Hi all,

I need help identifying a part on my "71 Cutlass 350 motor.

If any of you knowledgable Olds people know what the heck this thing is, I'd sure appreciate your sharing the information with me!

Thank you in advance!

 

That's the Thermal Vacuum Switch for the Transmission Controlled Spark, described in detail in your Chassis Service Manual. TCS was an early emission control system that locked out vacuum advance in the lower gears to reduce NOx emissions. Most people have bypassed the system. Do not destroy that valve, however, as it is not reproduced and sought after by restorers.

This comes up a lot:

https://classicoldsmobile.com/forums...eccessary.html

https://classicoldsmobile.com/forums...mog-stuff.html

https://classicoldsmobile.com/forums...but-whats.html

https://classicoldsmobile.com/forums...6-tcs-tvs.html

https://classicoldsmobile.com/forums...ontroller.html

https://classicoldsmobile.com/forums...emissions.html

 

That is the TVS/TCS switch. It combine the TVS (thermo vaccum switch) and the TCS (transmission controlled spark). Some say it may or may not be necessary on daily driver.

 

Thank you both for the response!

What would be the downside to removing it?

This is my daily driver and I'm trying to sort everything out for the best running car as possible.

Currently the thingamajig is unplugged from everything. The car runs ok but sometimes is a little rough and can stall once in a while.

 

It is not "necessary" for the engine to operate all - as Joe pointed out, it is an emission control device that reduces NOx. Without it, you get "regular" vacuum advance operation which translates to better throttle response and driveability.

edit: Was posting when you asked. There is no downside to removing it other than the increase in NOx which likely is a non-issue with the number of miles you will be driving per year. The upside I already posted above.

 

The only downside to bypassing the TCS is that you may have to reset the timing. Since the TCS disables vacuum advance in the lower gears, with the system bypassed and vacuum applied, you may get too much advance, causing preignition at the stock settings.

 

Ah, ok. I just got through replacing the ignition system with an MSD "ready-to-run" along with new wires and plugs (obviously).

So I guess I can just remove the unit all together and plug the hole in the manifold and cap the two vacuum outlets on the manifold. I can not find where it was hooked up to, other than the two manifold vacuum fittings.

Is there anything I am missing?

Thank you again guys!

 

I found that with a high compression engine, running today's gas, with the timing retarded to suit, you can get engine overheating during extended idling. Happened to me on a cruise night and again on the coastal hiway in CA, stuck in traffic, had to stop, a lot of PO'd folks behind me.

So, I would advise you to either
1) run the dist'r vacuum off the manifold, or
2) hook up the three vacuum hoses so that if the engine overheats, that valve will switch from carb vacuum to manifold vacuum and alleviate the heat issue. That's important if you drive in stalled traffic and/or summer weather.

The nipples are labelled
D for dist'r
C for Carb and
MT for Manifold Tap

Very easy. Test blow thru D-C while at room temp to make sure it passes air, and does not need the solenoid active to do that. If it DOES need the solenoid powered, you can remove that unit and install the 1968 TCV which has the thermal feature and vacuum but no electrical voodoo.

 

This is why Oldsmobiles that used ported vacuum for the distributor also had a thermal vacuum switch to run the distributor from straight manifold vacuum if the car started to overheat. Or, as Chris points out, just calibrate the timing for full manifold vacuum and avoid the problem completely.

Actually, the 1971-72 valve has a fourth port, which is the vent port that runs to the air cleaner so clean air is ingested instead of unfiltered outside air.

 

To add to this... reset all 3 timing events not just the base timing. A recurved distributor will gain you better and smoother throttle response to cope with today's fuel. You will need a new adjustable travel(not rate) vacuum advance canister and a decent assortment of centrifugal weight springs(not the cheapo Accel 3 set with feather weight springs). Jegs and Summit sell both. You can run one lighter and one heavier spring to achieve the goal. You other option is to send it out to someone with a Distributor curve machine. One of the many "super tunning" tricks is a recurve.
Set base to 12-14*
Set vacuum adv. to bring in 10-12* at idle on straight manifold vacuum 12+10=22* at idle.
Then the centrifugal should bring in the rest for a total of 36-40 at 2700ish RPM.
This is merely a guideline but start here and make small tweaks to each event until it produces favorable results. The gas quality/octane, compression, cam profile, altitude etc...all have a direct effect.

 

By the way, my car is a 4 speed (Manual). don't know that it makes any difference, but reading the threads that Joe linked to above, all the cars seem to be automatics.

 

Y'all ROCK by the way!
:^)

 

He has to do that anyway:

No difference. MT cars got TCS also. There just weren't than many 4spd cars from the factory, thus most questions come from folks with automatics.

 

Thanks guys!!