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#1
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68 Vacuum hoses off tvs?
I asked months ago and thought I’d had enough info but of course I’m confused.
I ordered the plug from Ames with hoses attached with one red pin striped hose, one yellow pin striped hose and three solid black hoses. It is a 400 with power brakes and manual steering all stock. However, I am missing the rear vacuum canister. Carb is original HO manual carb 7028267 we and has original distributor with a nipple on both sides of the vacuum advance. In my last thread on this way back my understanding was top two loop each other, ca nipple to the lower base plate right side of carb, DA front of vacuum advance, MI to port at back of carb or the stud port passenger rear of carb. What’s confusing is if top two loop then what hose runs to the front drivers side port of carb? |
#2
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Here are a couple of photos you can keep handy to help.
CR and DR looped. M1 to vacuum source on rear of carb. CA to metal tube, front of carb (this is your ported advance) DA to front side of distributor vacuum can. Plug the CR port on the base of the carb, right side. _______________________________________ The photo with the yellow markings show the setup for a 68 Manual Trans ... it has the deceleration vacuum can crossed out ... not sure if you are using that or not. Note that in this photo it shows where CR and DR would go if you don't have them looped. |
#3
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So where #2 is going to right side of carb am I going to run that to the pass rear carb stud and plug where #2 is in that picture? I’ll leave the tee that goes to power brakes for hideaways vacuum I assume.
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#4
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Nope ... #2 port on the carb gets plugged with a cap. #2 port (carb retard) on the TVS gets looped at the TVS into port #1 (distributor retard) with a short length of hose.
That leaves you three functional hoses on the TVS, #3 (CR - carb advance) goes to the metal tube #4 (DA - dist. advance) goes to the advance side of the distributor can (front). #5 (MI - manifold vacuum) goes to the T fitting on the back of the carb. (vacuum for the head lights is usually another T in this hose if I am not mistaken) The above assume you are NOT hooking up distributor retard, and are NOT hooking up the manual trans canister. Someone else check me on this stuff to make sure I am correct. Last edited by dataway; 05-03-2019 at 04:12 AM. |
#5
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untouched car 54K miles
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'68 GTO 4-spd Hardtop (11) '68 GTO Convertible AT (1) '70 LeMans Sport Land of Lakes Muscle Car Classic Facebook Event Facebook Wall (Kurt Smith,Minneapolis) |
#6
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That picture is fine as long as the hose running to the retard port of the distributor isn't connected on that end. if it is, then this picture will be a problem because the advance won't function correctly since there's a plug on the TVS effectively blocking the advance from pulling because the retard port would be be fighting it since it's effectively plugged in this picture. Air needs to be drawn in through the retard side of the advance for it to pull advance on the other side. The Service bulletin directed service to loop the 1-2 ports on the TVS as Dataway states with a plug on the carb base and disconnecting the hose from the retard port on the distributor.
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#7
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About 15 yeas ago when I first setup my vacuum line & routed my vacuum lines so that everything looked correct, but I truly only had the front ported vacuum line connected directly to the vacuum advance, the TVS and lines was just for looks. Now, I am redoing the vacuum lines because the colored stripes came off the lines. I decided to look at things closer before connecting.
I tested the TVS & studied the diagram & it appears this is how it works normally operating temps versus Hot temps. I do realize that the timing retard circuit is not something to hook up & will only cause problems on several levels, So that part I will block off the lines & just hook them up for show. So, that being said, is this how the TVS will operate? I have no intension of running my engine that warm on purpose just to find out. Assuming this happens around 230 the switch shuts off the the green loop for ignition retard, & the blue ported vacuum advance goes to manifold vacuum. Is it that simple? Also, My TVS switch has a 6th port on the bottom center. Anybody know what that does at high temps? its closed at room temperature. It was a replacement I bought many years ago, & I have no idea if it opens to another port on the TVS, or what it does. I believe the originals only had 5. I just had a plug on it. Planning on hooking up the vacuum advance to full manifold when hot circuit. I could see that helping with temps if stuck in traffic someday. Also, I was surprised my 68 service manual has nothing on this. Maybe those pages where carefully removed. Should be in the emissions section, but my book only goes to 6D-3 Further thoughts?
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68 GTO 4-spd Convertible 78 S/E Trans am L78, WS6 Auto 78 S/E Trans am W72, WS6 Auto 79 10th aniv W72 Trans am 80 Indy pace car Trans am 89 Trans am GTA |
#8
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Here are some diagrams from the Diagnostic manual. Printed in Nov 1968 but looks to be as originally designed without modifications.
__________________
Ed 1968 GTO (Thanks Mom) 2006 Silverado 2007 Cadillac SRX 2015 Chevy Express |
#9
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More
__________________
Ed 1968 GTO (Thanks Mom) 2006 Silverado 2007 Cadillac SRX 2015 Chevy Express |
#10
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Thanks!
So the big question left is, what will this 6 port valve I have do at 230 degrees? assuming that's the temperature it changes at. It appears to be plumbed internally like the diagram I crudely modified above. I have the retard (yellow) plugged off within the hose so it looks operational. Like most advance modules the retard diaphragm is bad so I can put a hose on it for looks & won't fight the functioning advance side. Also, are there only 2 cloth tape wraps? I had three on the last one, but that was so long ago I have no idea where I got that info. .
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68 GTO 4-spd Convertible 78 S/E Trans am L78, WS6 Auto 78 S/E Trans am W72, WS6 Auto 79 10th aniv W72 Trans am 80 Indy pace car Trans am 89 Trans am GTA |
#11
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There's three Carl. Blow up the attached photo and you can see the outline of the third tape just to the rear of the bracket
__________________
Ed 1968 GTO (Thanks Mom) 2006 Silverado 2007 Cadillac SRX 2015 Chevy Express |
#12
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Quote:
__________________
Ed 1968 GTO (Thanks Mom) 2006 Silverado 2007 Cadillac SRX 2015 Chevy Express |
#13
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Thanks again!
I have no idea where I bought mine, it was a long time ago. The ports are labeled, but not in any specific order. Aside from looking similar to an original, I have no idea if it functions the same. Also just learned after some vacuum testing that my oe rubber connector leaks at the valve barbs. So I need to find one of those.
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68 GTO 4-spd Convertible 78 S/E Trans am L78, WS6 Auto 78 S/E Trans am W72, WS6 Auto 79 10th aniv W72 Trans am 80 Indy pace car Trans am 89 Trans am GTA |
#14
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Quote:
__________________
68 GTO 4-spd Convertible 78 S/E Trans am L78, WS6 Auto 78 S/E Trans am W72, WS6 Auto 79 10th aniv W72 Trans am 80 Indy pace car Trans am 89 Trans am GTA |
#15
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After doing the research for my 68 in the diagnostic manual I quickly decided to reduce the TVS to a cosmetic function only. I'll be using straight manifold vacuum with various non-functional hoses routed to the appropriate locations.
1. Even Pontiac realized the retard function was a bad idea and did away with it by 69. 2. Hopefully my engine will never ever see 230 degrees so that function is not needed. 3. Not a believer in the ported vacuum switching (and my 71 Q-jet doesn't have it) Which pretty much leaves no function for any of the ports The 67's had no TVS correct? And when did they do away with ported vacuum ... 70 or 71? Did they start using it again later? |
#16
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Quote:
The one thing I have never been completely clear on was why the 4 speed cars got the advance control valve. it obviously works like a relay to give the distributer more vacuum, but is that because of the camshaft in the 4 speeds, or some other reason? Your comments Data make me think I might go back to making the whole thing for show & running ported vac #3 directly to the distributer. Thats how I had it before. I would like to make & hide a small "U" connector, or do what I did last time which was run the #3 connection the wrong way in the vacuum harness. That would be the only reservation I have, & its a petty one Yellow zip ties are temporary in the pict seeing the cloth tape peels the paint off the vacuum lines. I'll put that on once I know I am done messing with this. .
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68 GTO 4-spd Convertible 78 S/E Trans am L78, WS6 Auto 78 S/E Trans am W72, WS6 Auto 79 10th aniv W72 Trans am 80 Indy pace car Trans am 89 Trans am GTA Last edited by 68ragtop; 09-10-2019 at 06:53 AM. |
#17
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Can't remember for sure but I think the manual cars had the vacuum valve to reduce stalling on deceleration? Or backfiring?
I'm not sure if it was needed because of the other TVS functions or not ... in other words not sure it was added to help a symptom caused by the addition in 68 of the other TVS functions. Unfortunately my 71 carb doesn't even have the metal tube to the ported vacuum source so there is only so much I can do to make it look "68". It does have a larger port in almost the same location which is a vacuum supply to the charcoal canister used in 71. I've had to compromise my dream of perfect originality more than once. |
#18
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Looking at my own picture above I see I flip flopped #2 & #5 Geez, good thing I didn't tape them up yet.
I am just going to find some way to send ported number #3 directly to the vac advance & bypass the rest for now. But would like to have it go forward like the picture shows. I'll find something to loop it backwards. Edit: Data I have seen some of your detailed picts over the years. Amazing originality on many levels that most overlook. Heck you could probably drill and sink a non functioning barb into the base of the carb?
__________________
68 GTO 4-spd Convertible 78 S/E Trans am L78, WS6 Auto 78 S/E Trans am W72, WS6 Auto 79 10th aniv W72 Trans am 80 Indy pace car Trans am 89 Trans am GTA |
#19
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I've thought of modifying the carb .... but I felt so lucky to find a non SR, NOS 71 carb that I am afraid to touch it.
I have nightmares about the days when I could walk into a Pontiac dealership and get parts for my GTO .... and didn't |
#20
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I agree. So many things we didn't care about back then. My daily drivers back in the late 80's early 90's were 3rd gen F bodies. I used to go to the dealer and buy new floor mats for them. They were something like $40 for a set & wore out easily. Never dreamed that those cars would also be collected 30 years later & NOS floor mats are now worth gold! They were a consumable item back then. Never ever crossed my mind to buy a dozen of them, but that would have been pretty dang smart.....
I know your talking about just having the parts you need that we cannot get anymore. I too often think about the stuff we should have stocked up on for our own cars, & maybe a small retirement account
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68 GTO 4-spd Convertible 78 S/E Trans am L78, WS6 Auto 78 S/E Trans am W72, WS6 Auto 79 10th aniv W72 Trans am 80 Indy pace car Trans am 89 Trans am GTA |
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