Three years ago when I took on this project, I knew there would be some hurtles along the way. First and foremost, my goal from the git go was to keep things looking stock, or at least as close as possible. Right off the bat when researching an LS swap, I knew I'd had to contend with two big things if I wanted to keep a stock look. the speedometer and the tachometer. I also didn't want to have to rely upon 3rd party devices OR a tach and speedo change which reduces the size of those beautiful gauges altogether.

My 74 Stingray had both cable driven tach and speedometer-neither of which exist in the LSx architecture. The 4L60e transmission uses a VSS sensor to calculate RPM and doesn't even have a distributor, much less a tach driven one.

I know, some will say "no big deal". Get a later model tach. OK. I have to agree, that WILL work...to an extent. Here is why.




Theoretically, I COULD just bolt it up and leave it alone, however if I did, it wouldn't match the rest of the typeset between the speedo, oil, gas, temp, alt, ext. So that's out, as I want it to remain true to it's surroundings. The typeset is wrong, needle color and design -wrong. Need I go further>

Here's an example. Also note the two holes left and right of center. The distance between the early c3's are spaced different, so a simple gut change wont work either





Here's a side by side




Instead of making the motor mounting holes from the late model electronic to the early cable drive faceplate, I chose good old JB Weld








Once all sides were secured, I let sit overnight before proceeding




Remember those pesky holes that wouldn't line up?




I clipped them flush




Here's a view with the converted electronic tach guts. Note the early design mounting screw holes that don't line up with the later electronic tach motor




...and here it is with a few tiny beauty rings...




Now, your probably thinking we just made it through the worst, right?
Not so fast. In order to keep this looking just like GM designed it, we're not done yet. We need to transfer our bright orange stock needles over to our modded electronic tach...except one problem.

They won't fit.

The spindle diameter between a cable driven tach and an electronic tach from a later C3 aren't the same. So..... I guess it's time to remove the spindle from the late model C3 and integrate it into our much cooler looking original needle that matches her neighbors.




With the later model stainless spindle removed from the late model needle it was time to drill out the tiny brass insert, leaving it intact in the needle and working VERY carefully! (as you'll destroy the needle trying to separate the spindle on the early ones). If done correctly, it will net you a durable press-fit assembly






Here's a good view of the new spindle pilot hole, ready to press in to the old style needle







Even though it was press-fit and tighter than a hatband, I couldn't resist a drop of epoxy for good measure.




Here's a shot of her grabbing a 6800 rpm gear... (Not really. Dunno why, but with the key off, she bings to 6800 rpm. When the key hits the run position, she pops over to zero. Can't explain it, but it's kinda cool




I also kept my 4L60e and used it to drive my conventional speedometer cable...but that's another story!

 

Very nicely done. When putting the later model tach in my 71, I noticed the different typeset. Honestly, I thought I would have to change it, but I don't even notice it now.

My thoughts were to go ahead and change the speedo to the slightly later model to match