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Using the Reverse Servo test port for a Reverse Light Switch on A-466 TorqueFlite
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56D500boy
Posted 2020-02-01 2:17 PM (#593715)
Subject: Using the Reverse Servo test port for a Reverse Light Switch on A-466 TorqueFlite



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I posted most of this in my "PowerFlite To TorqueFlite conversion - Was it Worth it Thread?" but I thought that a separate post under Electrical might help somebody find the info in the future better (maybe)

The basic issue is when you convert a car with Powerflite to Torqueflite, there might be reverse light switch issue. For the Powerflites (at least until 1956), the reverse light switch is a two pin pressure switch installed on the passenger side of the transmission, in the area of the Reverse/Low Servo. For the Torqueflites, at least the early ones, I think the reverse switch was incorporated in to the shifter box as a mechanical switch, activated when the "R" button is pushed it. For my situation, I used a 1673 906 late 56 Chrysler (and Imperial) (and 57 D100 truck) shift box came with a mechanical reverse switch attached to left side of the shifter box:



For my conversion from PowerFlite to TorqueFlite , I was fully prepared to create "patch" harness to connect this Torqueflite shifter mechanical reverse switch and the OE Powerflite reverse pressure switch harness. However, it turned out that that was *NOT* necessary.

One day when I was visiting the transmission shop doing the A-466 rebuild and install, the tech who did the rebuild wondered out loud whether the Powerflite reverse switch (which is a two pin pressure switch, much like the OE brake light switch) would work on the Torqueflite if it was installed on the A-466 Reverse/Low servo test port (which is normally filled with a threaded plug). It took 2 minutes to confirm that the threads on the Powerflite reverse switch were the same as the Torqueflite Reverse/Low Servo test port plug. SO it was agreed, that during the install, my Powerflite's two pin pressure reverse switch would be swapped onto the A-466. And that is what happened. The wiring was long enough (as were all the cables (eBrake and Speedo and Neutral Safety Switch) so it was a really good idea that the tech had. (Thanks Chris).

The reason that this works is because the PowerFlite reverse switch is a pressure switch and when it is installed on the Reverse-Low Servo test port, it is activated by the higher pressure of the Reverse Pump (225 psi or so) but not by the lower pressure when LOW ("1") is engaged. At least that is what the A-466 manual that I have implies (see diagrams below)

Here is what it looks like before the installation:



Here is the Torqueflite after installation in my 56 Dodge, showing the PowerFlite 2 pin pressure reverse switch installed in the Reverse/Low Servo pressure test port:



Here is the factory A-466 diagram that shows the pressures and fluid flow when Reverse is engaged (with the engine running) (around 225 psi at the test port):



Here is the factory A-466 diagram that shows the pressures and fluid flow when LOW ("1") is engaged (with the engine running) (much lower pressures):



Hope that this helps somebody in the future.



Edited by 56D500boy 2020-02-01 2:22 PM
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56D500boy
Posted 2020-02-05 4:44 PM (#593852 - in reply to #593715)
Subject: RE: Using the Reverse Servo test port for a Reverse Light Switch on A-466 TorqueFlite



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UPDATE:

I discovered the other day that the reverse light switch is activated when the transmission is in Reverse (a good thing) *BUT* also in Low ("1") (a not so good thing). I guess that the 90 psi pressure at the test port in Low is enough to trigger the switch. 225 psi is definitely enough.

So either I live with that or create a patch harness and use the mechanical pressure switch on the torqueflite 5 button shifter box *OR* I seek out a pressure switch that needs more than 90 psi to work. Candidates might be the two pin brake light switches. (???)

In the interim, I will try not to use "1" when at a stop light and scare the guy behind me because he sees the reverse light come on in front of him.

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wizard
Posted 2020-02-06 1:44 AM (#593865 - in reply to #593715)
Subject: Re: Using the Reverse Servo test port for a Reverse Light Switch on A-466 TorqueFlite



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I really don't understand why you don't just use the back-up switch in the pushbutton unit Dave?
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56D500boy
Posted 2020-02-06 1:43 PM (#593880 - in reply to #593865)
Subject: Re: Using the Reverse Servo test port for a Reverse Light Switch on A-466 TorqueFlite



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wizard - 2020-02-05 10:44 PM

I really don't understand why you don't just use the back-up switch in the pushbutton unit Dave?


I was just avoiding creating a patch cord between the reverse light switch on the side of the shifter box and the OE wiring. Moving the reverse switch from the PF to the TF was very easy because the OE wiring was long enough to reach the switch on the TF.

We'll see. Normally this won't be an issue (that "1" also generates the back up lights) so I will put the patch cord on the list of things to do but not at No.1

In the meantime I might look for a different switch with a higher activation pressure.

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wizard
Posted 2020-02-06 2:25 PM (#593882 - in reply to #593715)
Subject: Re: Using the Reverse Servo test port for a Reverse Light Switch on A-466 TorqueFlite



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Route two wires from the back-up switch down to the hydraulic switch and connect it in series.
This way you don't modify the original harness and the back-up lights will only light up in R
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1960fury
Posted 2020-02-06 3:20 PM (#593883 - in reply to #593882)
Subject: Re: Using the Reverse Servo test port for a Reverse Light Switch on A-466 TorqueFlite



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wizard - 2020-02-06 2:25 PM

Route two wires from the back-up switch down to the hydraulic switch and connect it in series.
This way you don't modify the original harness and the back-up lights will only light up in R


Correct, this is what I would do. The OE back up light switch/push button mechanism can be considered a non wear part!
I hate hydraulic switches. I too always try to avoid cutting original parts, wires included. I wish more people had that restraint.

Edited by 1960fury 2020-02-07 6:51 AM
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56D500boy
Posted 2020-02-06 3:28 PM (#593884 - in reply to #593882)
Subject: Re: Using the Reverse Servo test port for a Reverse Light Switch on A-466 TorqueFlite



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wizard - 2020-02-06 11:25 AM
Route two wires from the back-up switch down to the hydraulic switch and connect it in series.
This way you don't modify the original harness and the back-up lights will only light up in R


I know how to do it, I just didn't want to add more wires when they weren't really necessary.

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