Muscle Mustangs & Fast FordsHow To Chassis Suspension
1989 Mustang LX Rear Suspension Upgrade - Bringing Back The Bite
Overhaulin' An Outdated Rear Suspension To Handle Today's Horsepower.
Another benefit of the Pro-Series control arms is the solid mounting points, which eliminates the rubber bushings that come from the factory. The rubber bushings collapse and distort under stress, causing inconsistent and unpredictable control arm movement. "Bushings flex and deflection occurs, which causes the control arms to lose adjustments. You then cannot tune for the track conditions. The UPR Pro-Series control arms have Heim joints, or spherical bearings, that are locked in and never change adjustment," commented Jeremy Martorella of UPR.
The Pro-Series upper controls also use a spherical bearing on the rearend housing to prevent binding. The upper control arms control side-to-side movement of the rear end, so the spherical bearing provides stability in straight-line performance but won't bind up on the street when the housing is moving up and down. A downside to the solid bushings is that the ride is rougher.
For those who don't want the solid mounts, there are control arms that have urethane bushings, which are much tougher and better than rubber, but not as harsh as the solid mounts. UPR does offer more street-friendly and less racy control arms with urethane bushings. For those who demand uncompromised drag-racing performance, there is the XD Pro-Series lineup that feature chrome-moly Heim joints, grade 8 bolts, and tool-steel sleeves.
One item we didn't install--but will in the future--is a UPR antiroll bar, which will be welded between the frame rails and has two arms that attach to the rearend housing. "The antiroll bar limits all body roll. If you watch cars at the track, a lot of the time they are twisting. Installing our antiroll bar eliminates the body twist by keeping the rear parallel to the body, which will lower reaction time and also help the car hook better," added Martorella.
He went on to inform us that in a typical 11-second car, the 60-foot times are consistently reduced by 0.06-0.07 of a second with the UPR antiroll bar. The reason we didn't install the antiroll bar was due to our cheap exhaust system that blocked the mounting of it. Most exhaust systems clear the UPR bar; ours was old, nearly 10 years ago. Martorella suggested the removal of the antisway-bar links when driving on the street. The links will break under the stress of street driving. It's meant for track use only. Our goal is to install the system down the road, when the tailpipes are replaced with a set of turndowns.
Strange Engineering was tapped for a pair of its adjustable rear shocks, built specifically for '79-'04 Mustangs. The shocks feature rebound adjustment to allow the user to compensate for a fast or slow rate of rebound.
In drag racing, setting the shocks up loosely (setting of 1) will allow the body to move quickly and help plant the tires. The loose setting works great when traction is poor as the tire will need to be planted harder. The downside to the loose setting is tire shake and/or wheelhop. As the tires plant and distort under load, it hooks and thrusts the car forward. But as the torque of the engine takes over, the tires want to eventually unwind and return to their natural state. If the body/chassis is moving too quickly, the tires will react accordingly and cause shake or hop. To counter this, the shocks can be stiffened to slow the body movement and lessen the hit to the tires. On tracks that offer excellent traction, it's good to stiffen the rear shocks to help ease the hit. At the track, we recommend starting at a shock setting of 2 for a serious street/strip ride. Move up a few clicks for slower rides, and a setting of 5 is ideal for the street. Those settings are, of course, starting points and can be adjusted up or down to properly suit your combination.