Willis MB.pdf

The American Society of

Mechanical Engineers

THE JEEP MB

An International Historic Mechanical Engineering Landmark

July 23, 1991

Jeep House, Toledo, Ohio

The Jeep

Born of Necessity.

speed transfer unit. Its engine had to be capable of 85 foot-

pounds of torque. It also required a rectangular body, a

fold-down windshield, three seats, and blackout lighting.

Original weight restrictions were a low 1,300 pounds. The

vehicle needed to operate from 3 to 50 miles per hour, and

the wheelbase was to be 75 inches (eventually lengthened

to 80). It also had to carry a 660-pound payload including a

.30-caliber machine gun.

These were the specifications sent to 135 U.S. automotive

firms on July 11, 1940. Bids were to be received by July 22,

just eleven days later. Due to the war then underway in

Europe, the rush was on.

Two companies responded initially: Toledo-based Willys-

Overland Company and the American Bantam Company

of Butler, Pennsylvania. (Ford Motor Company’s bid was

accepted later.)

The original Jeep vehicle was the answer to the U.S.

Army’s call for a light, four-wheel drive, general-purpose

vehicle and scout car. For years, the motorcycle and sidecar

had been deemed unsatisfactory. It was a call that, as of

March 1940, had attracted only a two-person vehicle

known as the “Bellyflopper,” a small four-wheel drive

vehicle that required the driver to lie on his stomach.

Within months, the Army’s search for the “perfect

vehicle” would lead to the Jeep MB.

Specifications for the vehicle were demanding. It had to

have four-wheel drive with a front driving axle and a two-

Jeep MB model in front of Jeep House, Toledo, Ohio.

® MB.

Bantam developed a prototype first, the “Blitz Buggy,”

which was delivered in two short months. It was the work

of Bantam’s designer, Karl Probst. After 20 days, the Blitz

Buggy was accepted, and Bantam earned a contract for

70 more. The first Bantam vehicles were field-tested by

Colonel (later General) Dwight D. Eisenhower.

Spurred by Bantam’s success, Willys-Overland, under

chief engineer Delmar Roos, continued to work on its

prototype, the “Quad,” so named for its four-wheel drive

system. By November, the Quad was ready.

It was symbolically pictured first on Armistice Day,

November 11, 1940, and arrived for testing ten days ahead

of the Ford model.

Unfortunately, the Quad was 250 pounds too heavy. First

thoughts were to replace the powerful Willys engine, an

engine Roos had been designing for years.

“The problem that confronted me,” said Roos, “was

whether or not we should redesign our pilot model to meet

this weight specification and stick to the Willys-Overland

engine, or simply go out and buy a Continental engine as

Bantam was doing and redesign our vehicle.” In what

proved to be the correct decision, the engine stayed.

The vehicle was taken apart piece by piece. Each part was

evaluated with respect to weight and whether a lighter

material could be substituted. Bolts that were longer than

necessary were trimmed, and other modifications were

made. For example, just one coat of paint was applied. The

refined vehicle made the weight restriction by seven ounces.

In the end, all three prototypes were similar in design,

with the Willys-Overland entry being the most powerful.

In fact, the Willys 105 foot-pounds of torque not only

exceeded the requirement, but also dwarfed Bantam’s 83

and Ford’s 85 foot-pounds of torque.

Contracts for 1,500 units each were given to the three

companies, with delivery to begin in June 1941. The order

accompanied the Army’s recognition that the original

weight requirement was neither sound nor realistic. The

new weight requirement was 2,160 pounds.

After studying these production models, the Army

decided to have Willys-Overland produce the vehicle,

although the final design incorporated some of the features

of the Ford and Bantam models. The general design and

bodywork were largely from Bantam; the front end, Ford;

the power unit, Willys.

Going back further, the driveline layout was used by the

Dutch Spijker in 1902; the type of driven front axle was

pioneered by Otto Zachow in 1907; and, mechanically, the

Quad was a scaled-down Marmon-Herrington half-ton 4x4

designed in 1936.

The key factor in the selection of the Willys-Overland

vehicle was its powerplant. The Willys Quad had a 60 hp

“Go Devil” 4-cylinder L-head engine (both intake and

exhaust valves were in the cylinder block). The Willys “Go

Devil” engine was rugged, strong, and reliable. It had

greater displacement and horsepower than that of either

Bantam or Ford. Furthermore, it had come from the Willys

Americar and had been tested and tried in years of service.

The horsepower of the basic Willys engine had been

greatly increased by Roos. Roos had joined Willys-Overland

in 1938 after a career of solving engineering problems for

Pierce-Arrow, Locomobile, and Studebaker.

When Roos arrived at Willys-Overland, the engine that

would later power the Jeep MB already was in production.

It had the same bore and stroke but developed only 45

horsepower at 3400 revolutions per minute (rpm) as com-

pared to the 60 horsepower at 4000 rpm it had after Roos’

mechanical ministrations.

His first step was to take the engine out of production

and run it at full throttle, or 3400 rpm, for 22 minutes.At

this point, the cylinders began to score and the rod bear-

ings burned out. To solve these problems , he redesigned the

cooling system and replaced the cast-iron pistons with tin-

plated aluminum ones. These changes, together with other

minor ones, made it possible to run the engine for 50 hours

at 3600 rpm. However, this caused the valves to burn out.

More redesigning followed and this weakness was elimi-

nated. Step by step, Roos got the engine up to the point

where it would run at 4000 rpm for 100 hours without

engine failure.

It was this engine that tipped the scales in favor of the

Willys-Overland entry.

Close-up views of Jeep MB instrument panel, driver’s front seat

over fuel tank, and rear end showing blackout lamps, pintle hook,

and bumperettes.

Ford was asked to co-produce the Willys to boost produc

tion and guard against delays because of accidents or sabo-

tage at Willys-Overland. From 1941 to 1945, Ford produced

277,896 Jeep vehicles, because Bantam’s Butler, Pennsylva-

nia, plant did not have the capacity to produce the numbers

needed.

Willys-Overland produced 1,800 Jeep MA models from

1940 to 1941, and 368,714 Jeep MBs from 1941 to 1945. The

Army requested changes before the MB went into produc-

tion. As a result, it díffered from the MA in a number of

ways. Most noticeable was the design of the front end,

which followed the Ford design.

Other changes were made as well. Unlike the MA, the

MB did not have vacuum ignition-advance control. The

Army also requested an improved carburetor air cleaner

and a larger generator with 4-ampere capacity, which was

standard on most government trucks. The battery was

standardized, using the government 2-H6-volt type in

place of the passenger-car type.

The hand brake was moved to the center of the vehicle

so it could be reached by either driver or passenger. The

single-bow top was changed to a double-bow for more

headroom.

In addition, the open shift lever and driving lights were

standardized to conform with other government vehicles.

Improvements were made to protect the steering tie-rods

and spring shackles. Seals were provided to keep water and

dirt out and hold the lubricant in, thereby tripling the life

of the shackles and reducing the frequency of lubrication.

From 1941 to 1945, a number of field modifications were

made. Improvements included installation of a surge tank

in the cooling system for desert service; conversion of the

electrical system from 6 to 12 volts for radio equipment;

installation of a capstan winch; oversize tires and engine-

driven air pump; and vacuum instead of manually operated

windshield wiper. Also available were field kits for winter

conditions, cold starting, heating, and deep-water fording.

During the war, variations of the Jeep vehicle were built.

The amphibious Jeep or “Seep” (for seagoing Jeep) was pro-

duced by Ford starting in September 1942. Production was

halted in 1943 as the vehicle was not particularly successful,

especially on land.

Jeep vehicles were also modified for ambulance duty.

Dubbed the “Jane,” a Jeep vehicle thus converted could

carry three stretcher cases. Lightweight variations for air-

borne assaults were also produced. Jeep vehicles were

lengthened and made into personnel carriers. They also

appeared as half-tracks. In some cases, skis replaced the

front wheels. In other cases, trailers were attached to carry

supplies and ammunition. Jeep vehicles were equipped

with many different kinds of ordnance, from mortars to

cannons to machine guns.

The origin of the Jeep name remains clouded in mystery.

One of the most popular theories is that the name came

from “General Purpose,” or “G.P.” Another widespread

theory is that it was named in honor of a character in the

Popeye comic strip, Eugene the Jeep. Eugene’s ability to

copyrighted the name “Jeep” in 1946. Since then, it has

been a trademark of Willys-Overland, Kaiser, American

Motors Corporation, and, now, Chrysler Corporation.

Although the mystery of the name may remain unsolved,

the Jeep performance during World War II is a matter

of record.

The late General George C. Marshall called the Jeep vehi-

cle “America’s greatest contribution to modern warfare.”

The Jeep MB model served in every WW II theater as a

litter bearer, machine-gun firing mount, reconnaissance

vehicle, pickup truck, front-line limousine, ammo bearer,

wire layer, and taxi.

In the Ardennes during the 1944-45 Battle of the Bulge,

Jeep vehicles, loaded with stretchers and draped with

wounded, raced to safety ahead of spearheading Nazi

armor. In the sands of the Sahara, the morass of New

Guinea, and the snow fields of Iceland, Jeep vehicles hauled

the .37mm anti-tank cannons to firing sites. In Egypt, the

British used a combat patrol of Jeep vehicles to knock out a

fleet of fuel tankers en route to Rommel’s armor forces on

the eve of the battle of El Alamein. At Guadalcanal, Jeep

vehicles went in with the U.S. Marines. In the end, the Jeep

vehicle was called “the most valuable weapon during the

war” by two U.S. Presidents.

The first post-war Jeep vehicle was the prototype CJ-1A

(CJ stands for Civilian Jeep). The first production CJ, the

CJ-2A, was introduced in August 1945 at a price of $1,090.

The CJ-2A was heavily based on the wartime MB model.

Vehicles with the C J designation were built until 1986.

Although the Jeep MB was not the first four-wheel drive

vehicle, it did bring together a series of engineering con

cepts that influenced every four-wheel drive vehicle being

built today. Four-wheel drive technology has been greatly

refined and horsepower tremendously increased, but much

of the success of these components is due to the Jeep MB.

The Jeep MB can be seen on display at the Henry Ford

Museum in Dearborn, Michigan, the Smithsonian Institu-

tion in Washington, D.C., and at the Jeep House in Toledo,

Ohio. The Jeep model at the Jeep House is a typical exam-

ple of the first high-volume production vehicle. Further

more, the MB displayed in Toledo is at the site of the original

Willys-Overland factory where it was conceived and built.

Historical Jeep MB models are on display at the Jeep House,

bound about and go just about anywhere was similar to the

Toledo, Ohio; Smithsonian Institution, Washington, D.C.; and

Henry Ford Museum, Dearborn, Michigan.

characteristics of the vehicle carrying his name. Willys

Jeep ® MB Technical Data

ENGINE

Willys model 441or 442 “Go Devil” 4-cylinder in-line water

cooled side-valve (L-head) gasoline engine, developing 60 bhp (54

net) at 4000 rpm and a max. torque of 105 lb-ft (95 net) at 2000

rpm Cubic capacity 134.2 in. (2199 cc). Bore and stroke 3.125 x

4.375 in (79.375 x 111.125 mm). Compression ratio 6.48:1. SAE

and RAC rated hp: 15.63. Firing order: 1-3-4-2. Valve tappet clear-

ance (cold) inlet and exhaust: 0.014 in. Spark plugs: Champion

QM2 or Auto-Lite AN7,14 mm, gap 0.030 in. Auto-lite ignition

distributor (dust-proof on certain vehicles); contact breaker gap:

0.020 in AC model AF mechanical fuel pump. Carter model

W0-539S downdraft carburetor. Note: Ford-built engines were vir-

tually identical but used studs instead of bolts for connecting rod

bearing caps; rods were interchangeable.

TRANSMISSION

Borg and Beck model 11123 single-dry-plate clutch; driven-plate

diameter 7 / 8 in. Warner Gear model T-84-J gearbox with three for-

ward speeds and one reverse; synchromesh on second and top gear.

Spicer model 18 transfer case/auxiliary gearbox bolted onto main

gearbox, with high (direct) and low (1.97) range. Separate lever to

engage or disengage front-wheel drive. Locking arrangement to

prevent use of low transfer ratio with rear-wheel drive only. Provi-

sion for PTO (power take off)at rear end of gearbox mainshaft.

Spicer U-jointed propeller shafts to front and rear axles. Spicer fully

floating driving axles with hypoid-bevel final drive, ratio 4.88:1.

Front axle with Bendix-Weiss, Rzeppa, Spicer, or Tracta constant-

velocity joints.

GEAR RATIOS

Gearbox

2.665

1.564

l.000

3.554

Overall

High Range Low Range

13.005

First

Second

Top

25.573

7.632

15.036

4.880

9.614

Reverse

17.344

34.167

CHASSIS

Midland Steel ladder-type chassis frame (with differences in front

cross-member and shock-absorber mountings between Ford and

Willys). Semi-elliptical leaf springs, front and rear with U-shackles

and screwed bushes. Rear spring assemblies identical left and right.

Left front spring had different spring rate from right-hand spring

to cope with extra load (engine offset to left)and was identified by

the letter “L” painted in yellow on the underside. Willys units, from

serial number 146774, and all Fords were fitted with a torque reac-

tion stabilizer spring below the left front spring (could also be

installed on earlier Willys vehicles). Hydraulic telescopic shock

absorbers. Bendix hydraulic service brakes on all wheels. Mechani-

cal parking brake on transfer case output shaft (externally contract-

ing on most, internally expanding on some late prnduction models).

Ross cam and twin-lever steering gear. Split-rim combat-type road

wheels (conventional drop-center type on early models) with

6.00-16/6-ply. tires, usually with non-directional cross-country

tread. Tire pressure, front and rear: 30-35 lb./sq. in.

DIMENSIONS AND WEIGHTS

Wheelbase: 80 in. Track (tread), front and rear: 48¼ in. (49 with

combat wheels). Overall length: 131 in. (early models 132¼ to 132

¾in.). Overall width: 62 in. Overall height (with normal load), at

cowl: 40 in., at top of steering wheel: 51¼ -52 in., with top up: 72

in. (early models 69¾ in.). Ground clearance: 8¾ in. Shipping

weight (less fuel and water): 2337 lb. Curb weight of complete vehi-

cle: 2453 lb (early models 2315 lb). Gross vehicle weight, off high-

way: 3253 lb, on highway: 3653 lb. Maximum payload: 800 lb.

Maximum trailer load 1000 lb.

ELECTRICAL

Jeep MB engine designed by Delmar Roos.

6-volt negative-ground system. Sealed-beam headlights, mounted

on hinged brackets. Lighting system controlled by blackout (main)

light switch on dashboard (later production models had rotary-type

light switch, replacing push-pull type). Auto-Lite generator, regula-

tor, and starter motor. The spring-loaded generator brace could be

pulled up to slacken the fan belt, thus preventing the fan from

throwing water over the engine when fording.

A radio outlet box was fitted against the bodyside panel at the

right front seat on later vehicles. Certain vehicles were fitted with a

l2-volt 55-amp auxiliary generator, V-belt-driven from transmis-

sion PTO.

1. Front-wheel drive and steering details with Bendix-Weiss type

CV joint.

2. Left front spring with additional torque-reaction spring

to stabilize front axle in rough service.

3. Cross-section of 2-speed transfer case.

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