Th400 being in 3rd by 25mph

[Hutch998]

I've never worked on an automatic before and really need some advice. My truck is an 86 k20, with a mild built 355. I'm trying to make it more road worthy, and I know it shifts into 3rd at about 25 mph. How do I fix this? Any help would be great!

 

[74 Shortbed]

If you want later shifts you can adjust the modulator valve, remove the vacuum hose and use a small screw driver and give it a 1/2 to 1 turn at a time clockwise and try it, if you can't get what you want out of the modulator then you'll have to change springs in the governor..

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[donnieray]

Yep, mine was doing the same thing. 1 1/2 turns in and now it shifts just right. Most people will install a new modulator and never adjust it.

 

[87scotty]

Ohh thats good to know thank you

 

[DoubleDingo]

Yep, mine did the same thing. Got a new one with the red stripe, and adjusted it until I got the shifting I wanted from the tranny.