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

[Greg Bourne]

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]

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]

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]

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]

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]

Do you have the kickdown adjusted correctly?

 

[mjlan]

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]

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]

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