How to test Cruise Control Vacuum Servo Unit for '85 911?
02-16-2010, 08:11 AM
#1
Track Day
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How to test Cruise Control Vacuum Servo Unit for '85 911?
Hi all,
Does anybody know how to test Cruise Control Servo units. I have performed the test procedures outlined in the Bentley manual and it has indicated faulty clutch switch/faulty servo unit. The clutch switch has tested OK so that only leaves the servo unit. The problem that I find though is how to actually test the unit. Hence the question.
I guess the problem could also be the main control unit but best to tackle one issue at a time.
Looking forward to any info on he subject.
Dave
Does anybody know how to test Cruise Control Servo units. I have performed the test procedures outlined in the Bentley manual and it has indicated faulty clutch switch/faulty servo unit. The clutch switch has tested OK so that only leaves the servo unit. The problem that I find though is how to actually test the unit. Hence the question.
I guess the problem could also be the main control unit but best to tackle one issue at a time.
Looking forward to any info on he subject.
Dave
02-16-2010, 02:13 PM
#2
I haddah Google dat
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For the vacuum one, you can take the unit out, and push the diaphram, then cover the large opening with your thumb. If it leaks, the diaphram will return to it's starting position. If it's good, air pressure will stop it. I'm not sure if you mean the steering column switch or not. The brains on these things are prone to failure too.
02-16-2010, 04:44 PM
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According to Bentley, mine also tested as a faulty clutch switch. I was willing to give it a try, since I'd replaced my faulty cruise control brain about a year earlier with a used one I'd purchased (small rectangular box, either on the back wall of the trunk or under the dash...don't remember exactly when it was moved). Of course, my wrench scoffed and said the clutch switches "never fail."
Turned out it was the brain...seems it's always the brain. They're easy to change out...you know anyone who would let you try theirs just to see what happens? New brains are spendy, but they can be rebuilt (it's the cold-solder joints that fail, and they can be resoldered, but it helps to know what you're doing...I had mine rebuilt--neither my eyesight or steadiness of hand were up to the challenge).
Turned out it was the brain...seems it's always the brain. They're easy to change out...you know anyone who would let you try theirs just to see what happens? New brains are spendy, but they can be rebuilt (it's the cold-solder joints that fail, and they can be resoldered, but it helps to know what you're doing...I had mine rebuilt--neither my eyesight or steadiness of hand were up to the challenge).
02-16-2010, 06:10 PM
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Track Day
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Thanks fellas,
I will try the tests, but it was interesting to note that the testing procedure pointed to the same diagnosis as mine and yet it was the brain.
This is a continuation of a retrofit that has been a real b------d and after all the effort of installation and cost of components it did not work. Very disappointing to say the least.
Yes , I was talking about the servo unit, the column switch tested fine.
Dave
I will try the tests, but it was interesting to note that the testing procedure pointed to the same diagnosis as mine and yet it was the brain.
This is a continuation of a retrofit that has been a real b------d and after all the effort of installation and cost of components it did not work. Very disappointing to say the least.
Yes , I was talking about the servo unit, the column switch tested fine.
Dave
02-19-2010, 10:04 PM
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If you are driving this car as intended... when you you be able to use the cruise control?
Thanks fellas,
I will try the tests, but it was interesting to note that the testing procedure pointed to the same diagnosis as mine and yet it was the brain.
This is a continuation of a retrofit that has been a real b------d and after all the effort of installation and cost of components it did not work. Very disappointing to say the least.
Yes , I was talking about the servo unit, the column switch tested fine.
Dave
I will try the tests, but it was interesting to note that the testing procedure pointed to the same diagnosis as mine and yet it was the brain.
This is a continuation of a retrofit that has been a real b------d and after all the effort of installation and cost of components it did not work. Very disappointing to say the least.
Yes , I was talking about the servo unit, the column switch tested fine.
Dave
