I've researched all I could and can't seem to find an answer. I bought a remanufactured C6 for my FE Highboy last summer and it's a great transmission spare the fact that the shift points are odd.
If I go from park, neutral, or reverse into 3rd the shift points are too high (around 2,800RPM regardless of load or throttle, and it kicks down far too easy) if I drop down to 2nd gear and immediately up to 3rd again, the shift points go down significantly (shifts at a very low RPM and, but won't kick down unless I fully mash the throttle or manually go down a gear)
To avoid the high shifts, I'll go from park to 2nd then up to 3rd, but as stated earlier it won't kick down unless I bury the throttle, which is very annoying in town and slow driving conditions where it's basically stuck in 3rd unless I intervent and manually put it into 2nd. It does this regardless of trans temperature, duration of drive etc... I can get off the interstate when it's at operating temperature and shift up to neutral and back down to 3rd and it'll shift at 2,800 rpm in all gears until I drop down to second and back up to third to lower the shift points. I've replaced the modulator, messed with the modulator screw full in full out and got minimal results, verified good vacuum at the trans, checked the metal vacuum line, etc... it was a remanufactured unit so it has a new tq converter and (correct type & amount) fresh fluid as well.


Anyone have any ideas? The only things I can think to do are either shorten the modulator pin, or install a shift kit.

 

do you have the kickdown rod adjusted?

 

It was, but the circlip that holds it to the shifter mechanism fell off and nothing changed from when it was on to after it fell off. The kickdown rod makes sence since if it was stuck up, the trans would 'think' it was under heavy accelaration and move shift points higher. Regardless of it being off, if the trans is placed in 2nd the shifts are dramatically lower and all-but refuses to kick down, which makes me pretty certain that it's unrelated to the kickdown rod.

 

The downshift rod should always be up until you push the accelerator WOT forcing it down.
It needs to be properly connected and adjusted.
Adjusting modulator to much can rupture the diaphram in it.
If you manually put the trans in 2nd it won't downshift by itself. If you put it in 2nd or 1st it stays there until you change it.

 

If the shifter goes into 2nd at any point -- the shift points will be dramatically lower;

If the shifter goes into neutral or park during any point -- the shift points will be dramatically higher;

I know the logical question here is "why are you shifting an automatic while driving" and the answer is "it screams in first gear unless I put it into second for a split second and then back up to third so it'll actually shift like it's supposed to." Then, I'll coast to a low speed and go to accelarate and it'll be stuck in third gear, so I have to bump it up to neutral and back down to third so it'll shift on its own without me having to put my foot through the floor. if I decellerate below 40mph it'll slam back down to second and I'll have to shift to second (then back up to third) to lower the shift points so I'm not screaming through town at 3,000rpm at 39mph while stuck in second gear.


I understand that by selecting second gear *and leaving it in 2nd* that it'll stay in second regardless of speed; selecting first *and leaving it in first* it'll stay in that gear regardless of speed... I've attached,detached, and reattached the downshift rod with no changes in shift charictoristics. I assumed that it was the kickdown immediately, but after messing with it, adjusting it, detaching it, reattaching it, I determined that it is not. I then assumed it was the modulator, adjusted it several times, replaced it, verified good vacuum presence and vac line integrity, and determined that wasn't the culprit either.

the downshift lever being off/on has zero effect.

 

Engine load effects shift points which is sensed by the downshift rod and modulator.

What position is the downshift rod in currently? If it is pushed down shifts are going to be delayed. Even if its not hooked up right now make sure its not pushed down any. The rod has to be up(no force on it) in normal operation until pedal is pushed enough to move it down.
Is the modulator connected to full manifold vacuum?

You may have valves sticking in valve body. Could also have a valve in the governor sticking. Governor mostly affects WOT shifts.

 

I'm deployed to the Persian Gulf right now, so I can't really go out to the garage and mess with it I learned to drive around it, but I saw another c6 post and it popped into my head so I thought I'd ask and see if anyone had some input
.
The kickdown is disconnected, and the Modulator is connected via the ported vac switch on the intake (can't remember which nipple).


By governer, do you mean the diaphram in the modulator?
Would dropping the pan and cleaning the valve body be worth while, or would a shift kit likely clear it up since I'd be messing around in that area when installing it?
By the way, thanks for the advice!

 

You will have to get yourself a transmission book if you want to remove the valve body and check it out. Many springs, valves, and ***** in there.

Governor is located in back of trans. You have to remove the tail housing. A book I have shows some of the symptoms you told me as a malfunctioning governor as well as many more things.