Long story short, I made a 85 2wd truck into a 4wd, got a C-6/205 outta a 78 F-250, rebuilt the C-6 myself. Got it in the truck, has a 2,800 stall converter, after other fabrication got it started, checked for forward and reverse in shop, good, went along with the rest of the conversion for the last month. Got it outside early this week and took it for a drive and it won't come outta 1st, manually shift to 2nd and it kinda drops like 300-500 rpms, but if you gas it, it just kinda acts like it's still in first or slipping maybe, had it all the way past 5K rpms and still no distinct shift manually shifting or in drive, kinda let it coast and it wouldn't catch 3rd either. Last night I pulled the valve body outta the old 2wd tranny, (this tranny functioned fine) afraid that I mis-installed the shift kit in the 4wd tranny or it had some sticky valves in it from sitting forever. Got the other valve body in and same problem, tried the governer off the 2wd tranny... no change. Re-adjusted the intermediate band to 10 ft lbs, backed off turn and half, no change. I assume since it holds strong in first that the forward clutch seal isn't leaking, my next guess at it is maybe switch out the intermediate band servo assembly from the 2wd tranny? This 4wd tranny came outta a junk truck I had bought for the front axle, was told it worked when it parked years and years ago, but went ahead and rebuilt it before I installed it due to bad looking fluid.

Just replacing this intermediate band servo could fix 2nd but doesn't really explain 3rd, but maybe I can't get it going fast enough in 1st for it to catch 3rd? Otherwise since I bought an aftermarket "red" friction kit I was maybe thinking the band was a little bit bigger and was gonna try adjusting the band adjustment screw in 1/4 turn at a time to see if it made any difference. Trying to do everything possiable before yanking the tranny all the way back apart and even then I wouldn't be sure what I'm looking for since looking at the clutch and band chart for the C6 there is no common clutch/band for 2nd and 3rd that would cause the issue.

Any suggestions or experience with this issue would be greatly appreicated. Thanks

 

Check your vacuum at the modulator and check your kick down linkage. You should have around 15 to 20 inches of vacuum at the modulator and it should drop as soon as you press the throttle. The vacuum should be routed to manifold vacuum on the intake.

 

The engine in the truck only pulls about 10" of vacuum at idle, so it's diffently low there I assume. I had the engine in it to test it out though when it was 2wd and everything functioned fine other then the factory torque converter causing issues with the cam I have. The kickdown isn't hooked up and never has been (when it was 2wd), it was manually shifted before and worked fine. As far as the vacuum line goes I didn't have my vaccum gauge at home last night, but I did stick my finger over it just to verify (running through the trouble shooting in the Ford Shop Manual) it had some sort of vacuum since none of that stuff was ever messed with and traced the vacuum line back to manifold looking for a pinch or something I may have caused swapin stuff around, didn't see anything, but I'll know more when I bring my vacuum gauge home from work tomorrow night.

 

Did some more tests:
1st: Switch the intermediate servo with a known good one: No change

2nd: On the test drive I noticed (especially on downshifts manually) that the tranny is shifting, so it must be slipping in 2nd and 3rd, b/c power braking in manual 2nd it goes flying past the stall up to like 4K rpms +

3rd: Tightened up the intermediate band a 1/4 turn: No change

4th: Did a main pressure test: Specs I found at idle for D,2,1:55-95 R:85-145Part throttle:100-120 R:160-185 WOT:165-190 R:250-280

My readings:
Idle: D,2,1:100psi R:160psi
Part Throttle (2K rpms): D,2,1:75psi R:145psi
WOT: I couldn't hold the brakes on the thing enough to keep it from going through the garge door, but from what I saw I wasn't making good psi, it was coming up, but not within spec.

5th: Checked vacuum at the modulater. 9" at idle and 17" off idle, so there is good vacuum there (good as it's gonna get with that cam in the motor anyways).

So now it seems I'm dealing with a slippage issue more then a shift issue I think. Why are my pressures good at idle but fall off above it? Gotta be a bad seal or something somewhere I would think, but where since reverse has the same symtoms? I would doubt it's in the clutches, so maybe the pump is junk since main pressures are low across the board?