The impact of extra weight on GMC handling

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kerry pinkerton

New member
Jul 13, 2012
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Most of yall have at least seen photos of the Princes custom coach. The black one with the custom EVERYTHING including a full size washer and dryer.

That coach was donated earlier this year to the RV Hall of Fame in Elkhart, IN. We saw it when we toured the museum. Rumor has it that the coach just
did not handle right and they gave up on it.

At first I thought that was BS because the air bag PSI could just be increased to carry basically any weight. And then I realized that our bogie arms
are part of the steering system...not supposed to be but they are. We've all seen or experienced the effects of rut wander and noticed the wheels
twist and move out of line when parking. When the leading arm bogie leaves the track it can steer the coach. The GMC engineers designed the bogie
arm casting for the standard weight of the coach.

My thinking is that when excess load (weight) is placed on the suspension, the front leading bogie arm, which we already know can move around quite a
bit, is more prone to move out of line because of the additional weight. This would explain why the Prince coach might have been a driving handful.

Just a theory. I'm not an engineer but I have stayed at a Holiday Inn Express.

Thoughts?

--
Kerry Pinkerton - North Alabama

Had 5 over the years. Still have the first a 76 that will be rebodied into an art deco car hauler.

http://www.bdub.net/pinkerton/

'03 Fleetwood Discovery 39L
 
Kerry, my wag is probably the steering box is off center.

> Most of yall have at least seen photos of the Princes custom coach. The black one with the custom EVERYTHING including a full size washer and
> dryer.
>
> That coach was donated earlier this year to the RV Hall of Fame in Elkhart, IN. We saw it when we toured the museum. Rumor has it that the coach
> just did not handle right and they gave up on it.
>
> At first I thought that was BS because the air bag PSI could just be increased to carry basically any weight. And then I realized that our bogie
> arms are part of the steering system...not supposed to be but they are. We've all seen or experienced the effects of rut wander and noticed the
> wheels twist and move out of line when parking. When the leading arm bogie leaves the track it can steer the coach. The GMC engineers designed the
> bogie arm casting for the standard weight of the coach.
>
> My thinking is that when excess load (weight) is placed on the suspension, the front leading bogie arm, which we already know can move around
> quite a bit, is more prone to move out of line because of the additional weight. This would explain why the Prince coach might have been a driving
> handful.
>
> Just a theory. I'm not an engineer but I have stayed at a Holiday Inn Express.
>
> Thoughts?

--
C. Boyd
76 Crestmont
East Tennessee
 
Kerry,

Helen and I met a Canadian couple at a RV Campgrounds in San Antonio, Texas. The owner complained to me about the handling. When I
looked inside I found that the builder had located everything down the driver side! I pointed him in the direction of Dave Lenzi.
Awhile later I was speaking with Dave and he noted that the owner had contacted him and came down from Canada so Dave could see what
he could do. Dave told me that when he weighed that coach it was 600 lb heavier on the driver side! GMC specs call for no more than
250 lb side to side difference. There was no way to correct it properly other that ripping the interior out and starting over. What
Dave did was to set the front and rear suspension ride height in such a way as to equalize the load as much as possible. It helped
but the handling / steering still wasn't what it should be.

I toured the Prince's coach at a GMCMI Convention somewhere (can't remember) and the guy that built it was there. I specifically
asked him if he had balanced the weight left to right and he said YES, however, he could have lied. As far as increasing the overall
weight I don't think it would cause handling problems. Clarence Buskirk's 26 footers were heavyweights and AFAIK they handled OK.
Hopefully JR Wright will comment on that.

I agree with Chuck, the steering box isn't centered.

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808


-----Original Message-----
From: Gmclist [mailto:gmclist-bounces] On Behalf Of Kerry Pinkerton
Sent: Saturday, December 16, 2017 12:48 PM
To: gmclist
Subject: [GMCnet] The impact of extra weight on GMC handling

Most of yall have at least seen photos of the Princes custom coach. The black one with the custom EVERYTHING including a full size
washer and dryer.

That coach was donated earlier this year to the RV Hall of Fame in Elkhart, IN. We saw it when we toured the museum. Rumor has it
that the coach just did not handle right and they gave up on it.

At first I thought that was BS because the air bag PSI could just be increased to carry basically any weight. And then I realized
that our bogie arms are part of the steering system...not supposed to be but they are. We've all seen or experienced the effects of
rut wander and noticed the wheels twist and move out of line when parking. When the leading arm bogie leaves the track it can steer
the coach. The GMC engineers designed the bogie
arm casting for the standard weight of the coach.

My thinking is that when excess load (weight) is placed on the suspension, the front leading bogie arm, which we already know can
move around quite a bit, is more prone to move out of line because of the additional weight. This would explain why the Prince
coach might have been a driving handful.

Just a theory. I'm not an engineer but I have stayed at a Holiday Inn Express.

Thoughts?

Kerry
 
Alex and I were talking about Princes coach and he was of the thought the two large awing cases on the roof would be an issue. He could be right, but
without knowing how much weight was added, there is no way to be sure.

It may just be that the reason I have now handling issues is that I have a 23 that scales well under 10K.

Between flying airplanes and loading ships, I have been around weight and balance problems for a long time.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Our 78 Buskirk Stretch runs straight as an arrow with one finger on the wheel. Getting it that way was a slow, and sometimes painful process.

The PO had always said it was a handful to drive, but I never drove it that way as the engine failed before I took delivery. Before I got it, it had
been weighed at GMCWS Casa de Fruta in 2012. That showed it to be 1600 pounds (no that is not a typo!) heavier on the curb side, with a total weight
of 12807.

After we (mostly Manny) replaced the engine, we (mostly Manny) installed the one-ton front suspension During that install we replaced a binding
Relay Arm with a Dave Lenzi modified one. Then I took it home and started trying to level it up.

I removed almost 1100 pounds of furniture, inoperative electronic equipment, & other things such as an 80 lb engine cover. That was good news. The
bad news is that the POs traveled pretty light, and we don't. The only way I am sure we are ready to go on a trip is if there is nothing left in the
house!

The coach had always been sort of a low rider, and even with a change in torsion bar anchors, I was unable to get the front high enough. Manny helped
me put in Peter Huber torsion bars, and now it was too high. Manny manufactured pork chops calculated to be just right, but they were too thick to
fit in Buskirk's specially reinforced crossmember, so I put in the Suspension Max adjustable torsion bar anchors (that only took two tries to get
correct). By now, I am an ace at changing pork chops and adjusting torsion bars, but the coach now stands at the correct ride height. Bogie steer is
probably minimized, as at some time in it's past True Tracks (the one with the roller) were installed. I took off the rear stabilizer bars (installed
sometime in it's life), as I found it almost impossible to level the coach in a campground.

The rear still has stock GMC air bags. Installed new KYB shocks. I am sure there is still a side to side imbalance as the curb side needs about 8-10
pounds more pressure to get correct ride height. There is not too much more I can do to balance things without a major redesign of the layout of the
coach. Looking forward to getting it on the scales in Tuscon in April.
--
John Shutzbaugh, Vacaville, CA, ncserv;
77 Eleganza, bought it new, can't blame PO, and
78 Buskirk stretch, "What were we thinking?"
 
I pull a 9,000 lbs enclosed trailer with a car/shop behind a 12,000 lbs 403 powered Royale. Thus a 21,000lbs GVW. Weight on the GMC from that trailer is in the 1,200 lbs range. Granted. This extra weight is carried low. But 5 feet behind the far back wheels. Pulls, and handles fine at 75MPH. There are no extra sway bars, or any tracking improvements. But not fast from a stop light. What is a must to carry these extreme weights. Is a GMC that's has a very good original suspension system under it. Bob Dunahugh 78 Royale
 
Re: I pull a 9,000 lbs enclosed trailer with a car/shop behind a 12,000 lbs 403 powered Royale
Are you saying the trailer contains a car/shop?
What brakes does the trailer have?
Does the trailer effect your stopping distance?
What is your final drive ratio?
--
Johnd01
John Phillips
Avion A2600 TZE064V101164
Rancho Cordova, CA (Sacramento)
 
> ... Thus a 21,000lbs GVW. Weight on the GMC from that trailer is in the 1,200 lbs range....

Bob, you're not suggesting you have 1200 lbs tongue weight are you?
--
Kerry Pinkerton - North Alabama

Had 5 over the years. Still have the first a 76 that will be rebodied into an art deco car hauler.

http://www.bdub.net/pinkerton/

'03 Fleetwood Discovery 39L
 
There is a lot I, and perhaps we, don't know about the Princes coach. Perhaps it was as simple as an out of center box. Cinnabar did the chassis
work. I'm not a Cinnabar fan but would THINK they know enough to check that....or perhaps not. Like I said, I'm not a fan...some of you are. I'm
going to be up in Goshen IN next fall. Perhaps I'll be able to talk the museum into letting me pop the hood and check the steering box center.

Regardless, yall are missing my point...not that I'm suggesting I'm right and anyone is wrong. As I said, I'm not an engineer and might be as full of
it as a Christmas turkey.

Let me restate my theory:

-I know that EVERYTHING MOVES. Skyscrapers, massive steel beams, concrete slabs, you name it...they all deflect with enough force.

-I know that our bogie arms move. I've seen it, we've all seen it any time we turn in a parking lot and look in the mirror.

-I know that the bogie arms are a cantilevered load. That is the bogie bushing is not in line with the tire (load) and that means that the bogie arm
is subject to a twisting load that varies based on weight. The more load is on the bogie pin (heavier the rear of the coach is), the more that weight
tries to twist the bogie arm. An analogy is holding wheelbarrow handles while someone adds weight to it. The wheel is the fulcrum and is the same as
the bogie pin. The handle is the offset tire and the load you feel when someone dumps a bag of rocks in the wheelbarrow is the same as the increased
twisting force on the bogie arm.

-I know that the leading arm (mid tire) will steer the coach.

-I know that true tracks keep (at least minimize) the bogie arm from steering the coach.

-I know that the bogie casting was designed for a certain load and to have certain characteristics at THAT LOAD. Changing that load will alter those
characteristics. It has to. Cantilever a rod off a workbench and put a weight on the end. Measure the deflection (bend in the rod). Then double
the weight. The deflection WILL increase SOME amount. In our case, at the very least, this will have some effect on how much the tire leans in at
the top (camber). It may not be enough to matter. Or perhaps it may???

-I DON'T KNOW if adding X lbs to a coach will cause the bogie to self steer more.

-I THEORIZE that the LEADING bogie arm (mid wheel) without true tracks will self steer MORE with additional weight added to the coach over the design
weight. I'm not talking about 1-200 lbs, I'm talking about 1000+ lbs. I don't think anyone knows what the Prince coach weighed???

-I also believe that True Tracks are one of the greatest things since sliced bread as it relates to the GMC. The handling of my 77 improved
dramatically and I've heard many of you say the same thing.

Just a thought for discussion.
--
Kerry Pinkerton - North Alabama

Had 5 over the years. Still have the first a 76 that will be rebodied into an art deco car hauler.

http://www.bdub.net/pinkerton/

'03 Fleetwood Discovery 39L
 
Generally my enclosed trailer with Yenko, parts/shop comes in at 9,000 lbs.=
Then sometimes it gets even higher depending on the road race track that I=
'm going too. May need parts along. I've twisted off the ends of the cran=
kshaft, trans input and output shafts, axles, and yokes. So to not have th=
e trailer not get to swaying from side to side. You need to have at least =
10% of the trailer weight as your tongue weight. Been using the GMC to d=
o this since 2003 from coast to coast with no issues. But yes. I do inspect=
the GMC frame often. The Royale's are the heaviest of the GMC's. And our 7=
8 has the 403 with the 3:70 FD. It has no engine cooling enhancements added=
. As to brakes. The GMC used stock 4 drums in the rear. The trailer has it=
s own brakes. Again. With no stopping issues. But I did just put disc on th=
e front rear axles just for added braking if needed. I have no true trac, w=
heel spacer, or reaction arms. I simply put our GMC back to it's original s=
pecs. And maintain that. That's what works for me. You need to do what put=
s you in YOUR Comfort Zone. Bob Dunahugh 78 Royale Iowa Member GMCMI =
________________________________ From: Bob Dunahugh Sent: Saturday, December 16, 2017 11:39 AM To: gmclist=
net.org Subject: RE: The impact of extra weight on GMC handling I=
pull a 9,000 lbs enclosed trailer with a car/shop behind a 12,000 lbs 403 =
powered Royale. Thus a 21,000lbs GVW. Weight on the GMC from that trailer i=
s in the 1,200 lbs range. Granted. This extra weight is carried low. But =
5 feet behind the far back wheels. Pulls, and handles fine at 75MPH. Ther=
e are no extra sway bars, or any tracking improvements. But not fast from =
a stop light. What is a must to carry these extreme weights. Is a GMC that'=
s has a very good original suspension system under it. Bob Dunahugh 78 Roy=
ale
 
Bob ,
​You must be utilizing the Weight distribution hitch system to decrease the
toung weight at the hitch.
Being a Blue Ox dealer we have employed them on some coaches that had over
500 lbs .​

>
>
> ________________________________
>
>
>
> I pull a 9,000 lbs enclosed trailer with a car/shop behind a 12,000 lbs
> 403 powered Royale. Thus a 21,000lbs GVW. Weight on the GMC from that
> trailer is in the 1,200 lbs range. Granted. This extra weight is carried
> low. But 5 feet behind the far back wheels. Pulls, and handles fine at
> 75MPH. There are no extra sway bars, or any tracking improvements. But
> not fast from a stop light. What is a must to carry these extreme weights.
> Is a GMC that's has a very good original suspension system under it. Bob
> Dunahugh 78 Royale
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
 
> -I also believe that True Tracks are one of the greatest things since sliced bread as it relates to the GMC. The handling of my 77 improved
> dramatically and I've heard many of you say the same thing.

With the thought that others will be reviewing this thread chasing their own handling demons, I'll chime in and second your opinion of the True Track
devices. My coach had fairly significant rut steer, and was "interesting" to experience dropping the right rear wheels off the edge of the road. It
ran straight and true otherwise, but it was fatiguing to drive on the interstate because of the truck ruts. FWIW, my coach is a Royale so it's at the
heavy end of the spectrum (though with a much lighter generator, though it's anyone's guess how much weight the internal modifications added or
subtracted).

I put the TT devices on and suddenly there just wasn't any more issue with truck ruts, and pulling the rear wheels up and over the edge of the road
was a non-event. Mine are the type where the steel "blade" runs between Delrin blocks. Simple and effective.

--
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
 
Mark,
The True Track system has been around for at least 30-35 years.
I have heard some dramatic changes after install.
My experiance was good, but not dramatic. We know each coach is different
so different kits effect them in various degree.
We supply few every month.

> > -I also believe that True Tracks are one of the greatest things since
> sliced bread as it relates to the GMC. The handling of my 77 improved
> > dramatically and I've heard many of you say the same thing.
>
>
> With the thought that others will be reviewing this thread chasing their
> own handling demons, I'll chime in and second your opinion of the True Track
> devices. My coach had fairly significant rut steer, and was "interesting"
> to experience dropping the right rear wheels off the edge of the road. It
> ran straight and true otherwise, but it was fatiguing to drive on the
> interstate because of the truck ruts. FWIW, my coach is a Royale so it's
> at the
> heavy end of the spectrum (though with a much lighter generator, though
> it's anyone's guess how much weight the internal modifications added or
> subtracted).
>
> I put the TT devices on and suddenly there just wasn't any more issue with
> truck ruts, and pulling the rear wheels up and over the edge of the road
> was a non-event. Mine are the type where the steel "blade" runs between
> Delrin blocks. Simple and effective.
>
> --
> Mark Hickey
> Mesa, AZ
> 1978 Royale Center Kitchen
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
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