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How does kickdown switch fail?


fordmerc

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Second kickdown switch is failing.A bump in the road may knock the car out of overdrive, sometimes it just won't go into overdrive. Bypassing the switch solves the problem. I replaced the original with a "refurbished " one, but problem has recurred  after 500 miles. What  inside the switch fails? Is there any repair I can do?

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Which OD or switch do you have?  R9s use a two terminal switch and R11s use a 4 terminal.  In both cases the switch has a normally closed set of contacts which open when the plunger is depressed to break the ground connection coming from the governor to the relay coil causing the relay to drop out and solenoid to release.  

 

In both systems, the ground for the ignition cutout comes from a set of contacts in the solenoid. The difference between the two systems and switches is in the R9 there is a second relay in the box and three sets of contacts in the ign cutout circuit. When the the kickdown switch releases the power relay and solenoid, the power relay dropping out also closes one set of contacts which connects the ground to the coil letting the engine miss and release torque so the solenoid and OD can drop out.  The second relay drops out after a few milliseconds to open its contacts and ensure the ground connection to the coil is broken and engine does not stall in case the set of contacts in the solenoid have not opened in time.  In the R11, as the first set of contacts on the kickdown switch opens to release the relay,  the plunger continues travel to close a second set of contacts on the switch to complete the ign cutout circuit causing the engine to miss and release torque so the OD can drop out.  There is no secondary relay or contacts to ensure the engine does not stall.  That timing is determined entirely by the action of the R11 solenoid opening its set of contacts and breaking the ground to the ign coil. 

 

Possible failure points in the switch is dirty or oxidized contacts, a warped phenolic contact support piece inside the switch resulting in a poor connection in the switch, improper adjustment so it is too far down and the switch plunger and internal slide contact is being forced when  the accelerator is pushed to the floor for kickdown and is damaging the switch.

 

The two terminal R9 switch is harder to come by and AFAIK, you will need to find the Packard item or open and clean or repair yours.  There is a modern 4 terminal universal replacement switch available at Napa which works well in the R11.   Except for having a longer threaded adjustment and mounting stem it looks very much the same as the original pre 51 rectangular R11 switch.  It will also work using only the set of contacts nearest the plunger for the R9 but will not look correct.

Edited by HH56 (see edit history)
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I have an R9 OD unit. The current switch looks like the previous one (?original). I am pretty sure the problem is in the switch since bypassing it  solves the problem . It sounds like opening it is the proverbial can of worms. I can readjust the plunger first. I'd be willing to try the NAPA item, since I'm OK With the looks and it can be returned to original easily.

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The Napa item is an Echlin OD6284   https://www.napaonline.com/en/p/ECHOD6284 currently around $25.  It's downside is the extra long mounting stem may need some fabrication and spacers due to the short distance between the accelerator actuator and plunger when mounted in the Packard bracket.  You also don't need the extra two terminals on an R9

 

There is a less expensive 91042 Cole-Hersee switch available from Ebay vendors  http://www.ebay.com/itm/Cole-Hersee-91042-SPST-Normally-On-Universal-Push-Button-Switch-10A-12VDC-/252988357868?hash=item3ae747fcec:g:oN8AAOSwtGlZFfEw&vxp=mtr  which is more in line with the R9 switch.  Cole Hersee lists it as a universal OD kickdown switch in their catalog as well as being able to be used for other functions but I have not tried one to know if or how well it fits the bracket.  Downside is it has different terminals and would need a change to the wiring although you might be able to rig up something using a small terminal strip or screws and nuts so you didn't need to modify the original Packard terminals. There is a 91042-05 model listed in the catalog as having screw terminals but on a quick search it seems to be harder to find or may no longer be available.  

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