What is this device?

[Gene Letke]

Recently I had my heads refurbish. Truck runs great but looking around I found this little canister near the carburetor. It has a vacuum line to it from the back of the carburetor. Looks to me it should have a vacuum line or two that goes somewhere else. I have a 1970 350 cu in motor. Anyone know anything about this device?

[Coley]

It is a TCS or transmission control switch.
It was an emission device that kept your timing from advancing until your transmission was in high gear.
It did this by interrupting the vacuum signal that supplied vacuum to your distributor
Yours appears (like most) to have been disconnected so you can enjoy regular timing advance.

Coley

[Coley]

On closer inspection....does it still have its vacuum line to your distributor? ..maybe not, but its hard to tell with the air cleaner and other plumbing in the way.
If so, you may not have any vacuum advance?...
Make sure you have a vacuum line that runs from your distributor, past this device completely.....and to the ported vacuum spiggot on the front right side of your carburetor.
Check this

Coley

[Gene Letke]

Thanks for the reply. The tubing you see laying on the valve cover is the vacuum hose from the front of the carburetor to the distributor vacuum advance device. There is a 2 wire terminal plugged into the canister, can't find anything like that on my wiring diagram. The tube to the canister comes from the back of the carburetor. The fitting on the canister that this vacuum hose is attached has a 90 deg nipple for another hose (this is in addition to the outlet nipple on the canister). Will check to see if I have a vacuum leak at that fitting tomorrow.

[kwmech]

GMs first attempt to control NOx emissions. You may find additional wiring down at the transmission also. As stated, it did not allow vacuum to the distributor until the transmission shifted into 3rd gear. Just remove all that stuff, all the parts are obsolete anyways.

[Coley]

Its interesting that you said its a 1970 motor. Is the truck a 1970?...or was the engine replaced into a newer truck or?
I think this emissions accessory was added in '71 or '72...but others can weigh in if they know specifically.
Regardless....its a redundant part if you want to have your engine run more efficiently from an overall performance perspective.
Make sure tho'...that any vacuum lines coming off the carb are not 'open' to atmosphere. They either have to be plugged or attached to a non-leaking device to ensure your carb and idle work properly.

All good
Coley

[Gene Letke]

To the best of my knowledge it is the original motor in my 1970 1/2 ton truck. Once I learned what this device was, I found a few older threads discussing this device. I plan to leave it bypassed.