Dad3Sons

Hey Corvette Forum. This is my second post. My first experience was a complete success - got the parts from Bree Miller (KY) to fix my key fob (Thanks Bree!!!); I'm hoping to stay on a roll.

Corvette: '96 LT1 base coupe. Cruise control quit working suddenly. 10A fuse is good. FSM says begin with checking vacuum on the control servo. No vacuum on "source" side. No obvious breaks or cracked lines or hoses at vacuum tank. I did replace the hose that runs from the servo through the firewall to the brake control switch, as exposure to 19 years of the battery area left it quite rotten. That was a Saturday morning spent...

Car doesn't run poorly or idle up like I'd expect if I had a bad vacuum leak or open hose somewhere.

Can someone point me to where the CC system picks up vacuum on the intake manifold? Any other ideas?

Thanks in advance!

Joe C. Northern California

Cliff Harris

There is a three way vacuum check valve under the passenger side fuel rail cover. It is quite common for it to crack due to the heat. That is the vacuum source for the cruise control. About $4 at any auto parts store.

Supreme112279

new member here with the same issue. My 3 way valve is in good shape. Where else should I look?

Dad3Sons

Hey Supreme 112279! There are a few other threads about the cruise control which may be helpful.

It's actually a pretty simple system. Just a vacuum line off the 3 way valve on the manifold that goes into the wiring harness around to the driver's side of the engine compartment to a "T". One side of the "T" it goes to the vacuum reservoir which is a plastic ball in front of the wheel -- make sure that line is intact and the vacuum ball isn't cracked or leaking. The other side of the "T" goes to one side of the vacuum servo near the battery. Make sure those vacuum lines are not cracked or split. Long exposure to the battery acid in the compartment will rot the rubber of those hoses. The other side of the vacuum servo goes into the firewall to a switch actuated by the brake pedal. Let me know if this helps.

Joe C.

Supreme112279

Yes it does, The hose that goes through the firewall to the brake petal is cracked at the connection at the battery, actually both hoses there are in pretty bad shape. I just broke the one off and reconnected it.

Is it a pain to run a new hose through the firewall?

Also I'm learning how to search the forum, looks like i'll be buying headlight bushings.

Dad3Sons

Hey Supreme --

Sounds like you found the problem. The vacuum line feeds through the firewall through a grommet. I had to pull mine through from the inside. The replacement vacuum line I bought was slightly thicker than the factory line. Save yourself a big headache and busted knuckles - buy at least a foot more than you need. Cut the end of the line on a diagonal with a pointy end. Then slice about 2-3 inches of the line in half along its length. Lube it up with WD40 or another silicone lubricant. Take that end an push it through the grommet - it will go easily since it's only half the diameter. Then grab it on the other end with a pair of pliers and pull it through. I stuck mine through from the engine side, then pulled it into the passenger compartment. Once you have it pulled through, clip off the cut part of the hose and attach it to the brake switch. Good luck and let me know how it goes!

Joe C.

sample71549

Just replaced the valve on my 96. Fixed my cruise control and as I suspected the vents on my dashboard now work. They also needed the vacuum.

Dad3Sons

I haven’t owned a Corvette since December 2020, but it’s nice to know there are folks out there still fixing the C4’s!!