C4 help, wont shift to 3rd gear

[drroy]

in process of 3 year frame off resto, I have a C4 transmission assembled from a busted C4 that came with truck, and "working when removed" 2wd pan fill from van or pickup. finally at point where truck is assembled enough to test tranny and it will not shift into 3rd gear. Engages in reversed fine. When in D, engages 1st, does not up shift, coasts when let off gas. 2 position will start in 1st gear and upshift to 2nd, 1 engages 1sst gear.

I have scoured the internet trying to find solution, to cut down on some common Q's, issues, here is what I know.
-transmission fluid level is where it needs to be
-linkage is fine, valve body is seated where needs to be, as is kick down lever.
-kickdown (cable on my build) is fine , not hung up,
-all new seals, clutches, steels, thrust bearings, endplay in spec
-pin is in modulator, modulator is seated fine, modulator opens completely at around 20inHg,
-manifold vacuum is low at 12inHg, measured at hose where it attaches to modulator (still need to tune holley carb)
-putting shorter pin in modulator to account for missing vacuum (8inHg) does not change shifting issue
-switching valve body to a another "sold to me as working VB" results in the same issues
-clutches, servos, bands all engage as they should when air tested.
-governor does not flutter when air tested
-the governor in there now is from a "working when removed" tranny, I did not go through it though. Rest of tranny looked fine, just old fluid, nothing in there led me to believe it had any issues.

I'm 3 years and ~$30K in. just want to drive this thing. Please, any help is appreciate. I'm at the point that next step is to send it to a local rebuilder.

 

[Viperwolf1]

The valve behind the modulator and pin might be in backwards.

 

[Pa PITT]

... OK I don't know squat about this .. but a lot of the regulars will read my post so that might help you..
.... But what I do remember about these C4. I HAD A PARTS STORE back in 1967 until 1995.. So back in these Bronco days . I had a trans man that thought he was Gods gift to the C4... wELL HE FIXED ABOUT 1 OUT OF 4 WITH OUT HAVING TO GO back into them.
... He always said the biggest problem with C4's was you couldn't get the Valve Body clean enough . He said any particle of dust kept them from working.
.. SO THAT ADVICE IS FROM 1970 BUB JURDON'S BIBLE. .
... BUT I've alway remembered clean every thing twice .. Any thread will stick a valve & keep it from shifting . Good Luck .

 

[drroy]

Pulled apart valve body last night. Looks like I had transition valve and transition valve spring in wrong order. Some of the valves felt a little sticky but moved without much effort. Will clean up Valve body and try again.
Hoping, but not sure this will fix it. Because I swapped in a valve body that I never touched and was supposedly working and had same issue. It will be a few days before I can do it, but will keep my fingers crossed

 

[drroy]

Pulled the transfer case today, as I did this the output shaft came out a few inches. Ultimately I was able to pull it all the way out......that sucks. The C clip in front of reverse ring gear should prevent that. So I removed transmission and that c clip was in place, I didn’t forget it. It must not have seated, I hope. It was the smaller of the 2 C clips, and the one behind governor was in place and seated.

I think with C clip not in place on the output shaft it was able to move back and the groves in governor distributor became misaligned with holes in housing. Regardless went through entire transmission again. Everything looks good. No visible damage on anything from that clip not seating.

Thanks to some advice from ford muscle forums I purchased a product called superior bench buddy. It’s a set of brushes to polish the bores in valve body and governor. I used 600 grit on the valves in a drill, cleaned with mineral spirits and compressed air. Valve and governor went back together with every thing sliding in their bores without the least bit of resistance.
Tomorrow will put transmission back in. If is still doesn’t shift into third, then I give up. I’ll just never drive faster than 35mph:-[

 

[drroy]

Yep, that was it. Transmission working fine now.....the c4 transmission is really quite simple and easy to rebuild, but unfortunately is also easy to screw up.

 

[sanndmann3]

Glad you got it worked out. C4 is a really sweet transmission. can be made to handle a lot of power.