vacuum advance questions

I've read in a few places that you can suck your advance unit to see if it still works. So I decided to try it when I set my timing the other night.
I could not get any movement from the advance unit by sucking the hose. I tried it with the unit removed from the car, so there should have been no resistance (ie, stuck plates in the dizzy).
I couldn't move it by sucking, but I also didn't find any detectable leak.
I did get some black sludge out of the unit when I removed the hose from it. Fortunately I didn't ingest it.
The lack of movement and the sludge led me to believe that the diaphragm was bad….worn/stretched so that it doesn't move the arm, and leaking enough to let some sludge come through, but not so much that I could suck through it. I admit, I was confused.
I set my idle timing at 10 BTDC. Increasing RPM's does give me advance, I assume mechanical only.
I ordered a new advance unit. The one I have is shown in the right of this photo, the one that arrived in the mail is shown in the left of this photo. (Thanks to Jeff Shlemmer for posting the photo).
http://www.mgexperience.net/phorum/file.php?1,file=27937
I was hoping to see movement when sucking on the new device. Always nice to see a difference in the old and new part. I guess I don't suck well enough because I couldn't cause any movement with the new device either.
I am now left with 2 questions…..
1. Was/Is my old device bad?
2. Is the new one I bought an appropriate replacement?
Notes about the car: I have the 45D dizzy, manifold vacuum, HS4's on a 76B. The car runs/feels fine right now, but I'm wondering if it should run even better! It sat for 18 years, and I just put it on the road this month (after much work).

well, there's some consolation in knowing you don't suck.

or not. depends.

(sorry!)

I do everything on a distributor with the damn thing out and in my hand. My back simply won't permit otherwise<grin>

with the SOB in my hand, I'd stick a piece of tube on the vac advance unit and give it a little suck (I have lots of folks who will testify that I do, indeed suck!) and watch the innard of the dis to see if the advance plate moves. yes, it moves, it works. no, it doesn't, it's broke. send it to Jeff. get it fixed, no problemo.

common for old vac advance to not work.

Any liquid that would be in your old vacuum advance is fuel, and that deteriorates the rubber diaphragm inside. Period. Is yours bad? Hard to tell since you haven't proven whether or not yours works. It seems like it doesn't leak, so that's a start.

Both the vacuum advances in that picture are for 25D distributors, not a 45D, so you may have the wrong new part anyway. The unit on the left is designed for use with manifold vacuum, and I have 100 new vacuum advances in route from England (should arrive Tuesday) for the 45Ds with manifold vacuum should you have the wrong item. A quick visual comparison will tell you if it will bolt on with 2 screw tabs (45D) or if it has a long steel rod out the back side that passes clean through the distributor and is fastened with a thumb screw (25D).

You can probably stop at a local auto parts store and see if they'll test yours with a vacuum pump. Or call a local club member or friend who may have one.

hmmm...I guess I made a mistake. Mine both attach with 2 screw tabs (45D), so I guess they are not the ones in the photo.

The reason I referenced the photo is the difference in location of the vacuum ports on the units. My old one has the port in the middle of the "hat." The new one has the port on the side of the "hat," like the difference in the photo.

Both parts fit my dizzy. I just don't know what the difference in port locations means.

I think I'm gonna take both parts to the local parts store to be tested. Thanks for the recommendation.

i checked the part numbers.
they are both Lucas 10-5-5, 54425516.

I tested them both like this: with one unit attached to the dizzy, removed the hose from the attached unit, hooked it to the other unit held in my hand, revved the engine. switched units and tested the other. they both operate the same way.

so now my question has changed....

does the little bit of sludge coming through the old one mean that the membrane will fail soon and i'm ready for a new part. or is the sludge a sign of a different problem that will simply damage the new part as well?

i hope it means i can just install the new part and be ready for another 30 years of use!

Kevin, are you sure the numbers aren't 10-15-5?
The sludge is oil/gas that has worked its way down the vacuum tube and collected in the diaphragm. The float may have stuck at some point in time and allowed raw fuel to enter the line, or small amounts acuumulated over a long period. Either way, it'll slowly damage the vacuum advance. Its possible to put a small clear fuel filter in the vaccuum line so you can at least prevent the solid fuel from reaching the diaphragm and also be able to keep an eye on what's condensing in there. MGAs had a small chamer in the vacuum line to collect this stuff. Other cars like Austin Healey 3000s never seem to get any gas/oil in the vacuum line, so it must be a port location issue. That's another resaon to use ported vacuum instead or (wet) manifold vacuum!