I have had my 23' GMC for 2 1/2 years and have put 25,000 miles on it so I
have some experience with the GMC wiggle waggle or what ever anyone wants to
call it. The unit had 90K when we bought it. When we bought it, it wondered
all over the road at slow speed. Some shocks were broken. We had all the
mechanicals gone over by Lamey Enterprises in Ontario Ca. He replaced a lot
of the front end parts. After driving the coach, we were still not satisfied
with the steering wheel play and he replaced the steering box which made
some more improvements. All shocks were replaced with Bilstein's. Six wheel
alignment was done before we drove the coach on a trip. It was aligned to
GMC specifications.
First off, when in highway truck ruts, the very wide tread of the back
wheels in combination with the narrower front tread will cause the back and
front to move from side to side at different rates as the wheels climb and
fall in the truck ruts. The truck ruts are narrower than the back wheels so
one set is climbing while the other is coming down. I have made lots of
changes that have decreased the white knuckle driving to just needing
attentive corrections when in deep ruts, but, the wander or wiggle is
inherent with the difference in tread. The faster you go, the more swing
from the wiggle you get. When I first got the coach, 50 mph is all that I
felt safe in when in deep truck ruts. With all the improvements, I can still
feel the wiggle at 75 mph in deep ruts and feel more comfortable slowing
down to 65. When you see the double trailer truck ahead that look like fish
swimming, then you know you are into deep truck ruts. By in large, the
improvements or corrections have made a world of difference in our cross
country traveling. Probably the worst truck ruts, actually car ruts which
make them even worse, were east of Spokane Washington. The roads are
concrete, but either chains or studs wore away the road creating two grooves
that measured 1 1/2" deep at the bridges. They were from cars and were
narrower than truck ruts. 55 mph was as fast as I felt comfortable driving
in heavy traffic in these ruts. Handling in truck ruts remains the only
"bad" thing I can say about the GMC.
Our coach darted all over the highway with the steel belted E rated tires
running at the maximum rated pressure. The Goodyear truck dealer recommended
that the tires be inflated to the match the weight on the tires. We weigh
the full coach and matched the tire pressure to the full up weight on each
wheel. That made a big improvement in reducing the darting or fast response.
The radial tires now do their design job of absorbing the differences in the
road surfaces. Not only is the ride a lot better, but the response to the
bumps, holes and dips is slowed down. Our coach, being a 23 footer, only
weighs in at 10,100 lbs ready for travel and all tanks full. We use 65 psi
on the front tires and 50 psi on the rear tires which are loaded to less
then 60% of their design rating. Not everybody will agree with these lower
pressures.
After 6,000 miles, I change to the four bag rear suspension system and that
doubled the spring rate of the rear suspension. The 23' runs at a relative
low bag pressure because we only had 6000 pounds shared by the four tires.
The four bag system stiffened the ride, which the wife, who gets sea sick
very easily, really appreciated. The biggest difference that made is the
recover when the right real wheels fell off the road surface into ruts at
the side of the road. Bringing the coach back on the road no long meant that
the back would swing sideways as much when the wheels got back on the road.
Some narrow roads have deep grooves where the trucks drive off the road,
particularly on right hand corners. We have driven on some roads in West
Virginia where the road was narrower than the GMC rear tread. When the
logging truck come over the hills in the opposite direction, both the trucks
and GMC pass with their right wheels off the roads in the ruts. Luckily, the
rear view mirrors were at different heights or they would have hit. We slowe
d down, the logging trailer trucks did not and they swished from side to
side when they got back on the road. The four bag system also greatly
reduced the wiggle waggle when on really bad back roads with lots of
variations in road surface and pot holes. Particularly notable when going
over the raised creek bridges with different surfaces.
It was the narrow back roads of New England that caused the biggest
problems. Those roads are a series of patches, one patch on top the other. I
stopped in at a New Hampshire truck alignment and service company that was
recommended by the GMC group. The owner had a GMC that he purchased new and
had experiments with all kinds of front wheel alignments. He settled on
increasing the caster to as much + as the individual unit would stand, with
the right side + 1/2 over the left. Toe in was a +1/16 (stock is -1/8) and
camber was 3/8 left and 1/8 right. It was a different vehicle on the
roly-poly roads back roads of New England. It was now easy to keep it on the
road, even though the painted lines were viewed in the rear view mirrors as
being right on the edge of both tires. Changing the alignment was the
biggest improvement.
I still have one improvement to do. The spline shaft on the steering has
some wear and clicks from side to side on rough roads. It has enough
friction to stay in one position on smooth roads.
Our GMC is now a very pleasant vehicle to drive that is only upset by truck
ruts, which can be seen. When we spot or feel them, we move to the high
speed lanes. Side gust, which used to bother it, are no longer a problem.
Trucks passing close in the opposite direction will still upset it. When on
the freeways, we travel at the speed limit + 5. This is now a one hand
operation. I have driven other truck based RV's with a narrow front track
and they have the same truck rut problem as the GMC. The GMC truck rut
handling is not unique and when you follow them down the road you can see
they also wander in truck ruts. Our GMC now wander less them they do, but we
both wonder in the truck ruts, just like the trailer trucks do.
have some experience with the GMC wiggle waggle or what ever anyone wants to
call it. The unit had 90K when we bought it. When we bought it, it wondered
all over the road at slow speed. Some shocks were broken. We had all the
mechanicals gone over by Lamey Enterprises in Ontario Ca. He replaced a lot
of the front end parts. After driving the coach, we were still not satisfied
with the steering wheel play and he replaced the steering box which made
some more improvements. All shocks were replaced with Bilstein's. Six wheel
alignment was done before we drove the coach on a trip. It was aligned to
GMC specifications.
First off, when in highway truck ruts, the very wide tread of the back
wheels in combination with the narrower front tread will cause the back and
front to move from side to side at different rates as the wheels climb and
fall in the truck ruts. The truck ruts are narrower than the back wheels so
one set is climbing while the other is coming down. I have made lots of
changes that have decreased the white knuckle driving to just needing
attentive corrections when in deep ruts, but, the wander or wiggle is
inherent with the difference in tread. The faster you go, the more swing
from the wiggle you get. When I first got the coach, 50 mph is all that I
felt safe in when in deep truck ruts. With all the improvements, I can still
feel the wiggle at 75 mph in deep ruts and feel more comfortable slowing
down to 65. When you see the double trailer truck ahead that look like fish
swimming, then you know you are into deep truck ruts. By in large, the
improvements or corrections have made a world of difference in our cross
country traveling. Probably the worst truck ruts, actually car ruts which
make them even worse, were east of Spokane Washington. The roads are
concrete, but either chains or studs wore away the road creating two grooves
that measured 1 1/2" deep at the bridges. They were from cars and were
narrower than truck ruts. 55 mph was as fast as I felt comfortable driving
in heavy traffic in these ruts. Handling in truck ruts remains the only
"bad" thing I can say about the GMC.
Our coach darted all over the highway with the steel belted E rated tires
running at the maximum rated pressure. The Goodyear truck dealer recommended
that the tires be inflated to the match the weight on the tires. We weigh
the full coach and matched the tire pressure to the full up weight on each
wheel. That made a big improvement in reducing the darting or fast response.
The radial tires now do their design job of absorbing the differences in the
road surfaces. Not only is the ride a lot better, but the response to the
bumps, holes and dips is slowed down. Our coach, being a 23 footer, only
weighs in at 10,100 lbs ready for travel and all tanks full. We use 65 psi
on the front tires and 50 psi on the rear tires which are loaded to less
then 60% of their design rating. Not everybody will agree with these lower
pressures.
After 6,000 miles, I change to the four bag rear suspension system and that
doubled the spring rate of the rear suspension. The 23' runs at a relative
low bag pressure because we only had 6000 pounds shared by the four tires.
The four bag system stiffened the ride, which the wife, who gets sea sick
very easily, really appreciated. The biggest difference that made is the
recover when the right real wheels fell off the road surface into ruts at
the side of the road. Bringing the coach back on the road no long meant that
the back would swing sideways as much when the wheels got back on the road.
Some narrow roads have deep grooves where the trucks drive off the road,
particularly on right hand corners. We have driven on some roads in West
Virginia where the road was narrower than the GMC rear tread. When the
logging truck come over the hills in the opposite direction, both the trucks
and GMC pass with their right wheels off the roads in the ruts. Luckily, the
rear view mirrors were at different heights or they would have hit. We slowe
d down, the logging trailer trucks did not and they swished from side to
side when they got back on the road. The four bag system also greatly
reduced the wiggle waggle when on really bad back roads with lots of
variations in road surface and pot holes. Particularly notable when going
over the raised creek bridges with different surfaces.
It was the narrow back roads of New England that caused the biggest
problems. Those roads are a series of patches, one patch on top the other. I
stopped in at a New Hampshire truck alignment and service company that was
recommended by the GMC group. The owner had a GMC that he purchased new and
had experiments with all kinds of front wheel alignments. He settled on
increasing the caster to as much + as the individual unit would stand, with
the right side + 1/2 over the left. Toe in was a +1/16 (stock is -1/8) and
camber was 3/8 left and 1/8 right. It was a different vehicle on the
roly-poly roads back roads of New England. It was now easy to keep it on the
road, even though the painted lines were viewed in the rear view mirrors as
being right on the edge of both tires. Changing the alignment was the
biggest improvement.
I still have one improvement to do. The spline shaft on the steering has
some wear and clicks from side to side on rough roads. It has enough
friction to stay in one position on smooth roads.
Our GMC is now a very pleasant vehicle to drive that is only upset by truck
ruts, which can be seen. When we spot or feel them, we move to the high
speed lanes. Side gust, which used to bother it, are no longer a problem.
Trucks passing close in the opposite direction will still upset it. When on
the freeways, we travel at the speed limit + 5. This is now a one hand
operation. I have driven other truck based RV's with a narrow front track
and they have the same truck rut problem as the GMC. The GMC truck rut
handling is not unique and when you follow them down the road you can see
they also wander in truck ruts. Our GMC now wander less them they do, but we
both wonder in the truck ruts, just like the trailer trucks do.
wner-gmcmotorhome]On Behalf Of Al C
