Claude writes;
>What sort of wheel alignment tools are you speaking of? Depending on
>what you are refering to I might be interested.
>Also someone told me that at the International meet someone was selling
>a small laser device that enabled on to do away with the string
>arrangement. Does anyone know about this, have one, or know what brand
>this was?
I'm thinking a tool that can clamp onto the wheels of the GMC and permit
failsafe measurement of the toe in and 'aim' of each rear axle relative to
the front (so as to detect dogtracking and interaxle problems) of a given
unit is best. The primary purpose would be to permit fairly speedy
inspection of the state of alignment, without getting bad readings from bent
wheels or play in the bogies etc. Camber measurements can also easily be
taken, as can caster with a chart to convert camber readings at wheel angles
into caster figures. A tool like this must be indexed to the wheel bearing,
and not the wheel to get accurate readings. This is easy.
I think it would be important also that a tool like this could be left in
situ during subsequent adjustment so a person could make corrections if they
wished to. One important part would be to compile a chart of approximate
corrections needed at any given point (which and how many extra shims to use
as example) to bring the wheels back in line. One thought I've had is making
it a self correcting unit, with a go-no go reading, but this may not be
possible with every combination of wheel and tire on all units.
The two most serious issues for alignment on a GMC as I see it would be
ensuring that the rear axles do not try to dogtrack, and that they are very
slightly toed-in. The GMC suspension at the rear is rather unique in its
geometry among light vehicles, as it does not have any inherent 'roll steer'
as the coach leans in a corner. Most suspensions will steer ever so slightly
into a turn as the vehicle rolls. This lends stability and also helps
considerably with crosswind resistance. Slightly toed in rear wheels will
help in this respect I think, with no penaties for tire wear or economy.
Close control of toe and rear wheel camber will also make the greatest
difference for lane wandering on worn highways. Front alignment is not too
hard if the rear wheels are DEFINITELY KNOWN to be correct.
In any event, rebuilding and overhaul of bogie pins and related parts might
be needed for many coaches, so home wheel alignments might be beyond what
many owners are going to undertake in the driveway. But on a pretty good
coach, or one that has recently been serviced, just fine tuning alignment
would be very possible and straightforward.
I suspect the final unit would need a string as a guide between rear and
front axles. A laser sighted unit is perfectly possible and not hard to do,
but I would want things super simple and straightforward so that regardless
of mechanical apitiude a person could follow simple directions and come up
with accurate readings.
I made units for some of the cars I've owned thoughout the years, notable
was the Corvairs which share many aspects of the GMC- namely, different
front and rear track, and an extreme sensitivity to correct wheel alignment.
I'm blind in one eye, so the unit I use on the Corvair uses no string, but
just is 'eyeballed' over a nine foot distance. Naturally, this works better
for me than it would for everyone! Hence strings and lasers etc.
I certainly don't have a stranglehold on good ideas in this area, I'm sure
others would be able to improve on any design I could dream up.
Anyhow, I have sufficent materials around here to make several sets of units
for the GMC list at no cost to me, and am happy to pass these out for anyone
who would like to try. I'll also make a blueprint so those so inclined could
make thier own. I'll make a chart of correction values so that for example
is one rear wheel needs a certain shim to come back into correct alignment,
you can just look up what size shim and where it will be needed.
I'll try later this week to do a drawing of the theory involved and make it
available to anyone who is curious. Drop me a note if you are.
deville
Brent Covey
