Seeking a bit of help from the 1969 428/C6 experts concerning kick down parts.

[cleandan]

I am working on a 1969 Shelby GT500. (This is a factory configured car)
This car has the 428 SCJ/C6 "Drag Pack" option and I don't know what is specifically supposed to be on the carb for the kick down lever adjustments.

Currently the kick down linkage consists of the lever on the primary throttle shaft that actuates the primary float bowl vent stopper and the kick down engagement.

The kick down lever has the standard tube/rod with the recieving lever that interacts with the previously mentioned lever.....but there is no adjustment screw like I usually find used to fine adjust the moment of throttle opening/kick down.

The first lever simply bumps into the pad on the second lever and, other than bending the first lever, there is no adjustment.
Am I supposed to bend the first lever to adjust the kickdown?
There appears to be no extra space to allow for the adjuster screw, making bending the lever seem correct, but I want to be certain before I get to bending things.

I am asking because this car is acts like it needs adjustment here due to the fact it will not upshift into third gear without lifiting the throttle ever so slightly.
I have adjusted the modulator valve from highest to least and have not been able to cure this shift issue....I recently replaced the modulator valve just to be certain and still the same thing.....Both valves checked good with my vacuum tester though.

I have not run the engine past 5,800 rpm to see if it might shift just a bit higher, so keep that in mind, but if I lift, even the slightest, it shifts nicely into third gear and stays there when floored again.

When driving around in modes other than full throttle, from slow to moderate, the trans shifts through the gears well.
It does feel like this transmission has a shift kit in it due to the firm shifts, but on that I am not certain.

Thanks for the help.

[jayb]

Dan, I had a cheap C6 shift kit once that wouldn't shift into 3rd with the engine floored at all.  This was back in the points days, and even with the good Accel points the engine would break up around 6200, and wouldn't shift.  The manufacturer said it wasn't programmed to shift until 6500.  It may be the shift kit that is causing the problem.  Have you been able to confirm with WOT that the lever on the trans is fully depressed?  Those tube linkage pieces can get bent up pretty easily...

[pbf777]

I am asking because this car is acts like it needs adjustment here due to the fact it will not upshift into third gear without lifiting the throttle ever so slightly.

I have not run the engine past 5,800 rpm to see if it might shift just a bit higher, so keep that in mind, but if I lift, even the slightest, it shifts nicely into third gear and stays there when floored again.

When driving around in modes other than full throttle, from slow to moderate, the trans shifts through the gears well.
It does feel like this transmission has a shift kit in it due to the firm shifts, but on that I am not certain.

     My impression based on your comments above are that First:   An "adjustment" to the 'kick-down' control lever is not for the purpose of "adjusting" the point of an up-shift, but rather the point in throttle position in opening that the "Passing-Gear" down-shift takes place.   Secondly:  If your description is accurately presented, in that with "even the slightest" lifting of the accelerator petal it up-shifts, then I would be under the impression that perhaps if anything the kick-down lever is actually mis-adjusted in the direction other than that of your intent.  Thirdly:  Since you indicated that under other low-speed driving scenarios the transmission seems to shift properly, then that sorta rules out the vacuum modulator, hydraulic governor, kick-down valve control, etc.; so I'd probably guess, and since you also seem to be under the impression, that there likely has been a shift-kit installed, or at least somewhere along the way the hydraulic control pressure has been increased in some fashion previously, as that would be consistent with what your experiencing. 

     And also, lifting the throttle from W.O.T. in order to disengage the kick-down valves' hydraulic pressure bump in order to facilitate the shift and still being of the intention to continue an aggressive acceleration rate into high gear is a bad functional process for producing  the best service fife from the transmission!    

    Scott.


 

[cleandan]

Dan, I had a cheap C6 shift kit once that wouldn't shift into 3rd with the engine floored at all.  This was back in the points days, and even with the good Accel points the engine would break up around 6200, and wouldn't shift.  The manufacturer said it wasn't programmed to shift until 6500.  It may be the shift kit that is causing the problem.  Have you been able to confirm with WOT that the lever on the trans is fully depressed?  Those tube linkage pieces can get bent up pretty easily...

Jay, the tube linkage appears to be in very good condition.
Not bent up, no kinks, no marks from being "adjusted" and the bushings on both ends are in good shape and as tight as one would expect.
The throttle opening seems about right too, meaning the kick down engagement is happening in the last 1/5th or so of the full throttle travel, but on this set up there is no apparent adjustment outside of bending the level attached to the primary throttle shaft.
Things appear to be good, but I am simply covering all my options in order to get this set up as good as it can be.
As it is things are pretty good, save for this third gear issue...I have things set and adjusted to make it very good leaving the gear selector in drive...No need to "gate shift" this C6.

My Galaxie (428/C6) was pretty specific with this kick down adjustment.
If adjusted too loose the line pressure would not come up at the right time and things lagged.
If adjusted too tight things would downshift early and stay for much more rpm than I desired.
All of this happened within two turns of the adjusting screw, which I found a bit odd with the general flexability of the linkage itself.
Once I got the kick down in the right position things suddenly became great, and have stayed that way ever since.

[cleandan]

I am asking because this car is acts like it needs adjustment here due to the fact it will not upshift into third gear without lifiting the throttle ever so slightly.

I have not run the engine past 5,800 rpm to see if it might shift just a bit higher, so keep that in mind, but if I lift, even the slightest, it shifts nicely into third gear and stays there when floored again.

When driving around in modes other than full throttle, from slow to moderate, the trans shifts through the gears well.
It does feel like this transmission has a shift kit in it due to the firm shifts, but on that I am not certain.

     My impression based on your comments above are that First:   An "adjustment" to the 'kick-down' control lever is not for the purpose of "adjusting" the point of an up-shift, but rather the point in throttle position in opening that the "Passing-Gear" down-shift takes place.   Secondly:  If your description is accurately presented, in that with "even the slightest" lifting of the accelerator petal it up-shifts, then I would be under the impression that perhaps if anything the kick-down lever is actually mis-adjusted in the direction other than that of your intent.  Thirdly:  Since you indicated that under other low-speed driving scenarios the transmission seems to shift properly, then that sorta rules out the vacuum modulator, hydraulic governor, kick-down valve control, etc.; so I'd probably guess, and since you also seem to be under the impression, that there likely has been a shift-kit installed, or at least somewhere along the way the hydraulic control pressure has been increased in some fashion previously, as that would be consistent with what your experiencing. 

     And also, lifting the throttle from W.O.T. in order to disengage the kick-down valves' hydraulic pressure bump in order to facilitate the shift and still being of the intention to continue an aggressive acceleration rate into high gear is a bad functional process for producing  the best service fife from the transmission!    

    Scott.


 

Thanks pbf777.
I understand the kick down lever is there to increase line pressure when load demands and the physical adjustment is there to set the point when this takes place in relation to throttle position.
But with the increase in line pressure also comes an change in shift point rpm....generally increasing shift point rpm when the line pressure is increased.

If the kick down lever is adjusted too soon (tight) it will increase line pressure earlier than required, which in turn increases shift point rpm....possibly resulting in a shift point that is higher than the usable rpm limits of the engine as built.

A similar thing is happening with the modulator valve where the shofit points are increased with the increased pressure (vacuum) required to activate the modualtor valve.
Simply put if the valve pressure is increased (turn screw clock wise/in) the shift points will be different due to the vacuum signal required to activate the valve.
Turn screw in for higher shift points, turn screw out for lower shift points.

Between the two external adjustments things can be fine tuned, to some extent, to best serve the demands and needs of the engine.

The modulator valve has been proven to be in good order, but no amount of adjustment will alter my third gear, WOT issue.....but I had to start someplace so I included that info in my post because I have been fiddling with the modulator valve in my attempts to figure this out.

The transmission needed a service so it has, just the other day, received a new filter and new Type-F fluid.
I found a fair amount of stuff on the trans pan magnet (donut style just stuck to the inside of the pan) but the stuff on the magnet was pretty indicitave of a rebuild rather than trouble.
The fluid had darkend slightly, but had no bad odor or feel, so it too seemed in order with trans fluid that just needed regular servicing.

Since that service I have been able to drive the car only a little bit (50 miles maybe).....The dang alternator bearings started making noise so I am rebuilding the alternator this weekend pending parts attainment.
In that drive the transmission shifts crisp and clean....maybe psychosomatic, but it does seem to shift better after the service....but ultimately there has been no change in the WOT issue.

Anyway, I'm working on figuring this out while either proving certain parts are at fault, or proving they are still in good order...and one of those items is the "adjustment" of the kick down lever engagement point that appears to require bending of the lever on this set up....But I wanted to check in order to help figure things out rather than assume and mess it up.

[frnkeore]

Have you checked the kick down rod, at full open, for alignment, when at WOT?

[cleandan]

Have you checked the kick down rod, at full open, for alignment, when at WOT?

Yes, all this seems pretty good.
Good rod/tube.
Good crushed ends with good bushings on both ends.
No damage or other visible issues with the tube.
No excess play or travel.
No interference with anything in the travel zone.

[pbf777]

I understand the kick down lever is there to increase line pressure when load demands and the physical adjustment is there to set the point when this takes place in relation to throttle position.
But with the increase in line pressure also comes an change in shift point rpm....generally increasing shift point rpm when the line pressure is increased.

If the kick down lever is adjusted too soon (tight) it will increase line pressure earlier than required, which in turn increases shift point rpm....possibly resulting in a shift point that is higher than the usable rpm limits of the engine as built.

     Yes the kick-down valve is all about raising the internal line pressure above the standard regulation pressure but this is for the most part just an "on-off" switching function and is intended for the most part to be adjusted for "point of actuation".  The obvious intention is to incur a down-shift function (if in something other than first), and holding the gear longer to a higher than the standard up-shift point, this by the resultant increasing of the hydraulic pressure at the modulator valve vs. the sprung and centrifugal weighted mechanical valve function which is attempting to overcome such; but this also raises the hydraulic piston pressure to increase the clamping load on the clutch packs and or band clamping force to resist slippage under the perceived to be greater torque loading from the engine.

A similar thing is happening with the modulator valve where the shift points are increased with the increased pressure (vacuum) required to activate the modualtor valve.
Simply put if the valve pressure is increased (turn screw clock wise/in) the shift points will be different due to the vacuum signal required to activate the valve.
Turn screw in for higher shift points, turn screw out for lower shift points.

The modulator valve has been proven to be in good order, but no amount of adjustment will alter my third gear, WOT issue.....

     Yes, the vacuum modulator is appropriately addressed as a pressure bleed-off valve function and is there to taylor the shifting points under low load, high vacuum scenarios reducing the internal line pressure, this allowing the mechanical/centrifugal function of the modulator valve mounted on the tailshaft to overcome the hydraulic pressure earlier and allowing for earlier up-shifts.  At higher loads leading to low to minimal vacuum sums the vacuum modulator is inoperable; and for example in many competition vehicle applications (drag racing, tractor-pulling, etc.) it is often deleted. 

.....and one of those items is the "adjustment" of the kick down lever engagement point that appears to require bending of the lever on this set up...

     I wouldn't be bending on the carburetor lever for adjustment, as typically the adjustment for the acceptable passing-gear engagement point in throttle position was made by bending the kick-down rod.............some.   

     Scott.

[allrightmike]

cleandan, have you tried running through the gears without the kickdown linkage installed? Might help sort out the problem a little bit through elimination.

[66FAIRLANE]

Sorry to Hijack but while we are on the subject of C6's I have noticed mine getting a little soft on shifts the last couple of times I have driven it. I had turned the modulator down slightly as it was very violent (would bark the tyres when not wanted) so thought I might have gone too far. I went in and turned it back up (in) but the adjuster screw was wet with fluid and 1/4 of a turn made no difference when it would usually be significant. So I think it might be rooted.

It is of course adjustable, screw in, silver zinc with what looks like the remnants of a white stripe. My questions are, how many types are there, what is the difference and is one replacement brand better than another? I want to put on exactly the same type as it has now as it is very well suited. Thanks.

[cleandan]

Sorry to Hijack but while we are on the subject of C6's I have noticed mine getting a little soft on shifts the last couple of times I have driven it. I had turned the modulator down slightly as it was very violent (would bark the tyres when not wanted) so thought I might have gone too far. I went in and turned it back up (in) but the adjuster screw was wet with fluid and 1/4 of a turn made no difference when it would usually be significant. So I think it might be rooted.

It is of course adjustable, screw in, silver zinc with what looks like the remnants of a white stripe. My questions are, how many types are there, what is the difference and is one replacement brand better than another? I want to put on exactly the same type as it has now as it is very well suited. Thanks.

First, if you have trans fluid in the vacuum tube, or coming out of the adjuster port, your modulator diaphragm has ruptured to some extent.
Eventually this will get to the point of the vacuum hose filling with fluid and being sucked into the intake....at which point your heart drops due to the HUGE cloud of white smoke billowing from the exhaust.

This is sort of a good/bad thing because at first you will think your engine is done......Then you find the modulator leaking and your day is all better because now you only need to unscrew a modulator to fix things.

There were a few different modulators back when these were the normal transmissions in use.
Today there are basically two (2) "stock" styles to use and there are a few performance versions you can source from trasnmission parts suppliers.

But your auto parts store, or Summit, or other places, can get you what you need.....just be certain you get the proper style (push in, or screw in)
They are spendy now too, often costing between $75-$100.

You will find the two available stock styles with a green stripe, or a white stripe.
The greens stripe is considered the "standard" modulator.
The white stripe is considered the "performance" modulator.

These work within a certain range of vacuum to best suit the engine vacuum profile.
Both will work, but you may not get high enough rpm before a shift with the green stripe....although it still goes pretty high itself when adjusted in all the way.

Some of the older modulators, with adjustment, could be turned enough to "unscrew" the adjuster.....what happens is the adjuster screw threads unseat instead of being retained by the adjuster screw.
All the way out and the adjuster can fall out, but not usually.
All the way in and the adjuster loses its place on the nut and tends to have a variance at times.
Both can be reinserted and adjustment restablished, but you have to be careful because finding the right spot for thread engagement is sometimes touchy....other times it just screws back in with no issue.
As always, be certain you still have the rod inserted into the modulator before screwing the modulator back into the transmission.

[cammerfe]

Related to a comment made above, it was common, "back in the day" to put a quarter-turn valve in the line to the vac pot so as to be able to easily negate the modulation offered by vacuum. The shift-control governor valve in (the tailshaft housing) was then ground so as to lighten it and thus raise the upshift RPM. (There was testing equipment available at T&C Livonia---if one knew where to look--- so as to be able to play with the valve weight.)

KS