Vacuum advance in distributor repairable? ('72 145 B20F) (2025 Update)

I suppose it would help to include something in the article... :-)

I'm fairly certain the vacuum advance mechanism in the distributor on my 145s' B20F has failed; if I pull and plug the hose, the engine is solid on the timing mark at idle; when I reconnect the hose, timing shifts 5-10 degrees, idle drops, runs rough and pops occasionally. Pull the hose, and it smooths out again. I suspect this is the source of the rough cold idle I've had for the past year.

So; can I repair/replace just the advance mechanism in the distributor, or is this a distributor-swap situation?

My temporary solution is to set the idle with the hose connected; this gives me a fairly smooth idle, though a bit high, and power is down a bit. Much more driveable than it was, though, so at least I can get around.

Anybody know where a NOS or know-good distributor could be found for a '72 B20F with D-Jet at a reasonable price?

Thanks,

Gary

Gary,

sounds as if the vacuum advance is doing what it should. I think you may have the timing set wrong. Have you followed the proper sequence for setting the timing? i.e. vacuum hose disconnected and plugged, reduce idle to 800 rpm using air restrictor.

The vacuum advance is replaceable, if memory serves. It is not repairable by mere mortals. It can only fail two ways: leaky diaphragm, which is indicated by no change in idle when hose is removed, or frozen, which can be observed by popping the cap and looking at the linkage while sucking on the tube.

Your Volvo dealer should have a replacement or you can get one on line from gcp and others.

Go to brickboard.com for more help.

chuck petterson

I'm trying to remember my old Trade School days these distributors run ignition points when the vacuum advance unit pulls the breaker plate in old distributors this plate wears out and as the plate is pulled to advance the timing it also changes the point gap causing the engine to misfire ect.you can check this by placing a dwell meter on and trying the vacuum advance the shouldn't change much. There is also under the breaker plate another set of contacts that have something to do with the fuel injection it has been a long time since I have played with one I hope I have been of some help. Joe

(Something's probably wrong with my newsreader so i couldn't reply to the original article.)

I noticed something yesterday. In the distributor there are two plates. The lower is static, the upper is mounted to the lower so i can rotate (for the vacuum timing to work).

While I was driving, suddenly the engine fell to idle and it popped a lot and had no power. I found out later that it was the "bearing" (it's a very simple thing with one bearing ball which rolls on the lower plate) that holds the upper plate to the lower that was broken.

The upper plate has to hold a force applied by the breakers. The reason for the popping and low power was obvious that the breakers didn't open every time because the plate attached to was loose.

A temporary fix I had todo to get home, was just putting a piece of rolled paper to push the upper plate against the lower and disconnecting the vacuum hose. I didn't run perfectly well on some rpms, but it was almost right. My point is that if something in the breaker appartment is loose, it could trigger all sorts of problem. It's a case of vibrations, resonance in parts etc...

In your (Gary Heston) case the vacuum mechanism may for example change breaker spacing so it runs uneven on idle, but on higher rpms the case could be that the breakers open just enough. Remember that you can never see the vacuum mechanism in action inside the distributor.

I would advice you to take out the distributor of the car (it's very easy by loosening the adjustment screw for ignition timing and lurk the distributor straight up). You should check that all parts in the breaker appartment is rock solid. If you want to you can also remove the oher parts (capacitor and vacuum mechanism) and finally the plates so you can look beneath at the centrifugal advance mechanism.