Fred....I have some experience with these cruise control units and have one
on my truck. From memory, the magnets didn't seem like anything that
special. I recall that there were 2 ea. mounted 180 degrees apart on the
driveshaft. Each magnet was about 1" long X 1/4" wide X 1/8" thick.
I had a problem on my truck where the cruise control began working
intermittently after years of trouble free operation. I couldn't figure out
the cause and finally it quit working altogether. I swapped out parts with
another unit for trouble-shooting. After replacing the control box and the
speed sensor, it still didn't work. So......after thinking about it for
awhile.......I suspected the mercury switch which is in a "normally closed"
position to function. This switch has a black covering (like shrink-tube)
which attaches it to a mounting bracket. The bracket and switch are mounted
in a vertial position somewhere. Mine was mounted on the engine side of the
firewall. I suspected a loss of continuity in the switch in the normal
closed position. To check this I "jumpered" around the switch and it worked
great. I believe that the purpose of this switch is to automatically
disengauge the cruise if the vehicle is heavily bounced around, such as
would be caused by an accident, roll-over, etc. When this feature was
working properly on mine, it would occasionally disengauge if I hit a major
dip or rough place on the road.
I think that some models did not have this feature....so I don't know about
yours. I did not replace the switch but removed it and connected the two
lead wires together.
- -Larry 73 Painted Desert
- ------------------------------
Date: Sat, 27 Feb 1999 11:49:35 EST
From: FBHUDSPETH
Subject: GMC: Cruise Control for SOB
Does anyone know the size and type of magnets that were used on
driveshafts in
aftermarket cruise controls? This type of cruise control is now
obsolete and
few parts store people relate to them. The magnets are part of the
vehicle
speed sensor (VSS) system.
Background (if you are interested):
Rather than subject a second GMC Motorhome to the abuse of the Yukon
and
Alaska, I bought an '82 Airstream 29' motorhome. It is built on a
GM P30
chassis/454 CID engine. I am preparing this SOB to take to and
leave in
Alaska where we spend summers. I have almost completed the
equivalent of an
aircraft inspection and repair program.
The only thing I have been unable to restore is the cruise control.
It is a
Dana model
# 1R 0911 A26 8 (# stamped on the electronics box). The driveshaft
magnets
were missing when I took delivery of the coach. I installed a
couple of
"hardware store" magnets. I then conducted a complete diagnostic of
the
electronic, vacuum and mechanical operation using the guide in the
Airstream
factory service manual. The diagnostic guide for the cruise control
is very
comprehensive, about six pages long. The cruise control passed all
of the
diagnostics. It still, however, won't engage. I don't know the
design and
specs for the magnets; until I get the correct magnets, I cannot
conclude that
a failure internal to the "black box" or the servo not addressed by
the
diagnostics has occurred. Yesterday, I e-mailed an inquiry to
Rostra
Precision Controls; they reportedly bought the portion of Dana that
manufactured the cruise controls (can anyone confirm or refute
this?). I have
not yet heard from them.
I have observed that we have some very competent technical people on
the GMC
Net. It occurred to me, that although it is an SOB issue, someone
may have
some valuable insight on this.
Thanks,
Fred Hudspeth
'78 Royale
on my truck. From memory, the magnets didn't seem like anything that
special. I recall that there were 2 ea. mounted 180 degrees apart on the
driveshaft. Each magnet was about 1" long X 1/4" wide X 1/8" thick.
I had a problem on my truck where the cruise control began working
intermittently after years of trouble free operation. I couldn't figure out
the cause and finally it quit working altogether. I swapped out parts with
another unit for trouble-shooting. After replacing the control box and the
speed sensor, it still didn't work. So......after thinking about it for
awhile.......I suspected the mercury switch which is in a "normally closed"
position to function. This switch has a black covering (like shrink-tube)
which attaches it to a mounting bracket. The bracket and switch are mounted
in a vertial position somewhere. Mine was mounted on the engine side of the
firewall. I suspected a loss of continuity in the switch in the normal
closed position. To check this I "jumpered" around the switch and it worked
great. I believe that the purpose of this switch is to automatically
disengauge the cruise if the vehicle is heavily bounced around, such as
would be caused by an accident, roll-over, etc. When this feature was
working properly on mine, it would occasionally disengauge if I hit a major
dip or rough place on the road.
I think that some models did not have this feature....so I don't know about
yours. I did not replace the switch but removed it and connected the two
lead wires together.
- -Larry 73 Painted Desert
- ------------------------------
Date: Sat, 27 Feb 1999 11:49:35 EST
From: FBHUDSPETH
Subject: GMC: Cruise Control for SOB
Does anyone know the size and type of magnets that were used on
driveshafts in
aftermarket cruise controls? This type of cruise control is now
obsolete and
few parts store people relate to them. The magnets are part of the
vehicle
speed sensor (VSS) system.
Background (if you are interested):
Rather than subject a second GMC Motorhome to the abuse of the Yukon
and
Alaska, I bought an '82 Airstream 29' motorhome. It is built on a
GM P30
chassis/454 CID engine. I am preparing this SOB to take to and
leave in
Alaska where we spend summers. I have almost completed the
equivalent of an
aircraft inspection and repair program.
The only thing I have been unable to restore is the cruise control.
It is a
Dana model
# 1R 0911 A26 8 (# stamped on the electronics box). The driveshaft
magnets
were missing when I took delivery of the coach. I installed a
couple of
"hardware store" magnets. I then conducted a complete diagnostic of
the
electronic, vacuum and mechanical operation using the guide in the
Airstream
factory service manual. The diagnostic guide for the cruise control
is very
comprehensive, about six pages long. The cruise control passed all
of the
diagnostics. It still, however, won't engage. I don't know the
design and
specs for the magnets; until I get the correct magnets, I cannot
conclude that
a failure internal to the "black box" or the servo not addressed by
the
diagnostics has occurred. Yesterday, I e-mailed an inquiry to
Rostra
Precision Controls; they reportedly bought the portion of Dana that
manufactured the cruise controls (can anyone confirm or refute
this?). I have
not yet heard from them.
I have observed that we have some very competent technical people on
the GMC
Net. It occurred to me, that although it is an SOB issue, someone
may have
some valuable insight on this.
Thanks,
Fred Hudspeth
'78 Royale
