Why wouldn't a C6 shift downward as the engine RPMs get lower?

Also, why would a C6 shift up too soon, causing the engine to bog down (as in accelerating away from a traffic light)?

 

Might wanna check your kickdown lever and vac modulator. Good luck with it, later

 

The trans shifts fine when shifted manually (a la B&M Megashifter-- ratchet shifter). It just doesn't like to do it by itself well...

 

Okay I would still check the previously mentioned vac modulator or kickdown lever. later

 

Aren't there different kinds of vacuum modulators (different colored stripes)? Which color/kind should I get?

 

You've lost me. The kickdown that goes from your carb/throttle body to your tranny might be out of adjustment. By the book it states to hang a 5-6 pound weight on the lever kickdown have someone hold the engine at full throttle then put a .060 feeler gauge between the throttle lever and adjusting screw. Check or replace the vacuum line from the engine to the vac mudulator if you think it is bad. Try that first before you mess with the modualtor, you might check the fluid level as well. Later

 

when my vacuum modulator went bad I replaced it with a black striped one from a NAPA dealer. This is an adjustable model that some trans shops use around here. The Ford dealer didn't list a black model. It works good though.

 

It is my understanding that the kickdown lever on the drivers side of the C6 is actuated (via the carb) when you stomp down on the throttle, basically used in an emergency situation or accelerating up a hill.

But it is also my understanding that this kickdown lever doesn't really get used unless the throttle is mashed (normal day-to-day, up & down minor hills and accelerating away from a traffic light use).

What I am really interested in with my particular C6 (which I should have made more clear initially) is why is it shifting into higher gears (2nd & 3rd) TOO soon in the power band? My kickdown lever is not even hooked up right now (need a Lokar kickdown cable).

 

C-6's dont downshift like chevy's as you slow down. They go into freewheel mode to conserve emissions and gas. As for upshifts it's the same thing. You need a shift kit and lot's of modifications to the valve-body to get what you are after. The kickdown cable must be hooked up or you are going to burn up the clutches because it also adjusts line pressure at wot.

Have fun you're going to need all the help you can get.

 

Wiild, I'm not asking for anything special.

I just don't want my engine to bog down because the tranny shifts too soon in the power band...

 

On the c-6 I can't remember what sets the point for the upshifts, but it is either in the valve-body or the governor located on the output shaft. If you have access to a schematic of the system it would help you out more than me. As far as upshifts go, the kickdown cable must be hooked up for the tranny to know what throttle position you are in. If it isn't hooked up it will think cruise mode and shift accordingly. As for the modulator valve it does several things. It senses engine load and adjusts line pressure and shift points correspondingly.

I might be wrong about the kickdown affecting the line pressure, it's been too long since I looked at the schematics to remember. but if you want to raise the shift points that must be done with a shift kit. If you have any questions on auto trannies I would suggest calling TCI or B&M since that is all they do.

 

wild
that is why I recommeded genestoner check the kickdown because it is my understanding as well the line pressure is controlled by the kickdown lever as well as the modulator valve.

genestoner
these are the only two things short of a complete rebuild that I know of that you can adjust (well you can adjust the intermediate/ front band as well) or change to control your problem of the tranny shifting too soon. Apparently there is a vac signal or mechanical position out of sync with the motor rpms/vacuum for your tranny to basically not know what is going on so it is shifting when it shouldn't, hope you get it straightened out. If the tranny is shifting well and there is no slipping then throw a modulator on it and adjust or check the band and kickdown. later

 

The C6 kickdown has nothing to do with line pressure..It is not like a AOD that has a TV cable that must be adjusted right to boost throttle pressure..The kickdown rod connects to the Downshift vavle in the valve body..When the rod moves the valve you are directing control pressure to the underside of the 1-2 and 2-3 shift valves..If control pressure in high enough to overcome governor and spring pressure, you get a down shift..Depending on road speed you either get a 3-2, 2-1 or a 3-1 shift..Throttle pressure is boosted or reduced with the vac. modulator on a C6..This can be adjusted to raise shift points slightly.. CW will raise and CCW will lower.. However NEVER back the screw all the way out as you can burn up the direct and foreward clutch assys.. With out boosted throttle pressure the clutches can slip under a high load..The C6 does shift down as road speed decreases.. It shifts from 3rd to 1st as the vehicle slows down..When you are coasting(closed throttle) you have no boosted throttle pressure(from the Vac. Modulator)so the governor will hold the 1-2 and 2-3 shift valves down until around 10-12mph..At that speed the governor pressure is exhausted and the C6 shifts from 3rd directly to 1st..It is so suttle you don't really notice it..

 

Learn something new everyday. Or re-learn stuff you forgot you used to know.

Thanks for clarifying .

 

Excellent work Metro!!!