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Topic: Cruise control surges

in Forum: C3 Fuel, Emission Control, and Exhaust Systems


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Cruise control surges (1/11)
 6/14/09 5:59am
Aussie79vette
Former Member

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, - Australia

Vette(s):
1979 corvette


Joined: 5/15/2009
Posts: 28

Hi Guys, after having my 79 for about 6 weeks now, I am going thru some of the things that need fixing (luckily it's not many, the guy who did the resto did a pretty good job), one of the jobs is the cruise control.
 
When I am driving (dosen't really matter what speed) and push the cruise control at 100 Kph, the Vette slow's down a bit then speeds up to 110 Kph then slow's down again and speeds up, then slows down again and then speeds up and so it goes on.
 
It seems that the cruise control is working but will not keep the Vette at a constant speed. 
 
Were do you suggest I start looking and is this something I can adjust my self ?.
 
Regards
 
Andy from down under
 
 


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Cruise control surges (2/11)
 6/14/09 10:27am
Gunslinger
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Frederick, MD - USA

Vette(s):
1969 convertible L71 427/435 4-speed black interior


Joined: 9/8/2003
Posts: 3398

You have a bad transducer...that's classic symptoms of it.  It's located under the master cylinder/brake booster inside the left fender well.  You can see the speedometer cables going into and out of it.

Not hard to change...if you have small hands.
Cruise control surges (3/11)
 6/14/09 10:55am
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 20126

I'm with Bruce on this one. Most likely a transducer issue. It could also be caused by a pin-hole in the vacuum actuator/"servo", but those are a little tricky to test, since they have a small amount of "bleed" built into them anyway.
The transducer can be opened up, and if the gears are not all rusted/damaged, you can sometimes clean, and re-lube them, and they'll work fine. If you open the tranducer up, and rusty stuff falls out, replacement is all you can do.


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Joel Adams
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Cruise control surges (4/11)
 6/14/09 11:51am
rraider1
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Woodland, WA - USA

Vette(s):
1977 T-Top,350,Auto Black Ruby Pearl,Steeroids R&P conversion


Joined: 10/14/2003
Posts: 1165

Just for the sake of learning what is the top speed for the cruise control I beleive their is a minumum around 35 to engage  but what is the maximum Aussie79 said 100 kph how does it work at lower speeds, not sure of the kalomitors
Cruise control surges (5/11)
 6/14/09 12:27pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 20126

I'm not aware of any upper limits on the cc...the speed for initial engagement is around 28-38 to keep it from operating at unsafe speeds around town/city. Unsafe as in setting it and forgetting when you go thru a school zone or something, or for accidental engagement in say a parking lot... 

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Joel Adams
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Cruise control surges (6/11)
 6/14/09 4:43pm
Aussie79vette
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, - Australia

Vette(s):
1979 corvette


Joined: 5/15/2009
Posts: 28

Thanks for the help.
 
If I take off the transducer am I still able to drive with out it on, while check it out and/or buy a new one.
 
What would be able reasonable price for one


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Cruise control surges (7/11)
 6/14/09 8:08pm
dskopp
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Oak Creek, WI - USA

Vette(s):
1981 Great White Shark. Red Interior, 350/190hp. PS, PB (SS), A/C CC, T-Tops, Going to remain as Stock as possible. Served three years in Active Duty Army, then Retired Air Force after 34 years! Badger State Vetts Car Club. 175,000 Original miles!!


Joined: 5/21/2008
Posts: 1958

You can drive your vette without the transducer, block vaccuume lines.  I have almost the same problem with my 81.  Shop manual says it may be a vaccuum problem.  I have not checked it out yet.  Let me know what you find out, my aussie friend!!
G'Day Mate
Dan


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Cruise control surges (8/11)
 6/14/09 8:20pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 20126

You can drive it, but the speedo won't work.

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Joel Adams
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             NCRS

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Cruise control surges (9/11)
 6/15/09 8:20pm
eddie20875Lifetime Member
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Lanoka Harbor, NJ - USA

Vette(s):
1975 metallic blue coupe with t-tops,L48, t/t steering, black leather interior. 1990 L98, white/red leather interior, auto,a/c


Joined: 12/21/2006
Posts: 828

on my 90 had the same problem and it was a vacuum leak. even the slightest leak like i had messed it up.

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Cruise control surges (10/11)
 6/17/09 1:13am
Aussie79vette
Former Member

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, - Australia

Vette(s):
1979 corvette


Joined: 5/15/2009
Posts: 28

I removed the "transducer" but to a  novice it looks fine, opened it up and no rust came out.
 
Would rather it turned out be a vacum leak, as to buy one here in Aus it is $AU440.00 Unhappy($US350.00) exchange, if pushed to buy one will look at ex USA (much cheaper)
 
I read in alot of the "post's" that many a problem was a vacum leak, is there a easy way to detect a vacum leak, it seems it would be hard to hear with engine running ?, would apprieciate your suggestion's.
 
Regards
 
Andy down under


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Cruise control surges (11/11)
 6/17/09 2:00am
indy99
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Newport, MI - USA

Vette(s):
1980 L-48 still in the middle of a frame-off.


Joined: 6/9/2005
Posts: 932

30 years is a long time for a rubber hose to be in service if they are the originals.  They become cracked or brittle over time which causes leaks in the system.  There are kits available with the correct size and length of hose for your car.
 
One way to find a leak is to spray some carb cleaner at a suspected hose while the engine is running. If the idle speed changes then that may indicate a leak.


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