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Thanks
Thanks to Lee McKay for his Window Channel Replacement contribution
in the last issue of Tech Center. Thanks to Egon Elssner for his
generous offer to summarize the seminars presented at the last
Roundup.
COMPLETE SYNOPSIS OF TECHNICAL SEMINARS MARCH 17-20,'93
GMC FRONT END AND STEERING SYSTEMS, Bob Fry
GMC steering stability is very good if all the front end suspension and steering components are dimensionally accurate, excessively worn parts replaced and the whole assembly accurately aligned for proper camber, caster and toe in/out. Bob gave procedures for checking wear, and checking the configuration of parts that make up the front end, including the steering box and steering coupling shaft. He stressed the need for accurate rear and front ride height in relation to steering geometry. He also gave us his preference in after market shock absorbers and commented on other after market components for improved handling.
THE IGNITION SYSTEM Duane Simmons and Bob Lamey
Ignition system fundamentals were presented for both the early model 'points' and later model "HEP" systems. The reasons for, and the details of both the mechanical advance and vacuum advance were given. Problems relating to ignition wires, points and the HEI high voltage coil, module, magnet, star wheel and pickup coil were covered in detail. Distributor rebuilding and availability of parts was also discussed. Data for all four OEM distributors and a 'Custom' distributor were tabulated and compared.
EXHAUST SYSTEMS SEMINAR Ed Burner
The original GMC exhaust system was always marginal in performance. Recently, most OEM parts have not even been available. Ed introduced his seminar with a rather theoretical discussion of what makes up a good exhaust system,
one that can add an additional 10% to engine power output. Starting with a Thorley header, custom made for the GMC, he detailed his ideas for the ideal exhaust system which includes Iow resistance flow mufflers and pipes. He shared his experience and emphasized the need for shielding of critical non-exhaust parts from the extreme heat radiated by headers, mufflers and pipes.
PAINT SEMINAR
Jeff Baker of Thompson Lacquer Co. and
Jeff Laliberte of Fleet Finish
This was primarily a question and answer session with Jeff Baker fielding most of the technical questions related to paint, primers and coach preparation. Jeff Laliberte suggested how to relate to paint shops in developing a paint scheme, choosing colors, and writing up a contract. He gave some tips that help reduce final cost.
CRACKED SUPPORTS
Cracks have been found in a surprising percentage of front
body supports. After Bob Lamey reported at Buellton that he had
found two cracked supports out of the two he inspected. I checked
mine and found 1.5 inch crack, Bob found another crack while he
was repairing the first one. I suggest that everyone who has the
newer type supports should inspect them or have them inspected.
These two welded-in supports connect the front body to the
chassis beside the engine. Older GMC's had a tripod type support
which appears to be trouble free. The newer GMC's {post 1975),
have a stamped aluminum triangular member with a 2 to 2.5 inch
flange. The cracks start in the flange, usually from the pointed
edge.
Dennis Richardson at the GMC RV shop has found several cracked
supports including one which had broken completely through. The
sooner you find the cracks, the cheaper it is to get them welded
together. If no cracks are found, file and sand along the edges
to remove any sharpness or irregularities.
DANGEROUS TIRES
At the Mount Hood Roundup, Wes Caughlan warned us to get rid of the Michelin XCA load range-D tires. Since then I have seen several coaches still running the tires. Owners still running these tires risk expensive damage to their coaches. When the fires blow out they damage the lower fiberglass body parts. Even though the fires are warranted for four years, they may fail much sooner than that. Eugene Slanter had two of these tires blow out through the tread while the fires were mounted on his spare fire carrier!. The tires had less than 1500 miles and were less than one-year old. The age of the tires can be determined by checking the three-digit code on the sidewall. The first two numbers indicate the week the fires were manufactured, and the third indicates the year (for example 345 would be week 34 in 1985).
EMERGENCY!
Have you thought about what to do if your coach breaks down
on the road in the middle of nowhere? Here are some tips to take
with you, hopefully you'll never need them, but they can get you
out of trouble. First, an essential item to carry is good towing
coverage. Good Sam ERS, and the policy offered by FMCA are excellent
lifesavers! These towing policies will properly tow your coach
to the nearest qualified repair facility. Check your policy to
ensure that there is no mileage restriction, the nearest qualified
facility might be one hundred fifty miles away. The second item
to have is a CB radio or cellular phone. Make sure that they are
in good working condition before you leave, the roadside at 10:00
P.M. is no place to find your CB does not work. In most states
the highway patrol monitors CB channel 9 and if you dial 9-1-1
on a cellular phone it rings in the highway patrol office. The
third is a good spare tire. Check its condition and tire pressure
after checking your CB radio. Once again, the roadside is no place
to find out your spare is flat! The fourth item to carry is a
good tool kit, nothing fancy, but you should have the tools to
change a tire, an air bag, air fittings, belts, and hoses. Even
if you don't do the work yourself, you can have someone else do
it while you guide them.
If you have a tire blow out (usually the rear tire blows),
you will lose ride height on the affected side. If the coach drops
to its lowest height, one of the only jacks which will lift it
is the OEM jack which came with the coach. If you don't have the
original jack, make sure the one you are carrying will fit underneath
to lift it from its lowest position. If the air line running to
the air bag breaks or is broken by flying tire tread you will
need to repair it in order to re-inflate the air bag. Carry three
or four feet of 1/4' air line (truck air brake hose) and a couple
of union fittings (used to splice two pieces together). You will
have to splice a new piece on to the section coming out from the
side of the coach and run it to the air bag.
If an air bag blows or gets punctured by flying fire debris,
it will feel just like a tire blow out. Again you will have to
raise the coach to remove the air bag. Some people carry a spare
air bag. Wes Caughlan advises that air bags come with a one-year
warranty and some are leakers. If you carry a bag for more than
a year before you use it, and find that it leaks, you'll be out
of luck for a replacement. Alternatives include checking the air
bag for leaks as soon as you get it. Fill it up and put it in
a bathtub to check for leaks. Another alternative is to call one
of the many GMC parts suppliers and have a new bag shipped overnight
to you, if you are in a place where you can stay. The final alternative
is to carry a threaded rod cut to about eighteen inches, put two
thick washers and two nuts on each end. You can put the rod in
place of the air bag and use the nuts to adjust the ride height,
place the suspension control on HOLD for the affected side. You'll
have a rough ride because the ak bag was your suspension spring,
but it will get you to a campground or home.
Many auto parts stores and catalogs carry universal replacement
fan belts. They look like a piece of tubing with a metal fitting
to hook the ends together. You simply remove the broken fan belt,
approximate the size and cut the tubing, loop it around the pulleys
and join it with the fitting. These belts are good for temporary
use only, but they will get you to a place where you can get a
replacement. You can also carry a spare set with you, the next
time you have your belts replaced as preventative maintenance,
carry the old ones with you as spares. The same goes for radiator
hoses. Hoses are more critical than belts because the GMC requires
a specially molded radiator hose. The universal hoses available
won't do the job properly, it's best to carry a spare set. Another
tidbit of information to carry with you is that the GMC radiator
core is the same as a Chevy C-10 truck radiator core. Find a shop
who can remove the tanks and attach them to a new core and you'll
be on the road again. Carry a heater hose union, the ones that
are sold for the do-it-yourself flush kits work just fine. If
your heater hose springs a leak you can cut it and put the union
in line to fix it. If your living area water heater preheat starts
leaking, you can cut the hoses up front by the engine and using
the union, connect them back together thus eliminating the water
heater from the loop.
More next issue!
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