Topic: Cruise control surges
in Forum: C3 Fuel, Emission Control, and Exhaust Systems
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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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Former Member
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Frederick, MD - USA
Joined: 9/8/2003
Posts: 3398
Vette(s): 1969 convertible L71 427/435 4-speed black interior
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.
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
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
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.
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.
Joel Adams
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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
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
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
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...
Joel Adams
C3VR Lifetime Member #56
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
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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Oak Creek, WI - USA
Joined: 5/21/2008
Posts: 1965
Vette(s): 1981 Great White Shark. Red Interior, 350/190 hp. PS, PB (SS), A/C CC, T-Tops. Served three years in Active Duty Army, then Retired Air Force after 34 years! Badger State Vettes Car Club. 175,000 Original miles!! Now own a 1998 C-5!
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
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
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
You can drive it, but the speedo won't work. 
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Lifetime MemberLanoka Harbor, NJ - USA
Joined: 12/21/2006
Posts: 828
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
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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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 $AU440.00 
($US350.00) exchange, if pushed to buy one will look at ex USA (much cheaper)
($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
in Forum: C3 Fuel, Emission Control, and Exhaust Systems
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