bonnevillegreg

I have a bone stock '72 CS (350/350) and for a variety of reasons, would like to remove the DVCS. And I have questions:

1) Is there any ill affect from running vacuum advance off the carb vs. off a DVCS?

2) Is there any ill affect on the tranny with the DVCS gone?

3) I assume the electrical connections go to the tranny?

4) Can I remove the vacuum line to the tranny completely without affecting anything else?

5) Is there a switch or some other part on the tranny that should be removed in conjunction with removing DVCS?

Thanks!!

jaunty75

Since you have a "variety" of reasons you want to remove this, tell us one of them.

To answer your question, yes, removing the vacuum switch will have negative consequences to the way your engine runs. According to the '73 Olds service manual, when the engine reaches a certain temperature, this switch opens and puts vacuum to the distributor vacuum advance when the car is at idle. Without it, the engine will run hot.

As far as the transmission, yes, removing the vacuum line from the modulator on the transmission will cause the transmission to not upshift when it should.

Again, why do want to remove these things?

bonnevillegreg

Maybe a better question is how is the same temperature issue managed in cars w/o a DVCS, and how does a stock TH350 work properly on a car w/o a DVCS?

jaunty75

I don't know how the situation is handled on a car without this. All Olds V-8 engines, at least for 1973, which is the service manual I have, featured the thermal vacuum switch.

As far as the transmission, this switch and the transmission have nothing to do with each other. The vacuum line for the vacuum modulator is connected directly to a vacuum port on the intake manifold.

You still haven't told us WHY you want to do this. Why do you want to defeat devices that, in one case, help the engine run properly and prevents overheating while, in the other case, allows your transmission to shift properly?

I've driven a car with a bad vacuum modulator and thus there was no vacuum getting to the transmission. It wouldn't shift out of first gear.

BlackGold

The DVCS of 1971 and later performs both functions of the 1970 TCS and TVS. Prior to 1970, I believe there was only TVS.

Your car does not need TCS and may perform better without it. TCS inhibits vacuum advance in all gears except the final 1:1 gear (3rd or 4th, depending on transmission).

TVS applies vacuum advance at idle if the engine reaches a certain high temperature. The advanced spark reduces the amount of heat generated, and it also steps up the idle speed, which in turn circulates more coolant and more air. The trip point for TVS is so high that, in my opinion, you should never see it engage. It's just shy of boil-over, sort of a last-ditch effort to prevent boil-over. So TVS is nice to have, and you gain nothing (performance-wise) by deleting it. On the other hand, it's not needed, unless your cooling capacity is inadequate to begin with. If you're currently supplying manifold vacuum (instead of ported vacuum) to your vacuum advance on the distributor, then you're already effectively bypassing the TVS.

As was mentioned, your automatic transmission absolutely needs the vacuum line connected to its modulator. This should be routed straight from manifold vacuum, not through TCS, TVS, or DVCS.

If you get rid of your DVCS, I would leave the electrical connection at the tranny alone and simply tape-up or heat-shrink any bare connections in the harness.

joe_padavano

What he said. The whole purpose of the thermal vacuum switch is to switch the distributor between ported vacuum and manifold vacuum if the engine overheats. The transmission controlled spark system on 1970 and later cars was an early NOx emissions control device. Bypassing all that hardware and running the vacuum advance directly off of manifold vacuum eliminates the need for either the TVS or the TCS.

OLD SKL 69

Exactly what I did on my 71. No problems at all.

bonnevillegreg

Thanks for the 411, guys.

This might be rhetorical but, would it be correct to assume that the overheating concern came about as a result of the drop in pump-gas octane ratings going on at the time? And that dished pistons (lowered compression) alone would not necessarily eliminate detonation? At least not enough to keep cars from showing up in service departments, under warranty, with steam coming out from under the hood?

Mark71

Mine is setup that way too. It was that way when I bought it. Nothing is connected to the electrical connector on vac tree, so I just never worried about it. Wonder where that harness connector went......

I do have a question, though... I've heard of folks removing the vac advance altogether and just relying on mechanical advance using a vac advance block off kit. Is there any advantage to this for a street-only car or is this a racing-only application?

The reason I ask is that a someone told me mechanical and vacuum advance "is too complicated."

455man

Deleting the vacuum advance is mainly for race only. Here is a good read on vacuum advance.
https://classicoldsmobile.com/forums...connected.html

joe_padavano

To the transmission switch for the Transmission Controlled Spark (TCS) system.

Well, with the wire off, you HAVE disabled the vacuum advance. The TCS system was designed to disable vacuum advance in the lower gears to control NOx emissions. The trans switch enabled the advance in high gear by activating a solenoid valve inside the vacuum switch. Without the wiring attached, you don't get vac advance in high, either.

That "someone" is not a person I'd be taking advice from...

Mark71

Joe, not sure I understand what you mean here. I have nothing connected to that vacuum switch. No wiring, no vac hoses, no nothing. It looks a little strange, actually, poking up with nothing connected.

I do have a vac line connected to the distributor advance canister, though. I am not sure whether it is ported or straight manifold vac. I'll check it tomorrow. Also, I know from my timing gun that there's some advance going on there...

Gotcha. After all I've read searching about this topic, I have to agree.

Thanks again!

Lady72nRob71

Many people bypass these TCS solenoids for slightly better drivability, esp when it fails.
You can bypass it and leave it in the manifold for a stock look. My car is this way. Unused vac ports were capped and disty run off manifold vacuum.

If you choose to remove it and plug the hole, be sure to sell the thing here in the parts for sale.
These are not reproduced and are sought by restorers who want everything factory.

The vac line to the tranny should by already connected to manifold vacuum (not to the TCS unit) and should not be disconnected or it will not shift right.

455man

I noticed mine has a vacuum hose going from the top to the bottom then the middle one goes to manifold vacuum on the TCS or whatever my '72 has. My vacuum advance is hooked to ported vacuum on the carb. I also noticed the vacuum can is not working so my HEI with adjustable vacuum advance is going in soon.

joe_padavano

Sorry, my mistake. I thought you were saying you still had the vac lines connected, just not the electrical connector.

ChefDeadpool

Oops, DOUBLE posted in wrong thread.

ChefDeadpool

Oops, posted in wrong thread.

ChefDeadpool

Everything is still hooked up on mine, and according to the factory tests I did on the DVCS, it still works as it should.

If I were to bypass it, should I hook the vacuum advance hose to where the the line from the DVCS was attached at the carburetor, or a nipple on the intake manifold?

Lady72nRob71

On mine, I capped the port at the carb that led to the DVCS and ran the disty vac line to manifold vacuum.
You could also run the disty vac to the that carb port and cap the manifold vac line that went to the DVCS. See which way the car runs better.

ChefDeadpool

I did once hook the vacuum advance directly to the manifold and the idle came up a few hundred RPM. What does that mean?

Lady72nRob71

It was originally set to run on ported vac.
Moving to manifold vac would mean your ignition timing would be more advanced at idle, so idle speed needs to be reset.

To make it easier on yourself, and the car runs okay, just hook up to ported vac.

JimMorrisonFan67

Hi,
My hubby broke this ported vacuum off (72 cutlass 350) at the threaded part and can not find a replacement for it that looks exact. They only show him one with the 3 ports and the threaded area but no top end which has a canister looking apparatus and plug at the top.
Can anyone help.

455man

Use the advanced reply and use the paperclip. I'm not sure what you are talking about but maybe a pic will help.

JimMorrisonFan67

ok I posted a pic on prev post...thanks for your help

dc2x4drvr

I have a few of those in stock, PM if you need one.

JimMorrisonFan67

Yes that is the part, how much do you want and how fast can we get it. Also I assume you have verified it to be in working order..