John:

Re-read Broader's answer.  The FMX kickdown is a mechanical off/on switch.  Nothing to do with vacuum.  Vacuum is the modulator's signal.  You can always delete the kickdown rod, and when you want to downshift, manually move the shift lever to 2 or 1.

John

John - "The Hoosier Hurricane"

Vacuum is 19-20 at idle, 15-18 in gear, or crusin down the road.

This is the reply from Broader Perf:  "The FMX kickdown does have much less travel than the FOM. Think of the kickdown as an on/off switch. It should only depress and WOT. You bell crank may not work for this. You will have to modify it Im sure. If it does not want to work for you you may need to try a Lokar kickdown kit or something similar. The FOM used the bell crank to sense throttle position. The FMX uses the vacuum line to sense throttle position. I would recommend disconnecting the kickdown until you can rig something up."

I assume it supposed to read, it should only "depress at wide open throttle" - Wouldn't 0 vacuum mean that the carb is at wide open throttle?  Could it be that the secondaries are opening early before the primary barrels are open all the way therefore making the engine think it is at full throttle - would this make sense since I have a 570 cfm carb which is clearly more than my 312 is pulling in?

If I'm wrong I might just have to create some custom linkage...

- John

John: Lake Forest, IL



'57 Fairlane 500 - Looking better every day.

You don't have a big ol' vacuum leak somewhere do you?

It could be assisting in lowering the total manifold vacuum.

 
 Steve Metzger       Tucson, Arizona

Thanks, you all have been extremely helpful on this, especially you John...  (I've probably made it a little harder on myself since I'm researching FOM shift linkage adjusting, but trying to apply it directly to the FMX.)

Based on what I've learned is it correct to assume the following:

1) The modulator controls the up shift and reads the engine vacuum to determine load (0-20 on vacuum), and so if it reads 0 it will hold out the gear until a determined rotational speed (I think 40 mph in 1st, 60 mph in 2nd???)  Hence the reason the car wouldn't shift, when I didn't have the vacuum hooked up; it thinks I've got the carb fully open.

2) Because of the existance of the modular in this application the kickdown is NOT a positive yes or no on the down shift...  The position of the kickdown in its path length determines how hard of a down shift is required?   The down shift will always occur at 0 vacuum,  but the kickdown all the way up would mean no down shift (what happened when I took the rod out) , and all the way down would be as hard as possible.

3) Then depending on the rotational speed of the trans, it determines what gear it should be in using the 2 items and variables discussed above, and then at 60 mph in 3rd gear, it is beyond the range of 2nd gear and therefore will not downshift.

So with all that in mind, my trans / linkage would be all functioning correctly if using the FOM - which is why I had no problems before the trans swap.  The issue is that because the vacuum drops out to 0 before full throttle, the modulator thinks I'm at full throttle and engages the shift.  (Thanks if you've made it this far through the post :hehe 

If all the above is correct, is there a reason/problem that I'm dropping vacuum pressure to 0 before full throttle?  Would it be that my secondaries are opening too quickly? 

In regards to adjusting the modulator, you're saying that would only change the timing of shifts occuring under normal driving (shifts occuring above 0 vacuum)?  So it wouldn't have any effect on the type of shifts I'm discussing.

If I'm wrong above I'm going to be really lost , so hopefully it all makes sense.  Thank you as always, all comments appreciated. - John

P.S. The tach/vacuum/oil pressure/fuel ratio gauges have been instrumental in all of my problem solving - I would highly recommend any of the above to anyone.      

   

John: Lake Forest, IL



'57 Fairlane 500 - Looking better every day.

John:

Try to think of it this way.  The kickdown rod is also a throttle pressure rod.  What it does is tell the transmission how hard you are pushing the throttle, so that it knows how hard to make the shift.  Light throttle, low pressure, soft smooth shift.  Heavy throttle, high pressure, firm no-slip shift.  The vacuum modulater tells the trans when to shift, based on engine load (vacuum).  Typically, you adjust the kickdown rod by road testing after you make the initial adjustments.  I ususally shorten it about 3 turns, verify no kick down, then lengthen it a turn at a time until I get kick down.

Also, many FMX modulators are adjustable.  Pull off the hose and use a pocket screwdriver to turn the screw inside the hose nipple.  Clockwise adjustment puts more tension on the modulator spring, making the shifts occur later.  Counterclockwise reduces spring pressure, making earlier shifts.  These are part throttle shifts, not full throttle.

John

John - "The Hoosier Hurricane"

I have both, because that's how the trans arrived at my door...  (bad reason I know, I don't like accepting things "just because") - I believe because of the configuration the vacuum modulator is necessary (the trans doesn't shift without it), but when I drove without the kickdown, it seemed that the trans wouldn't down shift...  All advice or suggestions appreciated.

- John

John: Lake Forest, IL



'57 Fairlane 500 - Looking better every day.

I'm glad this thread opened up some heavy discussion on setting these linkages properly.  To eliminate any confusion, I am not running a stock FOM.  I have a modified FMX trans.  I'm using the FOM bellhousing/tailhousing/outer lever arms, and then a number of FOM internal components inside an FMX case.  This was custom built by Broader Performance.

I adjusted all the linkages using the screw driver through the holes to line everything up properly.  I know my springs are not original, but after much testing I don't believe they are affecting the way the kickdown should operate.  In my attached picture I added points D (wide open throttle), E (point at which carb reaches full throttle), F (bottoming of kickdown).  When pressing the accelerator all the way down, the carb opens all the way, and once it stops, the kickdown plate continues to rotate down just a shade farther before bottoming on the kickdown rod.   If I understand correctly this is how it is supposed to work. 

After a lot of driving taking careful notes of the conditions at which the trans down shifts, I've noticed a trend.  It downshifts when the vacuum hits 0 (no matter what speed, as long as I'm below 60 mph), regardless if the kickdown lever is bottomed (at point E or F) or not.  If I take off the kickdown linkage and drive, it doesn't down shift at all.  So I would have to believe that it would be an internal issue in the way the trans was built.  It is looking for the lever to be pressed and the low vacuum but it isn't requiring the kickdown be pressed fully...  Does this make sense?

I think the only thing I could do would be to have to build some sort of secondary kick down similar to the positive stop that would not move at all until the pedal is fully pressed.  Any thoughts always appreciated. 

- John

Edit: Second thought - I do have a 1" carb spacer...  could this be affecting the amount of travel it takes to hit full throttle.  Maybe my point E should be 1/2 the distance that it is???

2nd Edit:  Would my secondaries opening too soon be creating the problem of the vacuum crashing to 0?  If i remember correctly from a post by Ted, with the vaccuum secondaries they only open as much as they need???

John: Lake Forest, IL



'57 Fairlane 500 - Looking better every day.

Brody -

Thanks for the tip about the washers - it raises up the "B" shaft pivot in short order. I've got some 1/8 strap around to make a common spacer - thick enough? I have to admit I was considering getting a big crescent wrench on the bracket and bending it up a bit. Old habits die hard.......

Did you adjust the spring hanger down (after you moved the bracket up) to lighten the return pressure a bit? Surely there's something I can bend on there.....

 
 Steve Metzger       Tucson, Arizona

This is where my problem lies - points C-A-B fall too close to a straight line - and the return spring is forcing A to go up above C.

I'm thinking that I can get a little mechanical stop to fit on the back of the block. It will then be the adjustment that sets the pedal height and the return spring can be fairly stiff. Extending the throttle rod and the original pedal adjustment link will move A down out of line. But yes, I see - it may be that the pressure control rod set-up will be too close to kickdown for comfort.

 
 Steve Metzger       Tucson, Arizona

Steve:

Is the pivot of the bellcrank worn to the point to allow the carb lever to toggle over?  If not, the positive stop looks like the safest solution.  Lengthening the carb rod would stop the toggling over, but full throttle would probably not happen.  I don't think the change in throttle pressure would be enough to matter at cruise, as long as it doesn't downshift too easily.

John

John - "The Hoosier Hurricane"