Repairing dual vacuum cans for distibutors..

[Marko]

Well seen as though good ones are non existent and NOS are made from unobtainium I thought I would look into the possibility of repairing these things!

..so, I bought a used item to take to pieces, and as suspected the retard section has a shot diaphragm. it looks to have been contaminated with something from the carburettor, not sure how but it has it would be very tricky to fab up a replacement diaphragm let alone fit one as they are riveted in place but the good news is it doesn't connect to the arm like the advance part does so maybe one from an alternative can will fit, these seem to be a common sized can from many different makes of cars and the only part (I hope) is different is the arm.

bottom middle and bottom right is the retard pieces..

[alex d]

that's very interesting! I have a spare totally broken one so I might give it a shot I think what's different from different cans is the arm and the tension of each spring

was the retard diaphragm cracked, did it have a hole, or??

[Marko]

was the retard diaphragm cracked, did it have a hole, or??

it was just brittle and rotten from contamination. these dual vac's are very tough, I couldn't prise the lip over to dismantle so carefully ground the top lip away until it fell apart! to reassemble it will need bonding together somehow..

[Editor]

Trying to get my head round this... I'm not sure I'm much wiser!

The two diaphragms are clamped in the same ring (single crimp) but can move independently and have return springs to push them towards the common plane.
The inner diaphragm (destroyed) is not connected to the operating rod, but a vacuum in that chamber does affect the outer diaphragm in the opposite sense to a carb-created vacuum in the outer chamber. So they do oppose (retard/advance) which is comforting!
The outer (intact) diaphragm is connected to the rod.

When the rod moves out from the distributor towards the dual vac unit, the baseplate moves anti-clockwise and the points heel moves away from the advancing cam lobe (also turning anticlockwise), so the spark comes later (spark is retarded).

Is that right so far?
It seems to do the opposite to what I would expect, but I'm not sure how the two diaphragms work. Does the notch on the rod fit on one of the discs? where was the spring for that diaphragm?

I guess I'll have to pull off vacuum lines individually and see what happens to the spark timing when the engine is doing various things.

It would be handy to have a sectional view to work out where the things went.

[Marko]

there is a sectional view somewhere on line, tried my best to find it yesterday but couldn't remember where I saw it over xmas!!

I thing the notch just restricts how much advance and retard the arm is allowed to impose.

from what I can make out the advance part works by pulling in the arm (like when you suck on the tube), this section is usually OK and the retard section like you say is not connected to anything and does not really retard the spark from rest BUT it does restrict how much advance is going on.

will try and find that cross sectional view!

[haz]

All very interesting, an obviously totally unfixable if the diaphram is no more.

Quite hard to envison without the other diphram, from the way you have laid it out;

1 2 3
4 5 6

I read the assembly went 1, 2, 4, 5, 6, 3?

Maybe the difernt arm numbers relate to the measurement of the notch on the arm, remember I was offered a 831 when the Type3 is a 813, would be interesting to see inside a 831, maybe they can be used or modified.

[Marko]

yes that order. the only difference will be in the notches as rest of unit should be same.. I've found someone selling NOS FI ones but not sure what differences they will have on curves.. I may just buy one and have a look, at least the diaphragms will be the same for the retard.

[haz]

This is interesting, seems to list a few of the different models & years and what 'vacuum can' they have, think its relevant but USA spec of course so poss different anyway!!

http://www.oldvolkshome.com/ignition.htm

[Marko]

being US spec they will be for FI cars (68>) and the arm will say 883 on of equivalent year.

[alex d]

I just got a spec chart for distributors, will try to upload it later, the FI cans have totally different vacuum specs! I guess the difference comes from the spring and not the diaphragm itself anyway, just wondering though.
oh, and I finally found some reference to the small restrictor thing I found in my retard hose, it even has a part number! turns out it's exclusive for 70-72 carbed type 3s and I assume the lack of it would easily break diaphragms!

[Marko]

I don't have that restrictor thing so will have to make do unless anyone has a spare! my engine is a 71 or 2 anyway so I have the right distributor and carbs to suit. if it is just the springs then maybe the old springs could be transplanted into the new cans.

this is the link to the cans I mentioned earlier, I've sent a message to ask if he has the ones we need, price seems very good and work buying one to take apart!

http://www.ebay.co.uk/itm/281044101791? ... 1423.l2649

[Editor]

That's for the FI distributor fitted to 1972 models - they are different from the '71 twin carb 205T distributor (don't know how different though).

[Marko]

well now I have 2 options! 1st and cheapest is to try the one in the link above for a FI (with a view to possibly taking apart and using the new diaphragm in the correct can).

and 2nd option is in the link below, the correct can NOS but at a premium price!! works out about £137 shipped

http://seekpart24.com/bosch/vacuum-cell ... 3?c=100148

[gizbeau]

Hello, using the link provided i ordered a NOS vacuum advance from fleabay and its the right one, came very quickly too considering it came from America, so thanks to Marko for the info

[Marko]

Hello, using the link provided i ordered a NOS vacuum advance from fleabay and its the right one, came very quickly too considering it came from America, so thanks to Marko for the info

which engine do you have and which can did you order? I'm still searching for the right one before I decide to go for the FI one, £137 shipped for the correct one at the moment is just a little crazy in price!

[gizbeau]

www.ebay.co.uk item number 281044101791

Marko i have the twin carb engine, fitted this today and its an exact match

..and yes i'd be reluctant to pay £137

Gary

[Editor]

The Parts book lists that as the correct one for dual vac FI distributors (I've a dual vac on a 1972 FI Fasty). It seems to disagree on the 205T distributor, including twin carbs from '69. I thought only the '71 twin carb was dual vac. I'll try to find out.

[Marko]

The Parts book lists that as the correct one for dual vac FI distributors (I've a dual vac on a 1972 FI Fasty). It seems to disagree on the 205T distributor, including twin carbs from '69. I thought only the '71 twin carb was dual vac. I'll try to find out.

you are correct Dave, it is for a FI 71 (883 on arm).

the carb'd engines have 813 on arm, both T and AA versions for manual and auto. not sure what differences there are between "T" and "AA" distributors but the cans are the same.

[gizbeau]

Gents not sure if this helps or not the car I fitted this to was a 69 manual fastback and as far as I am aware is totally standard but then 40 years is along time for things to get altered, I have a complete F1 engine in the shed I can pull the dizzy and have a look if it helps?

Gary

[Marko]

didn't think they had the dvda in 69? you can tell the year of engine from the engine number on case.

yes, have a look at that dizzy, I'm just curious!

[gizbeau]

My engine number T0705029
The vacuum can number on the F1 engine is 883, which tallies with what your saying so think this means i have fitted the wrong can to my car, altho it works a treat and so far no problems

[Marko]

My engine number T0705029
The vacuum can number on the F1 engine is 883, which tallies with what your saying so think this means i have fitted the wrong can to my car, altho it works a treat and so far no problems

http://www.hallvw.clara.net/t3engnos.htm

according to the link above that engine is a 69 twin carb, I don't think 69 had the dual vac can?

if it works fine then it's job done I guess, what was up with it before?

that's the problem with these old cars, you never know what has been swapped out over the years, my 68 has a 71 engine and a 71 "manual" distributor as opposed to an "auto" distributor like it should have.. spring is round the corner and I want to get it running super smooth and reliable, maybe I'm expecting too much for a 45 year old car?

Editor:- T0690001 started the 1970 year in Aug 1969, so it's a 1970 model.

[Editor]

That was what I thought Marco, but the parts book says that dual vac can (well, the carb version) was fitted to 205T (manual carb) and 205AA (auto carb) from engine T0 690 001, which does include the '70 models (chassis number from 310 2 000 001). I reckon gizbeau's car is actually a '70 with a long front. I must get a look in my son's Fastback - that is a '70. I hadn't appreciated it had a dual vac can (maybe it hasn't!).

[gizbeau]

Morning gents if it helps my 69 is a late model with the larger body styling and the dual can picks up from the intake manifold and left carb, don't know wether this helps but the intake manifolds have the smaller balance pipe and not the twin pipes fitted on my 72

Gary

[Marko]

I just bought one to try anyway.. Only £27 shipped.

I noticed on the can I took apart that it has an adjustable cam near the arm. I wonder if this can have an influance on timing advance?