| [GMCnet] Cruise Control Repair [message #258004] |
Wed, 06 August 2014 20:28 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
|
For the past year or so my ElectroMotor II Cruise Control (CC) has steadily
gotten more and more unreliable. At the start of a trip it usually engages
and operates normally -- for 5 minutes to 5 hours. It might drop out on a
dump, or not. It might re-engage after an intentional or incidental
drop-out, or it might not. It finally degraded to the point that it worked
about 20 miles out of the 400 mile trip to N. GA a couple of weeks ago.
My repeated efforts to find the intermittent connection causing the problem
were fruitless during several attempts over the year. Yesterday I decided
to try again, figuring the intermittent had finally become almost
permanent. When I finally got to the brake circuit, I found that the CC
interrupt switch on the brake pedal operated switch, which should ground
pin G, would instead pull it to 0.1 VDC, or 0.5, or 5, or 2.5, or 10 -- as
it chose.
Without being absolutely certain it was the problem, I still had no choice
but to undertake the onerous task of removing the switch from under the
dash above the brake pedal. It was a real PITA, but it eventually came out.
The switch is trivially simple, and very easily disassembled and
reassembled. It's a DPDT switch with separated poles. In other words,
there are two pairs of contacts, one NC and one NO. In the compressed (no
braking) position, there's a contact bar spring loaded to the NO contacts.
When the pedal is pressed, those contacts open and another spring presses
the bar against the NC contacts. The NC contacts (Open when no brakes
applied) operate the brake lights. The NO contacts (Closed when no brakes
applied) only control the grounding of pin G on the CC.
All eight contact points were eroded, causing the observed unreliable
grounding. After I polished them with 600 grit sandpaper and snapped the
switch back together, the closed contact resistances again read zero.
Today I drove about 40 miles testing EFI, the Super Vacuum assisted brakes,
and the CC. The CC never failed to operate correctly during probably 20
engagements. MAYBE I won't have to "drive" all the way to Chippewa Falls
and back now. :-)
One more benefit of the exercise: There are two operation-interrupt pins
on the EE II CC: Pin G must see 0 VDC for the CC to operate. Pin D must
see 12 VDC. For simplicity, I installed only the pin G wiring, and tied
pin D to IGN. Now that I see how the switch works, I realize that it's a
very well conceived redundant arrangement which is highly fail-safe. I'll
now connect pin D to the hot side of the brake light contacts on the
switch, re-implementing the double protection.
Ken H.
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
