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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
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"When I was a kid I used to pray for a bike everyday but then I realized that God didn't work that way so I stole one and asked him for forgiveness" '85 Carrera Coupe Dk. Blue, '64 Thunderbird Brittany Blue '68 Lotus Elan S4 Coupe Red, '62 Daimler SP250 [Dart] BRG |
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02-16-2010, 03:15 AM
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apply vacuum to the port then 12 volts to the terminals. Check the resistance between the terminals I think it should be 12ohm. When the cruise is not working it's almost always the the control unit. Do a search you'll find lots of posts.
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1974 sahara beige 911 targa 1982 chiffon 911sc 1985 prussian blue metallic carrera |
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02-16-2010, 05:36 AM
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Hi Kodioneill,
Thanks for your reply. Can I check with you one more issue? Obviously the the minor diameter vacuum hose is the one that comes off the 'T' Piece but my larger diameter hose that comes off the servo unit is attached to nothing and just goes to atmosphere. Is this correct? or is it attached to some other vacuum point to create a two way pulling system for the unit. I was afraid to check the servo with 12volts as I didn't think that it would in fact be 12volts. I thought it may have been a lesser voltage as it was all happening through the control brain but you have put me straight and for this I am grateful. Dave
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"When I was a kid I used to pray for a bike everyday but then I realized that God didn't work that way so I stole one and asked him for forgiveness" '85 Carrera Coupe Dk. Blue, '64 Thunderbird Brittany Blue '68 Lotus Elan S4 Coupe Red, '62 Daimler SP250 [Dart] BRG |
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02-16-2010, 12:55 PM
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The larger diameter hose is a exhaust /vent to dump the vacuum. I don't want to go out on a limb but I'm almost certain that the servo operates on 12v. I know the rest of the components switch,relay etc... operate on 12v. Wait to see more replies to the voltage question.
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1974 sahara beige 911 targa 1982 chiffon 911sc 1985 prussian blue metallic carrera Last edited by kodioneill; 02-16-2010 at 01:52 PM.. |
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02-16-2010, 01:49 PM
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1974 sahara beige 911 targa 1982 chiffon 911sc 1985 prussian blue metallic carrera |
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02-16-2010, 01:57 PM
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Urghh!! had a look at the link, methinks that side of the electronics is a little beyond my tiny brain.
R. Dave
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"When I was a kid I used to pray for a bike everyday but then I realized that God didn't work that way so I stole one and asked him for forgiveness" '85 Carrera Coupe Dk. Blue, '64 Thunderbird Brittany Blue '68 Lotus Elan S4 Coupe Red, '62 Daimler SP250 [Dart] BRG |
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02-16-2010, 02:04 PM
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1985 Porsche 911 3.2
Thunderbird
2010 Daimler SP250
1968 Lotus Elan S4 Coupe
1974 Porsche 911 targa 2.7
