SC Distributor Vacuum Advance/Retard Issue

Gunter · Gunter's Garage

My 1980 SC has a stock Bosch distributor with both vacuum advance and retard. The retard side does not work and it does not seem to make any difference. The advance works fine. There is no emission control, CAT or Ox sensor on this engine.
Why does the advance side work and not the retard? Are they not both connected to the same rubber membrane in the little housing? And: what is the purpose of a vacuum retard? I have some excessive coughing/spitting when coasting but other then that, it runs great. After adjusting the mixture, the idle is really smooth. Thanks John Walker; I tested the sequencer valve, it's o.k. My friend's 3.2 runs without any vacuum, just centrifugal. Question: would a working vacuum retard lessen the rumble when coasting? Anyone with some similar situation?

Gunter · Gunter's Garage

Any suggestions at all? The first real help here will receive an explanation of what "Kunstharzlack" means. Or, if that is not enough, how about "Bundesbahndampflokomotivefuhrerausweis"
How about it? Thanks anyone.

emcon5 · emcon5's Garage

Are you sure the far end of the vac hose is connected? You can test the retard by plugging in a length of vac hose to the distributer and sucking on it. Take the cap off and watch the roter, when you suck on the vac hose. If it is working, you should be able to see the roter move slightly.

If you are a sissy, you can use one of those mitty-vac hand vacuum pumps to do the same thing.

Tom

Gunter · Gunter's Garage

Thanks emcon 5. Of course, I tested both sides with sucking; the advance moves nicely but the retard doesn't move at all. To my mind, the two sides are connected to the rubber diaphragm inside the vacuum housing,so, if one moves, the other one should move too. Why isn't it? And what is the purpose of the retard on engine performance?

Tim Polzin · 05-21-2002, 08:37 PM

Don't know about the retard, but I think the other answer is a "national steam locomotive operator's licence", or something close to that (just visited the DB museum in Nurnberg).
Tim

Superman · 05-21-2002, 09:38 PM

I'm interested in this issue too. I'm interested in what benefit is achieved by the vacuum retard. And of course I'm interested in Bundesbahndampflokomotivefuhrerausweisology.

It seems to me that when I finally gave in to the urges to suck on my distributor hoses I also did not see much happening with the vacuum retard. Perhaps the engine has to be running. It so happens that I also have a little popping on the overrun. The Bundesbahndampflokomotivefuhrerausweis valve still puzzles me though.

Wayne 962 · Wayne 962's Garage

The 3.2 stock motor doesn't have any advance mechanisms - it is controlled completely by the Motronic engine management system...

-Wayne

Early_S_Man · 05-21-2002, 09:59 PM

Retard is used to improve emissions compliance at idle when the engine is not producing any significant hp under load. The position and design of the port providing the vacuum signal causes it to be at maximum in the 900 rpm to 1000 rpm range, and to fall off very quickly off-idle when the engine revs up to provide power under load.

Gunter · Gunter's Garage

Thanks Early-S-Man. The point here is that there is no movement on the retard at all with any RPM, or sucking, or any changes to the running in idle (900 to 1000 RPM) when connected or not connected.
Thanks Wayne. This is a 3 liter SC.
Still a mistery and still puzzled. Any more ideas anyone?

Early_S_Man · 05-22-2002, 08:16 AM

Gunter,

It has been my experience that the movable plate that the advance/retard diaphragm attaches to gets sticky or 'gunked-up' from aging of the Bosch grease applied at the factory. That is why I recommend periodic (every couple of years) removal, disassembly, and cleaning with brake cleaner/degreaser spray. Reassembly and lubrication used to be done with the traditional Bosch grease, but these days I prefer a high-temperature rated synthetic grease with moly, such as Valvoline's SynPower Synthetic Grease #986.

The following thread has a generic diagram of a Bosch distributor that may help with disassembly. Be sure to check for excessive end play, and wear of the two bushings that the central shaft is supported by.

distributor lube...