During reassembly of the engine on the XR7-G, the builder is confused by the dual-advance distributor that I bought to replace the incorrect one. I am sure this is the right distributor and advance, but I am at a loss where to find an engine vacuum diagram for a 1968 4v 390 with auto trans and A/C.
Everywhere I look, there are different variations (non-A/C or manual trans) but I need one for an auto trans and A/C.
If anyone can help, I would greatly appreciate it.
-Matt
That’s what I found before, believe me I searched. There is still no difinitive answer.
Would it be the same as auto with no A/C?
The AC plumbing doesn’t effect the distributor plumbing. They have no common connections.
Just making sure. I thought there would be a reason non-A/C would be specified on the diagram.
Advance port towards the front of the car connects to manifold vacuum the other connects to carburetor vacuum.
Did you Google it ?
My understanding is that only 4 speed cars got dual vacuum advance , auto was single, true of false?
I did a lot of research before purchasing this distributor as it was very salty. In 1968, both manual and auto transmissions came with dual vacuum advance. Here is an old thread - https://www.classiccougarcommunity.com/forum/viewtopic.php?t=1940
I also found a good website online that gives a diagram for manual with A/C and Auto without A/C.
http://www.mustangbarn.com/68vacuum.html
I also asked on facebook and got the same type of diagrams.
My first thought is just to go with the Auto-Non A/C diagram. There is just a nagging though in the back of my mind. If A/C were the same diagram, why would non-A/C be specified?
As of now, I am going to go with the non-A/C diagram. If any new information comes up, I will change it.
A shop manual would help a lot.
I just looked at my Jim Osborne manuals tonight and stuck back in the chassis manual is a diagram that shows vacuum routing for the engine. The problem with that is, it follows the same one as the manual transmission diagram from mustangbarn.com and says manual and auto are the same.
Really confusing. I will need to take pictures at Dearborne if someone lets me see under their air cleaner…
What my self and other big block guys I know over the years have gone by for 1968 was 428 CJ and 390 GT had single diaphragm for auto and dual for 4 speed no matter A/C or not. 390 2 bbl (x code) could have the IMCO smog system. This could have required dual for both trans.
Thanks for the info, but everything that I have read says the 390 GT auto used the dual diaphragm as well.
I am not trying to be hard-headed, but I can’t believe so many reputable sources are wrong.
http://www.mustangbarn.com/68vacuum.html
http://www.concoursmustang.com/forum/index.php?topic=14308.0
https://www.classiccougarcommunity.com/forum/viewtopic.php?t=1940
My 67 390 S code has dual dia. with an automatic. No smog system came on the engine, with A/C.
Is your dizzy the correct part number for your application ?