CC Tech: 1973-77 GM Colonnade Chassis Design – Corner Carving through the Brougham Era

When one discusses American cars of the 1970s, good handling is not typically something that pops into one’s thoughts.  If anything, most American cars of the 1970s have a reputation of being softly sprung wallowing beasts devoid of any semblance of road manners.  That said, every time the GM Colonnade cars come up in discussion on Curbside Classic, inevitably its good chassis dynamics are mentioned.  So, what was it that made these GM intermediates good handlers?  Was their chassis design really that different from past designs?  Quite frankly, more often than not there is a fair amount of misinformation about these cars that gets repeated.  So, let’s set the record straight and explore the GM Colonnade sedans chassis design in depth.

This is how the 1972 Chevelle may have looked had there not been the 100-day strike.


The GM intermediate A-body began its gestation in the late 1960s, with a planned released date for the 1972 model year.  This was delayed by the 100-day UAW strike in the fall of 1970, pushing the launch date up to the fall of 1972 for the 1973 model year.  Since the A-body was shared by the four divisions, they each shared in the development of the car.  The frame was designed by GM research, Chevrolet was tasked with the front suspension, Pontiac the rear suspension,  Oldsmobile designed the steering and Buick the brakes.  The development at Chevrolet was overseen by John Z. DeLorean.  He and Chevrolet’s chief engineer Alex Mair were advocates for good handling vehicles.  Their influence helped ensure that the handling of the A-body chassis was improved over its 1964-72 predecessors.

Although similar in appearance to the 1970 Chevelle chassis shown in the top photo, there were many improvements made to the A-body chassis for 1973 as shown in the bottom photo.


The 1973 A-body chassis was seemingly the same design as the previous generation.  Both were perimeter frame with short-long control arm front suspension and 4-link rear suspension with coil springs.  However, there was far more than meets the eye as the chassis was heavily revised.  The frame itself was more robust compared to its predecessor, while the suspension geometry was significantly improved.  No parts interchanged with the older generation’s chassis.

This is the 1967 F-body suspension, which had similar geometry to early Chevelles. Although very similar in appearance to the 1970 F-body suspension, the 1970 suspension was significantly improved design.


The revised suspension, in particular the front suspension, was the most influential change that lead to the good chassis dynamics.  Let’s rewind a bit to 1970 model year.  Chevrolet and Pontiac introduced the all-new F-body in early 1970.  The new F-body was much loved by the enthusiasts for its modern euro styling, its good performance and its great road manners.  Much of the road manners in the 1970 F-body came from its new front suspension design.  This suspension was the product of GM engineer Herb Adams.  Compared to the 1967 to 1969 F-bodies, the 1970 front suspension had a new control arm design with improved geometry.  It used taller spindles, had improved camber curves and had reduced bump steer.  This new geometry helped keep the wheel planted correctly as it moved through its range of motion.

This is the improved 1970-81 F-Body front suspension which was later adapted by the 1973 A-body cars and the 1975-79 X/K body cars.


When Chevrolet was designing the 1973 A-body front suspension, rather than reinvent the wheel, the front suspension from the F-body was utilized as the basis for the A-body suspension.  Since the F-body used a bolt on sub frame, the chassis was very similar to the perimeter frame of the A-body car from the firewall forward.  So, it was a bolt on affair to use the F-Body control arms, and spindles on the A-body chassis.  The 1964-72 A-body suffered from the same poor suspension geometry as the 1967-69 F-body, so these new A-body cars saw a similar improvement in handling.  The rear suspension was also revised, but to a less significant degree.  The 1973 A-body chassis used longer rear control arms, which improved the geometry by way of less acute convergence angles, and the rear shock absorbers were relocated.  The new rear geometry helped improved cornering stability with strong roll understeer.  The four-link control-arm system was designed to steer the axle to the right when the body leans left and vice versa.

Part of the success of the Nova 9C1 Police car was due to its excellent road manners. It utilized the same basic front suspension as the GM Colonnade cars.


GM got its money’s worth out of Herb Adams’ front suspension design as it was also used on numerous other GM vehicles.  These include the 1975-79 GM X/K-body cars and the 1977-96 B/C/D-body cars and the 2WD Astro/Safari 2WD vans.  While the basic suspension design was shared between these car lines, each used slightly different executions. This resulted in minor differences in the suspension geometry and each had slightly different suspension travel despite the fact that they used the same basic design.

This chart shows that despite these cars using the same short-long control arm suspension, once mounted on each respective chassis there were minor differences that resulted in slightly different wheel to spring ratios and suspension travel.


This road test shows clearly shows Cutlass’ superior handling to the Cougar. Many Fords of this era utilized excessively soft springs and it was noted by the testers that this Cougar’s springs were too soft .  The Cougar was also noted to understeer, which was exacerbated by the very heavy 460 engine and the lack of an rear anti-roll bar; it was a poorly executed suspension.  The Cutlass on the other hand was very well executed, and utilized stiffer springs and a rear anti-roll bar.

Much of the Colonnade’s good handling reputation was due to the good suspension design but it also had to do with GM’s good execution of design. Compared to Ford, GM used components that promoted better handling at a slight sacrifice to ride quality.  On average GM cars used stiffer springs, larger front anti-roll bars and more of its suspension configurations used rear anti-roll bars.  However, that doesn’t mean all Colonnades were great cornering machines.  It should be noted GM probably had hundreds of variations in the suspension configurations on this platform.  Not only did each car line have numerous coil spring choices, but there were differences in anti-roll bars, tires, steering systems and even alignment settings.  This resulted in a significant variation in handling prowess across the platform.

A good example of the variation in handling comes when comparing the Chevelle to the Monte Carlo.  As I have written about in the past, the 1973 Monte Carlo was lauded for its Mercedes influences handling and steering.  What exactly was so different about the Monte Carlo, was it not just a Chevelle with a longer nose? If so why did no one fawn over the handling of the 1973 Chevelle?  While it is true that the smaller and lighter Chevelle had the same chassis as the Monte Carlo, the Monte Carlo had significantly different execution.  Articles of that time discussed the Monte Carlo’s unique geometry, but the reality was that this was really just different alignment settings.  Many cars of this era, including the Chevelle, used very little positive caster and sometimes a negative caster setting, to reduce steering effort. More caster results in more steering effort. This was why cars equipped with manual steering often had different caster settings than those with power steering. The 1973-77 Monte Carlo used 5-degrees of positive caster, compared to the 1973 Chevelle which used 1-degree of positive caster with power steering and 1-degree of negative caster with manual steering.  The additional caster used on the Monte Carlo improved road feel and high-speed tracking, but also increased steering effort.  Since all Monte Carlos had power steering, this wasn’t really an issue for parking, but it gave the car a more “Mercedes-like” steering feel. There were other differences in the Monte Carlo too.  In addition to the extra positive caster, Monte Carlos typically used a faster ratio steering box tuned for more road feel, stiffer springs, and larger front and rear anti-roll bars.  This made a night and day difference in handling compared to Grandma’s 307 powered Chevelle, despite them both having the same basic suspension and chassis design.  Other GM divisions followed suite and had different suspension, steering and alignments used for different model Colonnade cars. Each division had autonomy to tune the chassis for their intermediate models.  At Oldsmobile, the Cutlass Salons and Supremes had better suspension setups than the Cutlass S, and at Pontiac the Grand Am had better a suspension setup than a LeMans.

Handling tests were not overly common during the 1970s, but Popular Science ran all of the cars it tested through a high-speed handling test.  I gathered results for numerous Colonnade cars along with a few of its competitors to show the wide variation in handling prowess.  Most, if not all of the cars tested by Popular Science were fairly run-of-the mill models, and not specially equipped high-performance models with uncommon suspension packages.  Looking at the results, we see our gross generalizations are correct.  The GM Colonnade sedans on average obtain the highest speeds in the handling tests, the Chryslers are in the middle and the Fords are on average the lowest.  What these results also clearly demonstrates is that each of GM, Ford and Chryslers had a large variation in the handling of their cars with the same chassis design.  This means that the suspension configuration had as big of an influence on the vehicles handling ability as the actual suspension design.

The 1973-77 GM A-body was clearly a good chassis design for its time, so much so that some believe it outlived that platform.  A common fallacy I often see repeated is that the 1977-90 B-body was just a new body on the old 1973-77 A-body chassis.  This is not true. Despite the fact that the 1973-77 A-body and 1977-96 B-Body had similar suspension components, the same 116” wheelbase and were similar in size, they were not the same frames.  In fact, even though both chassis use the same basic suspension design, the suspension components do not directly interchange.  While the control arms are very similar, they were slightly revised for the downsized B-body car.  Furthermore, compared to the 1977 B-body, the 1973 A-Body chassis has an extra crossmember at the rear, it has significantly wider and beefier side rails, the frame ends are shaped differently and the steering linkage is different.  Although I have never had the opportunity to weight either of the frames, I am willing to bet that the 1977 B-Body chassis is significantly lighter than the 1973 A-body chassis.  A big part of the 1977 B-body program was weight savings and improved space efficiency.  The modern and more space efficient body of the 1977 B-body sat on a modern lighter frame to create a car that was about the same size as the Colonnade sedans, but significantly lighter and more space efficient.  There is a reason the 1977 B-body was and is still considered a revolutionary car; it was not a rehash of an old car like Chrysler’s R-Body.

A 1977 Monte Carlo going through a slalom course during a Popular Science road test.


Without a doubt the 1973-77 A-bodies had a good chassis design for its time.  It arguably had the best overall suspension design of any of the 70s American intermediate sedans.  Road test results show that on average the GM cars out-handled the competition.  These A-bodies clearly established that GM had moved on from the “jet smooth” rides of the 1960s which had little consideration for good handling. And while not the same chassis as the much-loved 1977-96 B-body cars, undoubtedly the 1973-77 A-body chassis was an important evolutionary step in GM developing their vastly improved full-size chassis.