The Infamous Headlights
Thread Starter
Racer
Joined: Sep 2002
Posts: 293
Likes: 0
From: Englewood CO
The Infamous Headlights
On my 79 Vette when I turn on my head lights they only come up about 1 to 2 inches, then slowly go back down. I have pulled the hoses off the relays(think that is what they are called, has 3 big hoses positioned vertically, and 1small one at the top) and seems like they are functioning. When I pull up the lights they will stay up, and when I turn them off they go down. Any ideas as to how to get them to go all the way up. :confused:
Le Mans Master
Joined: Sep 2002
Posts: 5,228
Likes: 895
From: Myrtle Beach SC
Re: The Infamous Headlights (79corvette)
Essentially you've got relays (2), actuators (the big cannisters) and engine vacuum. The proper method is to diagnose beginning with vacuum from the engine to determine if engine vacuum is sufficient and determine if the problem is as simple as a cracked hose. Engine vacuum should be about 18 using a vacuum gauge. Once you know this figure...you track it to your relays and onto actuators, looking for any degradation of vacuum. It takes as a little as 5 mg to make the actuators pop up so there can be quite a bunch of degradation of vacuum.
It's a fun an instructive exercise if you really wish to take it on. Once you've learned the system...you'll have it mastered....well maybe. I'll have to look around for my cheat sheets but Dr Rebuild has excellent diagrams and instructions. Let us know how we can help...these are nagging problems for all C3 owners.
It's a fun an instructive exercise if you really wish to take it on. Once you've learned the system...you'll have it mastered....well maybe. I'll have to look around for my cheat sheets but Dr Rebuild has excellent diagrams and instructions. Let us know how we can help...these are nagging problems for all C3 owners.
Burning Brakes
Joined: Apr 2000
Posts: 870
Likes: 0
From: trumbull ct
Re: The Infamous Headlights (hunt4cleanair)
Sounds like a bad relay, or bad headlight switch.
The lights open with the headlight switch, because pulling the switch OUT, cuts the vacuum to the signal hose (the small one with the white stripe) and the spring inside the relay pushes the inner cylinder down, thus sending a vacuum to the "open" port. The headlight switch pushed IN, sends vacuum through the signal hose, thus pulling the inner cylinder back up (against the spring pressure) sending vacuum to the "close" port. If the lights close OK, but don't open well, I would say replace the relay first. If the lights work BOTH up and down with the pull down switch under the dash, then you need a headlight switch.
Best thing to do is make sure there are no vacuum leaks in the system, and order a full colored vacuum hose diagram from Doc Rebuild. The diagram is correct, and he also has a troubleshooting guide available.
George
The lights open with the headlight switch, because pulling the switch OUT, cuts the vacuum to the signal hose (the small one with the white stripe) and the spring inside the relay pushes the inner cylinder down, thus sending a vacuum to the "open" port. The headlight switch pushed IN, sends vacuum through the signal hose, thus pulling the inner cylinder back up (against the spring pressure) sending vacuum to the "close" port. If the lights close OK, but don't open well, I would say replace the relay first. If the lights work BOTH up and down with the pull down switch under the dash, then you need a headlight switch.
Best thing to do is make sure there are no vacuum leaks in the system, and order a full colored vacuum hose diagram from Doc Rebuild. The diagram is correct, and he also has a troubleshooting guide available.
George
Thread Starter
Racer
Joined: Sep 2002
Posts: 293
Likes: 0
From: Englewood CO
Re: The Infamous Headlights (hunt4cleanair)
On the relays I pulled the top big hose and the bottom hose to check the vaccum(I just put my finger over it to feel it). When I had the head light switches in the posistion to keep the head lights down there was more vacuum in the top posistion, then when I pulled either switch for the lights to come up, from the bottom position of the relay(same thing was with both relays). Is it normal for there to be less of a vacuum in the bottom postition of the relay than the top position? If it is not normal would it most likely be a relay problem? Also where would I be able to get vacuum guage? Sorry if my sentences don't make much sense, it was late at night when I wrote this.
Chad
Chad
