Vacuum Can Discussion Thread

[babarogue]

[babarogue]

On the diaphragm material, they are both same, similar to those in fuel pumps, only thinner.
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An optimist is a pessimist without any experience.

[babarogue]

A small update: the dimensions of the pull rods. First the big one.

It si interesting that the coutout near the diaphragm is 7 mm in size. This defines the total amount of movement of the rod. Converted to angular movement this turns out to be 20 degrees, which confuses me a bid, because the total amont of advance for 111 905 205AA should be 32 to 35 degrees.

Now the small pullrod, 461 dimensions.

Here the size of the gap is about 2.5mm.

The "t=2mm" is the thickness of the rods. t=1.2mm in the upper picture is the thickness of the disk for the bigger one. The thickness of the disk of the smaller one is 0.8mm
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An optimist is a pessimist without any experience.

[babarogue]

[tasb]

Excellent contribution to this thread Babarogue.

Thanks for moving it here Glenn.

you can certainly see why the steel line is so important and why the fumes from petrol will ruin the diaphrgam given time.

What does the canister look like when you are done?
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[Danpa]

With all the different distributors that Vw had, are the main differences with advance/retard in the vacuum cans? Or are there a lot of differences with the distributor bodies and the centrifugal weights themselves?
If its mainly with the vacuum cans, I'm surprised nobody makes a adjustable can that you can dial in your advance or retard. Or is this already available?

Dan

[glutamodo]

If you look at the charts in the various Bentley manuals you'll see there were differences in the centrifugal advances as well. Not huge differences but they were there. Some vacuum units were quite similar in characteristics as well.

There are no "dialable" units for stock distributors. Now, the distributors used from 1965-1970 DID have adjustable return springs for the vacuum advance - but the overall amount of advance for these was always a function of the canister, not the spring.

-Andy

[Danpa]

Are the weights and springs on the centrifugal advance similar to a small block chevy?
With a sbc, you can change springs to change rpm when the advance "hits" or modify the weights for more or less advance.

[glutamodo]

I've never seen the inside of anything except VW distributors so am not able to answer that question. Sorry!

[Glenn]

[babarogue]

[glutamodo]

Those not being distributors for US models, I've never seen either of them. However I do have some specs, and I thought the 111-AA distributor was supposed to be timed statically to TDC. Have you verified your total advance isn't too high?

[babarogue]

[glutamodo]

Yeah, the star pattern, from discussion earlier in this thread that would likely be a 07017/1237121210 canister, and I've only ever seen one of those with the arm marked on it and that is timed to TDC. I'd posted that photo but I guess it was in a different thread. Several distributors used that vacuum canister (not yours though) and it was a Type 3 distributor on which I found such a canister marked 210:

The big problem with that OldVolksHome site is all those "can use" listings - making it seem all the parts on those distributors are totally interchangable. In many cases they may be, or they may fit, but they may not be quite correct when you do so.

That online VW manual - yeah, I've seen it and referred to it more than once. It's more of the technical bulletins that have been of interest to me, the ones that list the specific carbs and the specific distributors matched to them. For years I've been seeking those out and been doing charts based on what they say. There's a handful up to the late 60s archvied on TheSamba, some of those I had copies of myself at one point. Recently I got a huge boost in this regard from a bunch of early 70s tech bulletins I found online, plus I gained a collaborator from Australia who has tons of these in hard copy. I just put up the latest version of the DOC file with all this data:

http://members.trainorders.com/android/temp/CarbBaseFlangeNumbersA.doc

At the bottom of that document, I ask if anyone knows of more sources to let me know - to this day, no one has. I've had to dig all that info up myself. Then many months ago, I discovered Andrew P had some such info after doing some internet searching, and contacted him. I thought he might just scan some of his documents and let me figure what data was useful, but he went several steps further by filling in many of the question marks and blanks on my chart. Then just recently I found this archive of German-language tech bulletins totally by luck - I was Googling a distributor number and got a match for a base-flange number I'd never seen before in the process. Much of the data that Andrew had added was listed there too, plus several more entries I'd never seen before, which I plugged in what I could, and then he went and filled in some of the blanks. He says he's got even more non-US data to add as well, eventually.


What 30PICT-3 do you have? According to the info I've got, as soon on that chart, the VW1200s with a 30PICT-3 and BEFORE they switched to SVDA (1971-late 74) with the 111-AA distributor had the base-flange numbers in the VW283 VW284 and VW320 series. It was because of that info that I added the distributor numbers to this chart:

The slot in that drive gear - typical. They are never exactly perpendicular like the manuals show. Well, they are at one point as you drop them in place, but.. the spiral shape of the gearing makes it so that once it engages it is a little bit off.

[babarogue]

[herbie1200]

Do not mix the big and the small canister, the carb and the behaviour are very different.

The big canister is for vacuum only advance, so the advance has to increase with speed. If you look at a 30pict3 carb for this kind of advance, you can notice a small brass tube between the starter valve and the throttle valve.

The small canister is for vacuum+centrifugal advance; if you look at the same carburetor but in the SVDA configuration, the brass tube I told before is not present. The behaviour is different at all! In this configuration, the canister is only to achieve some additional advance when the gas pedal is partialized, and its function is a sort of 'on-off'. The rest of the advance is obtained by the centrifugal masses.

So, the small canister, is:
- off at idle
- on only with gas pedal slightly depressed
- off at 40% and over throttle opening

Don't mess with a wrong mix carb-canister!

[Harris]

tasb,

[glutamodo]

[fassed]

[babarogue]