Anti-roll Bar: The diameter of the original bar is 22mm (7/8 inch). Ideally, a larger diameter bar should be installed in place of the original bar if increased front roll stiffness in wanted. As far as I have been able to research, no such bar exists. One could be fabricated, but probably at great expense. Addco and other companies offered bolt-on additional bars, although current availability is questionable. The most practical addition is to obtain a second original bar and mount it in tandem with the original bar. This can easily be done by first removing the stock brackets and bushings and then attaching the tandem bar to the original bar (left in place) with separate bushings and saddle brackets. End links can be made from a piece of heavy plate with two holes, one for each bar end. This is equivalent to a 31mm (1 7/32) bar. The addition of this bar will greatly reduce front body roll caused by weight transfer when cornering. Soft compound tires are highly recommended with this setup so that there will be sufficient grip to counter the increased force from the tandem bar. This bar can be tuned to some extent by using either rubber or urethane saddle bushings to hold it to the original bar. In no case, however, should the stock rubber bushings on the original bar be changed to urethane. This will eliminate the car's ability to effectively absorb severe bumps. I learned this the hard way in my early days of 131/Brava tuning by hitting an exposed rock on the shoulder of the road and leaving my car with a bent frame rail between the crossmember and the radiator support. The lesson here: don't make your car's suspension more rigid than the unibody. The weak link will always be the one to break.
Control Arms: No improvements are needed, and in order to prevent possible damage, no improvements should be attempted. If either the ball joint or the bushing is damaged the complete arm should be changed.
Springs: Unlike most FIAT models sold here in the USA, the 131/Brava springs are reasonably stiff and in my opinion should not be changed. Lowering the front suspension is not recommended for 1975-78 models since the strut will bottom against the rebound bumper when under normal load. 1979-on Brava models are not as sensitive because of the redesigned top bushing, but also will not benefit much from lowering.
Struts: The original oil units work very well when new, but provide less control as they gradually wear over time. Life expectancy is usually 30 to 40 thousand miles when driven hard and perhaps 70 to 80 thousand miles when driven carefully. The wagons use struts with larger pistons for higher load capacity, although externally they are identical to and interchangeable with sedan units. In sedans they provide a slightly stiffer ride for a small improvement in handling. KYB GR-2 low pressure gas struts (part # 233102) are available for 1979-on Brava. These improve handling greatly with a very stiff ride that may seem too stiff at slower speeds. Koni also makes gas struts, but are extremely expensive, so I haven't tried them. Brava struts can be made to fit 1975-78 131 by disassembling the upper bushing and removing sufficient material from the aluminum cone to allow strut piston threads to clear top collar. This will also serve to grip the top bushing tighter for more positive location, as the original arrangement doesn't prevent movement of the piston top in the bushing. The lower mounting bolt hole can be drilled to 1/2 inch allowing camber to be adjusted. The mounting bolt just above becomes a pivot point for this adjustment. I wedge the bolt outward by placing a suitable pin behind the bolt head on one side and behind the nut on the other. This corrects the negative camber that occurs from unibody settling. Each time the front suspension receives a heavy jolt the strut towers flex toward each other. Over time the unibody fatigues, leaving the strut tops closer together and the front wheels with negative camber. The other advantage of making this correction is more aggressive steering geometry. Front traction will be increased and understeer will be reduced.
Upper Stress Rod: If you regularly drive your 131/Brava hard through corners or on rough roads, then an upper stress rod should be added to the unibody. This rod mounts between the strut towers in the engine compartment to eliminate unwanted unibody flex. This rod will have to be fabricated since there are none to be purchased. European competition 131s used rods between the strut towers and the radiator support to triangulate strength into the unibody. Although this would be the strongest setup, production models have too much equipment in the engine compartment for more than a single rod between the strut towers.
Wheel Alignment: Nothing affects the way a car handles more than wheel alignment. The manufacturer specifies values for caster, camber, and toe that it deems correct. Remember that these values are for stock size tires and an unmodified suspension. In order for your car to handle it's best, these adjustments must be set to their ideal setting, which is often different from the manufacturer's values. Before making any adjustments be sure that the wheels bearings are properly adjusted. Loose bearings will give false camber and toe readings. Caster can be changed by adding or removing shims at the end of the anti-roll bar. Manufacturing tolerances often require more on one side than the other. More caster will quicken steering centering and improve traction in corners. It is for this reason that I re-move all shims from both sides and then replace only those necessary to restore symmetry. There is no provision for adjusting camber, although it can be changed by drilling the strut housing as described above. Try to achieve zero degrees on both front wheels. Toe adjustment is made by loosening the locknut at the tie-rod and screwing the steering link in or out as required. Because the tie-rods are behind the spindle, screwing the steering link IN produces toe-OUT and vice-versa. Always be sure to make equal adjustments on both the left and right tie-rods to prevent the steering wheel from becoming rotated in the straight ahead position. Adjusting toe should be done last after all other settings have been made. Proper toe adjustment will be achieved when the tires wear evenly across the width of the tread. Always keep an eye on tire wear as this is a great way to monitor the settings you have chosen. Remember that if your car handles the way you want it to and the tires wear evenly, then your wheel alignment is correct for your car regardless of the actual values.
REAR SUSPENSION
Control Arms - Lower: Because of their size and location, these offer the most support to the rear axle. When the axle housing is parallel to the car the control arm bushings are relaxed. When one side of the housing is closer to the car than the other the bushings are twisted which offers resistance to body roll. One method of increasing rear axle support and roll resistance is to double-up the lower arms by placing a second stock arm parallel to the original arm with longer bolts. This creates enough roll resistance that an anti-roll bar is not needed.
Control Arms - Upper: These control arms should not be modified. Typical failure is the weld breaking that holds the end to the rod. Weld back into position to repair, but not before pressing the bushing out to avoid damage from heat. Replacing the rubber bushings with urethane would likely cause more frequent failure.
Panhard Rod: Angled road bumps (such as RxR tracks, driveways, etc.) tend to wag the rear suspension sideways against the Panhard rod bushings. This rod would be more effective if the bushings were urethane instead of rubber. I have always intended to do this, but have never taken the time. If someone else has already, please let me know.
Shocks: The oil shocks work well when new, but gradually wear just as the fronts do. KYB GR-2 gas shocks (part # 343142) provide stiffer response and do not wear out. I have had great results with these shocks and highly recommend them.
Springs: The rear springs are a little soft and too tall. Cutting and retapering one end solves both problems. About 1 to 1 1/2 coils will settle the rear of the car level with the front and make the Panhard rod parallel to the road for reduced rear axle steer. Be sure to cut the bottom of the spring and position the same after cutting. Alternatively, 131/Brava wagon springs can be used in the sedan for the same result without having to cut the original springs.