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SM420 Transmission for Sale

(2 reviews)
  • Type: Manual Transmission
  • Model: SM420
  • Maker: General Motors (Chevrolet)
  • Torque Capacity: 250 lb-ft
  • Speeds: 4 forward gears
  • Condition: Used


99.5% Positive feedback
  • Consistently receives highest buyers ratings
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Reliable SM420 Transmission for Sale

The SM420 is a heavy-duty manual transmission, introduced into the competition by General Motors in 1947 which lasted for two decades before the production stopped in 1967. This SM420 Transmission for sale at our store was a favorite among off-road enthusiasts and truck owners. The SM420 was also used in the military as well.

Features of SM420 Transmission:

  • Durability and Strength: That makes the SM420 suitable to off-road and other heavy usages because the transmission is practically immune to wear and tear. It is assumed to bear more torque loads and other severe operational conditions as compared to the other components of the car.
  • Manual Control: Similar to most of the manual transmission types, SM420 has the features of direct selection and shifting of the gears. Manual changing is done using a shift stick that is provided on the interior of an automatic car.
  • Non-Synchronized Gears: It comes with a 5-speed non-synchronized manual transmission- the SM420 and has no synchronization for the first gear and the third gear. This means that in gear changes, due to the frequently high Engine Revolutions Per Minute, the driver has to double clutch to synchronize the revolutions of the engine to that of the gears.
  • Simplicity: The appearance of the SM420 is very simple and does not have any of the flash in modern automobiles but it provides a mechanical feel between the engine and the gearbox which people prefer.
  • Off-Road Capability: With time it may be modified for off-road use as it is well built to handle the amount of torque that comes with off-road exercises. 



  • Chevrolet Advance Design Trucks (1947-1955)
  • Chevrolet Task Force Trucks (1955-1959)
  • GMC New Design Trucks (1947-1955)
  • GMC Blue Chip Trucks (1955-1959)

V8 Engines

  • Chevrolet 235 cubic inch (3.9 L) V8
  • Chevrolet 261 cubic inch (4.3 L) V8


The SM420 transmission is renowned for its advantages in various applications:

  • Off-Road Capability: The exceptionally low first gear ratio (7.05:1) makes it ideal for crawling and rugged terrains.
  • Durability: Built to withstand heavy-duty use in trucks, buses, and heavy equipment.

Here at Find Auto Parts Online, you will find the best quality used SM420 transmission for sale at a very reasonable price. Get your SM420 transmission today and experience the difference in performance and durability!

Additional information

Input Shaft Length

6-1/2" with 1-1/8" 10 spline

Shift Pattern

"H" shift pattern, with reverse toward the left side and down

Fluid Capacity

4-5 quarts

Bellhousing to Tailshaft Length

29.9 inches


350 lbs

Gear Ratios

1st Gear: 7.05:1
2nd Gear:3.57:1
3rd Gear: 1.70:1
4th Gear: 1.00:1


1947 Chevy SM420 Transmission

2 reviews for SM420 Transmission for Sale

  1. Jake Hartman

    Bought an SM420 transmission from Find Auto Parts Online for my old Chevy truck. What a great decision! The transmission arrived quickly and was in excellent condition. Installation was straightforward, and it’s given my truck a new lease on life.

  2. Hank Garrison

    Extremely satisfied with the SM420 transmission I got from Find Auto Parts Online. It’s the perfect fit for my classic 4×4 project. The transmission was clean, well-packaged, and exactly as described. Shifts smoothly through all gears and handles the power of my rebuilt engine like a champ.

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Product Q&A

Availability of SM420 Transmission for sale?

Here at Find Auto Parts Online, you will find the best quality used SM420 transmission for sale at a very reasonable price.

Price of SM420 Transmission?

Here at Find Auto Parts Online, you will find the best quality used SM420 transmission for sale at a very reasonable price. Please call or Contact us here.

Is the SM420 transmission synchronized?

No, the SM420 transmission has non-synchronized gears for 1st through 3rd gears. This means that double-clutching is required for smooth shifting between these gears, a characteristic common in older manual transmissions.

What type of fluid does the SM420 transmission use?

The SM420 transmission uses gear oil (often 90-weight) rather than automatic transmission fluid (ATF). It's important to use the correct viscosity and type of gear oil as recommended by the manufacturer for optimal performance and longevity.

How reliable is the SM420 transmission?

The SM420 transmission is known for its durability and reliability, especially in heavy-duty and off-road applications. Its robust design and simplicity make it a favorite among enthusiasts and restorers of vintage vehicles.

Can the SM420 transmission be rebuilt?

Yes, the SM420 transmission can be rebuilt. Rebuilding typically involves disassembling the transmission, inspecting and replacing worn or damaged parts, and reassembling it to meet or exceed original specifications. Rebuild kits and replacement parts are available to facilitate this process.

What upgrades are available for the SM420 transmission?

Upgrades for the SM420 transmission include improved bearings, hardened gears, and aftermarket adapters for mating the transmission to different engines or drivetrains. These upgrades can enhance durability and performance for specific applications.
sm420 transmission for sale
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