I searched the archives and couldn't find anything about my particular problem. I have the troubleshooting guide for the vac systems but it mentions no probable causes to problems that occur. Surely someone has had this problem and can pinpoint what to check or replace...On my '71 the wiper door is closed when the car is just sitting. When I start the car it opens momentarily and closes. The override works properly and the wiper switch operates everything correctly. The door opens and closes as it should when the car is running as do the headlights. The car has good vacuum, wiper door and both headlights open and close swiftly. A guy told me sometimes this is caused by the checkvalve just down from the filter leaking vacuum. I Checked it with a vac gage and it was good. Would a leak in the system somewhere cause this? A bad actuator or actuator relay? Could there be a vac line not connected correctly somewhere?
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Re: C3 wiper door opens momentarily
Too bad those vacuum guides apparently don't explain the principles of operation of the vacuum system. That has been explained here in the past, mostly by Jack Humphrey. He could probably cut and paste the answer to this, but I'll try my keyboarding skills. He also would do a better job than I, but that won't stop me either. He'll step in and fill in the blanks I leave.
The vacuum system consists of two discrete systems. The control system -- the smaller hoses -- and the power system -- the larger diameter hoses.
Because the control system contains less volume -- smaller hoses -- when the car starts and vacuum begins to form, the control system vacuum should come up (or is it pull down) before the power system -- larger hoses and the volume of some part of the actuators.
The control valves (I believe GM calls them actuator valves) -- one for the wiper door and two for the headlamps on your 1971 -- have a spring to park them when there is no vacuum in the control system. If that spring doesn't set the shuttle valve (the part inside that ports the vacuum from port to port) -- either the valve is stuck or the spring is weak -- the item being controlled -- in your case the wiper door -- will operate as the vacuum comes up. Headlights will often wink for the same reason.
More commonly, if there is a leak in the control circuit for one of the vacuum controlled items. That item can operate as the vacuum comes up. It takes the engine some time to generate enough vacuum to overcome the leak. Same symptom as above.
Since the wiper door is controlled by both the vacuum override switch -- under the steering column -- and a solenoid on the back of the tachometer, there are a couple of not so easy to access places to check for leaks. I suggest you check for leaks first -- even though this is harder than swapping the control valve. The control valve is not inexpensive.
You may be surprised how much better your engine runs if you can get rid of those pesky vacuum leaks.Terry -
Re: C3 wiper door opens momentarily
Mark my turn.
This only if you have no leaks or broken hoses.
But I would do this first
On the drivers side of motor on the back you will see 2 round 1" dia disks 1 plastic and 1 steel.
The first 1 is plastic with 1 hose on each side.Take that off and if you can see threw it replace it.That is a filter.The other is steel with 1 hose in and 2 hoses out,Take that off if you can blow threw it replace it.You will find the parts in book under head lights.around $30 yes wipers in the head light section
Next
Pass side, With the wiper door open there is a plastic part with 3 hoses.A red /white /green Replace that part $30. The top hose goes no ware just a vent the hoses are also colored to match part.I hope that works if not go back to #3396 answer and find that pesky vacuum leak.Denny72Comment
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All well said!
Only a few extra comments.
(1) The 'fat' tubes Terry refers to as the 'power' side of the vac system are more properly called 'servo' while the thin tubes are called 'control'. The servo side routes vac that does actual work (open this, close that) while the control side tells invidual components WHEN to do their job...
(2) Both sides of the system have a common source (the intake manifold). When you start the engine and begin to draw vac, there's a natural 'race' condition. Which side will come up first, the servo or control side? The system was intentionally designed to 'bias' the race so the control side came up first during vac build-up and went down last during vac loss. That makes things nice and orderly without wiper doors 'dancing' or headlights 'twitching'
(3) You can 'lose' this natural bias for one of three reasons and frequently on these older classic cars there's more than ONE problem! You have to track down and kill ALL of the problems for the system to work as it's designed to.
(3.A.) You have leak's that prevent the system from working as designed.
(3.B.) You have a bad check valve (the metal disk mentioned with an input on one side and two output nipples on the other side). It should pass air in one direction (from output to input) and CRISPLY block air flow in the opposite direction. These ususally fail from natural aging OR from abuse (allowing airborne 'crud' to invade the vac hoses and migrate backwards to the vac source coating the umbrella valves inside the check valve with 'goo'). The terms 'crud' and 'goo' are highly technical and descriptive.
(3.C.) Through lack of proper periodic maintenance, you've changed the vac system's air flow characteristics. To have a vac system do its thing, air has to actually flow inside it and the intentional bias built-in by factory designers was based on 'normal' air flow rates.
The white plastic filter upstream from the check valve is there to trap interal airborn 'crud' and keep it out of your intake. GM intended owners to service this filter (by replacement) about once a year, but MOST all of the classic Shark driver cars I see sport filters that've been turned yellow by YEARS of service beyond their useful lives.
As mentioned, remove the in-line vac filter and sight through it toward a light source. If you see right through it, guess where the internal filter element went? Yep, sucked into your intake manifold and probably down into a combustion chamber. Not good...
If you see coal black, the filter is plugged with crud and goo, time to replace 'er. Plus, you'll regain the correct air flow rate designers intended!
Last, if you see snow white inside, GOOD! That's what it should look like...Comment
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Re: All well said!
I knew you could do it better than all of us. Thanks prof. Jack :-)TerryComment
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Re: All well said!
Thanks to everyone. I can't wait to check these things out this weekend. I did go ahead and order a new filter, check valve and actuator valve. One thing Denny mentioned, the actuator with the three hoses, the top hose is a vent that goes nowhere...except that someone has put a screw in it!! maybe I should take that out first. Thanks for all the help again. I'm going to have another posting on these anti-deiseling and blocking relays.Comment
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Re: All well said!
The item Denny mentioned sometimes has a short hose that just goes into the engine compartment and ends -- that achieves the same end -- it is a vent. I don't know what a screw in the hole would do, but it is worth a try to remove it since it doesn't belong there.TerryComment
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Re: All well said!
Guess what! Removed the screw and the door works properly, YES. Thank you!Comment
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Common...
Prior owners + Bubba mechanics see the 'stub' of the wiper door relay's vent hose protruding through the firewall grommet and don't understand, so it's often plugged.... The reason the vent hose goes into the engine compartment is because it's a 'naked' vent (no filter to eliminate airborn matter) and routing it into the engine compartment gets it free of exposure to rain water...
With the hose plugged, the wiper door will be 'sluggish' when it comes to changing positions because vac has to vent 'naturally' (via incomplete seal in the relay itself + at vent nipple to hose interconnect and around the plug. Remove it and 'pitch' it.
What questions do you have about the '71 CEC relays? One was GM 3990842, Reversing Relay, and the other was 3990843, Delay Relay. The 'reversing' relay is the 'brain' for the CEC emission system and is one of the first implementations of DTL (Diode Transistor Logic) meaning if you crack the case you'll find 'wierd' parts inside PLUS you can NOT treat it as a conventional electro-mechanical relay and attempt to troubleshoot with battery + ground jumper wires (you'll FRY the sucka!).
This one's still available from GM (last time I checked) but service replacements are slightly different in terms of packaging vs. factory originals. It takes input(s) from the transmission switch and temp switch (RH cylinder head) and decides when to fire the carb mounted CEC relay.
The delay relay has long been GM discontinued. It simply counts time via an internal RC timer to FORCE the carb mounted CEC relay to fire when the engine has just been started and holds the relay in its energized position for 15-40 seconds (timing is pretty sloppy) before relinquishing control to the reversing relay.
Correct starting proceedures are: (1) turn the ignition ON, (2) set the choke and prime the carb via accelerator and then, (3) key the starter. You do it this way because the CEC solenoid is NOT guaranteed to have enough plunger force to move the carb's throttle linkage, but it WILL hold its extended position against the throttle. So, by turning the ignition ON and then manually moving the accelerator, you free the solenoid to assume its fully extended position prior to initial engine fire....Comment
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Re: Rat's
You know I was going to give my self a {B} for my answer.
But now D- at best.
I have a long, long ways to go.
So I'll read on.
Thanks Jack!Comment
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Re: Rat's
You did fine Denny. One should check the vacuum filter and check valve periodically. That was good advice that I missed.
See you tomorrow morning -- 0-dark thirty.TerryComment
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Re: Actuator Relay Filters
These too are often overlooked.Located at the bottom end of the relay. Over the years they get dry and crumbly and fall out.Debris enters the unit and damages the internal spring and or plunger causing vac problems.You wind up replacing them.
GregComment
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