The Stovebolt Site Forums The Shop Area Engine Shop '65 C20 4Speed Conversion

I recently got a '65 C20, Original 292/6, longbed, fleetside.
Truck was previously converted from a stock 4-speed to a car(?) 4-speed, with a Hurst shifter. I think this was not an uncommon conversion, as I have seen at least one other '65 with the same set-up. The floor was cut (cleanly) to accomodate the side-mounted linkage so the shift lever sits closer to the driver than stock. Can anyone can tell me what type of tranny I have? Gearbox has the number 3851325 stamped high up on the right side, along with some General Motors Patent Numbers. Standard H-shift pattern with reverse lock-out toward the driver and forward.
What kind of trans have I got?

Google 3851325
http://www.5speeds.com/muncie2.htm


Or more generically
http://go.mrgasket.com/pdf/HURST.pdf

Pages 53-55

Thanks chuck. Do you know if this was a popular conversion for the period? Meaning somebody would have changed trannies to get better driveability, reliability or something like that? Better than the stock trans? Or just cooler than a granny-1st four speed?

By the way: The tranny rubber mounts on the rear carrier are kind of old and squashed showing the usual signs of age cracking.
I can feel the drivetrain jump around slightly through the throttle pedal when I drive. Will worn out tranny mounts change the angle of the powerplant and, likewise, put additional stress on the driveshaft?
What type of replacement trans mounts should I get for this Muncie M20, and who sells them?

A worn out mount won't help anything. Any good auto parts store (yeah - a dying breed) will have a replacement. Take the old one with, but I think old GM mounts are durn close to universal.

Why someone swapped the trans? A hundred guesses, none of which really matter. If it works, keep it. If not, lose it.

Here's a couple of guesses why nthe tranny was swapped. The original 4spd was probably a SM420. The 420 first gear was non-synchro and so low that you had to shift before you got to the other side o the intersection. Not too mention not real easy shifting though better than a 465. The passenger car 4spd is synchro in all four gears and lot easier shifting. Most folks with the heavy duty 4spd don't use first gear, unless they've changed the rear axle ratio. I've only found first gear usefull on very few occassions.
Larry

Thanks Larry.
Looks like these Muncie 4 speeds are used in Hi-Perf cars (Chevelles, 'vettes) so there's still a lot of parts available. This one's in pretty good shape. It's the only thing about the truck that's not original. But, it's a clean conversion so I don't mind. Shifts well, and makes driving the hills in San Francisco a lot easier.

Another (Stupid) question:
How do you drain the oil on a Muncie M20?
I see a filler plug, but no drain plug. Am I missing something? (except a few brain cells, that is)

If you don't want to keep the Muncie M20 make sure you have checked its value before letting go of it. There is more than one car-type Muncie, some are more valuable than others.

These transmissions have far more value than the SM420 that was original.