4 Wheel & Off Road – October 2019

42 OCTOBER 20194-WHEEL & OFF-ROAD 4WHEELOFFROAD.COM

COVER SECTION: JUNKYARD SPOTTERS’ GUIDES

JUNKYARD ID OF OUR FAVORITE

MANUAL TRANSMISSIONS

JUNKYARD

MANUAL

TRANSMISSION

SPOTTER’S

GUI DE

T

HE STORY GOES THAT A QUIET OLD LADY TOLD THE BUS

driver going over the alps that she was happy to “stir the oil

with that stick ...” if he wanted to focus on steering

the bus during their trip. We have stirred the oil, or

rowed the gears, a few thousand times since we first

heard that tale. Transmissions take the rotational

forces created by your internal combustion engine

(or, in a currently unlikely scenario, your electric motor) and

multiply them via varying shiftable ratios to help your 4x4

move at different speeds. To put it simply, transmissions make

your 4x4 go.

From crawling in a 7:1 First gear of an old -school manual

transmission designed just after World War II up to 80 mph in

Eighth gear, double overdrive, in the most modern six-speed

manual boxes, we have driven them all. Some are rough and

durable, while others are durable and refined. Each transmis-

sion has its strengths and weaknesses that might just make

it the perfect transmission for your next 4x4. Which are our

favorites? What’s the best for what you have planned? Below

we lay them all out, tell you the good and bad, and help you

identify them for your next 4x4 project. For space we avoid the

close-ratio, non-granny-geared transmissions when possible.

BY Verne Simons

[email protected]

PHOTOGRAPHY HARRY WAGNER

AND VERNE SIMONS

4-SPEEDS (w/granny First gears)

SM 420

Overview: The granddaddy of them all,

sort of. One of the most popular with rock-

crawlers because of the super-low 7.05:1

First gear. This thing shifts like the tranny

in a bread truck. No bang shifts here, but

it’s strong and geared low.

Found In: 1947-1968 Chevy trucks. Was

available for some military application

into the 1980s.

Identification: Cast iron case, cast iron

top cover with large bulge for the reverse

idler gear on the passenger side of the

case. Later versions have webbing on this

“bump.” Case length is 10^1 ⁄ 2 inches.

Ratios: 7.05:1 First , 3.57:1 Second , 1.7:1

Third, 1:1 Fourth, 6.78:1 Reverse.

SM420