Vacuum modulator
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Senior User
Joined: Jun 2007
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From: Springfield, Il
Vacuum modulator
Would a bad modulator allow enough trans fluid into the intake manifold to cause a problem. My 73 390 c6 started running a little rough upon acceleration. Also noticed a slight trans slippage. I pulled the vacuum hose off of the modulator and fluid rushed out. I realize it needs replaced now but could this be my stuttering problem. Vacuum gauge reads a strong 20hg. Thanks
Thread Starter
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Senior User
Joined: Jun 2007
Posts: 394
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From: Springfield, Il
Thanks guys, I had suspected that this was the problem. Never ran into this before. I pulled the hose off of the modulator and plugged it. It idles almost perfectly now. Haven't driven it to see about acceleration until I get a replacement. The one in the trans has an orange stripe. If I cannot find an exact replacement I suppose I will go with a black stripe modulator. What do you think of this idea?
Laughing Gas
Joined: Dec 2007
Posts: 796
Likes: 1
From: Minnesota
They also make adjustable ones that you can use. I bought one from summit racing back in the 1980's for my 73 thunderbird. You can put a screw driver in the end and turn the screw to adjust the shift points. Wasn't that exsensive back then, haven't checked them out lately.
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Senior User
Joined: Jun 2007
Posts: 394
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From: Springfield, Il
Update:
I changed the modulator, it now shifts much better. I found the real problem. A plug wire and burned out at the plug end. I pulled it off, and replaced the suspected wire and installed a spare. Wow, what a difference it made. The truck has never ran better. The connection to the plug had appeared to burn away making no contact to the plug. Thanks for all of the help guys.
I changed the modulator, it now shifts much better. I found the real problem. A plug wire and burned out at the plug end. I pulled it off, and replaced the suspected wire and installed a spare. Wow, what a difference it made. The truck has never ran better. The connection to the plug had appeared to burn away making no contact to the plug. Thanks for all of the help guys.
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