vacuum modulator question

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Feb 16, 2007 | 04:38 PM

bbgot

Thread Starter

New User

Joined: May 2006

Posts: 10

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vacuum modulator question

I have a 78 bronco w/ a 351/c6/np205 with the stock motorcraft 2150 carb. I recently noticed that the hose coming from the vacuum modulator is just hanging loose. Do I connect this to a vacuum source at the carb or intake manifold? Thanks for any help.

Feb 16, 2007 | 04:49 PM

rjent

Mountain Pass

Joined: Feb 2007

Posts: 152

Likes: 1

From: Truth or Consequences, NM

Quote:

Originally Posted by bbgot

You are probably experiencing high shift points as well. The vac modulator simply needs to see vacuum. Hook it to a straight vac port and you should be good to go. The transmission needs to "know" how hard the engine is working to override the govenor pressure!

Hope it helps

Last edited by rjent; Feb 16, 2007 at 04:49 PM. Reason: spelling error

Feb 16, 2007 | 04:52 PM

kenpobuck

Cargo Master

Joined: Mar 2006

Posts: 2,789

Likes: 5

From: Sand GAp, KY

I'm sure it connects to the carb. Check for a vaccum port that is open. the truck should run better once it is hooked back up as this would fix a vaccum leak.

Feb 16, 2007 | 04:57 PM

bbgot

Thread Starter

New User

Joined: May 2006

Posts: 10

Likes: 0

thanks for the help. this truck had several of the ports on the carb plugged when I got it so I'll bet that one of those ports i the one I'm looking for.

Feb 17, 2007 | 02:16 PM

alxsnmr

Fleet Mechanic

Joined: Mar 2005

Posts: 1,603

Likes: 1

From: St Louis

Actually, most of the late seventies cars that had the c-4 or FMX that I drove had the vacuum port off the vacuum tree shared with the brake booster. That was a direct port off the manifold if I remember right. You will want a port that has constant vacuum not regulated by the carb operation. The tree on my 78 351M comes off the back of the manifold and some people here recommend against using vacuum off these ports because it causes lean conditions in the number 4 and number 8 cylinders.