Vacuum manifold or valve

[Caddy Wizard]

Thanks to all who came before me for this great discussion.  My vacuum manifold (vacuum valve) was no good and using this information I managed to rebuild it.  I can't wait to see how the wipers perform!


I had a hard time making the new gasket/seal out of rubber and ended up using rubberized fiber gasket material.  I found that the key thing to making it work is to make the darned thing as delicate as you can muster.  The little flapper valves are urged (biased) by those little tiny, weak springs.  Well, the springs don't really push the flappers very hard but just sort of influence the valves toward the closed position, and low pressure on the back side of the flapper does the rest to keep them closed.


I have made up some rough schematic drawings of how I think this system works.  As shown in Figure 1, with the engine off, both flapper valves are gently urged toward the closed position.  With the engine running and producing good manifold vacuum and good vacuum from the oil pump based vacuum pump, both flappers are drawn open.  This is the situation when you are idling, going downhill or cruising under a very light load.  See Figure 2.  In this situation, the wiper motor has excellent vacuum power to drive the wipers.  When you put a load on the engine and lose engine manifold vacuum (like when going uphill), the flapper on the intake manifold port closes and only the vacuum pump flapper stays open.  See Figure 3.  In this way, the high vacuum created by the vacuum pump isn't lost to the intake manifold, but instead remains powerful for driving the wiper motor.  To accomplish this, the vacuum power from the vacuum pump is communicated to the back side of the intake manifold's flapper and tends to pull it closed, with a little help from the biasing spring.  So the spring doesn't have to do all of the work and is very delicate. 


The upshot of this is don't make the "hinge" (neck) of the flapper too stiff or thick, otherwise the thing won't close easily enough and won't work as intended.


By the way, not only is this little tiny part critical to proper wiper function, when this thing fails it can have disastrous consequences.  I spoke to the owner of that 56 red Eldo coupe at the GN yesterday and he said this part killed his engine three times before he figured out what was going on.  He would rebuild the engine and take the car on a long trip.  Going along the highway, the oil would get sucked from the oil pan up the vacuum hose and into the intake manifold, causing smoking.  The smoke was bad enough, but he ran out of oil and cooked the engine.  Same thing happened after the subsequent rebuild.  (and a third time, I think).

Art Gardner

[Roger Zimmermann]

Yes Art, it's the way it should work!
By the way, this manifold valve has nothing to do with the engine failure of that red Eldorado; the culprit is the check valve behind the starter motor. I had that problem too, but search the cause before all the oil was gone. I also can tell you, when the engine smoke, you don't see anything in the rear view mirror but a grey/white fog!

Roger

[Coupedeville]

Roger,

This is brilliant!
I have just accepted that vaccum wipers are useless and lived with it. Now thanks to this i will ckeck the valve on my 57 during the winter lay up.
Sometime in the past the washer system was converted to electric and the port on the valve has nothing connected to it. Would this cause any issues?

Joe

[Roger Zimmermann]

Joe, you have to close that port, otherwise you are sucking air from it.
I noticed a change in my wipers; anyway, electric ones are better...Anyway, for the number of time I'm under rain, they are acceptable.

Roger

[Coupedeville]

Hello Roger,

Would it be ok to pm you re the vacuum issue.

Joe

[Roger Zimmermann]

You are welcome, if I can help!

Roger

[Caddy Wizard]

Well, I think I have sorted out the little manifold on the firewall.  But I don't have any vacuum coming from the vacuum pump - zero inches of mercury on the gauge.  Does the brass check valve on the engine block (near the starter) sometimes get plugged up and block the vacuum from reaching the manifold?  Or is it more likely that my vacuum pump has failed?


Art Gardner

[J. Gomez]

Art,

From what I recall the vacuum pump provides about 17Hg at the high RPM mark. The check valve should be wide open with no vacuum pressure at the “out” side (tube going to the firewall manifold). If you show no vacuum pressure at this tube it could well be a stuck/restricted valve.

I know removing this valve is a pain due to its position and the starter blocking the access. Once you removed it you could check the vacuum from the pump, hopefully your pump is good.

Good luck..!

[Dan Koser]

Jose - I was also thrilled to get this explanation from Roger and others...what a help!

However, now I see there is something before the vacuum manifold on the firewall to be concerned about. I recall a port in the block with a brass fitting that, through a metal tube, brings the vacuum from the pump to the manifold.

Can you provide a bit more information on the "check valve" that is in this route of vacuum?

Thanks,      Dan

[J. Gomez]

Jose - I was also thrilled to get this explanation from Roger and others...what a help!

However, now I see there is something before the vacuum manifold on the firewall to be concerned about. I recall a port in the block with a brass fitting that, through a metal tube, brings the vacuum from the pump to the manifold.

Can you provide a bit more information on the "check valve" that is in this route of vacuum?

Thanks,      Dan

Dan,

I left that one hanging, sorry..!

The check-valve aka vacuum assist valve would be the brass fitting on the side of the block just behind the starter. You can reference David King’s comments and pictures under this post http://www.cadillaclasalleclub.org/forum/general-discussion/1956-1957-1958-cadillac-vacuum-check-valve/msg155026/#msg155026.

During normal conditions the engine vacuum pressure would be greater than the vacuum produced by the vacuum pump. 

Since the vacuum pressure is higher at the valve “out” port (pipe to the vacuum manifold) versus the “in” port (from the vacuum pump) the valve is closed. The small brass disc (see David’s pictures) with the small spring and high vacuum keeps the “out” port close.

When engine vacuum drops there is a difference of pressures between the “out” and “in” ports, the valve would start opening when the differences are at about 1-2Hg (small spring tension). This allows the vacuum pump to provide assisted vacuum to the wipers as they need about 10-13Hg to operate.

Now the manifold also serves as a regulator as described by Roger, Art and others on this post. The two port valve opens and closes depending on the pressure at the “VP” and “MAN” ports. So vacuum assist is “only” distributed to the wiper side via the manifold “VP” port, and thus the higher pressure at the manifold keeps the “MAN” port close during vacuum assist.

You do not want to re-direct vacuum from the vacuum pump up to the engine and skew the timing when engine vacuum is low. 

Hope this helps..!

[Kurt Kjelgaard]

Very, very interesting subject..thanks.

Now we are on the subject, I remember seeing some time back the special, combined vacuum/washer lines
- four rubber tubes, two small dia and two larger dia, side by side.
Can anyone point to from where they are availalble.

Also it would be interesting with a diagram of the vacuum lines in the case where the vacuum wiper motor
has been replaced with the direct fit electric motor (-59 through -62, I believe), that is which ones to plug
and which ones to leave operational.
It should be possible still to use the original vacuum driven washer pump and even
make some sort of pushbutton operated vacuum switch to turn on the electric wiper motor,
when the washer is activated.

Has anyone experimented with this?

Kurt

[Roger Zimmermann]

Kurt, I bought this combined tubes at Mastermind. As my cars still have the vacuum wiper motor, I cannot answer the second part of your question.

[Coupedeville]

Hello Guys,

On a 57 cdv Is the vacuum pump an integral part of the oil pump or is it a seperate unit attached to the oil pump?
The workshop manual only shows the oil pump with no mention of the vacuum pump.

Joe

[Walter Youshock]

The vacuum pump is explained in the shop manual.  It is the part of the pump with the vanes.  I'd have to look up the page number.

Even with it working properly, don't expect miracles.  It only draws 20 in. hg. which may be enough to give one wipe when manifold vacuum drops.  There is a reason cars have electric wipers--VACUUM SUCKS!  And there is no vacuum reservoir tank on '56 or '57.  1958 was the first year they installed a reserve tank.

Another critical part of the entire system is the washer pump itself.  Vacuum is applied to the washer switch on the dash; to the pump itself; and to the coordinator that turns the wiper on along with the washer.  I've found that if the fluid level is low in the washer bottle, the car will run like it has a vacuum leak. 

[Kurt Kjelgaard]

Thanks, Roger - do you have a more exact Mastermind address? Seems difficult to Google them.
About the second part of my question, I've looked at a Chrysler site and see that there is a dedicated
co-ordinator switch mounted sort of piggyback on the motor, bypassing the wiperswitch.
Anybody know if this was used on Cadillacs?

[Kurt Kjelgaard]

Just found a picture of the combo on a Corvette site

http://forums.corvetteforum.com/c1-and-c2-corvettes/2791634-1961-wiper-coordinator-question.html

[Walter Youshock]

Yes, Cadillac used the coordinator switch.  Pushing the washer button activates the washers AND turns on the wipers.  There is a brass adjustment screw on the washer pump that "tells" the wipers how long to stay on.  Once the circuit is closed, vacuum turns the wipers off by cutting vacuum to the coordinator on the wiper motor switch.  Spring pressure then moves the switch to the "off" position on the wiper motor.  It is fully automatic, unlike the first electric wiper systems.  On those, the washer switch activates the washers and moves the wiper switch to low speed but the driver has to manually turn off the wipers...

[Roger Zimmermann]

Walter, on my cars the wipers are cycling 3 or 4 times and then shut off automatically. This is also the reason why I "like" the vacuum wipers: the system, when working correctly was very modern. If you want intermittent wiper action, you give more gaz!

[Kurt Kjelgaard]

Roger - do you have more on Mastermind?

[Walter Youshock]

That's the way they're supposed to work.  Adjusting that brass screw will keep them on longer (turning out) or shut them off sooner (turning in).

Vacuum wipers do have some advantages...  INFINITE speeds (provided there is enough vacuum to keep them going and dependent on switch position); completely silent with the cable drive system; and the fully-automatic washer feature.  But why was Cadillac the last GM brand to adopt or offer electric wipers?!?!?!

A quirk of the '57 and '58's is that the passenger arm likes to wiggle loose and eventually walk off the cam, scratch the windshield then fly off the car, preferably before it plops around and bangs the hood.  I had to epoxy mine to the transmission.  Plus, the splines on the arm mount strip and won't hold to the transmission.

Follow the adjustment procedure in the Shop Manual.  If the transmissions aren't aligned properly under the dash and tightened down, they won't follow the angle of the windshield and that plastic cam will wear out and that will cause them to pop off the cam.