Adapting a manual column shift to an automatic

[vintage6t]

I’m in the process of repowering my 50 Desoto to a Mopar 383/727 TorqueFlight combination. I’m keeping the stock steering box and column. I’m not a fan of more modern columns in cars of this vintage so one of my tasks is to adapt the stock manual column shifter to the 727 transmission. To accomplish that three things are needed: Connect the shifter linkage to properly move through the 727’s shift detents, create an interlock for each gear position, and create a PRND12 indicator for the dash.

 

Step 1 - Connecting the shifter linkage

At first this seemed simple, just put a rod from the existing shifter bell crank to the 727’s shift lever.  That’s pretty much the same configuration as the stock manual shift rod. The catch is that the 727’s Park position requires the shift lever to move all the way towards the back of the transmission. The low gear position requires the lever to go all the way forward. Using just the stock bell crank results in shifting that is opposite of the normal convention. Park would put the shift lever on the steering column all the way down toward your lap.  Low gear would be all the way up. That configuration would shift the transmission fine but would just be too odd to operate.

 

To reverse the shifting action, I incorporated the no longer used clutch bell crank. That bell crank is now driven by the stock shifter bell crank on one end, and drives the shift lever on the other end. This worked out great in terms of the column shifter controlling all the gear positions and in the right direction.  The transmission itself has built in detents for each gear position so the lever has a positive stop at each gear. The problem is that once in a gear, there is nothing to lock the shift lever into position. An accidental hit of the shift lever can easily move it out of the selected gear. That’s why a gear interlock mechanism is needed.

Edited March 8, 2023 by vintage6t

[vintage6t]

[vintage6t]

[vintage6t]

Step 2 - Gear interlock

To create an interlock I took advantage of the fact that the column shifter has a built-in spring loaded in/out mechanism. In stock configuration this is used to move the transmission between low and high gears. When the shift lever is pulled it basically moves the shift arm at the steering box end of the column in towards the firewall. That same shift arm also drives a linkage connected to the shift bell crank up and down as the column shifter is moved up and down, causing the gear changes.

 

The interlock mechanism itself is comprised of two fabricated components. The first is a peg that is welded to the nut that secures the shift linkage to the shift arm. That means the peg can move in and out with the pull of the shift lever and move up and down as the shift lever is moved through the gears.

 

What’s a peg without a hole? The second fabricated component is a mounted plate with a series of drilled holes that are indexed to each of the transmission’s detent (gear) positions. When the shift lever is released at a given gear detent position, the peg drops into the corresponding hole in the plate. That locks the shift lever at that position. When the shift lever is pulled back the peg comes out of the hole in the plate and the shifter can freely move to another position. Let go of the lever and it will spring back into the hole indexed to the new location, locking the shift lever at that position. Great but how do I know what gear I’m in? That’s why a PRND12 indicator is needed.

Edited March 8, 2023 by vintage6t

[vintage6t]

[vintage6t]

Edited March 8, 2023 by vintage6t

[vintage6t]

Step 3 - PRND12 Indicator

You can buy indicators both electronic and mechanical. The problem with those options is they just don’t fit well with my goal of a stock looking cockpit.  So the task is to make something that looks like it came from the factory.

 

I’ve always had working stock radios in most of my classic cars. The thing is I never listen to them. First of all there’s nothing to listen to on AM and second even with a Bluetooth retrofit I’m still not likely to listen to tunes. I guess I just like to listen to the car and enjoy the driving experience of a classic. As a result I decided to forgo the Mopar 808 radio and use that space for the indicator. Basically, put the PRND12 indicator into the dash bezel for dial and use a factory radio delete plate at the tuning knob and button location. If I ever need tunes I guess it will be a hidden system.

 

To build the indicator, I know that some manufacturers use a cable driven slide mechanism. That seemed like a good solution especially because my indicator is in a location remote from the steering column. I’m only a bit of a pack rat, so a few years ago when I had to replace the electric window track in my Honda because of a broken cable, I hung on to it. That track is basically a slide on a track that is driven by two cables that are wound in and out on a reel to make the window move up and down. I also have 4 or 5 Mopar 808 radios in various states of repair.

 

The idea was to cut the window slide’s track down to size and mount it into the face cover of one of the radios. That assembly would then simply mount into the dash bezel the same as the original radio. I fitted a bicycle bake cable on one side of the slide and a return springs to the other. Pull the cable and the slide moves right, let go and the slide returns to its home position. The tuning indicator needle from the radio was mounted on the slide and I cut a new “dial plate”.

 

To get a stock factory look, the lettering for the PRND12 dial itself has to match the existing gauges. I probably spent 5 or 6 hours looking at online font libraries trying to find something that matched. Slim chance I thought but finally I was lucky enough to find a font that’s probably 95% accurate. It’s called DS-Roundup. If you study it, you can find slight differences between the existing gauges but it’s really just fine.

 

I already knew from making the interlock plate that the spacing of the letters on the indicator is not linear. As you go from Park to drive 1, the spacing on the detents on the transmission get closer together by almost half. To get the proper spacing for each letter I measured the distance between each hole on the interlock plate and directly used those measurements. After laying out the indicator I printed it for testing. The lines in the photo are just registration lines to help with placement and testing and will not be on the final indicator graphics.

 

What remains to be done is to create the a permanent indicator graphics. Most likely painted the same bronze background as the original gauges and then stenciled letters painted on with a mix of white/green blacklight paint. That’s so they will glow at night similar to the original phosphorescent gauge letters. Interesting enough the stock radio backlighting has purple covers over the bulbs so I think blacklight is the right direction.

 

Lastly, I connected the indicator’s cable to the shift arm that the interlock peg is mounted on. I cut up parts of a cable operated bicycle brake to get the cable adjuster and cable clamp. As the shift arm moves up and down it pulls and releases the cable accordingly and on the other end the slide on the indictor moves the pointer over the proper letter.

Edited March 8, 2023 by vintage6t

[vintage6t]

[vintage6t]

[vintage6t]

[vintage6t]

[vintage6t]

[vintage6t]

[vintage6t]

[vintage6t]

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[vintage6t]

[RNR1957NYer]

Hats off to you, sir - impressive engineering and fabrication effort!

[Dan Hiebert]

Ingenuity at its finest! Thanks for sharing!

[D35 Torpedo]

Now that is my kind of solution. Well done!

[Bryan G]

Great job! That indicator is my kind of project. Impressive.

[vintage6t]

Following up on this project. It turns out the most difficult part was creating a PRND12 face plate to match the factory gauges. After many tries I finally figured it out and made one that matches to my satisfaction. 

 

First thing to solve was the faceplate background color. The factory gauges look brown when not in the light. Under light they have a metallic sheen. Starting with a copper blank and many tries of mixed paint color, close but nothing acceptable. 

 

Next I tried a brass blank. I also realized the factory gauges are translucent. Almost like antique brass but without color variation, like a tinted lacquer or varnish. The solution turned out to be clear paint very slightly tinted with black paint. Sprayed on with a air brush.

 

Next was the lettering. Many tries here too. Started by hand cutting self-stick stencils used to apply an off white base color and then hand painted phosphorescent green paint. Those tries all ended up looking home made and trying to correct defects all ended up making it look worse. Not an acceptable method.

 

At this point I knew I needed a machine cut stencil. I already new about Cricut machines but couldn't justify buying one just for this project. Telling a friend about this project, it turns out his wife had just one a Cricut in a raffle. So we used my project to learn how to use it.

 

Bottom line, not too hard to create a perfect stencil on the Cricut. Stencil then used to spray on a white base layer for the letters and then hand applied phosphorescent paint on top. Mission accomplished, it even glows the same as the factory gauges!

[vintage6t]

[DakotaFrank]

Nice!!  Great workmanship.