Home » Public Forums » GMCnet » Driveability Issues (Suspension)
| Driveability Issues [message #252501] |
Wed, 18 June 2014 13:47  |
glenn2726
Messages: 234
Registered: June 2014
Location: Topeka, Kansas
Karma: 2
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Hi, as a new member and new to me 74 GMC owner I would like to ask for input on the driveability issue I detected when getting this old girl home. Prior to getting on the road I made sure the air ride was in the travel mode and that the unit looked level, aired up all tires to 60 lbs ( has 16.5 wheels and tires). On the drive I noticed that if you slipped off the side of the pavement no matter how slightly it would act like it wanted to stay there with the rear wheels. I've never encountered this with any previous class C motorhomes. What would cause this instability problem and what should I look for to make this thing drive like a motorhome straight down the road without worrying about the overcorrecting needed? I don't usually move off the pavement but the motorhome seemed wider or a wider track than what I had previously driven. My son was following me in my pickup and made comments later about my driving..lol...He said he would stay closer to the centerline and the other vehicles could get over..lol So all suggestions as to where to start and any previous encounters by other owners would be appreciated.
Glenn W
Topeka, KS
1974 GMC 26 ft. Color:Camel Interior:Canyon Land
Side Bath, Rear Sitting Area
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| Re: Driveability Issues [message #252507 is a reply to message #252501] |
Wed, 18 June 2014 14:05  |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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glenn2726 wrote on Wed, 18 June 2014 11:47Hi, as a new member and new to me 74 GMC owner I would like to ask for input on the driveability issue I detected when getting this old girl home. Prior to getting on the road I made sure the air ride was in the travel mode and that the unit looked level, aired up all tires to 60 lbs ( has 16.5 wheels and tires). On the drive I noticed that if you slipped off the side of the pavement no matter how slightly it would act like it wanted to stay there with the rear wheels. I've never encountered this with any previous class C motorhomes. What would cause this instability problem and what should I look for to make this thing drive like a motorhome straight down the road without worrying about the overcorrecting needed? I don't usually move off the pavement but the motorhome seemed wider or a wider track than what I had previously driven. My son was following me in my pickup and made comments later about my driving..lol...He said he would stay closer to the centerline and the other vehicles could get over..lol So all suggestions as to where to start and any previous encounters by other owners would be appreciated.
Most new drivers tend to keep too far to the right. The best way to judge your position on the road in my opinion is to observe the painted road lines in your side view mirrors and stay evenly between them.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Driveability Issues [message #252515 is a reply to message #252507] |
Wed, 18 June 2014 14:20 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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I find that if I try to keep my left foot on the center stripe, the coach is located where it belongs on the highway. Yes, it feels a little strange at first, but after awhile, it is very automatic.
I believe that you do not have enough air in the front tires, and perhaps too much in the rear pairs. Fronts need 65 pounds and rears need 55 pounds of pressure. This is close to correct. If you had weighted the coach, front and rear, then check the tire manufacture pressure chart for the pressure needed for the weight.
Check your height on the rear end. The side stripe should show a slight down hill run, with the front a little higher than the rear. It would look like the rear is too low, but that it the correct attitude.
Wrong tire pressure and rear end too high will make it drive very squirrelly.
Best riding vehicle that I've ever driven once set up.
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: [GMCnet] Driveability Issues [message #252520 is a reply to message #252501] |
Wed, 18 June 2014 14:24 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Glenn,
There are a LOT of things that have be right to make (most) of our GMC's
steer as they should -- like a '70's Cadillac. All of the assorted
bushings, bearings, etc., front AND rear must be in good condition. Then
the ride heights MUST be correct (as specified in the maintenance manual).
And the weight on each wheel must be reasonably close side-to-side.
Setting wheel alignment after all that's satisfied is an iterative process
which can, fortunately, easily be a DIY project with minimum, inexpensive,
equipment.
That said, I'll address your specific question: The rear suspension arms
are amazingly flexible. You can prove that to yourself by doing a hard
turn, in either direction, on a hard surface. Stop while still in the
turn, get out, and look at the middle and rear wheels. You may be afraid
to drive any farther because they'll be headed in different directions and
may be canted (cambered) in different directions also. That's if your
suspension arm bushings are in perfect condition; if they're badly worn, it
will look still worse.
After seeing that condition, you'll understand why I often say that our
center wheels are like one-handled wheelbarrows. Only the stiffness of the
arms keeps them going straight ahead, and they're not really very stiff.
So, when you try to get back on the pavement, yes, the center wheels will
try to STAY off the pavement until their flexibility limit is reached, then
they'll hop back up off of the shoulder of the road -- perhaps scaring the
daylights out of you in the process.
Over the years there have been several "solutions" to that problem --
stabilizer bars, cross-coach braces for the suspension arms, and track
guides which restrain lateral movement. The latter solution, is IMHO, the
best one. Over the years several companies have made them. They usually
consist of brackets on the rear of the suspension arm, behind the spindle,
holding wide ball bearings (cam followers). Those bearings travel up and
down in U-shaped channels attached vertically to the chassis. A recent
variation, by Tom Pryor, sold by Applied GMC, replaces the cam follower
with a flat plate and the channel with one lined with modern plastic
slides. I have no experience with that variant, but the single most
beneficial change I've made to my suspension, in 15 years of tinkering, is
the addition of those "true-tracks". Now, driving off and on the pavement
is usually noticeable only because of the different road noise. It's not
recommended, but the fact is, true-tracks MAY be a substitute for replacing
pretty badly worn suspension arm bushings. They're sold for all 4 middle
and rear wheels; I don't see any reason to put them on the rears -- they're
gonna follow the rest of the coach anywhere it goes.
JMHO,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
On Wed, Jun 18, 2014 at 2:47 PM, Glenn Whitt wrote:
> Hi, as a new member and new to me 74 GMC owner I would like to ask for
> input on the driveability issue I detected when getting this old girl
> home.
> Prior to getting on the road I made sure the air ride was in the travel
> mode and that the unit looked level, aired up all tires to 60 lbs ( has
> 16.5
> wheels and tires). On the drive I noticed that if you slipped off the
> side of the pavement no matter how slightly it would act like it wanted
> to stay
> there with the rear wheels. I've never encountered this with any
> previous class C motorhomes. What would cause this instability problem
> and what
> should I look for to make this thing drive like a motorhome straight down
> the road without worrying about the overcorrecting needed? I don't
> usually
> move off the pavement but the motorhome seemed wider or a wider track
> than what I had previously driven. My son was following me in my pickup and
> made comments later about my driving..lol...He said he would stay closer
> to the centerline and the other vehicles could get over..lol So all
> suggestions as to where to start and any previous encounters by other
> owners would be appreciated.
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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: Driveability Issues [message #252521 is a reply to message #252507] |
Wed, 18 June 2014 14:30 |
glenn2726
Messages: 234
Registered: June 2014
Location: Topeka, Kansas
Karma: 2
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Senior Member |
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Thanks Roy1, yes I think it will need some getting used to.. but didn't want to straddle the roadway..lol...it has newer mirrors and I hadn't been able to adjust them to my liking prior to driving. They're the Ramco mirrors and look to be mounted where the original mirrors were and I couldn't get them to adjust high enough for me...and yes I did see the centerline all the way home...lol
Glenn W
Topeka, KS
1974 GMC 26 ft. Color:Camel Interior:Canyon Land
Side Bath, Rear Sitting Area
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| Re: Driveability Issues [message #252523 is a reply to message #252515] |
Wed, 18 June 2014 14:35 |
glenn2726
Messages: 234
Registered: June 2014
Location: Topeka, Kansas
Karma: 2
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Senior Member |
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Thanks tphipps for the reply, I aired up the tires according to what it said in the motorhome, 60lbs all around. So I guess I need to take another look and try it with your settings and see how it works. Hopefully that will take care of some of the driveability issue. I will also look at where she is sitting when I take her out after getting things in order.
Glenn W
Topeka, KS
1974 GMC 26 ft. Color:Camel Interior:Canyon Land
Side Bath, Rear Sitting Area
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| Re: Driveability Issues [message #252524 is a reply to message #252501] |
Wed, 18 June 2014 14:38 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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One thing to keep in mind is that our GMCs don't have side by side duals on the rear. The outside track is about the same on all coaches and big pickups/big trucks. The difference is that if you run the outside dual off the inside dual will still be on the pavement. With the GMC, they both fall off. Make sure your ride height is correct before you do anything else. It can make a big difference. The correct ride height is somewhat rear down looking.
When I picked mine up, I knew nothing and jacked it up level or a bit more. It was squirrely to say the least.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: [GMCnet] Driveability Issues [message #252525 is a reply to message #252520] |
Wed, 18 June 2014 14:40 |
glenn2726
Messages: 234
Registered: June 2014
Location: Topeka, Kansas
Karma: 2
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Hi Ken that is informative. So the rear is similar to a fifth wheel trailer in how those suspensions without axles work. I hadn't taken a look at the suspension just yet due to other more pressing problems with the coach but I agree with you in that if it's not right it would be more of a problem with the edge and variations of the roadway. I have started at the front engine area and will be moving rearward as I progress so will encounter the rear suspension in due time...lol
Glenn W
Topeka, KS
1974 GMC 26 ft. Color:Camel Interior:Canyon Land
Side Bath, Rear Sitting Area
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| Re: Driveability Issues [message #252528 is a reply to message #252501] |
Wed, 18 June 2014 14:53 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Glenn,
Typically a Class-C is quite a bit narrower in the cab area than a Class-A. That puts both seats farther away from the center line of the coach. If you were riding in the passenger seat, you would probably swear the coach was going to run down mailboxes and roadside signs. You need to position yourself closer to toward the center line of the roadway when driving any Class-A. This is an unusual driving position but you will adjust easily once you get used to the coach.
One reason a Class-C feels more stable when driving off the shoulder and back on is the dual wheels. Even if your right outer wheel is on the shoulder, your inner wheel is still on the road. Not so with the 'tandem' wheel set-up on the GMC. Add to that the flexibility of the bogie arms, as Ken said, and you have the issue you experienced.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Driveability Issues [message #252530 is a reply to message #252528] |
Wed, 18 June 2014 15:00 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Carl S. wrote on Wed, 18 June 2014 12:53Glenn,
Typically a Class-C is quite a bit narrower in the cab area than a Class-A. That puts both seats farther away from the center line of the coach. If you were riding in the passenger seat, you would probably swear the coach was going to run down mailboxes and roadside signs. You need to position yourself closer to toward the center line of the roadway when driving any Class-A. This is an unusual driving position but you will adjust easily once you get used to the coach.
One reason a Class-C feels more stable when driving off the shoulder and back on is the dual wheels. Even if your right outer wheel is on the shoulder, your inner wheel is still on the road. Not so with the 'tandem' wheel set-up on the GMC. Add to that the flexibility of the bogie arms, as Ken said, and you have the issue you experienced.
To add to the above, I have the Chuck Aulgur Reaction Arm Brakes. This system uses sway bars to transfer the braking torque to the frame instead of through the suspension. As an added bonus, the sway bars tend to help keep the bogie frames in alignment. I noticed a dramatic improvement in the handling of the coach after installing the system, even though my rear suspension pins are not in perfect condition.
http://www.gmcmhphotos.com/photos/g5831-disc-brakes-chuck-aulgur-reaction-arm-install.html
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Driveability Issues [message #252536 is a reply to message #252528] |
Wed, 18 June 2014 15:10 |
glenn2726
Messages: 234
Registered: June 2014
Location: Topeka, Kansas
Karma: 2
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Senior Member |
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Thanks Carl S, that makes sense and this is my first class A...maybe they should be left hand drive so as to keep them on the road...lol I used to be a USPS letter carrier and drove the left hand vehicles and it kept all the head on traffic on what would be the passenger side...just saying...lol
Glenn W
Topeka, KS
1974 GMC 26 ft. Color:Camel Interior:Canyon Land
Side Bath, Rear Sitting Area
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| Re: Driveability Issues [message #252559 is a reply to message #252548] |
Wed, 18 June 2014 18:04 |
tphipps
Messages: 3005
Registered: August 2004
Location: Spanish Fort, AL
Karma: 9
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Senior Member |
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The tire pressure that is noted on the OEM GMC plate is for bias-ply tires. Radials act differently. There is even differences between steel sidewalls and fabric sidewalls.
My tire pressure references are based on 16" wheels, coach weight, and steel radials with fabric sidewalls.
JWID.
Tom, MS II
2012 Phoenix Cruiser model 2552
KA4CSG
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| Re: Driveability Issues [message #252578 is a reply to message #252548] |
Wed, 18 June 2014 22:00 |
glenn2726
Messages: 234
Registered: June 2014
Location: Topeka, Kansas
Karma: 2
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I can't remember which 5th wheel I had that had the spindles and no axles on it. It could have been the 38 ft Avion but I'm not certain. But I do remember the first time I saw the wheels turning when backing the trailer, they looked like they were coming off the trailer. As I haven't gotten very far in the manuals yet I'm still learning. I hope to get her on the road soon.
Glenn W
Topeka, KS
1974 GMC 26 ft. Color:Camel Interior:Canyon Land
Side Bath, Rear Sitting Area
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| Re: Driveability Issues [message #252665 is a reply to message #252649] |
Thu, 19 June 2014 18:11 |
glenn2726
Messages: 234
Registered: June 2014
Location: Topeka, Kansas
Karma: 2
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Thanks Hal, the PO put Michelin tires all around and they are the 16.5s. They are in good shape but I am going to have to experiment with tire pressure it looks like. Glenn
Glenn W
Topeka, KS
1974 GMC 26 ft. Color:Camel Interior:Canyon Land
Side Bath, Rear Sitting Area
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| Re: Driveability Issues [message #252691 is a reply to message #252665] |
Thu, 19 June 2014 20:00 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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glenn2726 wrote on Thu, 19 June 2014 18:11Thanks Hal, the PO put Michelin tires all around and they are the 16.5s. They are in good shape but I am going to have to experiment with tire pressure it looks like. Glenn
If you have Michelin 16.5's I suggest you check the date code. See here on Gene's site for how to do that:
http://gmcmotorhome.info/safety.htm
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: Driveability Issues [message #252695 is a reply to message #252691] |
Thu, 19 June 2014 20:14 |
glenn2726
Messages: 234
Registered: June 2014
Location: Topeka, Kansas
Karma: 2
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I have the receipts for tires and they are 5 years old. Put them on before he let it sit outside...lol..I visited with the PO yesterday and he said between the coach and the boat it took up too much room in his shop and he got tired of moving it in and out of the shop so he parked it outside...and 5 years later that is where I came in...lol
Glenn W
Topeka, KS
1974 GMC 26 ft. Color:Camel Interior:Canyon Land
Side Bath, Rear Sitting Area
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| Re: [GMCnet] Driveability Issues [message #252705 is a reply to message #252695] |
Thu, 19 June 2014 21:01 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Glen,
Check the date codes on the tires. The receipts are essentially worthless:
The tires might have been 5 years old when they were mounted. A blown
tire, even if it doesn't cause an accident, can easily cause $2000 worth of
body damage.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
On Thu, Jun 19, 2014 at 9:14 PM, Glenn Whitt wrote:
> I have the receipts for tires and they are 5 years old. Put them on
> before he let it sit outside...lol..I visited with the PO yesterday and
> he said
> between the coach and the boat it took up too much room in his shop and
> he got tired of moving it in and out of the shop so he parked it outside
> ...and
> 5 years later that is where I came in...lol
> --
>
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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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