Odd switch on transmission. (Vacuum advance cutoff)

[reservoirdubs]

I'm just getting my 72 Westy ready for its inspection, and found an odd switch. It's attached to the nosecone of the gearbox. There is a reverse switch on the side of the nose cone (reverse lights are working), then this one on the face of the nosecone (to the right and just below the shift shaft) that has a single wire attached to it (black wire, looks like power and ran into the engine bay). I've looked around and can't find out what it is. Any idea what it might be?

[raygreenwood]

It sounds like a neutral safety switch. Some VW cars had them. They were designed to make sure the vehicle would not start unless it was safely in neutral. I have never found one operating properly. Most had been disabled at some point. Ray

[Brian]

Doe it looks like this? this is not a bay transmission but

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[old DKP driver]

originally that switch went to a vacuum switch in the engine compartment
and was used for ignition timing for 4th gear

When shifted into 4th it cutout the retard side of the ignition distributor.

page 73 in the Green Bentley (engine and clutch section)
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[reservoirdubs]

Thanks for this. Is it ok that it's disconnected?

[old DKP driver]

Yes, most 72 's aren't stock anymore but, I would hold on to any original
parts you may have.

I have a 72 and all those parts are put away for the future>
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[raygreenwood]

[nathansnathan]

I've come across this wire wrapped around the top of the transmission and clutch bracket but not connected at the back.

I can't seem to find the 4th gear switch or the temperature switch on a wiring diagram. The Bentley p 73 (shoutouts to dkp driver) says this system is on all dual carbed engines except 74 with manual. Am I missing it?

As far as where the wire goes to, is it the mini canister thing up by the fan mount? I guess that canister is the the temperature switch? They call it a 2 way cutoff valve maybe (kind of looks like a canister thing in the drawing) in the Bentley schematic and looks to be something separate, not sure. So it looks like power off the coil, 15, goes to the cutoff valve; I will look for a 2 on that switch by the fan.

And other question, for bonus points, which hole would the wire go through?

In regards to how this is supposed to work, the Bentley says that the entire vacuum advance system is cut out except in 4th gear, except at temperatures below 54 degrees F. So, like, when it is over 54 degrees, you won't have any vacuum advance, except in 4th. I'm not super familiar with how the vacuum advance is setup.

I guess the advance side is the outer and the retard is the inner, like away from and toward the distributor, respectively? SOrry maybe dumb questions. It looks like it is to the outer of the cannister on the distributor in the schematic and is saying advance, just trying to figure it out.

[busdaddy]

The "canister thing" up beside the booster fan is the cutoff valve, the switch is on the nosecone of the transmission. As for which hole the wire goes though I can't say definitively, I've never seen the cutoff system as a whole, just bits left in place on various buses. It doesn't appear on any wiring diagrams. The advance nipple on the distributor is the one that faces away from the unit, you'll have to try sucking on both ends of the valve to decide which one goes to the carb, one will be vented to atmosphere when the valve is de energised, that one would be the distributor end.

But if you don't have the switch on the trans all of this doesn't really matter.
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[glutamodo]

Yes, it's for advance and yes that's the outer section of the vacuum canister.

I know it's not on the wiring diagram, VW didn't always have everything on those - often they'd put in a supplement for the things they missed but they didn't even do that for this circuit.

That circuit is "fun" when a wire gets hooked up wrong or comes off and grounds out, I've seen it where you'd shift into 4th and the engine would die!

Here, for direct reference, I've had a scan of that part of the manual in my images folder for like 10 years now:

You can see the electric valve attached by the heater booster fan in this image:

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[busdaddy]

Ahhhh.. yes, I recall seing that diagram somewhere before now. The 72 doesn't have that temperature switch, it's only found on 73 models, I guess the 72 just cut it off regardless of temp?
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[nathansnathan]

lol at the canister thing. Those for dummies books are written for me, I need it spelled out pictures etc. You guys are awesome. It seems pretty cool the system. Running a purely mechanical distributor for so long, it would be cool to have more advance in 4th. I'll be messing with it more for sure; I do have the 4th gear switch in the nose cone. I couldn't picture the temp switch being in there and thinking about it, doesn't seem like it would be in the cutoff valve either. Where is it on a 73?

[busdaddy]

[nathansnathan]

Yeah it is definitely nt there on a 72. So regardless of temperature, it's supposed to only get vacuum advance in 4th. Bunch of hot rodders disabling that.

[old DKP driver]

Nathan- I disabled mine too as I wanted it to run like the 914-4

actually I had only been a VW tech for about 6 months when we received
the 72's it was then I knew I needed to buy a bus.

Chris
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[nathansnathan]

It must have been amazing to see these things new, a 72 bus in the show room. Something from a thread over on 914world, a little off topic, but...

Found an old pic of you, Chris.

It would be cool to put a manual toggle front to a relay. I read somewhere old 911's used to have a cable adjust distributor advance right in the cabin. I've always thought that sounded cool, to adjust advance based on temps and how warmed up the car is, really get a feel for it in real time.

[Amskeptic]

[nathansnathan]

[Amskeptic]

[Tcash]