C4 transmission shifting issues

[Porter07]

I recently swapped a used C4 transmission into my 66 mustang and immediately found that the car had a lot of difficulty shifting gears. Even when trying to do it manually it will rarely leave the one gear. Me and my brother have been tinkering with the shift linkage hoping that would change it but it doesn’t seem to be doing anything. He did comment after adjusting it that he thought it still felt like it needed more adjustment, which still gives me hope that that is the issue. I was just hoping some people with more experience on this topic could help us flesh out the answer to why it won’t shift gears, even at high rpms. Anything helps and we really appreciate any wisdom you guys have!

Side note: when I mean it occasionally shifts I’m saying that after really rowing through the drive gears it’ll change em.

 

[89ripper]

I recently swapped a used C4 transmission into my 66 mustang and immediately found that the car had a lot of difficulty shifting gears. Even when trying to do it manually it will rarely leave the one gear. Me and my brother have been tinkering with the shift linkage hoping that would change it but it doesn’t seem to be doing anything. He did comment after adjusting it that he thought it still felt like it needed more adjustment, which still gives me hope that that is the issue. I was just hoping some people with more experience on this topic could help us flesh out the answer to why it won’t shift gears, even at high rpms. Anything helps and we really appreciate any wisdom you guys have!

Side note: when I mean it occasionally shifts I’m saying that after really rowing through the drive gears it’ll

Ford C4 & C6 Transmission Trouble Shooting Guide - DIY Ford

Ford C4 and C6 Transmission Trouble Shooting Guide- Detailed Guides Covering Ford C4 and C6 Automatic Transmissions. Don’t miss to read step-by-step guide!

www.diyford.com

Check link. I have little experience with c4s (friend had one in his foxbody)

 

[Realmongo]

Have you already adjusted the kickdown linkage and verified the vacuum supply to the modulator/modulator replacement?

 

[Porter07]

Have you already adjusted the kickdown linkage and verified the vacuum supply to the modulator/modulator replacement

I don’t have much understanding on the subject but when we installed the new transmission the selector shaft head broke off so I replaced that. I tried to leave it untouched but I do worry that I could have messed something up there. Of course I recently discovered that on a 66 c4 the shift pattern is different from 67 and up so when I reattached the linkage it’s most likely misadjusted. I don’t know though. This is new for me so I’m basically flying blind

 

[Porter07]

Ford C4 & C6 Transmission Trouble Shooting Guide - DIY Ford

Ford C4 and C6 Transmission Trouble Shooting Guide- Detailed Guides Covering Ford C4 and C6 Automatic Transmissions. Don’t miss to read step-by-step guide!

www.diyford.com

Check link. I have little experience with c4s (friend had one in his foxbody)

I really appreciate it. Seems like the vacuum modulator might be something to look into!

 

[89ripper]

I really appreciate it. Seems like the vacuum modulator might be something to look into!

Good deal, may not understand it but gotta start somewhere