TR2/3/3A Distributor vacuum advance hook up to the inner plate

[sp53]

Looking for some help because I do not understand how the vacuum advance really does.

Anyways, I am making a distributor out of an old box of distributor parts. The hooking up of vacuum advance hook has me concerned that I might break the vacuum advance somehow. I really do not know the difference between a functioning vacuum advance and a broken is , or how fragile they are and just what is side other than they should advance the timing. Maybe it just holds stuff steady. I assume there is some kind of diaphragm that moves out with the vacuum of the engine when it pulls.

Moreover, I do not see how that little diaphragm could pull much inside the distributor because the little knurled not assembly holds the plates kind of tight.

Here are some questions I have if somebody is schooled working on the distributor.

Distributor vacuum advance hook up to the inner plate pin is done how and when?

Should I hook the loop to the pin last or first? Should I roll the distributor inner plate off to side to get some wiggle room or just lift the looped cable up with a small hook and drop it on the pin? one thought it seems to me that a good vacuum advance should have echoing noise like it is hollow to be working, but just a guess.

Thanks Steve

 

[CJD]

Suck in the fitting hole of the advance and it should pull the rod in. You should not feel any leaks in the assembly as you suck on it. You can't hurt the advance unit. You are right, it is a rubber diaphragm attached to the rod, but it is tough. The only thing that kills them is time, rotting the rubber, or perhaps certain chemicals that could attack the rubber. Nothing you can do to it will hurt it, though.

It's been so long I can't remember how the advance rod hooks into the point plate. I know it hooks easily into the point plate, and once the point plate and advance unit are secured, it is held in by a positive stop. Nothing fancy. The port for the vacuum at the front carb is just on the air-cleaner side of the throttle blade, so it sees no vacuum at idle or full throttle. As the pedal is pressed, the port starts to see vacuum, which then pulls the diaphragm...which pulls the rod to rotate the point plate in an advanced direction.

More advance makes the engine more fuel efficient...all the way up until it starts to pre-ignite and ping. The idea is to increase the advance when it can take the extra advance...that is, low load, which is also a time of high vacuum. At full throttle there is no vacuum, the advance drops back to normal, so it will not ping. It also drops back to no advance at idle, just to keep the idle speed consistent.

That's vacuum advance in a nutshell.

 

[mezy]

one way to test you diafragm is to suck on the pipe till you see the rod pull into the diafragm body, thin put your tongue on the pipe to sel it.see if the rod creeps out or stays put

 

[sp53]

Thanks guys after I got a little deeper into putting a collection of parts together, I started to see a better picture. One thing that I am having trouble visualizing is how the 2 plates can slide on each with such a small amount of force from the diaphragm. Perhaps there is more force that I realize.

The plates are stuck together pretty tight with a spring clip on the one plate and rotate in the center with the center pieces inter connected. I guess the little nylon pins in the plate provide a sliding surface.

I do have some plates that slide better than others, so I probably have a bent plate or too tight fit on the clip or something. I need to find a plate that slides the most easily and perhaps put a little oil/ special grease on that and give that a try in the car.

Steve

 

[Sarastro]

They should slide smoothly and fairly easily, and there definitely should be a little grease on the mating surfaces. I have a "mity-vac" vacuum pump that I use to test such things. I like having a quantitative measurement. But in any case, it should move easily at a few inches of vacuum and return completely to the original setting.

 

[CJD]

+1...the point plate should rotate easily.

 

[sp53]

I did find some problems with the sliding plates. One plate had a slightly too long condenser screw and that rubbed on the lower plate under the screw. On another plate there was no slot in the lower plate for the screw that holds on the points. Here again the screw need to be shorter maybe 3/8 to half of an inch long, so it would not rub. in this case, the screw went through a hole in the lower plate and would not let the plates slide. All the other plates would take a screw that could be ¾ long or shorter because there was a slot cut in the lower plate at the factory and not just a hole. I have some of those short screws for the points before there was a slot in the lower plate and they were a little more difficult to get in place. plus i found some of those short screws and condenser screws inside some old distributors.

Lastly I took some 500 sand paper on the large center hole and cleaned up some small burs to help the plates spin more freely in the center. In the end i got a couple of plates working well and smooth

I wish I would have bought some new vacuum advance units years ago before they were a 100.00 bucks. Back in the day, I would go to the neighborhood parts store and purchase a rebuilt distributor for like 35.00 or maybe less just cannot remember. I think the Lucas 404 distributor fit on a lot of European cars.

steve

 

[CJD]

My TR2 vacuum advance was no longer available, so I sent it off to have it repaired. I can't remember where, but I am sure it's in one of my old threads.

 

[poolboy]

Maybe British Vacuum Units ?

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[sp53]

thanks Poolboy for the site. There sure is a lot of information on distributors there that I had no idea about.

Steve