1983 SC Vacuum Advance Help

[Mach.925]

Looking to see if anyone has a source for repair or replacement for a distributor vacuum advance for a 1983 SC. Mine is Tango Uniform.

[Mach.925]

Hi, I'm reposting this with a few photos of the dizzy and part numbers. It's a 1983 US SC. The part number of the distributor is 0 237 304 016. The number stamped on the vacuum advance arm is 2763.

The advance diaphragm works fine, but the retard side has a gaping leak.

Any help would be greatly appreciated!!

[gomezoneill]

I looked all over the net and I cant believe the price for the advance/retard can!

[Mach.925]

Originally Posted by gomezoneill

I looked all over the net and I cant believe the price for the advance/retard can!

I found one for $589... what a bargain! What did you find?

[gomezoneill]

Originally Posted by Mach.925

I found one for $589... what a bargain! What did you find?

All about the same or more. Maybe you should look into the 123 distributor instead.

[Mach.925]

I'm in California and it has to be stock to pass smog... aggravating!

[arbita1]

If the vacuum advance works you can just plug the retard nozzle and keep it. The retard only affects idle and is used to reduce emissions. Although not sure if CA would have an issue with that for state regulations.

[Mach.925]

Originally Posted by arbita1

If the vacuum advance works you can just plug the retard nozzle and keep it. The retard only affects idle and is used to reduce emissions. Although not sure if CA would have an issue with that for state regulations.

Yeah the advance side is fine I'm chasing an aggravating idle issue. It idles at about 1800-2000 rpm, but when you bog it down in gear, is goes right to 950 and idles smooth and solid. I've replaced/checked/calibrated/tested everything in the system except for the AAV.... but found this issue with the retard, so I thought I'd eliminate it but might try plugging the line first. CA will not allow any disconnect of the hose... I'd have to put a stealthy block in the line!

[juanbenae]

how do we all miss parts heaven about now.

[arbita1]

Originally Posted by Mach.925

Yeah the advance side is fine I'm chasing an aggravating idle issue. It idles at about 1800-2000 rpm, but when you bog it down in gear, is goes right to 950 and idles smooth and solid. I've replaced/checked/calibrated/tested everything in the system except for the AAV.... but found this issue with the retard, so I thought I'd eliminate it but might try plugging the line first. CA will not allow any disconnect of the hose... I'd have to put a stealthy block in the line!

I had a similar issue. Using the “crush” method on the decel valve seemed to resolve the issue. Did you try plugging that to see if the high idle went away.

[Mach.925]

Originally Posted by arbita1

I had a similar issue. Using the “crush” method on the decel valve seemed to resolve the issue. Did you try plugging that to see if the high idle went away.

Haven't tried that yet... but that an the AAV is what I'm down to now. Thanks for your input.

[Mach.925]

Originally Posted by juanbenae

how do we all miss parts heaven about now.

Ain't that the truth.

[2jmotorsports]

I went through the same issue rebuilding my 83 engine. I sent my distributor to Kurt at Parts Klassik for a rebuild and he notified me my vacuum can was dead. Since they are not available I had to go with a Parts Klassik CDI which receives both advance and retard signals and adjusts timing inside the box. The distributor was rebuilt and the advance/retard was disabled somehow (I dont know the details). The car runs perfectly but the plugged vacuum can nipples wont make the s m o g guy happy. I suppose one could run vacuum lines in such a way to pass the visual part.

[AndrewCologne]

If the two way vacuum unit/can is that expensive and you need an ignition retard of approx 7-8° ATDC at idle and at 2000 rpm, just to match the smog tests HC values, then, just set the dizzy to that ATDC value at idle with still retard vacuum disconnected and try the smog tests. After that, set the advance back to 5° BDTC at idle and re set the proper idle rpm.

Other option would be using a 6pin CDI compatible version of the 123-ignition dizzy where maybe you can set the curve at idle to 7-8° ATDC, and from 1000 rpm on to 8° BTDC and ... rising. But ask them at 123 if such uncommon retards are really supported at such low rpms like when idle.

[Walt Fricke]

If the vacuum can works one way, but not the other, doesn't that suggest that the diaphragm inside is OK, and a leak externally has developed? You ought to be able to force air in and soap the outside to find bubbles? JB Weld over a pin hole you find somewhere?

Or flood the recalcitrant side with penetrating oil, and exercise the arm manually, see if there is some kind of asymmetrical pivot or arm bind in there?

But maybe you did all this with no cause emerging?

[Mach.925]

Originally Posted by gomezoneill

I looked all over the net and I cant believe the price for the advance/retard can!

It's insane. A single point obsolescence!

[Mach.925]

Originally Posted by 2jmotorsports

I went through the same issue rebuilding my 83 engine. I sent my distributor to Kurt at Parts Klassik for a rebuild and he notified me my vacuum can was dead. Since they are not available I had to go with a Parts Klassik CDI which receives both advance and retard signals and adjusts timing inside the box. The distributor was rebuilt and the advance/retard was disabled somehow (I dont know the details). The car runs perfectly but the plugged vacuum can nipples wont make the s m o g guy happy. I suppose one could run vacuum lines in such a way to pass the visual part.

That's an option I was looking into at one point before this problem arose. But the CA smog situation makes this a royal pain. I was shocked to learn these cans are so rare and expensive if you can find one. So, still exploring options.

[Mach.925]

Originally Posted by Walt Fricke

If the vacuum can works one way, but not the other, doesn't that suggest that the diaphragm inside is OK, and a leak externally has developed? You ought to be able to force air in and soap the outside to find bubbles? JB Weld over a pin hole you find somewhere?

Or flood the recalcitrant side with penetrating oil, and exercise the arm manually, see if there is some kind of asymmetrical pivot or arm bind in there?

But maybe you did all this with no cause emerging?

The advance port pulls strong and holds vacuum. The retard side won't even begin to hold vacuum... like a gaping hole. You can blow and suck into the port and hear air escaping inside. I've never taken one of these apart, and had the same question - how can it work one way and not the other with only one diaphragm? But in a cutaway diagram I found, it's not that simple. There appears to be little rubber check valves (at least 2) or something similar inside on the retard side. I am assuming one of these valves has failed.

[Mach.925]

Originally Posted by AndrewCologne

If the two way vacuum unit/can is that expensive and you need an ignition retard of approx 7-8° ATDC at idle and at 2000 rpm, just to match the smog tests HC values, then, just set the dizzy to that ATDC value at idle with still retard vacuum disconnected and try the smog tests. After that, set the advance back to 5° BDTC at idle and re set the proper idle rpm.

Other option would be using a 6pin CDI compatible version of the 123-ignition dizzy where maybe you can set the curve at idle to 7-8° ATDC, and from 1000 rpm on to 8° BTDC and ... rising. But ask them at 123 if such uncommon retards are really supported at such low rpms like when idle.

Thanks Andrew, this sounds plausible but I might put it at the "last resort" position on my list.

[Mach.925]

Here's an update to the vacuum advance/retard issue. First, I was able to source a brand new one from Vertex Auto. They use a current production Bosch unit for a Mercedes, then modify it to fit the SC distributor. The only trick is that the vacuum advance port is clocked to the 5 o'clock position putting it very close to the engine tin. I purchased a plastic vacuum 90 elbow from Pep Boys to solve this issue. Works perfectly now and my high idle issue is history... it runs and idles perfectly. In my case, only the retard side of the unit had failed and there was some question about how one side could work and the other have a leak. Well, it was driving me nuts so I disassembled my bad unit and mystery solved. There are two diaphragms inside separated by a thick black plastic spacer.

For anyone who's interested what goes on inside this thing, here are some photos...

Here is the advance side of the unit. The advance diaphragm was stiff but still worked:


Here is the retard diaphragm. It was torn at the attach point:


Retard diaphragm completely torn away from attach plate:





Lots of corrosion inside the housing which likely led to failure of the retard diaphragm:


They all sandwich together like this; retard housing, large spring, retard plate & diaphragm, spacer, advance diaphragm, small spring, housing (left to right):


Fun stuff... !!