The 'Big J4T'


A 'Big J4T'. Courtesy of Brian Shaw.

 The 'Big J4T' was designed at a time when articulated tractor units and trailers were becoming commonplace. The 2-axle tractor was available as a 24-26 or 30-32 G.C.W. vehicle, and with wheelbases of  108 inches, 114 inches, and 145 inches.

The 32 ton model became the most popular 32 ton tractor unit in the United Kingdom. It could be fitted with a dual 46 gallon petrol tank to give a capacity of 92 gallons, and so was ideal for long distance use.

Like the other models in the 'Big J' range, the 'Big J4T' was built on an all-bolted frame assembly for added strength and rigidity, and had a spacious and comfortable cab, with a wide windscreen and good all-round visibility.


T he 'Big J4T' chassis. Courtesy of Brian Shaw.


A 'Big J4T'. Courtesy of Brian Shaw.

The ‘Big J4T’ Specification:

24 ton G.T.W. tractor.

Engine
V6 diesel, 170 B.H.P. at 2,600 R.P.M., maximum torque 370 lbs. ft. at 1,700 R.P.M., or AV 505 (right hand only) 170 B.H.P. at 2,400 R.P.M., or AV,471 (right hand only) 150 B.H.P. at 2,400 R.P.M.

Clutch
Single plate, cushioned drive.

Gearbox
5 speed constant mesh gearbox. Ratios: 1st 6.5 to 1; 2nd 4.49 to 1; 3rd 2.769 to 1; 4th 1.49 to 1; top 1 to 1.

Propeller shaft
1600 series universal joint with rubber mounted centre bearing.

Rear axle
Single speed spiral bevel differential assembly. Fully floating hubs. Ratio: 6.5 or 5.57. Alternative rear axle with 2-speed differential, with electric shift. Ratio: 5.57/7.6 to 1.

Front axle 5 tons capacity. Stub Axle 2½" diameter. Axle beam section 4" x 2⅞".

Steering
Re-circulatory ball type steering gear. 21" diameter steering wheel. Power steering an optional extra.

Suspension
Semi-elliptic springs. Front: 54" long; 4" wide; 8 leaves; single rate. Rear: 54" long; 3½" wide; 11 leaves; single rate. Telescopic shock absorbers available on front axle only.

Frame
Carbon steel side members. Section 10"x 3"x 0.28".

Brakes
Cam brakes (leading and trailing shoe) with dual circuit full air operation. Front: 15½" diameter x 6" wide. Area=362 sq. ins. Rear: 15½" Diameter x 7" wide. Area=422 sq. ins. Single-pull air assisted hand brake, mechanically linked with rear brake cam shaft. Rear brake actuators of the triple diaphragm type.

Electrical
24 volt insulated return system of wiring. 35 amp alternator fitted as standard.

Fuel tank
Circular tank of 46 gallons capacity.

Cab
All steel welded construction with a forward entrance, and one piece screen of generous area giving good visibility. A shock absorber type driver and passenger seat, available as optional extra. A sleeper cab was also available on export models.

10 to 32 ton G.T.W. tractor. Specification as above, except for the following:

Engine
V6 diesel, 200 B.H.P. at 2,600 R.P.M., maximum torque 444 lbs. ft. at 1,700 R.P.M., or 6LX (right hand nnly), 150 B.H.P. at 1,700 R.P.M.

Propeller shaft
1700 series universal joint with rubber mounted centre bearing.

Front axle
93" Wheelbase: 5 ton capacity. Stub axle 2½" diameter. Axle beam 4" deep, 2⅞" wide. 144" wheelbase: 6½ tons capacity. Stub axle 2.625 diameter. Axle beams 4⅜"x 3⅛".

Rear axle
Spiral bevel with planetary hub reduction. Fully floating hubs. Ratios: 7.69 to 1 (V6); 5.26 to 1 (6 LX with splitter)6.35 to 1 (V6 with splitter and 6LX).

Suspension
Semi-elliptic front and rear. Front: 54" long; 4" wide; 10 leaves; single rate. Rear (93" wheelbase): 54" long; 3½" wide; 13 leaves; single rate. Rear (144" wheelbase): 58" long; 3½" wide; 13 leaves; single rate. telescopic shock absorbers available on front axle only.

Frame
93" wheelbase: carbon steel side members. Section 10"x 3"x 0.28". 144" wheelbase: high tensile alloy steel side members. Section 10"x 3"x 0.28". Pressed steel cross members. Cross members and spring brackets attached to frame side members by high tensile bolts. Frame width 34" international standard.


A 'Big J4T' and a trailer loaded with a container. Courtesy of Brian Shaw.


A 'Big J4T' tanker. Courtesy of Brian Shaw.

Return to the
previous page