Re built C6 trans constantly shifting 3 to 2 back to 3 under slight load

Greg Bourne · Aug 27, 2024

Hi
Just had my C6 re built to hold approx 500 hp. shifts well under load, firm and crisp. But when cruising under part load it will keep shifting between 3 down to 2 and back up to 3 again. It will do this until load comes off and it will stay in 3.
Any ideas of where to start fault finding this?
Thanks

Edit, should note that at this stage no kick down bracket or cable is installed

Barrysmach1 · Aug 27, 2024

Greg Bourne said:
Hi
Just had my C6 re built to hold approx 500 hp. shifts well under load, firm and crisp. But when cruising under part load it will keep shifting between 3 down to 2 and back up to 3 again. It will do this until load comes off and it will stay in 3.
Any ideas of where to start fault finding this?
Thanks

Edit, should note that at this stage no kick down bracket or cable is installed

1st off is 1-2 shift at light throttle at the same speed as before ?

Greg Bourne · Aug 27, 2024

Barrysmach1 said:
1st off is 1-2 shift at light throttle at the same speed as before ?

Yes I think so, it has a 2800 stall, under light throttle it feels the same. Hard throttle and it will shift hard.

Bentworker · Aug 27, 2024

https://7173mustangs.com/threads/general-automatic-transmission-valve-body-info-c4-c6.39375/

I’d read the above, follow the linkage adjustment instructions contained in it. Also would not drive it until you get a proper kickdown rod on it. There is a guy (KickdownRods.com) that can make you one that is correct for whatever intake manifold/ spacer/ carb/ transmission combo you have.

It could be the modulator too, but your transmission needs all of the inputs to it correct and functional for the output to be correct and functional.

Barrysmach1 · Aug 27, 2024

Greg Bourne said:
Yes I think so, it has a 2800 stall, under light throttle it feels the same. Hard throttle and it will shift hard.

Sounds like modulator set to light , you can try turning screw where hose books on 1 full turn to see if helps

will e · Aug 28, 2024

Do you have the kickdown adjusted correctly?

mjlan · Aug 28, 2024

Some information from what I would consider to be a knowledgable source.

I think you may need to play with the vacuum modulator adjustment for your issue.

Bentworker · Aug 28, 2024

mjlan said:
Some information from what I would consider to be a knowledgable source.

I think you may need to play with the vacuum modulator adjustment for your issue.

That is a nice video by Jay at Broader

c9zx · Aug 28, 2024

Long shots; modulator pin length is wrong or governor has a problem. I am NOT an auto trans specialist .Chuck

Re built C6 trans constantly shifting 3 to 2 back to 3 under slight load

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