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How the 1975 Chevrolet Nova
Became A 1976 Cadillac Seville

A suspension redesign was just one of many considerations

How Cadillac turned this $3,209 1975 Chevrolet Nova...Image: 1975 Chevrolet Nova 4-Door Sedan


Image: 1976 Cadillac Seville...into a $12,479 1976 Cadillac Seville!

Once the Cadillac Motor Car Division of General Motors Corporation made the decision to introduce a smaller Cadillac to compete with the luxury imports, many different configurations of wheelbases, bodies, engines, drive train, and suspension systems were considered. Cadillac brought in cars from other GM divisions, as well as imported a few GM models from Australia and Germany, for testing purposes and to see if they would be good candidates upon which to build the new Cadillac.

It was determined that all of GM's mid-sized platforms would be too large, and the imported models would require too many costly modifications to make them suitable, which would drive up the target base price of the new car. Eventually, it was determined that the platform used for the Chevrolet Nova, Pontiac Ventura, Oldsmobile Omega, and Buick Apollo four door sedans would be a close enough fit, although Cadillac would use very few stock parts from those assemblies on its new car, requiring almost everything to be designed from the ground up.

One of Cadillac's biggest concerns was making sure the new smaller car provided a smooth, quiet, comfortable ride typical of other Cadillac products. For many years, Cadillac had used coil springs on its cars, with some models equipped with an automatic leveling feature for the rear suspension to maintain proper ride height. After much testing, Cadillac decided on a solid rear axle with leaf springs as the best combination, with suspension engineers promising to design a system with ride and handling characteristics comparable to the independent designs of the time.

Front wheel drive was considered for the new Cadillac, but the cost to redesign the front drive components to fit in the smaller platform wasn't cost effective, nor did it fit into the development time frame. However, this dilemma did spark later development of a smaller front wheel drive design that was used in the smaller Cadillac Eldorado, Buick Riviera, and Oldsmobile Toronado models for 1979. It would also find its way into the second generation 1980 Cadillac Seville.

The main considerations were providing a smooth ride on a shorter wheelbase, and ensuring a lack of exterior noise, isolating the passenger compartment from harshness and vibration, providing interior amenities comparable to any car in the world, and have styling that was distinctively Cadillac but not controversial. Since the Seville's smaller size was a radical move for Cadillac, the division wanted to make sure there was nothing else about the car's appearance that would invite concern among its traditional customers.

Due to the limited amount of time for development (16 months), Cadillac knew it must rely heavily on components that were readily available. The power plant was a concern, as Cadillac's huge 472 and 500 cubic inch displacement V-8s that were being installed in production Cadillacs at the time were too large to fit in the engine bay. So, Cadillac looked to other GM division engines and decided that the Oldsmobile-built 350 cubic inch V-8 was the best choice. This engine was recognized as the best design available at GM at the time for medium-sized vehicles, and was powerful, dependable, smooth running, and there was enough capacity to ensure availability to Cadillac once production got underway.

Cadillac wanted something special to promote on its new car, so it decided to modify the Olds engine to include an electronic fuel injection system. Cadillac was already working on such a design for introduction on some of its 1975 models, and that electronic fuel injection system could be modified to work on the new smaller Cadillac as well. Cadillac's vendor for this was Bendix, which was later purchased by Bosch. Both Bendix and Bosch had a long history with fuel injection, as Bendix had worked with Chrysler to introduce the "Electrojector" electronic fuel injection back in 1958 on the Chrysler 300D. This was the first time a computer was used on a Chrysler vehicle, and very few were actually sold with this fuel delivery system. Service issues in the field resulted in a recall program in late summer 1958 to replace the fuel injection with dual 4-barrel carburetors. Original cars that weren't converted are now quite rare, and demand a huge premium when sold.

Bosch had worked with Volkswagen and introduced a similar system in 1966, although the VW system was more dependable and didn't have any of the service issues associated with some of the earlier fuel injection designs. Chevrolet had used a mechanical fuel injection system on some of its cars in 1957, including the Corvette, and they performed better than some of the other systems, and had been improved upon over the years as well.

Image: Cadillac Electronic Fuel Injection computerCadillac's Bendix fuel injection system would use an analog computer, which was named the Electronic Control Unit (ECU). Bosch introduced a similar design about the same time, and major European auto makers like Mercedes, Jaguar, Porsche, Saab, Volvo, and Citroen began offering it on their models. On its introduction, Cadillac was the first American automobile manufacturer to introduce a state of the art electronic fuel injection system as standard on one of its models. Initially called "Manifold Injection," it included a fuel rail that distributed fuel to the individual injectors in each cylinder. Later, a simplified design was called "Throttle Body Injection" which was far superior to the dated carbureted fuel delivery, and provided better overall performance and fuel economy, easier starting, lower emissions, and a smoother idle.

Electronic Fuel Injection (EFI) would be standard equipment on Cadillac's new small car, which was given the name Seville, and was introduced in the spring of 1975 as a 1976 model. EFI was a $600 option on all other 1975 Cadillacs, although production of this option was held back on Cadillac's other models until March 1975, when the new model was officially introduced.

GM's strong and dependable Turbo-Hydramatic three speed automatic transmission was fitted to transfer power from the engine to the drive shaft. This was the only transmission considered for the new car, as it was generally considered one of the best automatic transmission designs in the world, and was a very smooth, reliable unit. Millions of miles and decades of use have only proven this statement more.

Front and rear suspensions, along with other components, were heavily modified as noted above right to make sure Cadillac's traditional customers would not experience any discomfort, vibration, or harshness. Cadillac knew it had to balance the fine line between European-like handling and typical American comfort, luxury, styling, and amenities. They were quite successful.

CADILLAC SEVILLE SUSPENSION SYSTEM

In order to provide a smooth, quiet ride that would meet the high standards expected by Cadillac customers, Cadillac engineers modified the Seville suspension and body mounts from the configuration used by the other models based on this platform, such as the Chevrolet Nova. The results were quite acceptable, and those changes included:

1. The front coil springs used rubber insulators to isolate the upper coils from their towers.

2. Teflon interliners were added to the rear leaf springs to keep spring rates constant.

3. To reduce steering wheel and column vibrations and shake, a hydraulic damper was fitted.

4. The drive shaft used a double-trunion Cardan joint in front of the axle pinion to eliminate drive line shudder.

5. The front Isoflex subframe mounts varied in their flexibility as did the rubber grommets which isolated the front frame member where it attached to the body.

6. Small tubular hydraulic shock absorbers were used to support the front end sheet metal where it mounted to the subframe.

7. A lateral strut insulated the rear of the transmission from the body, and an additional link ran below the drive shaft to tie the bottom sides of the tunnel together for additional support.

8. Hydraulic dampers were used to mount both the front and rear bumpers. In all, 11 tubular-type shock absorbers were used on every Seville.

Additionally, for 1979 Cadillac retuned the Seville suspension to provide a better ride, and modified the body mounts to reduce vibration and the transfer of noise.

Image: Cadillac Seville chassis diagram