The 1955 Chevrolet Design Story: Part II

{In this second part of a three-part series on the innovative 1955 Chevrolet, David
Temple looks at the chassis development of the all-new ’55 Chevrolet.}

In the last issue, Old Cars detailed the development of Chevrolet’s small-block V-8. Part 2 continues the 1955 Chevrolet design story by detailing the development of the car’s chassis and additional electro-mechanical features.

In addition to a modern, optional V-8, Chevrolet developed a new chassis that marketing described as “Quadra-Poise Ride” through a “Glide-Ride Front Suspension,” and “Outrigger Rear Suspension.” The “Fingertip Facts” booklet for the 1955 Chevrolet explained the features of the new chassis this way: “From the new Glide-Ride Front Suspension to the location and construction of the seats… from the softer-riding tubeless tires, to the new Outrigger Rear Suspension, new designs and features have been incorporated… to assure better riding comfort, better roadability, and even greater stability. Its lower center of gravity, well-distributed weight, and wider tread combine to give a safer, road-hugging ride.” Everything was designed with weight as an important consideration, though function and reliability were, of course, foremost in the minds of the engineers. Ed Cole noted, “The whole concept of the car was built around lighter components. We started, in other words, to get away from the heavier torque-tube drive and went to the Hotchkiss type. We went to a Salisbury-type axle instead of the banjo-type. And then we went to a ball-joint front suspension for weight savings and to a tubular frame.” It all added up to the best chassis design to date for Chevrolet.

Harry Barr, who was deeply involved in the engineering of the V-8, also participated in designing the chassis. Also involved in its development was Maurice Olley, recognized as one of the most knowledgeable suspension engineers. Working under Olley, starting about mid-1953, was Zora Arkus-Duntov, who later made his mark in automotive history through his work on the Corvette. Others included Al Kolbe and Don McPherson, an assistant to Kolbe. Russell Sanders, a mechanical engineer, was yet another member of the chassis development team.

A new frame and suspension

The new Chevrolet frame side rails were a square-tube type with consistent wall thickness and greater cross-sectional area, thus providing an 18 percent improvement in strength over the prior design, as well as an increased resistance to twisting. Convertibles had an added X-member fabricated from I-beams. While the side members for closed models were rolled and welded square tubing made from flat steel stock, those of the convertible were made from stamped channels — one slightly narrower than the other — joined by overlapping them slightly, then welded together to form a rigid unit. Both the convertible and the hardtop bodies had extra body mounts. Rather than a cross member for rear engine support, an engine support bracket was welded to each inner surface of the side rails.

Integrating the front cross member into the frame structure also contributed to the rigidity of the frame. The previous design had the front cross member as an assembly with the front suspension and attached with eight bolts per side to the bottom flanges of the frame side members. Structurally integrating the frame-to-front cross member allowed the frame side member to form part of the coil spring tower and made the provision for the mounting of the rebound control bumper.

In regard to the front suspension, the book “1955 Chevrolet Engineering Features” stated, “Chevrolet’s Knee-Action suspension, time-tested by millions of owners, incorporates important new design features for 1955 and an innovation exclusive to Chevrolet — braking dive control.” Their new front suspension retained the short-and-long-arm, parallel-link principle of independent suspension, but all of its components were newly designed. Among the innovative components were light-weight spherical joints with non-metallic (phenolic impregnated fabric laminations) concave bearing surfaces; rubber-mounted control arms that required no lubrication and reduced the transmission of road shock and vibration; and diagonally mounted coil springs and shock absorbers. The advantage of the non-metallic bearing surfaces included improved durability, was less affected by infrequent lubrication compared to metal-to-metal bearings, and was less sensitive to foreign matter. Mounting the coil springs and shocks diagonally positioned them nearly tangent to the lower control arm arc of travel, thus minimizing distortion of the springs and providing a nearly constant deflection rate for the suspension. Furthermore, the spherical joints, in combination with the front suspension geometry, reduced braking dive by 45 percent.

The Outrigger Rear Suspension allowed for a lower vehicle profile as well as improved handling, ride quality, and smoother drive train reactions to torque and braking application. Its leaf springs were nine inches longer and a 1/4-inch wider than in 1954, which reduced their deflection rate and increasing their durability; they were spaced farther apart by 3/4-inch and mounted outboard of the frame, too, improving roll stability. Sedans and coupes had four leaves while station wagon models received five. Hotchkiss, or open drive was employed rather than torque-tube drive. (Torque-tube drive has the driveshaft enclosed in a tube filled with oil and utilizes only one U-joint, which is mounted at the transmission end.) The setup gave greater durability and higher torque capacity, and also eliminated the oil seal assembly problems associated with torque-tube drive. More rigid pinion shaft supports, cast Armasteel differential housing, higher-capacity differential bearings, heavier axle shafts, integral bearings and wheel seals, and a more rigid axle housing were included in the design.

Tubeless tires were now standard equipment on all models; a new tread design provided a quieter ride. Because of the use of tubeless tires, extra quality control for the wheels was necessary, but other than having four stamped lugs on the outer horizontal portion of the rim for more secure attachment of the wheel covers, the wheels were little changed.

In the December 1954 issue of Motor Trend, test driver Walt Woron had high praise for the new chassis: “The way it performed around the winding, twisting, asphalt handling road at GM Proving Grounds, I wouldn’t be afraid to stack it up against many of the so-called sports cars. The long, outrigger rear springs, lowered center of gravity and good weight distribution all add up to a car that stays where you put it in corners. If you take it too fast, it’ll break, as it should. But, all you need do is to punch the throttle and you’re out of trouble.”

New, too, between body and chassis

Chevrolet switched to a 12-volt electrical system for 1955, thus making all of GM’s passenger car divisions uniform in this respect. The 12-V system provided improved starting capability for the V-8, more efficient generator output, and allowed for smaller-gauge wiring and cabling.

While there were many resources given to the V-8 project, Chevrolet’s engineers did not ignore the six-cylinder engine. It received a new, side-mounted air cleaner to fit under the new, lower hood contour; an improved water pump with a larger impeller; larger cooling fan; redesigned oil pump with a floating-type pickup; and grooveless main bearings. An oil pan baffle was added to reduce oil surging upon hard stops. Furthermore, several design changes reduced its overall dimensions to adapt it for installation in the new chassis. Output was now rated at 136 hp at 4,200 rpm with Powerglide and 123 hp at 3,800 rpm with the three-speed manual transmission.

Both the V-8 and the six, when coupled to the manual transmission, could also be had with the newly optional overdrive unit made by Borg-Warner. The “Touch Down” overdrive option cost an extra $ 108. It had a 0.7:1 ratio, cut in at about 31 mph, and reduced engine speed by 22 percent.

The three-speed manual transmission was modified to provide increased torque-transmitting capacity and greater durability. Improvements consisted of a larger diameter mainshaft, more intensive surface treatment of the gears, a sliding spline with a better fit, and wide-spread mounting centers for a more rigid attachment to the clutch housing. Another improvement associated with the manual transmission was actually both a cosmetic and mechanical one — the concentric gearshift control. It gave a new look to the steering column and reduced rattles associated with the old design.

The Powerglide transmission was extensively redesigned for 1955 to give smoother operation, increased durability, and easier servicing. A greatly simplified hydraulic system resulting from a double-wrap low band was the most significant change. The improved brake band was composed of three circular segments providing greater holding power and faster and more positive disengagement of the band. Since it had up to four times more holding power than the previous single-strap band, it could be operated with lower main line pressure. The vacuum modulator, the primary and secondary clutch valves, and high-clutch low-servo valve were no longer required as a result of the lower pressures. Other changes were made to adapt the Powerglide to the Hotchkiss drive and the new small-block.

Power steering, an option costing $ 91.50, was redesigned to give more efficient operation and greater driving comfort. Key components were relocated to increase their effectiveness, and a longer pitman arm reduced the overall steering ratio to 23.1:1 from 25.7:1. A vane-type hydraulic pressure supply pump similar to the one used for 1954 was used, but the pump was mounted on the rear of a special generator and was driven by a splined extension of the armature shaft. A hydraulic fluid reservoir was placed in a concentric arrangement around the pump. Also, the non-power steering system incorporated the recirculating ball-and-nut principle formerly only available with power steering. The recirculating ball-and-nut steering gear transferred rotating force into a linear force through many free-rolling balls that performed like threads in a bolt acting against a nut. Because a ball rolls with very little friction, the recirculating ball-and-nut steering gear provided very efficient, smooth operation.

Also improved was the power brake system, which was now available on all Chevrolet models. The pedal mechanical ratio was changed to 1.55:1 from 1:1. This change was said to reduce the pedal effort under power-off conditions by one-third.

At mid-year, revised optics to the headlamp lens resulted in an increase in the low-beam visibility by as much as 80 feet.

Chevy gets cool

During the early part of the design phase of the 1955 Chevrolet, the decision was made to include factory-installed air conditioning in the Bel Air (except the convertible) and Two-Ten series; the purchase of a V-8 was required with either series in order to order factory air. The option, which became available about two months into the model year, was quite expensive, thus it was not commonly ordered. Still, the new air conditioning system was a first in the low-priced field. (While it was a new and innovative option for Chevrolet, it was not new in automotive use, having first been introduced by Packard for 1940.) At the time, no other car air conditioning system paralleled the system’s ease and accuracy of controlling humidity. The entire assembly, designed by the Chevrolet and Frigidaire divisions of GM, was installed completely within the engine compartment, which differed from other systems of the day that took up a portion of the trunk space. The air conditioning system was built as a ready-to-drop-in unit at the Frigidaire plant in Dayton, Ohio. There, it was pre-charged and placed on a pallet for shipment to the assembly plant. While on the assembly line, the car was fitted with the air distribution system, controls, and mounting brackets. Once it reached the end of the assembly line, the car was taken to an open area where the air conditioning system was lowered into the engine compartment and bolted in place. This was followed by connecting the wiring harness and heater hoses to complete the process.

The assembly of the air conditioning system was performed by placing the individual components on a processing rack where the refrigerant hose was connected to the fittings on the compressor, condenser, and evaporator. Then the components were placed on the rack in the same positional relationship as they would be when installed inside the car’s engine compartment. This procedure kept the refrigerant hose from being twisted or stressed as the unit was lowered into the car at the assembly plant.

The unit was a package-type combining cooling and heating capabilities and was a first of its kind. Early automotive air conditioning systems consisted of multiple sub-assemblies installed in, or on, the car prior to the final assembly operations. Oldsmobile, Buick, and Cadillac were the first GM brands to get factory air conditioning as an option (1953). Frigidaire’s unit, which supplied both cooled and heated air for all-year comfort, consisted of just three major components: compressor, evaporator, and condenser-receiver-dehydrator-filter assemblies. The systems for the higher echelon GM cars consisted of a compressor, condenser, receiver, dehydrator-filter, evaporator and blower assembly, and the refrigerant lines and fittings. These were installed independently of each other, such as the installation of the compressor on the engine, the condenser to the radiator, the evaporator and blower assembly in the trunk, etc. These components were then connected by approximately 10 sections of copper tubing. Not surprisingly, this type of air conditioning system was more complicated to test, as each component had to be leak-tested prior to installation, plus it created problems in handling and assembly operations. Frigidaire’s air conditioner was completely fabricated, assembled, evacuated, charged, and leak-tested prior to shipment to a Chevrolet assembly plant.

The package-type design was made possible through two very critical features in combination with other important, but less challenging, ones to develop. These two crucial factors were, the creation of the flexible hose for use with Freon 12 to replace the copper refrigerant lines used on previous systems, thus providing the needed flexibility between the major A/C components; and the development of a thin condenser permitting ease of installation between the radiator and the grille. Other contributing factors were the use of cowl intake vents to bring outside air into a front-mounted evaporator, which negated the need for expensive ducts, and combining multiple components into one assembly (condenser, receiver, dehydrator, and filter). To combine the cooling and heating capabilities into a single system, a hot water coil was added to the downstream side of the evaporator.

The system was said to be the equivalent of 24 household refrigerator compressors, was capable of draining a gallon and a half of water out of the air in one hour, could drop the temperature in the passenger compartment to 15 degrees below the outside temperature in 5 minutes, and could hold the inside temperature to 20 degrees below the outside temperature for as long as desired.

Check out Part I of the 1955 Chevrolet Design Story

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