Yah- so what are we all doing here at 3 AM ??
May have to start an all night group.
gene
>I was looking through some articles that I have kept from years ago from
>"Trailer Life." One was a column called Coach/Chassis in 1984 by Wes
>Caughlan. This information is still valid today and might be of interest to
>some GMCnet members. Cinnabar also now sells a kit to add the micron
filter,
>water separator and new check valve to the air system.
>
>Emery Stora
>77 Kingsley
>Santa Fe, NM
>
>Following is the text:
>
>"I have owned a 1977 GMC motorhome for about a year, and I am starting to
>discover and work out some of its inherent problems. I have soap-checked
the
>air-bag/cone assemblies, air-line fittings, as well as all of the air lines
>in the rear, and have not been able to find any leaks. Nevertheless, the
>coach tends to settle quite a bit in a 24-hour period. Can you help?
>Jerry M. Turner
>Raleigh, NM"
>
>Once you realize that the air bags are isolated from the control system when
>the ignition is off, Jerry, rear leakdown while parked is easy to
>trouble-shoot. The leak is either in the air bags themselves, the
connecting
>fittings at the ends of the blue and the gray lines, the blue and the gray
>lines themselves, or the first solenoid valve in the three-valve assembly
for
>each side.
>
>First, place blocks under the tandem axles and exhaust the air bags. Then
>install temporary Schrader valves (GMC Part No. 2214695) in the air bags.
>Reinflate the air bags from an alternate source (shop air or a portable
>compressor), and measure each side to a pencil mark placed on the side of
the
>coach. The following day, or after whatever interval leakdown has been
>experienced, measure the same marks again at hopefully the same ambient
>temperature. If the air bags are the cause, the coach will have measurably
>leaked down. If they are not the cause, the measurement will be the same as
>when the bags were inflated.
>
>Assuming that the air bags are OK, the original-equipment plastic fittings
>are the most common source of leakage. As a matter of course, I recommend
>replacing the plastic fittings on the ends of at least the blue and the gray
>air lines with Parker NTA 1/4-inch brass air-brake fittings that were used
on
>the 1973 and 1974 GMCs.
>
>If the air bags, the fittings on the ends of the blue and gray lines, and
the
>blue and gray lines themselves are not the cause, that leaves the solenoid
>valves (rotary valves in earlier models). Lately, I have been hearing that
>some of the solenoid valves have been simply turned around backwards,
>allowing the air-bag pressure to open them and cause leakdown. To check for
>this condition, the arrow on each solenoid valve should point away from the
>air bag and toward the compressor module. This is backwards to some
>mechanics, but it is correct for all Electro Level 1 models. Dual-purpose
>solenoid valves (no arrow) must be installed to eliminate leakdown in 1978
>Electro Level II models.
>
>If the solenoid valves turn out to be the cause, they can either be replaced
>or overhauled. They usually just need new rubber parts to replace those
that
>have become contaminated with compressor debris. A 5-micron air filter
>between the compressor and the check valve will keep compressor debris out
of
>the system. It will also act as a water trap in most of the GMC motorhome
>air-suspension leakdown in any motorhome equipped with an air-bag
suspension.
> Since the air bags are the end of the line and often the cause, it just
>makes common sense to isolate them and check them first. If they are not
the
>cause, progressively add upstream components until leakdown is measured.
>When it is finally measured, the last component added stands out like a sore
>thumb!
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
May have to start an all night group.
gene
>I was looking through some articles that I have kept from years ago from
>"Trailer Life." One was a column called Coach/Chassis in 1984 by Wes
>Caughlan. This information is still valid today and might be of interest to
>some GMCnet members. Cinnabar also now sells a kit to add the micron
filter,
>water separator and new check valve to the air system.
>
>Emery Stora
>77 Kingsley
>Santa Fe, NM
>
>Following is the text:
>
>"I have owned a 1977 GMC motorhome for about a year, and I am starting to
>discover and work out some of its inherent problems. I have soap-checked
the
>air-bag/cone assemblies, air-line fittings, as well as all of the air lines
>in the rear, and have not been able to find any leaks. Nevertheless, the
>coach tends to settle quite a bit in a 24-hour period. Can you help?
>Jerry M. Turner
>Raleigh, NM"
>
>Once you realize that the air bags are isolated from the control system when
>the ignition is off, Jerry, rear leakdown while parked is easy to
>trouble-shoot. The leak is either in the air bags themselves, the
connecting
>fittings at the ends of the blue and the gray lines, the blue and the gray
>lines themselves, or the first solenoid valve in the three-valve assembly
for
>each side.
>
>First, place blocks under the tandem axles and exhaust the air bags. Then
>install temporary Schrader valves (GMC Part No. 2214695) in the air bags.
>Reinflate the air bags from an alternate source (shop air or a portable
>compressor), and measure each side to a pencil mark placed on the side of
the
>coach. The following day, or after whatever interval leakdown has been
>experienced, measure the same marks again at hopefully the same ambient
>temperature. If the air bags are the cause, the coach will have measurably
>leaked down. If they are not the cause, the measurement will be the same as
>when the bags were inflated.
>
>Assuming that the air bags are OK, the original-equipment plastic fittings
>are the most common source of leakage. As a matter of course, I recommend
>replacing the plastic fittings on the ends of at least the blue and the gray
>air lines with Parker NTA 1/4-inch brass air-brake fittings that were used
on
>the 1973 and 1974 GMCs.
>
>If the air bags, the fittings on the ends of the blue and gray lines, and
the
>blue and gray lines themselves are not the cause, that leaves the solenoid
>valves (rotary valves in earlier models). Lately, I have been hearing that
>some of the solenoid valves have been simply turned around backwards,
>allowing the air-bag pressure to open them and cause leakdown. To check for
>this condition, the arrow on each solenoid valve should point away from the
>air bag and toward the compressor module. This is backwards to some
>mechanics, but it is correct for all Electro Level 1 models. Dual-purpose
>solenoid valves (no arrow) must be installed to eliminate leakdown in 1978
>Electro Level II models.
>
>If the solenoid valves turn out to be the cause, they can either be replaced
>or overhauled. They usually just need new rubber parts to replace those
that
>have become contaminated with compressor debris. A 5-micron air filter
>between the compressor and the check valve will keep compressor debris out
of
>the system. It will also act as a water trap in most of the GMC motorhome
>air-suspension leakdown in any motorhome equipped with an air-bag
suspension.
> Since the air bags are the end of the line and often the cause, it just
>makes common sense to isolate them and check them first. If they are not
the
>cause, progressively add upstream components until leakdown is measured.
>When it is finally measured, the last component added stands out like a sore
>thumb!
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
