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  Mustangsandmore Forum Archive
  '64 1/2 to '68 1/2 -- The Classic Mustang
  Intake Manifold Vacuum "tree"

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Author Topic:   Intake Manifold Vacuum "tree"

Posts: 916
From: Tupelo, MS - USA (CA temporarily)
Registered: Jan 2005

posted 01-14-2006 12:17 AM     Click Here to See the Profile for SkinnyMan        Reply w/Quote
I'm looking for the vacuum "tree" on the back of the intake manifold for 351W. On the motor I took out it is a four branch. Small - 1 capped, 1 runs forward to distributor and thermostat housing. Large - 1 for FMX transmission, 1 for power brake booster. Can't find part or numbers in NPD or my books.

Also, is there a vacuum conneciton needed for AOD?


Tupelo, MS

Thank you, Thank you very much!

Scott H

Posts: 1480
From: Chicago area
Registered: Mar 2005

posted 01-14-2006 06:31 AM     Click Here to See the Profile for Scott H        Reply w/Quote
You don't need one for the AOD, it is shifted via throttle position and the throttle cable adjustment is CRITICAL.

The piece on the thermostat housing is called a Ported Vacuum Switch. In theory it is changing the vacuum signal based on temperature of the engine, but most likely it isn't working correctly if there are only two lines attached to it.

Does your distributor have two vacuum lines? The one on the front is to advance the timing, the port on the rear is to retard the timing and is for emissions purposes. Check where your vac lines go from the thermostat housing.

You don't want a vac line going directly from the intake to the distributor. The distributor vac line shouldn't have constant vac to it, that would defeat the purpose of it advancing the timing (the timing would always be advanced). Run the distributor line from the ported vac nipple on the carb instead of the thermostat housing. To find out which one this is use a vac gauge and check the carb connections at idle. One of them should have zero vacuum, but as you increase the engine rpms the port will open up to give you vacuum. This is the signal that tells the distributor to advance the timing.

If you set it up this way and if you are using the AOD, the only vac connection you will need on the intake is for the power brakes. For this you could get a brass fitting that is 3/8" pipe thread on one end to go into the intake and a 1/4" or 3/8" barb on the other end for the booster hose. These are readily available in the plumbing section of your local hardware store.


Posts: 8198
From: So. Fl.
Registered: Aug 2000

posted 01-14-2006 09:54 AM     Click Here to See the Profile for mellowyellow        Reply w/Quote
Got a quesion re AOD. Ron Morris Performance, a conversion parts supplier, and a few suppliers of AOD conversion stuff, list a "conversion wiring harness"-goes from the trans to the the original neutral safety witing hookup on the firewall, that in turn goes under the dash. Anyone used it?

Going with Edelcrock carb, and a dist with a single line vacuum advance. Don't have the original 68 dist. Have a regular 66-7 one with a steel gear-running an 89HO.
Had planned on EFI but decided against it. This project got derailed when I did another car in between. Car being used for this is a 68 cv. Have the Lokar TV cable, crossemember from NPD, which is a Ron Morris piece, and a Windsor-Fox shift rod. Trans is a Lentech setup to use original shifter. My understanding is that original front yoke can be left on driveshaft by cutting an inch off it. Rear will have to be cut as it was originally with an 8" rear-now running a 3:25 9" open.

[This message has been edited by mellowyellow (edited 01-14-2006).]

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