Can anyone tell me what this vacuum switch (?) is ?? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

allengator · 12-22-2010, 08:04 PM

This appears to be a vacuum switch with wires on one side an a vacuum port on the other... Mounted on the firewall btween the brake booster and the power junction block.

anyone know what it does??

benoit454 · 12-22-2010, 08:45 PM

I think that's the tip in switch for the lock up trans convertor be it a 700r4 or a th350c.

The 84 dad has had that one and one on the PS firewall forget what the other was for but one for sure was the tip in switch.

big_b · 12-22-2010, 09:04 PM

yes, it is the lock up torque converter switch for a 700r4,th350c, etc.
if you are running either of those transmissions you should hook it back up to prolong the life of your trans.

dwragon · 12-22-2010, 09:14 PM

If the truck was or is a diesel, I think it is a special "LOW Vaccum" switch special to the diesel, to possibly the tranny or something else.

allengator · 12-23-2010, 09:48 AM

TH-350C...!!!!!

I didnt know there was such a beast!!!
After you guys suggested it, I did a little research, and you are right...!
It didnt dawn on me when I saw the electrical connection on the side of it.

I normally play with much older cars!!

Thanks guys!

Mattman2010 · 12-23-2010, 10:38 AM

Yes it is the lockup for the TH350C. You do not have to hook it up, if you hook it up it will allow you to run 300 - 500 RPM less when you are running highway speeds. It will not hurt the transmission if you do not run it, it will just act as a normal TH350.

allengator · 12-23-2010, 12:00 PM

Might as well use it...! Save a little on gas....

big_b · 12-23-2010, 01:02 PM

not having it hooked up does let it function like a regular th350 but it creates more heat in the transmission. heat and auto trannys dont work well together. it is worth it to hook it back up for gas mileage and the life of your trans. it is just a vacuum line from the switch to the manifold vacuum supply.

*nbpro* · 12-23-2010, 01:29 PM

i have the TH350C gas mileage is better with it hooked up

Jonboy · 12-23-2010, 04:53 PM

Since you already have that there, it would work to control the TCC in a 700R4 also. A 700 would also give you a lower first and 2nd gear, as well as overdrive. I mention this since you are on the fence for a trans.

12-22-2010, 08:04 PM	#1
allengator Registered User Join Date: Dec 2010 Location: Burleson, Texas Posts: 596	Can anyone tell me what this vacuum switch (?) is ?? This appears to be a vacuum switch with wires on one side an a vacuum port on the other... Mounted on the firewall btween the brake booster and the power junction block. anyone know what it does?? Attached Images __________________ Allengator Outta the Blue (my band - available for hire in the DFW area!) 1980 Chevy SWB Pickup (build thread) 1951 Chevy Sedan Delivery 2004 Chevy Tahoe Z71 2011 Harley Davidson Street Glide 2018 Silverado Z71 Crew Cab

12-22-2010, 08:45 PM	#2
benoit454 Chris Join Date: Nov 2004 Location: Monaville, WV Posts: 3,737	Re: Can anyone tell me what this vacuum switch (?) is ?? I think that's the tip in switch for the lock up trans convertor be it a 700r4 or a th350c. The 84 dad has had that one and one on the PS firewall forget what the other was for but one for sure was the tip in switch. __________________ Chris GIT R DONE!!!!!! Check out all our rides, http://www.cardomain.com/id/benwa454

12-22-2010, 09:04 PM	#3
big_b Registered User Join Date: Oct 2010 Location: Capital City B.C Posts: 59	Re: Can anyone tell me what this vacuum switch (?) is ?? yes, it is the lock up torque converter switch for a 700r4,th350c, etc. if you are running either of those transmissions you should hook it back up to prolong the life of your trans.

12-22-2010, 09:14 PM	#4
dwragon Registered User Join Date: Dec 2010 Location: dallas tx Posts: 19	Re: Can anyone tell me what this vacuum switch (?) is ?? If the truck was or is a diesel, I think it is a special "LOW Vaccum" switch special to the diesel, to possibly the tranny or something else. Last edited by dwragon; 12-22-2010 at 09:15 PM.

12-23-2010, 09:48 AM	#5
allengator Registered User Join Date: Dec 2010 Location: Burleson, Texas Posts: 596	Re: Can anyone tell me what this vacuum switch (?) is ?? TH-350C...!!!!! I didnt know there was such a beast!!! After you guys suggested it, I did a little research, and you are right...! It didnt dawn on me when I saw the electrical connection on the side of it. I normally play with much older cars!! Thanks guys! __________________ Allengator Outta the Blue (my band - available for hire in the DFW area!) 1980 Chevy SWB Pickup (build thread) 1951 Chevy Sedan Delivery 2004 Chevy Tahoe Z71 2011 Harley Davidson Street Glide 2018 Silverado Z71 Crew Cab

12-23-2010, 10:38 AM	#6
Mattman2010 Registered User Join Date: Jun 2010 Location: Pittsburg, KS Posts: 953	Re: Can anyone tell me what this vacuum switch (?) is ?? Yes it is the lockup for the TH350C. You do not have to hook it up, if you hook it up it will allow you to run 300 - 500 RPM less when you are running highway speeds. It will not hurt the transmission if you do not run it, it will just act as a normal TH350. __________________ 1980 K10 - 6.2L Diesel/SM465/NP205 Build Thread 1984 K30 CC Dually - "The Tank" 12V Cummins/Nv4500/Np205/D60/D70HD 4" lift & 37's Build Thread 1960 C-60 Dump Truck Make it road worthy! Thread

12-23-2010, 12:00 PM	#7
allengator Registered User Join Date: Dec 2010 Location: Burleson, Texas Posts: 596	Re: Can anyone tell me what this vacuum switch (?) is ?? Might as well use it...! Save a little on gas.... __________________ Allengator Outta the Blue (my band - available for hire in the DFW area!) 1980 Chevy SWB Pickup (build thread) 1951 Chevy Sedan Delivery 2004 Chevy Tahoe Z71 2011 Harley Davidson Street Glide 2018 Silverado Z71 Crew Cab

12-23-2010, 01:02 PM	#8
big_b Registered User Join Date: Oct 2010 Location: Capital City B.C Posts: 59	Re: Can anyone tell me what this vacuum switch (?) is ?? not having it hooked up does let it function like a regular th350 but it creates more heat in the transmission. heat and auto trannys dont work well together. it is worth it to hook it back up for gas mileage and the life of your trans. it is just a vacuum line from the switch to the manifold vacuum supply.

12-23-2010, 01:29 PM	#9
nbpro Account Suspended Join Date: Dec 2008 Location: Huntsville,AL Posts: 2,119	Re: Can anyone tell me what this vacuum switch (?) is ?? i have the TH350C gas mileage is better with it hooked up

12-23-2010, 04:53 PM	#10
Jonboy Slots go on anything! Join Date: May 2003 Location: Richardson, TX Posts: 5,957	Re: Can anyone tell me what this vacuum switch (?) is ?? Since you already have that there, it would work to control the TCC in a 700R4 also. A 700 would also give you a lower first and 2nd gear, as well as overdrive. I mention this since you are on the fence for a trans. __________________ 1974 Jimmy- 5.3/4L80e/NP241



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