Transmission Question
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Junior User
Joined: Dec 2011
Posts: 91
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From: Dallas, TX
Transmission Question
77 F-150, 400cid, C6 tranny. Truck is idleing at about 700rpm. When I put it in gear, D or R it shifts super hard. The truck actually lurches forward and it makes loud noise. Any suggestions?
Thanks
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Elder User
Joined: Oct 2009
Posts: 871
Likes: 1
From: New Albany, MS
If it engages harshly, that can often mean the tranny has excessive backlash. A lot times it will make a thud type of sound and chirp or make other strange noises in reverse.
If its a shifting problem it could be lots of things. Easiest of which being a malfunctioning modulator as mike suggested.
If its a shifting problem it could be lots of things. Easiest of which being a malfunctioning modulator as mike suggested.
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Junior User
Joined: Dec 2011
Posts: 91
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From: Dallas, TX
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Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
Checked the vacuum line and found the PO put a "T" in the vacuum line going to the distributor, and had the modulator running off it. I was told that this was wrong and the tranny needed vacuum coming off the intake. Removed a plugged line from the intake and hooked it up. No more shifting problems.
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With no vacuum signal, the modulator "thinks" you're at wide open throttle and increases the hydraulic pressure to the max. making for a very harsh engagement.
Glad it was something simple, easy and cheap to fix
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