Douglas Brown

Ok ..I'm looking at the throttle springs and the CC servo. I push in the servo expelling the air pull back the throttle close off the servo air port and the spring pulls the servo diaphragm back .
SO, I recheck manual and two springs are called for. SO how many springs are used if there is a Cruise control? How much spring tension is needed, can one spring do the job. How much vacuum??
It looks like the spring over rides the vacuum.

any one know. If you have a car with cruise C. take a photo of the springs Please.

DB

LenWoodruff

My 78 has Cruise. It only have the Inner & Outer return springs on the carburetor.

Douglas Brown

Ok..Thank you....that helps.
This rebuild has been a learning process.
DB

calwldlife

if the spring overrides the vac then the diaphragm is leaking or your car doesn't have enough vacuum or plus the chain is set too short.

Douglas Brown

A leaking Diaphragm is possible....so is lack of vacuum, but there is no chain connection to carb, it is a rod...
The car is a 78 C3, 350ci 300 hp with mild cam.
it has NO computer carb. it has an Edelbrock 1400 600cfm carb w/ vac. ADVANCE. Thermostat is 195. The CC is not working and I am beginning to trouble shoot the system. since it is a rebuild I do not know if the components are working correctly, ie... brake switch, electrical connection, vacuum needed to operate.
DB

calwldlife

if you have a hand held vacuum pump, sold as brake bleeders,
some have gauges, easy to see if it leaks.
so all this is about cruise control.
get a bigger diaphragm, don't know what the size of yours is but the 81 has a big one.
check with a parts counter man and see if he lists different spec'd ones.
a hand held vac pump gauge is a necessary tool for the vette


chain, cable, rod basically all pull open the carb butterflies
with a servo, vac can, motor, whatever

Douglas Brown

Yes.. Cruise Control vac.

bmotojoe

The servo should hold 14" of vacuum or it is defective, I would start there. Could you post a picture as to how your servo rod connects to the carburetor? FYI, Your servo fits 78 through early 79 cars. Later 79 through 81 cars used the servo unit linked below.
https://www.ebay.com/itm/Corvette-C3...1aHA0a&vxp=mtr

Douglas Brown

[QUOTE=bmotojoe;1596324360]The servo should hold 14" of vacuum or it is defective, I would start there. Could you post a picture as to how your servo rod connects to the carburetor? FYI, Your servo fits 78 through early 79 cars. Later 79 through 81 cars used the servo unit linked below.
https://www.ebay.com/itm/Corvette-C3...1aHA0a&vxp=mtr[/QUOTE

Yep, that is what I have right there.
A pic..sure..I'll get one.

Douglas Brown

Rechecked vac. lines.
Took a look under dash.



Brake switch and Cruise vac release switch<br/>

It appears the CC vac release is not seated properly to peddle, possibly not closeing and staying open creating a vac leak???

calwldlife

maybe not telling cruise that it is ok to work.
meaning the switch says the brake is on?
won't engage.
hope that is it.
easy fix.
checking all the wires and getting to
the wires is

Douglas Brown

I was able to twist my self up under the dash area, tried to push the vac release down but no go. So found a large screw driver, the type used to replace the door springs, it worked just fine. Now if I can just get out from under this dash.

lvmyvt76

amen there!