I need a vacuum advance unit for my 78 L28 dizzy. It's got anautomatic trans. What would work? I'm not looking for an exact match, just need to get the spark a little closer than what the mechanical advance gives.

I was thinking of one from an L28 from 79-81 with any trans?

thx

They are available at the parts store, little pricey, $42 at rockauto.com, might be cheaper in the long run to buy a rebuilt dizzy.

Do you mean a used one? Can you get them in certain advance rates (curves?) what would be about right?

My contact at NAPA tells metere is nada for that engine (75-78, or even 79-83) from any source.

What, and how much, difference is there between the MT and AT versions? just total degrees, or what?

thx

Tomohawk, I'm not certain but, IIRC the difference between the advance curves on a MT and AT distributors are in the mechanical advance mechanisms...not in the vacuum advance pot.

Tom

So what is the purpose of the "vacuum advance" unit? If I put a large amount of vacuum on mine, I could see it moving, and rotating, the sensor plate inside the distributor, so it has to be changing the spark timing. Mine must be leaking or worn out, because t barely moves, and won't hold its position without a large & constant amount of vacuum; more than I think is available normally.

thx

Tomohawk

Black Dragon list one for the 78 manual trans for $59. Total degrees is probably the difference between the MT and AT but either one would probably make a big improvement over not using any.

I do know that the 240 advance unit and the 280 advance unit are not interchangable. They will not physicaly mount up to the wrong distributor and the 240 unit has a spring loaded mechanism that is adjustable with washers.

Whether there is a mounting difference between the 280 MT and AT distributor I dont know.

Anyone else know?

I ordered one from MSA, and then BD, and both said they are NLA. That was back in June.

They are available at the parts store, little pricey, $42 at rockauto.com

That unit is for a MT engine, 75-78, so you think that would work, right? Just making sure. I'd still like to know how much more (or less) advance the MT unit gives versus the AT one. Either way, I hope it will get me back into the power on my L28.

thx

Not sure if this helps much but the factory parts list shows six different versions of the vaccum control.

I spoke with Darryl Reilly before about this, but he has been unavailable lately. I'll keep trying his number. He knows lots of this swell stuff.

Stephen- I can't find my engine microfiche file!

Tomohawk, I'm not certain but, IIRC the difference between the advance curves on a MT and AT distributors are in the mechanical advance mechanisms...not in the vacuum advance pot.

The vacuum advance pot must be adding additional advance to what the mechanical part does. I'm still wondering, in that case, why there are different ones for manual and automatic transmissions, and CA or federal emmissions spec engines. Like Stephen said, there are 6 in all.

Thanks Lance, for the tip about Rock Auto.

I bought a vacuum pod for a 79 AT dizzy, and it hooked up correctly. The engine works fine, but I want to do a tune up (plugs & timing) before I can tell for sure. It seems to be running smoother at WOT off the line; used to run a little rough at WOT from a stop.