New'n72

OK......I have a question about hoses and routing to and from the above mentioned switch.

I have a 350, 4bbl, with factory air. I have a service manual also. The manual, good as it is, shows several pictures of the routing of the hoses that connect to this switch but none of them is for a 350, 4bbl, auto transmission.

The Vac Control swith has 3 ports coming off the side of the shaft and one on the very top of the can. One of the 3 on the shaft goes to the back of the carburator. Another goes to the front drivers side of the carburator, The third is a short hose that loops from the middle port of the shaft to the top port on the can.

Understanding that this is difficult to describe and a first hand explaination would be much easier, can anyone tell if these hoses are on the correct locations?

I really question the short hose that goes from the Vac Cont. Sw. shaft to the top of the switch can???

The write up in the service manual probably tells a knowledgable person what I am trying to figure out but since I am not automative literate I need a little help.

rocketraider

In the 1972 Olds Chassis Manual- look on page 6K-10 (engine cooling), Fig 6K-19 which is for all 4-bbl engines except Toronado and 350 w/ manual trans. This shows vacuum hose routing for 350 2 and 4bbl automatics, and all 455's except Toronado if that makes it easier to understand.

Then look on page 6K-7, figure 6K-11 which is a picture of the switch itself, and identifies the four ports. An original equipment GM switch should have letters cast into it identifying the ports- C, V, D and M (which may be MT on some switches).

Connect hose from port M to the intake manifold as shown in 6K-19. This is bottom port on the switch. It tees into the manifold vacuum line to the transmission modulator.

Hose from port D goes to the distributor vacuum advance. This is middle port on the switch.

Hose from port V goes to the vent fitting at the top rear of the carb (one of these is choke fresh air intake, the other is the switch vent). This is the upper port on the side of the switch.

Hose from port C goes to vacuum port at driver's side base of the carburetor. This is the port on top of the switch.

Now that you know where each hose goes, do you need to know how the thing works? That electric plug on top has a lot to do with whether it functions as designed, or functions better for driving.

Page 6K-9 gives a complete description of its operation. If everything, vacuum and electric, is hooked up it will prevent any vacuum advance to the distributor until transmission is in high gear, but will also switch the distributor to manifold vacuum to advance timing if engine overheats at idle.

So, unless you're going for a concours restoration, I'd pull it out and use a non-electric distributor vacuum switch for a later engine. I think you'd be a lot happier with the driveability and fuel economy.

New'n72

Thanks....ya know I looked at that page a dozen times. Read the caption under it as many times. Just couldn't get the meaning correct.

I am not going for a "Show" quality restoration on this car but I would like to keep things as much original s possible. When I can't drive it any longer the next guy can decide if he wants to change anything.

Now that I understand the picture I am still confused about who and when the hoses were routed the way that they are now. They are all old hoses that probably should be replaced but the point is that I have not put anything new in the mix (as for as these hoses are concerned) since I started working on this car last year.

As I recall it ran fine several years ago when I stopped driving it and put it up in the garage. Actually it still does run fine. My only problem is a "not starting when hot" symptom that I have another thread on the site to discuss.

The hoses, as they were before you replied to my question and I figured out the correct diagram in the servcice manual, were as follows:

"V" went to the back of the carburator ( as it should)
"MT" went to a "t" fitting and on to the manifold (as it should)
The hose from the distributor was spliced, with a metal tube, to a shorter hose which was connected to the front of the carburator, where "C" should connect to.
"C" on top of the DVC sw. was looped down to the "D" port on the DVC switch.

Unless this was an after market enhancement that some mechanic emplimentd 30 years ago, I would guess that somebody didn't connect these hoses up correcly some where along the line many years ago and I just never knew it.

I wonder if this will affect my "not starting when hot" symptom?

Thanks for jogging the ol' brain.

rocketraider

What someone did was bypass the DTVS, and I've seen them done like this many times. Running hose from the ported vacuum connection at front of carb to the vacuum advance canister effectively puts the distributor on ported vacuum as earlier non-smogged cars were. Ported vacuum is above the throttle plates, so the vacuum signal varies with throttle opening for best fuel economy. Surprising they didn't just plug the manifold vacuum fitting instead of leaving all that banjowork in there. Anyhoo, now you know how to hook it back up factory. I think you can expect some loss of fuel economy and driveability, and you should make sure the transmission switch is functioning, otherwise you'll have no vacuum advance at all.

When you say no start hot, do you mean turns over slow, or turns over normally and doesn't fire? The vacuum routing as is shouldn't affect starting.

New'n72

Well at least I know what was going on there, now.

I really didin't think it got very good gass miliage as is. Now that I have put it back you say the miliage will be worse. Good thing I don't have to drive it every day.

The starting problem is not a cranking problem. It cranks just fine, hot or cold. This winter with tempurature below 40 degrees it didn't have a problem starting after it was up to temperature however, last summer when the outside temperature was in the 90's I would have to crank and crank before it would fire. It wasn't an immediate failure in that if I turn it off and then try to start it it works fine. But if I get the engine up to temp. and then turn it off and let it sit for 20 minutes or so, its a a reall bitch to get started again.

There's a thread under the 'elecrical' forum on this.

I have replaced everything I can think of; fuel pump, hoses, points, plugs, plug wires, gas line on both sides of the fuel pump. Choke seems to be working as it should.

Just can't figure it out. I will have to wait until things warm up a bit though, to get the symptoms back.

Thanks for all the help.

New'n72

After putting the hoses back to the original configuration I got to thinking about that vacuum control switch. It is probably as old as the car is. I don't know that it was ever changed out and the one that is with me now hasen't been touched in a long time, from the looks of it.

I did a bit of searching on the internet for such an item and didn't come up with anything. There were some 'ported' vacuum switches but they don't have the 4th port, only 3 on the shaft and non on top of the can.

You wouldn't know of anyone producing this part, should someone decide to change it out, or a source of supply for this item?

Thanks in advance,

rocketraider

It's a 71-72 thing, and it's either old stock or a used one. OE part # is grp 2.410, part # 410052, switch, distributor vacuum control on intake manifold. It listed for $8.10 in 1974, but you can expect to pay several times that for an NOS one now since 442 and Hurst/Olds use it.

The three port switch will function just fine as it takes the transmission controlled spark completely out of the picture. You would then connect the DTVS to: manifold vacuum, ported vacuum and the distributor and you would have vacuum advance when it could do you some good.

Can you tell I'm not a total purist about some things?

New'n72

Being a purist can make a hard row to hoe.

I am a purist in most things but this car is begining to change my philosophy.

I may be upgrading this baby instead of frustrating myself with trying to find obscure parts.

The thing about keeping things 'stock', at least for guys with minimual mechanics savy like me, is that it matches the service manuals.

liftrocket

Sure glad I was directed to this thread.

I have a 350 4bbl on a stand that I am trying to put the finishing touches on before I put it into my 72 Cutlass Supreme. I have one of the newer 3-port switches since the original Distributor Vacuum Control Switch somehow went missing between dropping off my mostly disassembled engine at the machine shop and picking it up a month later.

On this new part (STANDARD MOTOR PRODUCTS Part # PVS1 {PORTED VACUUM SWITCH}), the ports are labelled from top to bottom "1", "D", and "2" and no documentation came with it. The mechanic I talked to thinks the bottom port goes to the manifold, the middle "D" port goes to the distributor, and the top port goes to a port on the carb (not sure which). Here is a picture of it: http://thegraves.ca/72Cutlass/new.jpg

Rocketraider, you said this below when talking about the original 4-port part:

"Connect hose from port M to the intake manifold as shown in 6K-19. This is bottom port on the switch. It tees into the manifold vacuum line to the transmission modulator."

Would I do the same thing for the bottom port of my 3-port switch?

Also, is the manifold vacuum line to the transmission modulator the thin steel pipe (instead of rubber hose) that runs down to the transmission on the passenger side?

Basically, I'm hoping for a recommendation as to the best way to route the hoses.

Thanks for any guidance you can offer.

Lady72nRob71

Hmmm... I have been wondering about this switch for a while as mine is not hooked up correctly at all. In fact it may be giving me vacuum leaks at times. I think the manifold vacuum goes right to the distributor and some ports are open to air...

How would one hook it up for best drivability, performance, and economy?

J-(Chicago)

Would one from a 72 Skylark be the same part?
I have 2 motors with these units on them.

I'm sorry that I can't answer your questions.

88 coupe

From post #4:

What he said.

Norm

Lady72nRob71

Okay, I studied my setup good last night.
I assume ported vacuum is the connection above the throttle plates?

My vacuum advance on the distributor is currently hooked directly to the rear manifold vacuum. So given what was said, it is better to use ported vacuum then. That can be easily changed.

I found that my ported vacuum line from the carb goes to the top of the TCS solenoid. Since the open ports were not capped, it is sucking air when the valve is deenergized. The front manifold vac sucks air when energized. This all sounds very wrong but the car runs great. I would figure there should be no loss of vac. anytime.

Yes, it has been a while since I really understood the whole vacuum and distrib. advance concepts but it is coming back...
Thanks for the help...

Lady72nRob71

>>>I assume ported vacuum is the connection above the throttle plates?

Okay, this question was answered already... I need to wake up...

88 coupe

Common mistake. Usually made by Chev/Pontiac guys.

Yes. Run one hose from the vacuum canister to the ported source on the carb, plug all remaining openings, reset initial advance (with the vacuum hose disconnected) and reset the idle mixture/speed per factory specs.

If you don't like the way it runs, set the initial back to where you found it.

Norm