rubber in between, each arm contacts its companion bar near the mid point. These arms have little or no effect under upward or downward travel of the wheels. Only when the rear axle tends to rotate, usually under acceleration or braking, do the arms come into play, resisting the “wind-up” with a bending action in the traction bars.
Working alone, single-leaf springs on a rear suspension have a number of duties to fulfill besides supporting the spring weight of the car. They must provide sidewise and fore-and-aft location to the rear axle as well as prevent it from rotating on its own axis or “winding up” due to the action of the pinion on the ring gear. Given engines of low to medium torque and the cushioning effect of automatic transmissions, the single-leaf spring does a fairly creditable job. But better location is desirable with stronger engines and practically mandatory with engines like the big 400 or the snappy Sprint 6.
Characteristically, Pontiac stepped right up with the proper card to take each trick and solved each engine/transmission problem individually. You get two traction bars (as on both our test cars) with the 400 manual and the automatic, 326 manual, and 4-barrel ohc 6 manual. The following combinations get one bar on the right side only: the 326 automatic, 4-barrel ohc 6 automatic transmission when ordered with 3.23 to 4.33 rear axle ratios. It was decided that the 1-barrel 6 with the automatic transmission and 2.56 to 3.08 axle ratios didn’t need any at all, so none is supplied with those combinations.
In many cases where additional restraints have been added to leaf-sprung rear suspensions such as the one in question, there’s a penalty in the form of harsh jolts and noises that renders the whole arrangement unacceptable to all but the competition minded. But in designing this particular suspension, Pontiac seems to have avoided these drawbacks entirely by careful attention to geometry and the use of rubber bushings and sandwiches at all pivots and contacting surfaces. We weren’t able to get so much as a single “clunk” out of it under any condition.
Our tow test cars, both convertibles, were strictly lead sleds when compared to the other available body style, the coupe. In fact, both test cars weighted more than either of the tow GTOs (which were minus only some insulation and under-coating) we tested in January. Sealed containers weighing around 35 pounds apiece – which, we suppose, contain fine old wind and unspecified springs and masses – occupy all four corners of convertible models. Put there to damp-out body shake which results form the rather imber structure that is inherent in convertible body styles, these containers account for a big part of the weight increase.
If you’re really interested in carrying the mail, the coupe body style is devoid of several hundred pounds compared with the convertible and is more rigid to boot. Our Sprint 6, which was better balanced than the 400 due to the lighter engine, is still quite heavy for a car of this class. We would expect substantial improvement in acceleration times for both had they been coupes.
Both test cars were tight and rattle-free despite having several thousand miles on their odometers, including a cross-country trip. This general solidarity, tout suspension, and the F70 x 14 tires add up to what can best be described as a lot-of-car-under-you feeling. (These tires, standard on all Firebirds, happened to be Wide-Ovals by Firestone – who pioneered the shape and has rights to the name – on one car and Goodyears on the other. Now that other manufacturers are making similar tires, 70-series has become the generic term for these wide, low-section- height tires.)
This Firebird has optional instrument cluster console, automatic on floor, custom steering wheel for sport and comfort.
This fine-feathered fowl’s hood lumps mark it as 400 as does grab bar. Wheel, column shift for 3-speed auto are standard.
It’s four-on-the-floor and not much more for this Sprint 6. Real goodies are in engine, suspension, external markings.