[william]

Well, I found that my vac advance control is toast. I can blow (or suck, if I am brave) clear through it. My local parts drone says that there is one listing for 74 and earlier, one for 75-76 and one for up to 78 (which is the same as the 74 and earlier). He can't get the 75-76 one, so he ordered in the other one. I will pick it up in the morning and see if it works. Does anyone know what might be different about these controls, or why they were changed for 75-76? Is the parts guy on crack?
william

 

[Chump]

Not sure either..is there a part number on the vacuum advance and what is the part number on the distributor? Is this a stock 440 from a 75 truck?

The most popular distributor used in that era was part # 3755157 and it used vacuum advance # 3656310. You can use this part number to cross over the vacuum advance.
The real way that Mopar looks at this is what engine size/emissions setup..then they assign a distributor to the engine based on this info. Once you have the distributor part number all special parts for the distributor are ordered to fit that number. In the aftermarket, many times they will go by year alone and if there are too many choices they may not try to supply the correct part and thus NOT list it in their books...it also depends on the brand crack that they guy behind the counter uses.

 

[william]

I s'pose it would help if I gave some details...
The motor is a stock 75 440. I did not see a PN on the distributor. The distributor has a reman tag on it though. There is a number on the vac assembly (on the arm) but it is only like 2 numbers and a letter, 95-T or something, I can't remember. I guess I will learn more when I get the new part.
william

 

[Evildriver-3]

Why didn't you just order an adjustable from MP

 

[william]

Why didn't you just order an adjustable from MP

I can't wait the 2 weeks it takes to get any MP parts from my dealer...
Anyway, the difference is the arm. If you look at a pickup from any electronic distributor, you will see on the base plate 2 holes which are used for the vacuum advance arm. My original vac used the outer hole, the new (and most common one) uses the inner hole. Now, assuming that there is no other differences in the vacuum can, I would expect that this would give more vacuum advance, just based on the physics of the setup. If there are other differences, then that theory is wrong. At any rate, the truck does run better now, but I would like to know wht the difference for the 75-76 year. Here are some pics of the two:

 

[Chump]

Some more thoughts....how do we know the original one you have is correct as you said the distributor is a rebuild? Second, the part number I gave you was for 440 74-77 direct from the Factory Parts Manual...the aftermarket parts catalogs should NOT be counted on to be exactly correct..that's why restorers use the factory manuals for restoration. Once again, the vacuum advance part number goes by the distribtor number that is stamped on the side or on the plate, if you want to be technically correct. You will also notice that with any rebuilt part you may not get the same part number as you pulled out. Below is just ONE specification chart from a 77 FSM concerning distributors. Hope this helps as the vacuum advance days were frenzied, to say the least..glad they are history!