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Question,

I have a 1986 chev big block engine with a 4 barrel on my motor home. If I am driving 45 miles an hour or just under, the passing gear will kick in. But If I am doing 50 it won't kick in. How would I go about changing this so that it would kick in at 50 or higher. Thanks again for your help. JackOak
 

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You can't change it.. at least not easily. If your tranny has an adjustable vacuum modulator on the case, it can be adjusted, but be careful.

The tranny is tuned so that it shifts up when the governor reaches an RPM at which the 454 doesn't make any more power. It also won't shift down via the vacuum modulator past a certain speed if the RPMs would be too high... in your case above 50. If its out of whack, then you can correct it by altering the vacuum modulator. If its operating as planned, all you'll be doing is overrevving the engine and you'll lose speed and possibly damage the engine. My 454/TH400 is the same way, but I have 2.73 gears, so my speed at which it will no longer downshift is about 63. If I'm going 65 and I floor it, it won't downshift which is a darn good thing, because that would put it at about 6000 RPM and my 454 stops making good power after 5500.
 
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