1966 Chateau Slate L78 Chevelle

[OneStopRestoration]

I was able to document many unique things that helps verify the car such as:

Frame Stamped Twice with Vin Seq



Rear End Date Code, and Stamping from May of 66




Harrison Radiator with Date code on the upper tank of D(sorry no picture) and code UN and Lower Tank BP. Side Straps are Dated C(March)





Seems little has been known why GM had a separate tag for the M20 with L78. I think I found why. 2 things that made the L78 muncie M20 different than the regular M20

Stiffer side cover dentent spring, muck like you would see in an M21 or M22


In the following 2 pictures notice the gears are painted differently from the factory(when I cracked the side cover I was like why!?)



I got the slider out and found out why. GM put an M21 slider with the locking groves for 4th gear in the M20 with High performance engine


Trans vin Stamp. Appears to be stamped off line after the car was assembled



Well I hope everyone can enjoy my story and learn as I have. Full Restoration to start later this year! Already have another NOM and plan to have this car back to better than new with a High End restoration

[Big Block Bill]

Great story! Did all 1966 & 1967 High Horse SS-396 Chevelles come with the finger guard on the top tank? My original 1967 SS-396 / M-20 Coupe had the guard on it when I bought it but I thought someone put a GTO or 442 radiator in it prior to me buying it. Keep us posted on your progress.

Bill

[novadude]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: OneStopRestoration</div><div class="ubbcode-body">
I got the slider out and found out why. GM put an M21 slider with the locking groves for 4th gear in the M20 with High performance engine


</div></div>

Are you saying this slider was normally only used with hi-perf close ratio M21/M22 transmissions? I thought the locking feature was relatively common on ALL Muncies from the era.

[OneStopRestoration]

Novadude, My dad is restoring a low miles 67 Chevelle SS that came with an M21. In taking that trans apart we found the same torque locking slider for the 3/4 gear set. We know that cars history back through 2 previous owners, neither of which touched the transmission since new. It had been a mystery to me why GM pulled a speacial part number M20 separate from the 325 or 360hp cars. It became clear in finding the same torque locking slider in my 66 L78 M20. I cant speak to the M22s of the era. Its funny so many people probably never have checked or just toss the originals in the trash during a rebuild. Like i stated this is my theory but I believe its good evidence to represent an additional distinguishing difference.