MikeP

Morning fellow forum members

I have a wiper issue that just happened yesterday. When I start my 69 coupe the wiper door opens up without any switches (wiper or manual under the dash) being activated.
- I activated the wiper switch to ensure the wiper arms/blades still operated normally, thought when I turned off wiper switch it would cause wiper door to close, it didn't!
- With car running I attempted to operate the wiper door manually with the under dash manual override push/pull switch - nothing happened open or close.
- I operated the manual head light pull/push switch that's next to the wiper manual switch under the dash, head lights open/closed with manual switch as they should
- I removed the vacuum line from the front of the wiper door canister and applied vacuum which slowly closed the wiper door while engine wasn't running.
- Restart the engine wiper automatically opens up.
- I notice a switch on the firewall that works with wiper door when in the open position, it makes contact with a spring loaded contact on firewall side, the switch has a red wire that looks like its routed in front of the plunger and spring loaded contact point. Is this red wire route correctly? Whats this wires main purpose?
- I checked to ensure all vacuum lines coming from the Manual under dash switch, Vacuum manifold canister in front driver side and Wiper door canister were all connected. Vacuum lines and canisters have all been replaced when frame off restoration was performed
- I have attached pic's of the wiper door switch, vacuum manifold and wiper door vacuum canister so you can see what I'm dealing with, might help visually to solve me wiper door issue.





Any assistance with this issue would be greatly appreciated
v/r
Mike

71 Green 454

Go to the wiper door vacuum relay in the second photo and make sure you have vacuum on the control line (small hose) with the engine running. I just replaced mine due to a ruptured diaphragm.
Vacuum on control line = wiper door closed
No vacuum on control line= wiper door open

xpoc454

I have a similar problem on my 69. Except when i start car, wiper door goes up and after a few seconds it pulls it down. This is all with no interaction.
these vacuum systems are tricky.

wwiiavfan

Mine opens the door a smidge and closes it again all within a 1/2 second during startup, but only when the vac reservoir is disconnected. Connect the reservoir, no cycling.

MikeP

71 Green 454
Thanks for your reply, I'll check the small hose on top for vacuum with engine running.
- Should also check the other small hose towards the bottom of the vacuum relay also?
- How much vacuum pressure should be looking for on the gauge?

v/r
Mike

MikeP

I checked for vacuum at the wiper door relay as suggested, there was no vacuum, wiper door open when engine was started with small hose disconnected from wiper door vacuum relay!
- I also checked for vacuum at the big round wiper door relay passenger side,
- Rear vacuum port registered 14 lbs vacuum with engine running.
- Front vacuum port registered 0.0 vacuum with engine running.
Do these results confirm that my wiper door relay (drivers side, second picture) has a ruptured and needs replacement??

p.s. there was no second small vacuum line on the wiper door relay as I mentioned earlier, I misspoke.
v/r
Mike

71 Green 454

Do you have a small piece of hose? If so, disconnect the control hose on the vacuum door relay and attach a hose to test it. With the engine running, suck on the hose and see if the wiper door closes. It doesn't take much vacuum.

MikeP

I accomplished the vacuum test you requested with my hand held vacuum pump, No vacuum registered on gauge. I also confirmed by sucking on hose also, Zero restriction/suction felt. Does this trouble shooting confirm that I have a ruptured diaphragm in the wiper door relay assembly?

v/r
Mike

71 Green 454

To answer the above question, when you apply vacuum or suck on the control port, it should move the plunger inside and stop. There's not much travel to accomplish this. It sounds like it's ruptured if it doesn't hold vacuum...I took mine apart to verify and it had 2 separations.
Before I installed the new one, I checked that it held vacuum on the control port.

Just to clarify, with the engine running do you have vacuum on the control hose going to the vacuum door relay?

Here's what it looks like inside of the vacuum relay:

Hopper12

This vid may help:

MikeP

Thank you for all the help today!! I going to order a new wiper door relay. Just didn't quit understand the whole vacuum system my vette has, was surprised that my headlights open/closed but my wiper door would open every time i start the car. Just started acting up this yesterday. How hard was it to open the ruptured relay? Would like to confirm thats was my issue before I toss it into the trash.
v/r
Mike

71 Green 454

I started with a screwdriver, then used needle nose pliers to finish uncrimping. If yours doesn't hold vacuum I would assume it's either a ruptured diaphragm or a bad crimp. Yours looks pretty new, mine was 52 years old and working fine until after washing the car one day.
I pulled it into the garage and the wiper door stayed up.

jbhammer

Just spent the last few days dealing with the same issue. All advice given so far is good. If you want to investigate further, there are several YouTube vids on testing the safety switch under the wiper arm. Also, use your mighty vac to test the integrity of the vacuum lines going from one point to the other, such as the relay to the wiper safety switch, relay to actuator, etc. My problem ended up being at the manual over ride switch under the dash/steering column. The 90 degree rubber boot that holds the two hoses and attaches to the switch was leaking. Once I attached the hoses directly to the switch, problem solved.
As far as vacuum values: take a reading with car running just off the manifold, before the check valve. Note the value. Then use that as a basis for all other readings. Those subsequent readings should not be more than 3-4 PSI less than your base reading. If so, you have a leak at that section.
Best point to remember, it takes vacuum to hold the wiper door down. If it comes up when you turn on the car, the actuator is not getting vacuum. So you need to test everything that provides vacuum to the actuator. Good luck!

MikeP

jdhammer
I checked the vacuum suction at the little hose coming off the top section of the wiper door vacuum relay, my vacuum gauge reading was 14 lbs of vac. Couldn't obtain any resistance with blowing into a hose attached to the small hose nipple and wiper door didn't move. Must ave a rupture in the diagram so replacing the wiper door vacuum relay.
thanks for your reply.

Mike

wadenelson

1968....

Anybody got a diagram / map of the wiper door and hidden headlight vacuum hoses BEHIND the dash? Similar to this but showing also the wiper door hoses? Or could you add those in red on this drawing?





Found this on a hose kit: https://www.fullthrottlecorvette.com/cdn-cgi/image/quality%3D100/assets/images/68diagram.jpg

https://shop17092.sfstatic.io/upload_dir/shop/1968-Vaccum.jpg


See also:

A partial list of the firewall penetrations: (Two each of three hoses, plus wiper relay hose)

Bung #1 (driver's side) has vacuum input for hidden headlights, wiper door ELECTRIC solenoid , and output to headlight relay. (white stripe)

Bung #2 (passenger side) has vacuum input for HVAC controls, heater valve? and fresh air door? outputs.

on my '68 the wiper relay control hose (larger) comes out a large hole along with the tach cable and an assortment of wires. Is that stock?

This, from a much earlier thread, is invaluable information.

---------------------------------------------------------------
Understanding Your Windshield Wiper Circuit
by: Larry Ingram

One of those seldom understood parts of the 68-82 Corvette is its wiper
system. This is particularly true of the 68-72 versions which had a unique
door system interconnected to the electrical circuit. If the vacuum part of
the door opening mechanism fails to open the door fully or the wipers don't
park properly, then the whole set up becomes very difficult to get back into
proper operation.

Step one, as usual, will be to briefly describe each component as well as
it's function.

Wiper Switch - Most people expect the switch to be the power source but it
isn't. It simply grounds the wiper motor and / or the washer pump. If the
pump is wiper motor mounted it grounds a relay.

Wiper Motor - The motor is of a two-speed design using different field
windings to produce the two speeds. Incorporated inside the gear reduction
area of the motor is an electrical park relay and a small resistor. The
relay serves multiple duties and can be the source of most of the electrical
problems. Also as part of the motor (until about 77 or 78) was a mechanical
washer pump driven on demand, by the driver, by the motor's gear reduction
unit.

Park Relay - The park relay, when energized, allows the motor to turn. It
does this by simultaneously releasing its gear driven transmission and
closing a set of points which are concealed within its plastic housing.
(photo # 15 - optional as per space) This then allows battery power to the
field windings; this power keeps it running. Internally, the motor has a
field winding in series to its armature, as well as another winding called a
shunt. The shunt when energized limits RPM, causing the slow speed mode of
operation. The high speed current path is powered through the park relay's
points, through the field to the positive brush, and through the armature to
the negative brush, from that brush to ground, via an internal circuit
breaker. When the wiper switch is turned off the relay drops a hook (pawl)
into the path of the rotating reduction gear, stalling the movement as well
as pushing the points open to stop the motor.(photo #18) showing park pawl
assembly) Observing the rotation of the shaft where the linkage is attached
will show how the wiper arms get parked lower than in the normal sweep area.
The shaft parks in an offset path relative to where it is rotating during
normal operation. This is accomplished inside the gear mechanism by a slot
that controls shaft position.

Limit Switch - Used only on 1968-72 cars this switch controls main power to
the wiper motor, and is actuated by a linkage connected to the wiper door
opening mechanism. The switch is open (off) until the wiper door opens to
about 90% of its travel. Only if the wiper door is open should there be
power to the motor on this circuit.

Override Switch (1968-72 only) - Placed under the dash below the steering
column is a rotary switch as well as 2 vacuum switches. These switches allow
servicing the related components, since the wipers will park and be hidden
by the door even if the key is turned off, if not otherwise controlled by
the override switches. Many a frustrated owner has had the experience of
(apparently) failed wipers because someone turned the rotary switch to see
what it operated. If the wipers were off at that time no response was
noticed; but the first time wipers are demanded they won't work, if the
switch was left open.

Electrical Control Relay (1969-72 only) - A relay mounted inside the
console to the right of the radio, used to supply wiper switch information
to the motor circuit. The relay is needed to allow parking of the wipers
when the key is turned off.

Vacuum Circuit - 1968-72 cars featured a heavily advertised feature touting
the missing or concealed wiper blades, actuated by a vacuum circuit. The
vacuum circuit consisted of a large vacuum motor to open or close the door,
a vacuum relay used to send vacuum to the motor, an override switch under
the dash, an electrical solenoid behind the tach to send the vacuum signal
to the relay and an interlock vacuum switch moved by the right hand wiper
arm. Connecting all these parts are several feet of vacuum hose which can
rot, be pinched, knocked off, or simply connected incorrectly. Problems tend
to go un-noticed until the driver is caught in a downpour.

How Does This System Work

So, with these basic system components, the question now becomes, "How does
this system work?"

I will begin by describing the operation of the wiper door system. The door
is opened or closed on demand using engine vacuum, stored in a tank under
the left fender beside the master cylinder. The tank is evacuated (supplied
vacuum) by the running engine through a check valve and a filter. Vacuum is
directed as two separate circuits to the vacuum relay: one operates the
relay and one operates the vacuum motor (tank or double pie plate part
mounted above the heater on the firewall, just to the left of the hood
catch.) The relay is a spring loaded valve that can be pulled against the
spring using vacuum on a diaphragm. This causes it to direct vacuum from the
center port to one side of the vacuum motor while opening (ie: venting) the
motor's opposite side to atmosphere. Four hoses will attach to it, three
large and one small one (it's signal). (use photo # 4) When there is no
signal, engine vacuum is applied in at the large center nipple, routed
internally to the nipple farthest from the diaphragm end and via a hose to
the vacuum motor to open the wiper door via its linkage. When this happens
the top nipple is vented to very bottom of the relay where there should be a
foam filter in a square plastic framework. All of this is reversed if vacuum
is sent through the signal hose to pull the diaphragm up; the valve pulls up
opening the lower port to atmosphere and routing vacuum to the top nipple.

A vacuum signal is used to control the opening or closing of the wiper door.
This signal is applied to the relay's diaphragm to close the door, or the
signal gets blocked off and the diaphragm is vented to atmosphere to open
the wiper door. This job is done using a multiple switch path. The control
circuit consists of three switches in series, the interlock valve under the
wiper arm, the over-ride valve, and the solenoid valve. (photo # 20) This
solenoid is wired to the wiper switch and therefore whenever the switch is
turned on it is supplied a ground. The solenoid is live whenever the key is
on receiving its power through the wiper fuse.

Here Is How It Works

Vacuum is applied to the vacuum relay diaphragm. Engine vacuum goes to the
interlock valve via a hose. If it's depressed by the wiper arm, the vacuum
continues via another hose to both the underdash over-ride switch and vacuum
control solenoid. Either or both of these shut the vacuum off when
activated, and simultaneously vent the vacuum that was in the diaphragm thus
allowing the spring in the vacuum relay to switch vacuum to the opposite
side of the vacuum motor and open the wiper door. Remember that the relay
opens a vacuum path between two nipples and also vents the remaining nipple
to atmosphere; it does not just switch vacuum only. When the wipers or the
ignition is turned off, vacuum from the reserve tank will again be applied
through the interlock valve, after the electrics park the arms, through the
solenoid to the relay, unless the over-ride switch is pulled down. When the
vacuum pulls the relay's diaphragm and piston up, it directs vacuum to the
vacuum motor as well as venting the opposite side of the vacuum motor. It
would be difficult to pull the motor diaphragm if the opposite side was
sealed. Of course, if the override switch is pulled down the door will
remain open as the vacuum path to the relay diaphragm is blocked.

By using vacuum valves in this way GM engineers were able to prevent changes
in engine idle due to vacuum leakage below the carbs butterfly valves. If
the hoses get reversed at a switch or valve, then whenever it gets activated
a small vacuum leak is introduced and some change in idle should be noticed.

Now I Will Explain the Electrics

To begin, I will explain the basic set-up for the 1973 and later, and then
add in the extras used in 1968-72. Even though these latter years had
differences, there was a basic set of principles which applied.

As stated earlier, the wiper switch is only a ground source. The motor and
washer pump are supplied power on a yellow wire that is fused by the wiper
fuse & powered through the ignition key. If the key is on, then power is
supplied to one side of the park relay (hidden inside the area covered by
the washer pump or if the pump is under the jar then behind the cover over
the gear drive). The other two terminals of the motor control circuit are
wired as follows: terminal # 1 is used to create the high speed, while
terminal # 3 controls slow speed as well as the parking command, when the
wipers are switched off. These commands are received as follows, the wiper
switch grounds both # 1 and # 3 for low speed and only # 1 for high speed.
When the ground is provided the park relay magnetically pulls back the park
pawl, allowing the motor to rotate the gear reduction unit. Simultaneously,
a set of points inside the relay close allowing the power to the motor
field, armature and brushes which are all in series to each other, with one
brush being connected to ground via an internal circuit breaker. If the
points fail to close, are burned or pitted, or a brush is worn down or
simply hung up by rust or corrosion, then nothing happens other than the
pawl moving. IMPORTANT NOTE: Because the wiper motor is mounted to a
plastic body there is a ground wire attached to a terminal on the gear
cover. This can also get knocked off, corroded or it's other end
mis-installed. Whenever there is a problem begin by verifying the ground.
(Photo # 23 # 6 shows under dash override switch with pen pointing to
"vent to atmosphere" hole which is only visible with the override switch
pulled down in the "open" position - ie: to hold wiper door open)

1968 version - The circuit for 68 is unique and so far I have not found it
in any service manual so this information was arrived at the hard way, 1
wire at a time on a car that had been messed with. The motor in 68 is not
grounded conventionally. The ground brush is wired to the under dash rotary
switch. This prevents using any other year motor without making internal
changes. The park relay turns the motor on and off but the power to run the
motor comes through the wiper door actuated limit switch (live at all times,
fused at the horn relay by a fusible link ). This wire goes into the motor
and attaches to one side of the park relay point set, through the points,
field, brushes and armature and then back out of the motor into a harness
that takes it to the rotary switch, the other side of which is grounded
(switch closed). According to my notes there is a three-wire plug coming out
of the motor, red is power, brown goes to the vacuum solenoid on the back of
the tachometer (photo # 3 - optional for space), and a light blue which
changes to a black going to one side of the limit switch, through the switch
it changes to a brown, then to a brown with a white stripe, and ultimately
goes to the rotary switch. Each of the color changes takes place at terminal
plugs. Why it kept changing colors I don't know.

1969-72 version - To the best of my knowledge these years were all the same.
In 1969, an inside console relay was added, as well as grounding the
armature brush internally rather than via the rotary switch. The new circuit
put the rotary switch in series with the door actuated limit switch. This
means that power must flow through the switch and is easily checked with a
test light at a connector going into the motor (heavy red wire). The wiper
switch controlled the motor using the console mounted relay as follows.
Energizing the relay switches motor control to the wiper switch, closing a
set of points inside the relay case which grounds the motors # 3 terminal to
cause low speed operation. If the wiper switch is moved to high then both #
1 and # 3 terminals are grounded causing high speed. When the wiper switch
gets turned off, the relay looses it's power and the spring loaded point arm
opens completing another ground circuit. This grounds the # 3 terminal
allowing slow motor speed. Because the park relay lost its power when the
wipers were turned off, it has dropped its hook out to stop the gear in the
parked position, which (as it parks) will also open the field points within
the park relay. This stops the motor. Ultimately the wiper door will close
and disconnect the main feed by opening the contacts in the limit switch.

In this circuit set up the vacuum solenoid is wired in parallel to the
relay. Whenever the relay is energized so is the solenoid. The control relay
is wired, using 5 - 18 gauge wires, as follows:
- light blue, wired in parallel to the wiper motor # 1 terminal, the wiper
switch high speed terminal, and the vacuum solenoid;
- yellow, wired in parallel to the wiper motor # 2 terminal, the vacuum
solenoid, and the wiper fuse;
- light green, to the wiper motor # 3 terminal to provide the ground
necessary for low speed operation;
- black, to the wiper switch for low speed, connected by the relay when
energized;
- black /white stripe, to ground, this is connected to the light green if
the relay is not energized.

The wiper switch used for all years has three terminals, # 1 grounds the
washer pump when the switch is depressed, # 2 is for low speed, and # 3 for
high. In actual fact both # 2 and # 3 are connected to ground for low
speed. This translates to grounding # 1 and # 3 at the motor to get low, or
# 1 for high. For the years 1968-76 the wiper switch receives its ground
from the white metal dash cluster housing the gauges, later years had a
proper ground wire. Note: Many of these housings have been broken by
improper dash assembly causing intermittent operation. If your bezel is
broken at the sides just above the gauge area I suggest that you add a
ground wire directly to the switch. In some cases I, as well as others, have
received a substantial shock touching here during troubleshooting. I guess
the motor builds up like a coil looking for a path to ground.

So, that's it. A rough guide to the whole wiper/wiper door issue. When I
took on the assignment I thought I knew pretty well how the whole system
worked. Once I started looking at the service manual, however, I realized
how many important facts were left unstated and how badly the circuit
diagrams of the day explained the situation. I suspect that a lot of other
"guides" are equally poorly described, because this is a complex system. But
how are you going to fix it, if you don't know how it is supposed to work?
If you want to add any important points from your experiences, I welcome
your comments.
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