignment.
Jim Hupy
Salem, OR
78 GMC Royale 403
_______________________________________________
John R. Lebetski
The thicker pads would lift the body off the frame, but leave the rear bumper where it was, creating a very unappealing gap. The effect though minor would not help CG and effect of crooswinds would be worse will a longer lever arm, though slight.
--
John Lebetski
Chicago, IL
77 Eleganza II
Dan Gregg
I personally like the low look in the back of GMCs. And, I have driven the Columbia Gorge several times in our coach, that Jim mentioned. Our coach handles great through there. When I was a kid I kept the rear of my 65 Mustang Fastback raised with air shocks. Now I keep the rear end of our GMC lowered with Quadrabags.
Life was good then and life is good now. Our 16 grandchildren also love the GMC low in the rear. They say it makes for good tread wear on the front tires.
Dan
--
Dan & Teri Gregg
Soft White LED Lighting
http://danandteri.blogspot.com/
Jim Melberg
Somebody check my reasoning, please, and tell me what is wrong with it. When one peruses the GMC parts manual, one soon discovers that there are two (2) distinct major categories - - the frame assembly which includes the motor, transmission, front running gear, rear suspension and running gear, fuel tanks, etc., etc., etc. - - and the body assembly which includes the aluminum/fiberglass shell, seating, cabinets, etrc., etc., etc. Way back in the GMC mail list days (before the Forum became a gleam in Batman’s eye) it was noted.by someone that the body could be removed from the frame and the frame could theoretically be driven down the driveway (not street legal anymore). The suspension, if it had not been fiddled with during the removal of the body, would still be at the proper ride height since there are no, repeat, no suspension connections to the body components. It should be noted here that the accepted suspension settings are from the ground up to specific slots
in the frame, not to any points on the body. It should also be noted that there is a one and seven sixteenths inch (1-7/16”) differential in the dimensions, the front being higher than the rear. WHY??? Are the two slots at different gauges on their respective members? It has been too long since I was capable of crawling under my coach to look. But, if the slots are both at the same gauge, then the whole frame is higher front than in the back. And since the body rests flat on the main longitudinal frame rails, it too is higher in the front than the rear. Why?? Only the original GMC engineers know for sure and it may be noted in some obscure engineering notes, now forever lost. However, it is most probably because the cost to make the body level was not in the bean counters books.
Lets put the body back on the frame. Before we do that, tho, just for grins, lets lay an eight inch by eight inch (8” x 8”) timber across the frame, just behind the bogies. Yes, I know an 8 x8 is not a true 8 inches, closer to 7-1/2”, let’s not pick nits. Now let’s set the body on the frame. It would now have a nice rear high rake. This move has done nothing to the suspension other than apply the original load back onto it. The coach should handle the same as before, as we have done nothing to the suspension. Oh, yah. Some will say it will be different in the wind. Well, tell you what. Add that rear air conditioner and a possible large size pod, and I would say we are at least even.
With this all said, and I hope understood, what very slight difference would it make if the body were raked forward that one and seven sixteenths inches. Take a look at your thumb. The typical mans thumb is one inch wide. At the first knuckle, it approaches 1-1/4” wide. Let’s face it. Another quarter inch will not make that much difference. Your eye would hardly notice it, except the body, repeat, BODY of the coach would be level. The frame would still be unchanged. No affect on the suspension or steering or ride or etc., etc. etc.
What would require some changes to do this? Well, the waste pipes from the coach to the waste tank(s) will have to be longer. Depending on how your coach is plumbed, you may have to reroute the LP lines. Some electrical wiring may need attention, but that should be about it. The cockpit is within a very small tolerance of where it should be. Probably closer.
Now, where did I go wrong in my analysis?
--
Little Yimmy - W9VUA
75 PB - F260206
Twin Cities, MN
Jim Kanomata
were lower than the center or the rear wheels.
I know several have mentioned that the pins should be around the sane
height as the center of the rear.
There must be a cradle effect when the pins are lower, thus less sway.
Every coach is different to where one set of rules do not follow on every
adjustment.
On Mon, Feb 6, 2012 at 5:34 PM, Jim Melberg <pb75...@yahoo.com> wrote:
>
>
> Somebody check my reasoning, please, and tell me what is wrong with it.
> When one peruses the GMC parts manual, one soon discovers that there are
> two (2) distinct major categories - - the frame assembly which includes the
> motor, transmission, front running gear, rear suspension and running gear,
> fuel tanks, etc., etc., etc. - - and the body assembly which includes the
> aluminum/fiberglass shell, seating, cabinets, etrc., etc., etc. Way back
> in the GMC mail list days (before the Forum became a gleam in Batman’s eye)
> it was noted.by someone that the body could be removed from the frame and
> the frame could theoretically be driven down the driveway (not street legal
> anymore). The suspension, if it had not been fiddled with during the
> removal of the body, would still be at the proper ride height since there
> are no, repeat, no suspension connections to the body components. It
> should be noted here that the accepted suspension settings are from the
> ground up to specific slots
> in the frame, not to any points on the body. It should also be noted
> that there is a one and seven sixteenths inch (1-7/16”) differential in the
> dimensions, the front being higher than the rear. WHY??? Are the two
> slots at different gauges on their respective members? It has been too
> long since I was capable of crawling under my coach to look. But, if the
> slots are both at the same gauge, then the whole frame is higher front than
> in the back. And since the body rests flat on the main longitudinal frame
> rails, it too is higher in the front than the rear. Why?? Only the
> original GMC engineers know for sure and it may be noted in some obscure
> engineering notes, now forever lost. However, it is most probably because
> the cost to make the body level was not in the bean counters books.
> Lets put the body back on the frame. Before we do that, tho, just for
> grins, lets lay an eight inch by eight inch (8” x 8”) timber across the
> frame, just behind the bogies. Yes, I know an 8 x8 is not a true 8 inches,
> closer to 7-1/2”, let’s not pick nits. Now let’s set the body on the
> frame. It would now have a nice rear high rake. This move has done
> nothing to the suspension other than apply the original load back onto it.
> The coach should handle the same as before, as we have done nothing to the
> suspension. Oh, yah. Some will say it will be different in the wind.
> Well, tell you what. Add that rear air conditioner and a possible large
> size pod, and I would say we are at least even.
> With this all said, and I hope understood, what very slight difference
> would it make if the body were raked forward that one and seven sixteenths
> inches. Take a look at your thumb. The typical mans thumb is one inch
> wide. At the first knuckle, it approaches 1-1/4” wide. Let’s face it.
> Another quarter inch will not make that much difference. Your eye would
> hardly notice it, except the body, repeat, BODY of the coach would be
> level. The frame would still be unchanged. No affect on the suspension or
> steering or ride or etc., etc. etc.
> What would require some changes to do this? Well, the waste pipes from
> the coach to the waste tank(s) will have to be longer. Depending on how
> your coach is plumbed, you may have to reroute the LP lines. Some
> electrical wiring may need attention, but that should be about it. The
> cockpit is within a very small tolerance of where it should be. Probably
> closer.
> Now, where did I go wrong in my analysis?
>
> --
> Little Yimmy - W9VUA
> 75 PB - F260206
> Twin Cities, MN
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
Bob de Kruyff
Gary Bovee wrote on Mon, 06 February 2012 09:53
> Well it must be too early in the morning or maybe just a plain attack of CRS, but I can't seem to remember what the affect is on the front-end alignment when the rear ride height is set too high. Can someone refresh my memory?
>
> Thanks,
>
> Gary Bovee
> 1978 Royale by Coachman
> Red Bluff, CA
> Free â Idiot's Internet Guide to Finding 1973-1978 GMC Motorhome Information
> http://www.gmceast.com/about/guide/index.html
> Alternator & A/C Belt Tensioner Adjustors
> http://www.bdub.net/bovee/
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
A good simple question that turned into a runaway train! I high rear trim height will reduce the caster and will alos transfer a bit more load to the front and affect toe. As some have pointed out, GM did not pull these numbers out of their a.s, and I would stick as close to specs as possible. As Rob mentioned. a reasonable tolerance will go unnoticed.
--
Bob de Kruyff
78 Eleganza
Chandler, AZ
John R. Lebetski
Where you went wrong....
that the body could be removed from the frame and
> the frame could theoretically be driven down the driveway (not street legal
> anymore). The suspension, if it had not been fiddled with during the
> removal of the body, would still be at the proper ride height since there
> are no, repeat, no suspension connections to the body components.
As soon as you remove the body from the frame, the unloading will cause the front ride height to be way off, probably to the top bump stops.
The rear, if the height valves were attached to the frame (relocated) and not the body and if you "brought with the air pump and plumbing", would self level back to the normal height.
You'd be sitting nose high.
--
John Lebetski
Chicago, IL
77 Eleganza II
Mike Miller
Little Yimmy wrote on Mon, 06 February 2012 17:34
> Somebody check my reasoning, please, and tell me what is wrong with it. ....
I see nothing wrong with your analysis.
If you repositioned the body to sit on the frame a little higher in the rear, you could have the body level to the ground and the frame "low in the back" as needed for the correct front end geometry.
-- But why? --
If your air suspension is working properly, set it to "travel" when on the highway. When pulling into town put it in "raise" for a few counts as needed to level the coach. You'll have more clearance under the rear and slightly quicker steering (both good for in town driving) PLUS the "level look" for around town.
I do it a little backwards. (But that is me.) My #2 coach is set to level when in "travel." I set it to lower for the count of four when getting on the highway. I put it in "travel" when getting OFF the highway.
--
Mike Miller -- Hillsboro, OR -- on the Black list
(#1)'73 26' exPainted D. -- (#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
http://m000035.blogspot.com
Greg and April
If it is simply a visual thing, and the coach **just** appears to be
dragging it tail while on the move, why not just use an optical illusion to
make the rear of the coach to appear to be on the level or even higher?
Paint a matt black stripe right along the bottom sides of the coach, perhaps
a 1 inch wide at the front of the coach, and 2-2 1/2 inches wide at the
back. This will give the illusion that the rear of the coach is level
with ( or higher than ) the front since the human brain tends to ignore the
dark area under a vehicle as the eye is attracted to the lighter colors.
So what the matt black stripe at the bottom of the coach does, is making it
appear that the shadow at the rear of the coach appear to be higher than it
actually is, because unless the person observing the coach has very sharp
eyes, to see less than .5* of angle over the entire length, or goes up and
measures it, the brain is going to assume that the stripe is the same width
along the entire length.
Just a thought.
Greg H.
I don't just march to the beat of my own drum - I have an entire brass band
to keep me company.
.
Rob Mueller
Clever idea!
Regards,
Rob M.
-----Original Message-----
From: Greg and April
Stupid question.....
If it is simply a visual thing, and the coach **just** appears to be
dragging it tail while on the move, why not just use an optical illusion to
make the rear of the coach to appear to be on the level or even higher?
Paint a matt black stripe right along the bottom sides of the coach, perhaps
a 1 inch wide at the front of the coach, and 2-2 1/2 inches wide at the
back. This will give the illusion that the rear of the coach is level
with ( or higher than ) the front since the human brain tends to ignore the
dark area under a vehicle as the eye is attracted to the lighter colors.
So what the matt black stripe at the bottom of the coach does, is making it
appear that the shadow at the rear of the coach appear to be higher than it
actually is, because unless the person observing the coach has very sharp
eyes, to see less than .5* of angle over the entire length, or goes up and
measures it, the brain is going to assume that the stripe is the same width
along the entire length.
Just a thought.
Greg
_______________________________________________
Don Adams
<<<Paint a matt black stripe right along the bottom sides of the coach, perhaps a 1 inch wide at the front of the coach, and 2-2 1/2 inches wide at the back.>>>
Now is you did that in reverse on the top of the front you might have something ???
--
Don
Dallas, TX
1976 26' Glenbrook
rebuilt by R Archer
powered by J Bounds, Koba
Greg and April
inch wide stripe of roof color below the gutters about the middle of the
coach and make it 1 1/2 inches wide in front, giving the illusion that the
roof starts lower in the front than in the back.
When the military is painting camouflage, they all ways keep in mind that
normally the lower areas on an object will be darker colors from shade, and
lighter colors on top where they are normally exposed to more light - so to
fool the eye, they intentionally reverse the situation putting lighter
colors where shade would be and darker colors where the object would be
exposed to more light ( after that it's just a matter of breaking up the
outlines of the object ).
This applies to the illusion of the coach being level while on the move by
bringing a lighter roof line down a inch or so in front and raising the
shadow line in the rear by a couple of inches.
.
Greg H.
I don't just march to the beat of my own drum - I have an entire brass band
to keep me company.
.
----- Original Message -----
From: "Don Adams" <dj.a...@att.net>
To: <gmc...@temp.gmcnet.org>
Sent: Wednesday, February 08, 2012 15:49
Subject: Re: [GMCnet] Affect on alignment of rear ride height set too high
>
>