1975 Chevy/GMC Pickup Truck

Chevy C10/GMC K10 Third Generation

An all-new clean sheet redesign of General Motors’ Chevrolet and GMC brand C/K-Series pickups débuted in 1972 for the 1973 model year. Development of the new third generation trucks began in 1968, four years prior to production in 1972, with vehicle components undergoing simulated testing on computers, before the first prototype pickups were even built for real world testing. The redesign was revolutionary in appearance at the time, particularly the cab, departing from typical American pickup truck designs of the era. Aside from being near twins, the Chevrolet and GMC pickups looked like nothing else on the road. As a result, the third generation trucks are officially known as the “Rounded-Line” generation. Some people may refer to them as “square bodies”, given that the trucks appear square-like when compared to more modern automotive design standards.

GM’s design engineers fashioned the “Rounded-Line” exterior in an effort to improve aerodynamics and fuel efficiency, using wind tunnel technology to help them sculpt the body. Third generation design traits include “double-wall” construction, sleek sculpted body work, flared secondary beltline and an aerodynamic cab which featured rounded doors cutting high into the roof and steeply raked windshield featuring an available hidden radio antenna embedded into the glass.

There were two types of pickup boxes to choose from. The first type, called Fleetside by Chevrolet and Wideside by GMC, was a “double-wall” constructed full width pickup box and featured a flared secondary beltline to complement the cab in addition to new wraparound tail lamps. Both steel and wood floors were available. The second type, called Stepside by Chevrolet and Fenderside by GMC, was a narrow width pickup box featuring steps and exposed fenders with standalone tail lamps. Initially, only wood floors were available.

The wheelbase length was extended to 117.5 in (2985 mm) for the short wheelbase pickups, and 131.5 in (3340 mm) for the long wheelbase pickups. A new dual rear wheel option called “Big Dooley” was introduced on one-ton pickups, along with a new Crew Caboption on the 164.5 in (4,178 mm) wheelbase.[14] Crew Cabs were available in two versions: a “3+3″ which seated up to six occupants and “bonus cab” which deleted the rear seat and added rear lockable storage in its place. The fuel tank was moved from the cab to the outside of the frame, and a dual tank option was available which brought fuel capacity to 40 US gallons. 1980 was the first year that a cassette tape player could be purchased, along with a CB radio.

The Rounded-Line generation ultimately ran for a lengthy 15 model years (1973–1987) with the exception of the Crew Cab, Blazer, Jimmy, and Suburban versions, which continued up until the 1991 model year.

Interior and Safety

Soft touch materials were used throughout the passenger cabin, such as the dashboard, doors (arm rests), steering wheel, and shift levers. Subtle grained interior panels and bright metal work was used on the inside with high-quality materials also used on the outside, like chrome, aluminium, and polished stainless steel, particularly on top-of-the-line luxury Silverado or Sierra Classic trim levels. Custom Vinyl vinyl or soft Custom Cloth cloth and velour seating surfaces were used along with fabric headliners, door inserts, and plush carpeting, depending on the trim level. Upper class trim levels also used acoustic deadening materials for quieter ride comfort.

Other safety features included soft-padded interior panels for appearance and safety, 3,329 square inches of tempered and laminated safety glass, prismatic rearview mirror, six turn-signal indicator lamps with asymmetrical flash, four-way hazard function, and lane departure function.

Chassis and Powertrain

Third generation Rounded-Line C/K-Series pickups gained an all-new, high tensile strength carbon steel ladder type frame with “drop center” design. Steering controls included variable-ratio recirculating ball steering gear with optional hydraulic power assist. Braking controls included front self-adjusting disc brakes with rear finned drum brakes and optional four-wheel hydraulic Hydra-Boost or Vacuum-Boost power assist. Engines choices initially consisted of six or eight cylinder engines with either manual or Turbo Hydra-Matic transmissions.

C-Series pickups included two-wheel drive and featured an independent front suspension (IFS) system with contoured lower control “A” arms and coil springs. GM’s new Load Control rear suspension system took up residence in the back. The Load Control rear suspension system consisted of a rear live axle with dual stage Vari-Rate multi-leaf springs and asymmetrical (offset) shock absorber geometry, to help sort out any “wheel hop” under heavy loads or hard acceleration.

K-Series pickups included either ConventionalPermanent, or Shift-on-the-move four-wheel drive. The latter system was introduced for 1981. Regardless of the type of four-wheel drive system equipped, all K-Series pickups featured four-corner Vari-Rate multi-leaf springs, front live axle with symmetrical (inline) shock absorber geometry, and the Load Control rear suspension system. K-Series pickups also featured an off road oriented design, with the transfer case bolted directly to the transmission and running gear tucked up as high as possible under the vehicle to reduce the chances of snagging vital components on obstacles, as well as to achieve a low silhouette and optimal ground clearance. Exposed brake lines wrapped in steel were standard, with underbody skid plate armor optional for further protection.

Conventional four-wheel drive pickups featured manual locking hubs and a two-speed dual range New Process 205 transfer case with four drive modes: Two HighFour HighNeutral, andFour Low. Two High gave a 0:100 torque split, while Four High yielded a locked 50:50 torque split. Four Low applied reduction gearing. The front and rear propeller shafts were locked at all times in Four High and Four Low. Neutral allowed for flat towing, or use of the power take off (PTO).

Permanent four-wheel drive pickups featured a two-speed dual range New Process 203 transfer case with planetary center differential and lock. Five drive modes were provided: High,LowNeutralHigh Loc, and Low Loc. In High the center differential was unlocked and allowed the front and rear propeller shafts to slip as needed for full-time operation. The system could be manually shifted into High Loc which locked the center differential for a locked 50:50 torque split. Low and Low Loc applied reduction gearing with or without lock, depending on the mode selected. Neutral was also available for use of the PTO.

A new Eaton Automatic Differential Lock (ADL) was introduced in 1973 as an optional extra on the Rounded-Line C/K-Series pickups, for the rear hypoid differential. The new automatic locking differential was offered under the G86 code, replacing the Eaton NoSpin differential, and eventually replacing the old Positraction limited-slip differential in 1974, at which point it assumed the G80 code. The Eaton ADL featured intelligent differential control via an internal governor which monitored vehicle speed and wheel slip to know when to automatically lock and could lockup 100 percent at or below 20 mph (32 kph) increasing tractive effort. The differential lock would unlock and deactivate at speeds above 20 mph for safety reasons, such as the vehicle being on dry pavement.

Towing and payload capacity ratings for Rounded-Line C/K-Series pickups varied, depending on how they were configured. Factors such as engine and transmission combination, differential gear ratio, curb weight, and whether the pickup was two-wheel drive or four-wheel drive decided how much the pickup could safely tow or haul.

A properly equipped C-Series half-ton class pickup could tow up to 8,000 lbs (4 tons) of braked trailer, while a properly equipped C-Series three quarter-ton or one-ton class pickup could tow up to 12,000 lbs (6 tons) of braked trailer.  Adding four-wheel drive reduced towing capability due to increased curb weight, which resulted from additional driveline components (transfer case, front axle, front differential, front propeller shaft, and so on) needed to facilitate four-wheel drive. A properly equipped K-Series half-ton or three quarter-ton class pickup could tow up to 6,500 lbs (3.25 tons) of braked trailer, whilst a properly equipped K-Series one-ton class pickup could tow 500 lbs more, up to 7,000 lbs (3.5 tons) of braked trailer. The decreased towing capability of K-Series pickups, when compared to their C-Series pickup siblings, is a valid tradeoff for all-weather, all-terrain capability.

Heavy-duty towing equipment was available for both C and K-Series pickups, such as the Trailering Special package (included power steering, uprated battery, and uprated generator), 7-pin trailer electrics connector, heavy-duty engine oil cooler, heavy-duty transmission oil cooler, and a weight distributing trailer hitch.

1975 Chevy C10/GMC K10 Differences

For the 1975 model year the trim levels were revised and the base trims were now Custom Deluxe/Sierra, mid-range trims wereScottsdale/Sierra Grande, luxury trims were Cheyenne/High Sierra, and the top-of-the-line luxury trim levels were now known as Silverado/Sierra Classic. They remained in this configuration up to the 1987 model year.

The third safety advancement was the introduction of dual front lap-and-shoulder safety belts with emergency locking retractors for outboard occupants in 1975 for the 1976 model year. These replaced the outdated and inadequate lap belts previously used. A center lap safety belt with slack adjustment was provided for the center occupant. Ford and Dodge would follow one model year later adding lap-and-shoulder safety belts to their pickups

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Classic Chevy & GMC Truck Parts