Vacuum advance kaput??

Billschroeder5842 · Jun 14, 2014

I think my vacuum advance is dead on my 75 road runner with a 400 4bbl.

I put a vacuum tester on the advance and I was not able to 1) get it to hold any vacuum pressure or 2) get the advance to move with the distributor.

My thought is that the diaphragm is broken. Isn't the arm supposed to move when you apply vacuum and fully hold pressure?

Any way to fix this? I DO have another distributor that I pick up tomorrow if this is unfixable.

So, IF I make a swap and the vacuum advance works, what should I notice? The car runs great, but lack a bit of power (compared to my 69 charger anyway)

Thanks!

khryslerkid · Jun 14, 2014

Yes, it's blown. Replace with a new one or one that holds vacuum. You will notice quicker responce in your throttle and smoother accelerating.
You can watch your advance working useing a timing light. Rev up the throttle while watching your timing mark. You got this!

eric383 · Jun 15, 2014

X2 on that although I use the poor mans tester on vacuum diaphragm. Just put a piece of vacuum hose on the advance and suck on it. If it holds vacuum it is good if you keep sucking it is no good. I have had 2 vehicles in the past 3 years with this problem. This is a good thing to check when trying to sort out a vehicle. Good luck.

Billschroeder5842 · Jun 15, 2014

eric383 said:
X2 on that although I use the poor mans tester on vacuum diaphragm. Just put a piece of vacuum hose on the advance and suck on it. If it holds vacuum it is good if you keep sucking it is no good. I have had 2 vehicles in the past 3 years with this problem. This is a good thing to check when trying to sort out a vehicle. Good luck.

I tried both the "suck" and the gauge method---no movement or hold of the pressure.

I pick up a reman this morning for install later today (PERFECT Fathers Day) while watching NASCAR.

Oh, I have put the emissions systems back together--this is a stock car. Will the OSAC value jack up the acceleration portion?

eric383 · Jun 15, 2014

You should notice a little better acceleration, have you tried dialing a little more advance into the motor also? When I see your name this is what first came to mind....
http://en.wikipedia.org/wiki/Bill_Schroeder_(baseball)

Billschroeder5842 · Jun 15, 2014

Successful installation!

The only change is that the timing went from 8 to 12. The motor runs great and idles at 800-850. I'd like to keep it at stock specs but I figure that 4 degrees after 40 years is acceptable.

I took it out for a quick spin-- I didn't notice too much, but that is okay.

Anything else I need to check or do?

A383Wing · Jun 15, 2014

answered on other forum, Bill

Vacuum advance kaput??

Billschroeder5842

Well-Known Member

khryslerkid

FBBO Gold Member

eric383

Well-Known Member

Billschroeder5842

Well-Known Member

eric383

Well-Known Member

Billschroeder5842

Well-Known Member

A383Wing

Well-Known Member

Similar threads