Control valve & Servo

autonewbie · 02 April 2018, 20:02

Hello All,
My car began running lousy and I found that I had a vacuum leak. If I remove the servo hose from the control valve and cap the valve servo nipple, the car runs perfectly.
This causes me to believe I have a leak in the servo hose or servo diapham. However here is the problem I have:
My next door neighbor, a retired mechanic and vintage VW owner, tells me that in his opinion, the control valve should NOT be giving vacuum to the servo can unless I am changing gears. He can't understand why there is vacuum to the servo when the car is running and not being shifted. He suspects a bad control valve.
I still think it is the servo. This mechanic is very knowledgeable and has helped me many times. He has also rebuilt many 1600 engines. I trust him and he is a nice guy.
My question is: Does anyone know if the control valve supplies some vacuum to to servo all the time? If it does, then my problem is the servo hose or diapham.
Any help is greatly appreciated.
Thanks.

bhartwell59 · 02 April 2018, 23:01

running lousy how?

usually if it's the servo diaphram, it's hard to shift. i've heard (on here) the control rarely goes out... but it does happen.

autonewbie · 03 April 2018, 00:32

It starts fine but the idle surges up and down and I have to move the throttle or else it will die.
This afternoon I removed the servo hose from the control valve and attached a spare servo to the control valve.
This spare servo was not attached to the transmission, rather it was just a test to see how the engine reacted. With the spare servo attached the engine smoothed out and ran perfectly. I was able to adjust the idle to the correct rpm, check the mixture and timing. All is well with the spare servo attached. But it is 50 years old.
I just ordered a servo rebuild kit to install in my servo and I predict all will be fine.
The debate still exists between me and my mechanic neighbor.....Should any vacuum be going to the shift servo if the car is running but no shifting is taking place. I can't seem to get that question answered.

sb001 · 03 April 2018, 05:44

Technically no. The way it works is, when the engine is running and you are not shifting, the control valve is open between the vacuum supply hose from the intake and the hose down to the vacuum storage tank under the left rear fender, allowing vacuum to be sent to the tank for storage. Then, when you shift, the control valve solenoid operates, closing the valve between the intake and the storage tank hoses, and opening the valve between the storage tank and the hose going to the clutch servo canister.

However, if you have a leak in the clutch servo diaphragm, it is probably possible for SOME vacuum to leak through between the intake and the clutch servo hoses (even though that valve should be closed) which could cause an idle surge AND difficulty shifting (it would be MUCH worse trying to shift from neutral into gear.) I am having the EXACT SAME problem at the moment, idle surge and very difficult to shift into gear from neutral (although not as hard once the car is going.)

I just removed my canister and opened it up and yep there is indeed a small tear in the diaphragm.

volkenstein · 03 April 2018, 10:10

Newbie,
WHS ^^^. One of the few reason's is could be drawing vaccum is that your CV electrical circuit (stick to Solenoid)
has grounded somewhere and thus is more or less permanently engaged/fired. Dubious however.

Get methodical and isolate............

I would break issues up thusly :

55% - Vac Servo diaphragm toast
20% - Vac hoses shot/holed/worn out
15% - Lousy electrical set-up
7% - CV solenoid dead
3% - Other - Although your could throw total mis-adjustment of everything by a P.O. as 75% of issues encountered

HTH
Volkenstein

autonewbie · 03 April 2018, 15:47

Maybe I really screwed up??? I have a 1970 Karmann Ghia.
I am 71 and avoid as much as possible getting under the car, therefore....I have not actually looked under the car to see where the servo is located. Maybe I got the hoses mixed up?
The hose on the control valve that leaves the CV and goes under the drivers side of the car is the one I thought went to the control valve. Am I wrong?
Where is the vacuum tank on the Karmann Ghia?

autonewbie · 03 April 2018, 17:15

UPDATE------
Ok I jacked up the car (not easy for me) and slid underneath. Lo and behold the hose I thought went to the servo actually DOES go to the servo. So I guess the servo is the problem. WRONG!!
I reread Volkenstein's post and checked out the CV solenoid. When I turn on the ignition key the servo clicks instantly. Hmmm that does not seem right. I took off both wires and found that one wire has 12v with the key on, the other wire has ground on it all the time. That I believe is not right. This means the servo has been pulled in all the time. How was I able to shift? Have I harmed something?
The ground wire comes from the shifter contacts so it should only have ground when one presses down on the shifter. I believe I need to check out the contacts and the wire from the shifter.
But after jacking up the car etc I am exhausted. Maybe tonight I will feel well enough to give it a go.
Thank you all for you excellent guidance, this site is a real blessing.

sb001 · 03 April 2018, 17:54

Hi newvie,
yes you are correct that is a good sign that it is the fault of the contacts in the base of the shifter and NOT the clutch servo diaphragm. You are correct that the brown control valve wire should only be grounded when shifting the gear lever, thereby completing the circuit and causing the CV solenoid to activate. If you show continuity to ground all the time on that wire, (which would gel what you said about the CV "clicking" all the time when you turn the ignition on) then it is constantly active, meaning either that your CV ground wire is grounding out somewhere short of the shifter contacts, or your contacts in the base of the shifter are touching each other even in neutral which is not correct. Most of the time when there is a problem with the contacts in the base of the shifter, it is either that the contacts are not tocuhing each other even when shifting (too far apart) OR the ground wire from the contacts back to the control valve is broken somewhere, in either case causing the control valve not to operate at all when shifting. But it sounds like you have the opposite problem.

P.S. I have never owned a ghia, but from what I have read I believe the vacuum storage tank is under the RIGHT rear fender on the Ghia, whereas it is under the LEFT rear fender on other cars. I am not positive on that though.

autonewbie · 03 April 2018, 18:09

More confusion---
Ok I went back into the garage (I just can't stay away from this problem) and did the following:
I hooked up one wire of a 12v buzzer to the control valve shifter wire. I applied a constant 12v from the battery to the other buzzer wire. (The actual control is not hooked up to this test jig.) As soon as I hooked up this buzzer it began to buzz. I took off the top shifter handle with the top contact inside and the buzzer continued to buzz, indicating it still had ground. I moved the lower shifter stub into gear and the buzzing stopped. If I put it in any gear the buzzing stopped. I only got buzzing (ground) when in neutral.
Could the neutral safety switch be doing something wrong? Is the CV valve supposed to get ground when in neutral? If the shifter wire was shorted to ground somewhere, the buzzing would not have stopped when shifted into gear. At least that is my conclusion at this point.

autonewbie · 03 April 2018, 21:49

next update--
I placed my multimeter on buzzer position (continuity) and attached one lead to the lower shifter contact. I placed the other lead on a good ground connection. The buzzer sounded and continued to sound, indicating that the contact was at ground potential. I then removed the back seat and opened the blue wire connector which removed the shifter contact from the cv ground wire. (the cv ground wire is connected to nothing in the engine compartment during this test). Opening that under seat connection stopped the multimeter buzzer. So ground is somehow getting to that short segment of wire that runs from under the rear seat and into the engine compartment.
I know that wire is connected to a dummy spade tip on the neutral safety switch, and another wire on the same connector is what appears in the engine compartment as the cv ground wire from the shifter contact.
Because my car has air conditioning, tracing that wire under the car is problematic. I plan to leave it alone and run a new wire from under the rear seat into the engine compartment.
This has been exhausting but I think this replacement wire will allow the cv to operate properly ONLY when I press down on the shifter. Amen.

sb001 · 03 April 2018, 21:54

This is a tough one-- going to have to think about it for a little bit!
I do wonder if the neutral safety switch is somehow grounding out the wire to the control valve-- but if the switch itself were somehow defective and grounding out, you wouldn't be able to start the car.
Do me a favor-
There should be a plastic wire connector in the car toward the back, where the wire from the shifter connects to the wire that goes through the floor pan down to the neutral safety switch on the transmission. disconnect those wires, then route a separate wire around the outside of the car from the shifter wire to the control valve. Then start the car and see if it goes into gear properly. If so, then we can narrow it down to either a problem with the neutral safety switch or the wires to/ from that switch.

sb001 · 03 April 2018, 21:56

Ha- it looks like you beat me to testing that theory!

I bet your problem is down there in that wiring to/ from the neutral safety switch. Just route another wire around the outside of the car to the control valve from that connector under your rear seat and see if that fixes everything. If it does, you can actually route a wire through the car that way and run it like that-- my mechanic routed that wire that way on my car for years before I noticed it.

autonewbie · 03 April 2018, 22:31

Thanks sb001 for your input. Great minds think alike! I hope to complete the rewire tomorrow. We shall see if it cures my issues.

68autobug · 04 April 2018, 03:23

Hi Guys,
Yes, sounds like the wire going from the gear shifter points has shorted out to ground which will send a signal back to the control valve... First time I looked at that wire on My car, the PVC coating was just coming off due to all the flexing when You change gears, plus the age of the cable/wire. When I rewired all of My car I actually put in two new wires to the gear shifter , only connected one, the other is a spare...lol... You can solder the new wire onto the bottom points contact easily... I can't remember the original wire, but it should have been special flexible wire with multi thin wires that are made to flex, but any standard cable will do the job and last many years. The PVC coating on mine was coming off where the wire comes out of the bottom of the gear shifter rod.... You could use some heat shrink pvc to cover the cable so it doesn't happen again.. but a new wire will fix the problem...

cheers from Australia - LEE

autonewbie · 04 April 2018, 19:00

Today I installed the new shifter wire into the engine compartment. Before I hooked both wires to the cv, I hooked my 12 buzzer to the shifter wire in the engine compartment. I then reassembled the shifter and used the buzzer to indicate correct shifter adjustment. It was very easy to set it perfectly just by listening to the buzzer.
Next I removed the buzzer and hooked the wires to the cv. Started the car, shifted into all gears, and all is well.
My baby is back in running condition.
Thank you all for your input.
Ken