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08-25-2016, 05:09 PM
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#1 |
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Registered User
Join Date: Oct 2014
Location: mi
Posts: 359
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What is this
I've got an 80 with a 305 and I noticed this. What is it?
Posted via Mobile Device
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TJ 76 gmc 1500 swb patina finish Dropped 4/5, 350/4 speed 80 Chevy c10 lwb 305/350 |
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08-25-2016, 07:50 PM
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#2 |
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Registered User
Join Date: Sep 2009
Location: Beaverton, OR from WA State
Posts: 1,515
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Re: What is this
Vacuum actuator for the heat riser valve located between manifold and exhaust pipe.
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Devin 1983 GMC High Sierra 2500, 4x4, RC/LB, 400 S.B., SM-465, NP-208, Corporate 10 bolt & 9.5" 14 bolt 1996 GMC Sierra SLE 3500 DRW, 4x4, EC/LB, Vortec 454, NV-4500, BW-4401, AAM 925 & AAM 1050 1997 GMC Sierra SLT 1500 4x4, Z71/F44, EC/SB, Vortec 350 My Introduction with my '83s History New Daily, the '96 |
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08-26-2016, 04:59 PM
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#3 |
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Registered User
Join Date: Oct 2014
Location: mi
Posts: 359
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Re: What is this
It looks like it's all one assembly that has 4 plus on it. Does anyone have a part number or know what the part is called?
Posted via Mobile Device
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TJ 76 gmc 1500 swb patina finish Dropped 4/5, 350/4 speed 80 Chevy c10 lwb 305/350 |
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08-26-2016, 06:40 PM
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#4 |
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Registered User
Join Date: Oct 2014
Location: mi
Posts: 359
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Re: What is this
This is what the other end looks like.
Posted via Mobile Device
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TJ 76 gmc 1500 swb patina finish Dropped 4/5, 350/4 speed 80 Chevy c10 lwb 305/350 |
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08-26-2016, 08:09 PM
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#5 |
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Registered User
Join Date: Aug 2005
Location: Louisiana
Posts: 711
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Re: What is this
Looks like smog crap
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08-27-2016, 07:51 AM
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#6 |
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Registered User
Join Date: Feb 2007
Location: Memphis MI
Posts: 1,851
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Re: What is this
As noted above, it is the vacuum actuator for the heat riser. When the engine is cold, it uses exhaust heat to help the engine warm quicker, improving cold driveability and yes, reducing cold emissions. The tubing is part of the vacuum control system that goes to a Thermal Vacuum Switch (TVS) that looks at the engine temp to turn the actuator on or off. One line vacuum to the switch, the others are to devices to be turned on or off.
If you do remove the actuator make sure to wire the valve in the open position.
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1987 2 ton  1982 250/TH350 beater in progressDad's 1981 3/4 L6 3 on tree posi and no options, awaiting restoration or scrappingPlus a mess o' tractors |
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08-27-2016, 11:18 AM
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#7 |
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Registered User
Join Date: Oct 2014
Location: mi
Posts: 359
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Re: What is this
Ok. We're getting closer. Is it possible to replace the tubing or do I need to replace the entire plug. Is there a name or part number for the thermal vacuum
Switch plug. Posted via Mobile Device
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TJ 76 gmc 1500 swb patina finish Dropped 4/5, 350/4 speed 80 Chevy c10 lwb 305/350 |
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08-29-2016, 11:10 AM
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#8 |
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Registered User
Join Date: Sep 2009
Location: Beaverton, OR from WA State
Posts: 1,515
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Re: What is this
Vacuum tubing should be available over the counter at any auto parts store, just need to size it correctly. Vacuum tubing can be sized in increments of 32nds of an inch, I'd just make sure it fit snug and didn't leak. I've always maintained this portion of my '83 and I find that it runs well and performs well from cold-hot.
I'd be surprised if there was an original/NOS one of those vacuum tubing harnesses laying on a shelf somewhere, but I suppose it is possible. If you want to find on I would suggest, looking for a user on here named "Hatzie" he's got a link in his signature to many .PDFs including the original parts catalogs. You can use them to find the part number and then go hunting.
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Devin 1983 GMC High Sierra 2500, 4x4, RC/LB, 400 S.B., SM-465, NP-208, Corporate 10 bolt & 9.5" 14 bolt 1996 GMC Sierra SLE 3500 DRW, 4x4, EC/LB, Vortec 454, NV-4500, BW-4401, AAM 925 & AAM 1050 1997 GMC Sierra SLT 1500 4x4, Z71/F44, EC/SB, Vortec 350 My Introduction with my '83s History New Daily, the '96 |
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