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#1
08-20-2012, 06:57 PM
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70 Grand Prix vacuum diagram
Does anyone have any pics or a proper diagram of a stock 70 GP 400 4bbl auto showing the routing of the vacuum lines. I do have the 1970 service manuals on CD ROM but they do not show all of the vacuum line routing. I was hoping to see a picture of the stock fitting off the back of the carburetor (the one that feeds the power brake diaphragm).
It looks like the original carburetor on my car was replaced with a late model Q-jet from a Chevrolet. I have what appears to be the original dual snorkel air cleaner but it appears to be missing the thermal sensor and vacuum source line. The vacuum lines from each of the snorkel motors connect to a port on the underside of the air cleaner but there is no source vacuum?!?! The TCS system is also bypassed. The solenoid is still in place on the back of the engine but there are no vacuum lines attached to it. The distributor vacuum line is run directly from the ported vacuum source on the front of the Q-jet. I've also noted that there are no thermal vacuum switches at all mounted on the intake coolant cross over. Much confusion here 
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#2
08-24-2012, 08:29 PM
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P/B Vaccum
Here is what my 70 GP looks like. Center large hose P/B
Wes |
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#3
09-01-2012, 11:09 AM
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Quote:
thank you, Paul |
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#4
09-01-2012, 12:03 PM
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Paul,
Do you have the original 3-prong temp switch on the right front of the intake? '70 did not use a thermal vacuum switch. As far as the two smaller ports out the rear of the carb base fitting... one is for your heater/ac controls and the other is the vacuum source to the TCS solenoid (forward port just below the two prong connector). The rear side port of the solenoid is the vacuum source to the distributor vacuum advance unit. The rear port of the solenoid is just a vent and is left open (originally it had a small foam filter over it). Hope this helps... |
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#5
09-03-2012, 09:39 AM
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Vacuum
Paul,
The hose on the drivers side comes off the back of that fitting and goes to a round restrictor and feeds vacuum to to the inside of the car for the accessories. A/C, heat, etc. The hose off the pass side supplies vacuum to the distributor vacuum advance. Pass side of front carb.. the green striped hose goes to a vacuum reserve tank located behind the window washer tank in the right fwd fender well. Next post the hose below the carb off manifold goes to the PCV valve, and the empty connection goes to the air cleaner. I could only upload 5 photos .............see next post Wes Last edited by indyav8n; 09-03-2012 at 09:49 AM. |
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#6
09-03-2012, 09:45 AM
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Vacuum
Paul .
Also, I only have the temperature sensor with wires as you can see mounted on the front of the manifold just ahead of the PCV hose. Hope this help Wes |
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#7
09-03-2012, 03:01 PM
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Wes,
It appears that your car has a manual trans carb on it with no port for the trans modulator line? Also, it looks like your TCS solenoid is by-passed. The temp sensor is correct. Your car is probably a 49 state and your carb would differ from mine. Do you have an evap canister at the RH side inner core support? Here's a few shots of my CA type setup. |
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#8
09-03-2012, 09:20 PM
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Grant,
Not exactly, I have a metal line down to the modulator valve, this is and has always been an Indiana car. I have the original window sticker, and purchased it from the original owner. So as far as I know this is an unmodified original car. Wes |
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#9
09-04-2012, 12:30 PM
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Wes,
The metal line is correct going the modulator, but you can clearly see that someone has bent yours at the carb end. That three-way rubber "T" is absolutely not correct. It almost looks like your carb's center section was replaced with another at one time looking at the difference in color between the top air horn and center body. An easy way to verify this would be to check the number on the side if the carb body. Anyway, I just wanted to make you both aware that it wasn't right to be used as an example. |
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#10
09-04-2012, 08:21 PM
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Wes and Grant - you guys are awesome! Thanks for posting all of the pictures. You have already helped solve some of the mysteries regarding my new Grand Prix. I did verify that I have the 3-prong temperature switch on the intake. My biggest dilemma is that the owner of the car before me put on a different Quadrajet and I do not have the original carb. The carb on the car codes to be from a 1980 Chevrolet. It has an electric choke and side feed fuel inlet. I have acquired a late model Pontiac Quadrajet (1980 301) that Cliff Ruggles recommended and he is working on a tune up of it for my particular application. Your pictures have helped me identify the correct base plate vacuum fitting that I need for the new carb although the Performance Years Catalog does not show a three port fitting - only a two port fitting. I attached a pic from the catalog. If you can see a part number stamped on this fitting I'd sure appreciate it!
I was definitely confused about my air cleaner. It's a dual snorkel unit that I think is original to the car. Note the hole in the base of the air cleaner next to the air cleaner thermal switch. I could not figure out what that hole was for (stuffed with an ink marker cap when I bought the car!) but in looking at the pictures of Grant's carb it's for the carburetor vent for my original carb. Also as you can see in the pics they have the snorkel vacuum motors both plumbed to the thermal switch with no vacuum source. I'm guessing I'd get the source from the vacuum port on the manifold and install a tee to source vacuum to each snorkel motor. My TCS solenoid is also definitely bypassed. I have some work to do to get this back to a factory type setup. I'm not too worried about minor differences due to the use of a late model carb as I'm not striving for an original restoration of this car. I would like to re-route the vacuum lines as close to possible as factory. Thanks again guys!     
Last edited by Punks70GP; 09-04-2012 at 08:25 PM. Reason: spelling |
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#11
09-06-2012, 12:19 AM
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Paul,
You're welcome, glad to help. I'm thinking that only the CA cars got the air cleaner with the vent hole in '70... '71 and '72 I believe all had that vent hole. If your car came with a 400 engine originally it would have come with a single snorkel air cleaner, only the 455 cars got the dual snorkel from the factory. You are correct, the vacuum motors on the dual snorkel did have a small plastic "T" to connect the two to one port on the thermal sensor. The other port on the sensor is for the intake vacuum fitting. Most guys bypass the original TCS solenoid, but if you'd like to try to get the system working I can help you with that as well. If you go to inlinetube.com they show a two port carb fitting. Here's the part number and description... Part Number - INL10688 1968-74 Pontiac Carb Vacuum Fitting PB With 2 Vacuum Outlets 1pc $16.00 |
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