Author Topic: Another Vacuum Leak Fixed  (Read 2636 times)

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Offline tmea

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Another Vacuum Leak Fixed
« on: 29 April 2018, 20:42 »
All:
After experiencing a difficult to find vacuum leak hidden under the intake manifold heat riser jacket I thought I was done with the issue but.. I began to notice the symptoms of a vacuum leak again; erratic idle and stumbling acceleration while moving off.  With a can of starting fluid and the engine running I sprayed all of the likely culprits with no effect. Lastly, I sprayed near the the vacuum control valve and had effects on the idle. In checking the control valve I found a serious vacuum leak. To my knowledge, there is no procedure for checking for vacuum leaks on the vacuum control valve. Here is what I did and learned:

With the control valve at rest (no voltage applied), the vacuum reservoir line off and the fitting plugged there should be no free flow between the manifold vacuum line and vacuum reservoir tank line. I confirmed the vacuum leak by plugging the vacuum reservoir  tap while applying vacuum to the manifold tap and there was a free-flow of air. This meant that the vacuum control valve was the source of my leak. I bolted up my spare VCV and the symptom was gone.

In taking the valve apart I found three causes for this  leak. First, the main valve was not seating correctly due to rotted and well worn neoprene sealing surface. This turned out to be a minor portion of the overall leak. I re-surfaced the seal with 400 grit wet and dry sand paper. Second, and this one is odd. Air was also leaking in through the hole where the solenoid plunger protrudes and the solenoid jacket. This leak was fixed by laying a bead of gasket sealer around the the outside of the jacket and solenoid (picture). The third leak was between the solenoid and the valve body. There is a rubber O ring for this but mine as flat and rotten. I applied a thin layer of sealer here too. Problem solved. With the reservoir tap plugged and vacuum applied to the intake line there was no more leak.

I exchanged re-mounted the VCV in the car and the vacuum leakage problem was solved. To my surprise, after a week of sitting in the garage I turned the key to ON and heard a surge of vacuum from the reservoir tank go into the system (after a week)! I might suggest that if you do not hear this happen when you get in to start up after a few hours you definitely have a leak in the VCV. I should have noticed and caught this a long time ago. In addition to running correctly again this repair will not doubt ensure the engine runs cooler this summer and will definitely be appreciated by the exhaust valves.

Hope this was useful. Wondering if anyone has had a similar problem.

Tom

Offline sb001

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Re: Another Vacuum Leak Fixed
« Reply #1 on: 29 April 2018, 22:07 »
Thanks for the info and procedural Tom! I can't say i would have fully known how to even check for a vacuum leak in the VCV so this really helps.
As far as I know the VCV on my car is still the original- I posted a thread over on the samba sometime back where I took mine apart to check everything (think you had done a similar on here already.)  But yeah whenever I turn the key to ON there's that small sucking sound from the back of the car, so I guess it's still good for right now. Something else I noticed after fixing my clutch servo canister a few weeks ago is the much louder and longer "moo cow" sound whenever I turn my car off now (some folks on here call it a duck sound but I've always thought it sounded more like a cow call can when you turn it upside down.) I guess that is vacuum being evacuated from the system back into the canister... it is a hilarious sound the all the neighborhood kids get a kick out of  ;D
« Last Edit: 29 April 2018, 22:11 by sb001 »

Offline tmea

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Re: Another Vacuum Leak Fixed
« Reply #2 on: 29 April 2018, 22:43 »
Ha, I noticed the same thing. A sign that all is well. So I think for the future, the absence of the sucking sound when the ignition is turned to on is a clear symptom of a leak in the VCV. I know mine held vacuum for a week but I think if you get nothing and it has only been sitting for a couple or few hours there is a problem.

Tom

Offline 68autobug

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Re: Another Vacuum Leak Fixed
« Reply #3 on: 01 May 2018, 02:21 »

Hi Guys,
Firstly, I have never dismantled a control valve as I have a spare. So, that was interesting about the leaks.. and I guess most rubber items would be well past  their used by date....  Plus the vacuum in My tank is still there after a few months...
Lastly, I cannot remember the Cow sound You are talking about.????  seems that Your control valve is leaking when the ignition is turned off....

I cannot remember anyone commenting on a control valve failing electrically.... the solenoid always seems to work..

LEE in Australia
-- Helping keep Autostick beetles on the road --
   -1968 Silver metallic 1600 single port Beetle - with BOSCH  SVDA and new BROSOL H30/31 carburetor with GENIE Extractor exhaust system with a quiet thunderbird muffler

http://photobucket.com/68autobug

Offline sb001

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Re: Another Vacuum Leak Fixed
« Reply #4 on: 01 May 2018, 19:48 »

Lastly, I cannot remember the Cow sound You are talking about.????  seems that Your control valve is leaking when the ignition is turned off....

My car has made that sound when turning off since I was a little kid. It's a very distinct sound- if yours doesn't make it I think you have problems.

Offline 68autobug

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Re: Another Vacuum Leak Fixed
« Reply #5 on: 02 May 2018, 03:49 »

Hi Again,
When I drive into My carport I select neutral and then I  turn the engine off...  Hand brake on..
I'll have to do it with My hearing aids in... lol.. :) :) :)
another thing I have always had a flow thru exhaust which is rather noisy...

Lee in Australia..
-- Helping keep Autostick beetles on the road --
   -1968 Silver metallic 1600 single port Beetle - with BOSCH  SVDA and new BROSOL H30/31 carburetor with GENIE Extractor exhaust system with a quiet thunderbird muffler

http://photobucket.com/68autobug

Offline sb001

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Re: Another Vacuum Leak Fixed
« Reply #6 on: 02 May 2018, 03:56 »
I suppose the loud exhaust might drown it out, but I'd really be surprised if you've never heard it. It's very consistent amongst autosticks
I might try to take an audio recording of it sometime

Offline bhartwell59

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Re: Another Vacuum Leak Fixed
« Reply #7 on: 24 September 2020, 19:46 »
Adding to this older thread

In trying to track down a possible vac leak (cold start erratic idle) via the control valve I did what tmea has done (spraying carb cleaner around hoses, the CV, intake manny port). No change in revs... still idles on the choppy side.

For grins, I decided to pinch off the hose between the intake manny port and the CV and found the car revved higher and smoothed out. Is this normal? Or did I just find my vac leak?

Thanks all!



1974 zambezi green Ghia vert

Offline tmea

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Re: Another Vacuum Leak Fixed
« Reply #8 on: 28 September 2020, 21:35 »
It is not normal. If I understand your terminology, I suspect your vacuum control valve is leaking from somewhere inside. If you plug both the manifold vacuum hose and the vacuum line coming from the carburator and the engine runs well your vacuum control valve has a leak somewhere. I posted some pics on this forum indicating where my leaks were.

Tom

Offline bhartwell59

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Re: Another Vacuum Leak Fixed
« Reply #9 on: 30 September 2020, 15:58 »
Yes, I have reviewed your post re: the control valve leaking several times. Good info step by step.

I'll have to get into the CV and see what I have. Thanks!

1974 zambezi green Ghia vert

Offline Checker

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Re: Another Vacuum Leak Fixed
« Reply #10 on: 29 October 2020, 02:46 »
I guys, after reading this topic, I think I might have found my problem, for sure I will at least take appart my CV and check it out.
My little Bug ran fine the whole summer when about two weeks from now, at the end of the "classic cars season", no vacuum sound from the CV as the ignition was turned on, I started the car, the idle was different, higher revs, could not engage the transmission as if the clutch was not working.

BTW, my 1970 Bug is original so everything made of rubber that I touch, needs replacement.

I guess it would be a good idea to take the servo apart and replace the diaphragm as well.

Two "wintertime jobs" !!

Just wondering, are there Control Valve rebuild kits out there ?

Thanks

Offline volkenstein

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Re: Another Vacuum Leak Fixed
« Reply #11 on: 29 October 2020, 12:58 »
Checker,
           Nope. Unobtanium. Get a working second hand one that holds vacuum (ask for proof!!!) and the solenoid works. Got a mityvac thing handy? The hose from carb to CV needs to hold 5" Hg vacuum. Don't trust the hose? Pull it off the CV and get the mityvac onto the brass spigot.

HTH
Volkenstein
'71 RHD A-S Super - "Klaus"

Offline Checker

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Re: Another Vacuum Leak Fixed
« Reply #12 on: 29 October 2020, 16:01 »
Yes I do have that tool to bleed my brakes... I will certainly do that test, thanks.

I checked my solenoid and I can ear a click when powered so that should be fine... the fact that my problem appeared suddenly along with a change in Idle rpm / behavior leads me to a vacuum problem... I also checked and readjusted my shifter lever switch / gap because I found the shifter lever was quite easy to turn.. suspected too big of a gap adjustment...

This is going to be a step by step trouble shooting but you guys provide good tips to put a newbie like in the right direction !

Thanks again

Offline volkenstein

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Re: Another Vacuum Leak Fixed
« Reply #13 on: 29 October 2020, 23:24 »
Checker,
           Most of my attempts at repairing a CV were documented but all the photos associated were with Photobucket...so mostly lost. If your solenoid clicks - that is good. Don't rip that section apart - just have a look in the spigot where manifold vacuum enters - and see if the spring and sealing valve are correctly positioned. One of my CV's had the spring twisted and the flapper valve was sideways as a result. Judicious poking got it oriented correctly.

The part you are having troubles with has four screws locating the top cover. Remove them and then very gently you can extract the innards which consist of a dished cup which is inside of the piece of large diameter rubber which has been exposed by removing the cover. Go really careful here as the other end of that diaphragm is VERY thin rubber. Use eyeballs and a torch to see if that thin rubber bit has any holes/tears.

You can also remove the brass spigot & washer and clean 'em up.

Enjoy
Volkenstein
'71 RHD A-S Super - "Klaus"

Offline Checker

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Re: Another Vacuum Leak Fixed
« Reply #14 on: 01 November 2020, 17:16 »
Volkenstein,

Being in Eastern Canada, my Bug is stored for the winter and the only access I have to, is the engine compartment

Following your tips, first thing I just did today is a vacuum check with my Mityvac, I unplugged the small hose from the Carburator and did the check from there, the vacuum is perfectly held at 5 and 10 Hg, absolutly no leakage. I re-checked my solenoid with a little 9V battery and confirmed I hear a click when powered.

Being the kinda guy that goes by the say: "if it aint broken, don't fix it !", I'm not tempted to take appart that control valve anymore.

I systematically replaced all the vacuum hoses last year, so those are all new.

I checked my electrical connection at the CV and the 8A fuse. Fuse is ok but the wire that goes from that fuse to the CV terminal had it's connector kinda loose and dirty. I cleaned it off and re-crimped it, now is tight.

I can't check much more than that until spring. Don't know if that loose connector could have been the problem.

From there, what do you think ? I my problem is still present, what would you target next ?

Thanks

 

anything