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09-07-2014, 10:48 PM
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#1 |
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Post Whore
 
Join Date: Aug 2014
Location: Sacramento, CA
Posts: 10,868
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1974 GMC 15 Hundred - Vacuum Hose Questions
Please brace yourselves for some pesky anal vacuum hose questions, but hey I want to learn and understand what these doohickeys due and where they go?
So first up is this pinky sized hose coming off of the air cleaner housing, where does it connect to? (Obviously I lifted it over the air cleaner to isolate it and show you, it actually goes underneath it) |
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09-07-2014, 11:00 PM
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#2 |
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Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,733
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Re: 1974 GMC 15 Hundred - Vacuum Hose Questions
To the thermac switch on the front of your intake.
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09-08-2014, 12:19 AM
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#3 | |
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Post Whore
Join Date: Aug 2014
Location: Sacramento, CA
Posts: 10,868
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Re: 1974 GMC 15 Hundred - Vacuum Hose Questions
Quote:
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09-08-2014, 01:04 AM
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#4 |
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Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,733
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Re: 1974 GMC 15 Hundred - Vacuum Hose Questions
I believe so.
If you use google images and search for '74 chevy vacuum diagram' you might find where all the hoses go. https://www.google.ca/search?q=1974+...h=709#imgdii=_ |
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09-08-2014, 11:32 AM
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#5 |
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Moderator
 
Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,977
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Re: 1974 GMC 15 Hundred - Vacuum Hose Questions
The Vacuum diagrams are in the GM service manuals and maybe on the radiator support label. At least some of them are...
__________________
1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. |
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09-10-2014, 10:08 AM
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#6 | |
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Post Whore
Join Date: Aug 2014
Location: Sacramento, CA
Posts: 10,868
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Re: 1974 GMC 15 Hundred - Vacuum Hose Questions
Quote:
but you guys have been helpful, piecing together all the information provided it appears the EGR valve connects to the top of the two port thermal vacuum switch mounted in the thermostat housing while the bottom port of the thermal vacuum connects to a supply port in the carburetor. Where my doohickey goes remains a mystery? Here's a shot of what lurks beneath the air cleaner housing. |
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09-10-2014, 10:56 AM
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#7 |
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Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,733
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Re: 1974 GMC 15 Hundred - Vacuum Hose Questions
I've been wrong before!! LOL!!
So I looked on my 84 and your doohickey plugs into a manifold port on my carb. But I bet your choke would work a lot better if you hook up the choke pulloff pot!! |
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09-10-2014, 11:02 AM
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#8 |
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Registered User
Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 2,611
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Re: 1974 GMC 15 Hundred - Vacuum Hose Questions
Your air cleaner THERMAC gizmo connects to the dusty looking capped pipe coming out the side of the carb. The small clean looking vacuum pot end connects to the small clean pipe on the carb. There may be a missing piece as the picture I have of a 74 carb shows that pot hose connector rotated about 90 degrees so it mostly points at the carb connection. Or a PO may have used the wrong pot during a repair.
The THERMAC flapper pot connects to a temp sensor in the air cleaner, then from the other side of the temp sensor to the carb. |
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10-09-2014, 05:18 PM
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#9 |
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Registered User
Join Date: Oct 2014
Location: TN
Posts: 294
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Re: 1974 GMC 15 Hundred - Vacuum Hose Questions
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