Mystery Parts...what are these?

[Steve W]

I was doing a bit of cleaning up the engine bay...wires, hoses, etc...and came across these two parts on the engine...neither of which were hooked up.

The first part was bolted to the engine, if front of the carb on the drivers side, one of the coil mounting bolts anchoring it in place. No wires or vacuum tube connected, just sorta sitting there doing nothing, so i took it off, What the heck is it?

Also, the second one is below the distributor, coming out of the front of the engine, has 4 vacuum ports, and nothing at all hooked up to it...like the other part, just sitting there doing nothing.

Can anyone identify these? What do they do? Are they even neccessary? The car seems to run fine without them. I am just curious.

[Steve W]

OH, and here's a pic of the back ot the first part...maybe it will help in identifiying it?

[Roger H]

Hi Steve
The first looks like it is a vacuume operated switch.  Possibly the 2 wires would be connected and operate some device or turn a light on when vacuume was applied.

The second looks like a heat controled vacuume switch.. Some vacuume operated device probably didn't want to come on untill the engine was hot ( egr valve for example)
so the vacuume signal for it ran thru the switch. the switch would only allow the vacuume to pass when the engine was hot.

Since their were so many possibilites I reeccomend a trip to the library,  look up a vacuume hose routing schematic in a mitchel manual.  They have a lot of info.

Roger

[Sweede64]

I think the first one is a idleup device, when tha AC i is operated it rerutes the vacum direct to the distriburator and the idle rises, a similar funktion is when the car is overheating and idle, ignition rises and it runs cooler.

[John Morris #23947]

Might help if you tell us what year the Caddy is.

[Jeffrey Burland]

Says '68 Coupe deVille at the bottom of his posts, which may be since '68 had it's one year wonders.

[bill henry]

the one at the front of the engine is the Thermal Vacuum Switch which controls vacuum to the vacuum advance of the distributor.

[Steve W]

Yes, it is a 68 CDV. Sorry I didn't mention that.
Yes, Bill, it looks like it probably is some sort of device to control vacuum advance. I would assume that it should be hooked up between the vacuum source, and the vacuum advance? I'm not sure. And where would all the vacuum lines go?

[Bob Hoffmann CLC#96]

Steve,
The vacuum thermal switch was disconnected for a REASON. It's a useless device to reduce emissions and make the cars performance worse.
HTH, Bob

[mario]

i cant say for the 68 caddy but the TVS on the 70 eldo was used to switch distributor vacuum from ported to manifold at a certain temp.
if the engine temp was climbing the switch changed the vacuum supplied to the distributor to manifold vacuum thereby causing the engine rpm to increase and aid in cooling the engine. once cooled the switch reverted the flow back to ported vacuum, thereby lowering the engine rpm.

ciao,
mario

[bill henry]

If you intend to run manifold vacuum to the advance at all times do not hook up the switch. Bob is correct that it was a pollution control device and did lower performance . If you want to go back to the original hook up I would get a shop manual , but the hook up went like this with 4 ports  one to the vaccuum advance , one to ported vacuum above the throttle plates , one to manifold vacuum and one to an idle bump up device probabley the other part you pictured.

[Sweede64]

Listen to mario, it does not effect performance, its to keep it cool and to control EGR if equipped. i Had a similar setup on my Cad-69 conv and a Caprice -72, i have experienced when i build the car back to factory specs they run better than before when some knowitall have decided that they know more then GM did.......

my 2 cent...

[Joe]

The coil like affair appears to be an anti-dieseling solenoid as used on 1972 cars , maybe a year older or newer too. The ported vacuum switch with 4 hose connections is for the same vintage too. the '75-76 used a 3 hose unit as there was no air pump.  A shop manual is your best bet to sort out the vacuum plumbing.

[Steve W]

Yes, I checked my 68 shop manual and finally found it. It mentions the unit, but shows no pictures of it, and does not explain how the vacuum is routed. It simply states that is is filled with some sort of wax that melts at a certain temp, allowing certain ports to open, affecting the vacuum advance, and when it cools down, the wax hardens and does the reverse somehow. But it seems to happen at about 230 degrees? I don't know, maybe I will just leave well enough alone! Even the shop manual doesn't have much info about it.