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| [GMCnet] DIY Wheel Alignment [message #150719] |
Sat, 26 November 2011 22:43  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
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I've published before the link to my simple DIY wheel alignment jigs; here
it is again:
http://www.gmcmhphotos.com/photos/showgallery.php?cat=5634
I've no intention of getting as deeply into wheel alignment documentation
and equipment production as Jerry Work has so generously done. But after
having now done several rough as well as careful alignments, I've devoted
more thought to the process and have learned some lessons. This note is to
present some of those as they relate to the setting of toe:
I'll assume that all of the preliminary steps, such as ensuring tight
linkages, and bushings, setting tire pressure, adjusting rear and front
ride height, and setting the steering gear box on its high spot with the
steering wheel centered have been completed. Also, the caster and camber
should have been set.
The first step in setting toe is to ensure that each of the front wheels is
set parallel to the frame side rails. I do that by attaching my
level/laser to the horizontal bat at the bottom of the wheel jig and
leveling the beam using the spirit level in the tool. As a target for the
laser, I use a rectangular piece of plywood, the narrow dimension of which
is about 11" -- enough to slide vertically beneath the body and touch the
side rail. The wider dimension of the target is about 18" -- enough to
extend from the frame rails well beyond the wheels. I've always used it
with a helper holding and moving the target, but a "foot" attached to the
long dimension would allow it to stand alone for solitary use.
I'll describe my procedure for setting the wheel parallel to the frame on
one side; the same procedure applies to both sides. It's best if both
front wheels are positioned on turntables or, in my case, multiple sheets
of 6 mil polyethylene. The tie rod adjusting sleeve clamps on both sides
should be loosend
First the target is slid under the body with the narrow edge vertical and
against the chassis side rail as close to the front splice as possible and
the long edge on the level floor. Be sure the target is not positioned on
a nut, washer, or other obstruction, but on the rail itself. With a pencil
make a mark at the location of the laser dot. That is as accurately as you
can determine the laser's distance from the frame rail at this time.
Now move as far to the rear of the coach as possible and again position the
target against the frame rail. Without disturbing anything else turn the
adjacent tie rod adjusting sleeve to position the laser dot on the mark
just made on the target.
Repeat the preceding two steps until there is no need to adjust the laser
beam when the target is moved to the rear. Two or three iterations should
be sufficient. Just remember: Mark at the front & adjust at the rear.
Now do the same alignment on the other wheel. When completed, both wheels
should be parallel to the frame rails (0" toe). However, we want to verify
that fact and, perhaps, set the toe a little positive or negative. So,
remove the laser level and attach the toe adjustment beams. In my case,
that is two 60" long square aluminum tubes which can be attached to the
horizontal legs of the wheel jigs with two bolts and wing nuts each.
Ideally two people will perform this step: While ensuring that the wheel
jigs stay firmly in place, use a tape to measure the distances between the
fore and aft ends of the alignment beams. If the laser alignment was
perfect, the two tape measurements will be the same. Expect a little
difference. That difference defines twice the toe (twice because the beams
are twice as long as the wheel diameter).
To change that toe, adjust BOTH tie rod adjusting sleeves the SAME amount
in the SAME directions. That is, to increase toe-IN, adjust the left wheel
IN by X rotation of the left adjusting sleeve then adjust the right wheel
IN by X rotation of the right adjusting sleeve. Remember that the
measurement difference at the ends of the beams is TWICE the actual toe;
i.e., if the rear measurement is 92-3/8" and the front is 92-1/2", for a
difference of 1/8", you have 1/16" of toe-out -- a pretty good GMC setting.
Why didn't we accept the laser beam determined parallelism? Because the
laser beam MAY not be truly parallel to the base of the level. It probably
is, but we don't want to depend on it. The procedure described above
ensures that it doesn't matter. How so? Let's presume that the laser
diverges UP from the base of the level. When we perform the described
procedure, the laser beam will be set parallel to the chassis rail -- the
beam IS straight. BUT, the wheel, because of the error, will actually toe
OUT, as the wheel itself is parallel to the base of the level -- NOT the
laser beam. Bad news? Not too bad: When we move the level to the other
side, the same error will exist, but in the opposite direction. So, the
other wheel will also wind up toed out by the same amount! Then, when we
adjust the toe using the alignment beams, we'll eliminate that error -- by
adjusting each side by the same amount. Sort of confusing, but it WORKS.
:-)
HTH,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
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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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