Vacuum Modulator problem?

Clutch, transmission, rear axle

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Vacuum Modulator problem?

Postby Pat Crash on Fri Aug 12, 2011 8:03 pm

New problem just started today.  Transmission is rough when pulling from a stop (different than last weeks problem that I posted on).  I had the engine and undercarriage steam cleaned and that might have done something as this problem wasn't happening before the cleaning.

Problem: When I pull from a stop, I like to press gently on the accelerator, then I increase the pressure to get going.  When I do this the transmission hits pretty hard.  There is no problem when I pull from a stop an accelerate quickly.  On top of this, the problem is intermittent.  Also, shifter on the steering column moves moves a little to the left when I accelerate.

I check the vacuum hoses and everything seems ok - even the hose connected to the vacuum modulator.

Does this sound like the vacuum modulator?

What color modulator do I need for a C6 transmission on a 360 auto? I believe it is the one with a white stripe - this guys video says white http://www.youtube.com/watch?v=UtiY4sfFpxs. I checked on the old one and I could not see the color stripe.
1971 Ford F100 Ranger XLT - 360 with C6 Automatic
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Re: Vacuum Modulator problem?

Postby forrestbump on Fri Aug 12, 2011 8:24 pm

White it is!  Part # C4AZ-7A377B.  Your C6, assuming it's O.E.M., requires a screw in, white stripped, vacuum modulator.  Brown, Purple and Green stripped vacuum modulators are for later year applications and are of the push in variety.
1970, 2WD, F-250, C/S, Dual Tanks, 390 FE (of course), C6, Power Steering, Power Disc Brakes, Dana 60 3.73, Sky View Blue, Ranger XLT

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"One of the greatest discoveries a man makes, one of his great surprises, is to find he can do what he was afraid he couldn't do" - Henry Ford

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Re: Vacuum Modulator problem?

Postby Pat Crash on Fri Aug 12, 2011 8:30 pm

forrestbump wrote:White it is!  Part # C4AZ-7A377B.  Your C6, assuming it's O.E.M., requires a screw in, white stripped, vacuum modulator.  Brown, Purple and Green stripped vacuum modulators are for later year applications and are of the push in variety.


Thank you.  :D

forrestbump - does this sound like a vacuum modulator problem to you?
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Re: Vacuum Modulator problem?

Postby forrestbump on Fri Aug 12, 2011 8:44 pm

Pat Crash wrote:does this sound like a vacuum modulator problem to you?
Well...could be.  Where I'd begin is making sure that your vacuum line is intact and not split or pulled off either the vacuum modulator or the vacuum source on the intake manifold.

Since you pressure washed your under carriage, that was my thought.  Check this FIRST before you buy a vacuum modulator that you may not need.

By the way, also be sure and check that the vacuum line is not plugged with debris/oil/dirt.
1970, 2WD, F-250, C/S, Dual Tanks, 390 FE (of course), C6, Power Steering, Power Disc Brakes, Dana 60 3.73, Sky View Blue, Ranger XLT

1970, 2WD, F-250, C/S, A/C, Dual Tanks, 390 FE (again, of course), C6, Power Steering, Power Disc Brakes, Dana 60 3.73, Wimbledon White & Sky View Blue, Ranger (almost twin brothers!)

"One of the greatest discoveries a man makes, one of his great surprises, is to find he can do what he was afraid he couldn't do" - Henry Ford

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Re: Vacuum Modulator problem?

Postby Donnie on Fri Aug 12, 2011 8:54 pm

Pat Crash wrote:New problem just started today.  Transmission is rough when pulling from a stop (different than last weeks problem that I posted on).  I had the engine and undercarriage steam cleaned and that might have done something as this problem wasn't happening before the cleaning.

Problem: When I pull from a stop, I like to press gently on the accelerator, then I increase the pressure to get going.  When I do this the transmission hits pretty hard.  There is no problem when I pull from a stop an accelerate quickly.  On top of this, the problem is intermittent.  Also, shifter on the steering column moves moves a little to the left when I accelerate.

I check the vacuum hoses and everything seems ok - even the hose connected to the vacuum modulator.

Does this sound like the vacuum modulator?

What color modulator do I need for a C6 transmission on a 360 auto? I believe it is the one with a white stripe - this guys video says white http://www.youtube.com/watch?v=UtiY4sfFpxs. I checked on the old one and I could not see the color stripe.


Pat, when diagnosing a tranny problem the 2 things that you want to watch are;;Is the shift on time according to your throttle position and the quality of the shift , to firm,too soft, or ok.
The harder that you push on the throttle the later your shifts will be, there is a direct correlation between, the later your shifts are the firmer they should be..Check your vacuum line fitting at the manifold with a drill bit in your hand & be sure that carbon is not building up in your manifold. pull you line off at the mod. & check for fluid. Are you using a steel line all the way from the engine down to the rubber elbow?  High pressure H2o could soften your hose?? If you pull the hose at the tranny with the engine at idle, it should run rough..
   I am concerned as to why your shift lever moves..engine mount??? food 4 thought.Donnie
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Re: Vacuum Modulator problem?

Postby BobbyFord on Fri Aug 12, 2011 9:51 pm

Have you checked left engine mount and trans mount? ( since you said the gear selector is moving).
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Re: Vacuum Modulator problem?

Postby Pat Crash on Tue Aug 16, 2011 3:57 pm

BobbyFord wrote:Have you checked left engine mount and trans mount? ( since you said the gear selector is moving).


Changing out all of the engine and transmission mounts this week - Thanks for the tip.
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