'83 - "leaking" cruise control
#1
Instructor
Thread Starter
Join Date: Oct 2015
Location: San Diego
Posts: 184
Likes: 0
Received 0 Likes
on
0 Posts
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
'83 US spec, auto trans, 68k miles
When a speed is set, it holds for a moment and then begins falling off. I assume there's a 33 year old vacuum line somewhere, or a diaphragm, that's begun leaking. Where should I look and how can I test to identify the fault?
Thanks!
When a speed is set, it holds for a moment and then begins falling off. I assume there's a 33 year old vacuum line somewhere, or a diaphragm, that's begun leaking. Where should I look and how can I test to identify the fault?
Thanks!
#2
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
#3
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
These are most of the threads I'd collected as of march of this year. Your problem is common, Search is your overly chatty friend. There are multiple failure modes, the workshop manuals have a detailed test procedure.
https://rennlist.com/forums/928-foru...the-place.html
https://rennlist.com/forums/928-foru...cruise+control
http://members.rennlist.com/sharkski...ugeGremlin.htm
https://rennlist.com/forums/928-foru...ion-fixed.html
http://forums.pelicanparts.com/porsc...ml#post3789513
https://rennlist.com/forums/928-foru...cillation.html
https://rennlist.com/forums/928-foru...-a-change.html
https://rennlist.com/forums/928-foru...l-problem.html
http://members.rennlist.com/pirtle/svc_cc.html
Porsche 928 S4 Service - Cruise Control
***** http://jenniskens.livedsl.nl/Technic...0/MyTip022.htm
https://rennlist.com/forums/928-foru...e-control.html
https://rennlist.com/forums/928-foru...the-place.html
https://rennlist.com/forums/928-foru...cruise+control
https://rennlist.com/forums/928-foru...ke-lights.html
http://forums.pelicanparts.com/porsc...ght=tim+polzin
10/07 - 2/08 LEADS TO .........................
http://forums.pelicanparts.com/porsc...ml#post3789513
Understanding the VDO Cruise Control Amp SCHEMATICS & PIX
2/08 -1/14
https://rennlist.com/forums/928-foru...cillation.html
https://rennlist.com/forums/928-foru...-a-change.html
https://rennlist.com/forums/928-foru...l-problem.html
http://members.rennlist.com/pirtle/svc_cc.html
http://jenniskens.livedsl.nl/Technic...0/MyTip022.htm
http://www.nichols.nu/tip003.htm
https://rennlist.com/forums/928-foru...-actuator.html
https://rennlist.com/forums/928-foru...-the-oven.html
https://rennlist.com/forums/928-foru...trol-woes.html
https://rennlist.com/forums/10007721-post7.html
https://rennlist.com/forums/928-foru...-actuator.html
https://rennlist.com/forums/928-foru...trol-help.html
https://rennlist.com/forums/928-foru...t-working.html
Cruise Control - Not working - Oven Method
5/13 -
https://rennlist.com/forums/928-foru...l-rebuild.html
Cruise control rebuild
12/13 -
https://rennlist.com/forums/928-foru...ntrol-amp.html
Naïve idea: is it possible to re-fabricate VDO Cruise Control Amp?
3 pp now with schematics, pix, part #'s and so on.
1/14
http://www.silvercircuits.com/index.htm
http://www.americancircuits.com/aci/...6/Default.aspx
https://rennlist.com/forums/928-foru...ain-stuff.html
Interesting Cruise Control Brain Stuff
https://rennlist.com/forums/928-foru...l#post11853249
Mine had the same symptoms as the one on the left. Would accelerate but not hold. Sent it off to Beckman Technologies . For $160. it was repaired and hasn`t missed a beat since. They do rebuilding of MB parts and VDO parts.
https://rennlist.com/forums/928-foru...e-control.html
Cruise control 10-11-2014, 09:54 AM
https://rennlist.com/forums/928-foru...the-place.html
https://rennlist.com/forums/928-foru...cruise+control
http://members.rennlist.com/sharkski...ugeGremlin.htm
https://rennlist.com/forums/928-foru...ion-fixed.html
http://forums.pelicanparts.com/porsc...ml#post3789513
https://rennlist.com/forums/928-foru...cillation.html
https://rennlist.com/forums/928-foru...-a-change.html
https://rennlist.com/forums/928-foru...l-problem.html
http://members.rennlist.com/pirtle/svc_cc.html
Porsche 928 S4 Service - Cruise Control
***** http://jenniskens.livedsl.nl/Technic...0/MyTip022.htm
https://rennlist.com/forums/928-foru...e-control.html
https://rennlist.com/forums/928-foru...the-place.html
https://rennlist.com/forums/928-foru...cruise+control
https://rennlist.com/forums/928-foru...ke-lights.html
http://forums.pelicanparts.com/porsc...ght=tim+polzin
10/07 - 2/08 LEADS TO .........................
http://forums.pelicanparts.com/porsc...ml#post3789513
Understanding the VDO Cruise Control Amp SCHEMATICS & PIX
2/08 -1/14
https://rennlist.com/forums/928-foru...cillation.html
https://rennlist.com/forums/928-foru...-a-change.html
https://rennlist.com/forums/928-foru...l-problem.html
http://members.rennlist.com/pirtle/svc_cc.html
http://jenniskens.livedsl.nl/Technic...0/MyTip022.htm
http://www.nichols.nu/tip003.htm
https://rennlist.com/forums/928-foru...-actuator.html
https://rennlist.com/forums/928-foru...-the-oven.html
https://rennlist.com/forums/928-foru...trol-woes.html
https://rennlist.com/forums/10007721-post7.html
https://rennlist.com/forums/928-foru...-actuator.html
https://rennlist.com/forums/928-foru...trol-help.html
https://rennlist.com/forums/928-foru...t-working.html
Cruise Control - Not working - Oven Method
5/13 -
https://rennlist.com/forums/928-foru...l-rebuild.html
Cruise control rebuild
12/13 -
https://rennlist.com/forums/928-foru...ntrol-amp.html
Naïve idea: is it possible to re-fabricate VDO Cruise Control Amp?
3 pp now with schematics, pix, part #'s and so on.
1/14
http://www.silvercircuits.com/index.htm
http://www.americancircuits.com/aci/...6/Default.aspx
https://rennlist.com/forums/928-foru...ain-stuff.html
Interesting Cruise Control Brain Stuff
https://rennlist.com/forums/928-foru...l#post11853249
Mine had the same symptoms as the one on the left. Would accelerate but not hold. Sent it off to Beckman Technologies . For $160. it was repaired and hasn`t missed a beat since. They do rebuilding of MB parts and VDO parts.
https://rennlist.com/forums/928-foru...e-control.html
Cruise control 10-11-2014, 09:54 AM
#4
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
replaced all my vacuum lines and got nothing. replaced my cruise brain and got nothing. replaced the brake pedal switch (PITA) and got nothing. replaced the actuator and BAM BABY! the thing works!
Hope this helps!
Brian
Hope this helps!
Brian
#7
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
![banghead](https://rennlist.com/forums/graemlins/banghead.gif)
I'm bettin' I'm older than you. Next year I have to start MMD's.
Trending Topics
#9
Nordschleife Master
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
Sounds like a vacuum loss. Trace line from the 'Y' off the master cylinder, through the fender wall, to the appliances behind the driver front tire in the wheel well.
#10
Three Wheelin'
#11
Nordschleife Master
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
Your Bowden cable in good shape ? Cable moves freely ?
I'm not versed in diagnostic algorithm for cruise units. Just some basic ABC's.
I once lost my cruise while cruising in the 70's. Heard/felt a pop - car immediately decelerated - ran fine though - I was panicked for a moment and expected to see Mr. [!] - got home 150 miles later - looked under the hood and at once I see a broken/split cruise Bowden cable. For it to break like that it must have already been kinked/damaged and obstructed. I remember using the cruise stalk to accelerate at the time of the event - it wasn't just setting the cable tension, it was actually drawing on it.
I'm not versed in diagnostic algorithm for cruise units. Just some basic ABC's.
I once lost my cruise while cruising in the 70's. Heard/felt a pop - car immediately decelerated - ran fine though - I was panicked for a moment and expected to see Mr. [!] - got home 150 miles later - looked under the hood and at once I see a broken/split cruise Bowden cable. For it to break like that it must have already been kinked/damaged and obstructed. I remember using the cruise stalk to accelerate at the time of the event - it wasn't just setting the cable tension, it was actually drawing on it.
#12
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
Your Bowden cable in good shape ? Cable moves freely ?
I'm not versed in diagnostic algorithm for cruise units. Just some basic ABC's.
I once lost my cruise while cruising in the 70's. Heard/felt a pop - car immediately decelerated - ran fine though - I was panicked for a moment and expected to see Mr. [!] - got home 150 miles later - looked under the hood and at once I see a broken/split cruise Bowden cable. For it to break like that it must have already been kinked/damaged and obstructed. I remember using the cruise stalk to accelerate at the time of the event - it wasn't just setting the cable tension, it was actually drawing on it.
I'm not versed in diagnostic algorithm for cruise units. Just some basic ABC's.
I once lost my cruise while cruising in the 70's. Heard/felt a pop - car immediately decelerated - ran fine though - I was panicked for a moment and expected to see Mr. [!] - got home 150 miles later - looked under the hood and at once I see a broken/split cruise Bowden cable. For it to break like that it must have already been kinked/damaged and obstructed. I remember using the cruise stalk to accelerate at the time of the event - it wasn't just setting the cable tension, it was actually drawing on it.