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| Suspense Stories Suggested suspension modifications for fast road use: GGR urethane suspension bushes, what is the benefit of these? What is the purpose of the rear beam mounting kit? How does the rear beam mounting kit fit? Why is the rear beam mounting kit only recommended for two wheel drive cars? Why do GGR not usually recommend urethane rear beam mounting bushes? Why do you always set Koni dampers on their mid way setting? Why do you not generally suggest the front strut brace for Escort Cosworths? Why is the rear strut brace rarely used? I have heard that the rear suspension subframe is fragile, is this true? I have just bought a GGR front strut brace for my Cosworth, but it doesn't fit between the strut tops, what's wrong? Since lowering my 4x4 Cosworth, I've had problems with the off-side front driveshaft pulling out of the inner joint, how can I cure this? | |
The suspension lay out used on the Cosworth range of cars is basically to the same design on each model. The front suspension consists of MacPherson strut spring & damper units, with lower track control arms, and an anti-roll bar that also controls longitudinal movement of the wheels. The independent rear suspension consists of semi trailing arms, with inboard coil springs, separate shock absorbers, and an anti-roll bar. The complete rear suspension is fixed to a tubular subframe beam that also holds the rear differential unit, and is fixed to the body in only three places. The suspension mountings and pivot points use numerous rubber bushes to prevent the transmission of road noise into the car. Detail improvements have been made throughout the production life of the Cosworths, but the basic design remains the same. | ||
As explained above, many factors have to be considered before deciding exactly what suspension modifications are suitable, as a rough guide, here are our general recommendations. | ||
Koni Sports Adjustable gas dampers, Eibach lowered road spring set, full set of urethane front suspension bushes (with later type anti roll bar if necessary), GGR rear beam mounting kit, and a front strut brace. | ||
Same recommendation as for the 3 door car, but use GGR progressive rate lowered road springs in place of the Eibach units | ||
As recommended above for the 4 door car, (obviously different GGR road springs), also rear beam mounting kit not usually required | ||
As recommended above for the 4 x 4 Sierra, without the front strut brace. | ||
GGR urethane suspension bushes, what is the benefit of these? | ||
On a race car, flexible suspension bushes are usually replaced by rod end bearings (usually called rose joints) or similar to ensure that there is no change in the suspension geometry due to movement. This would not be acceptable for a road going car because of the high levels of road noise & harshness that would be transmitted into the vehicle. The urethane bushes are really the best of both worlds, they have little flexibility, so retain suspension geometry, but still retain a certain level of compliance to insulate road noise. The overall effect is that the car becomes more positive, and stability under braking is improve tremendously. | ||
This kit actually fits around the outer two rear suspension mountings. As described above, the rear suspension is connected to the car only in three places, and when the outer bushes become worn, the suspension will pivot around the centre, and give a steering effect from the rear. The two parts of the rear beam mounting kit actually reduce the free movement of the bush, and therefore prevent the rear wheel steering effect. | ||
To fit this kit the rear subframe must be lowered away from the underside of the vehicle. It is recommended that this is done one side at a time. There are two parts to the kit, a smaller cone shaped piece, and a larger dish shaped item. The cone shaped part fits into the top of the mounting bush, (above the subframe), with the tapered side facing down into the bush. The larger dish shaped part fits directly below the subframe, with the shaped surface pushing into the rubber part of the rear beam-mounting bush. | ||
Why is the rear beam mounting kit only recommended for two wheel drive cars? | ||
The rear wheel steering effect is most noticeable on two wheel drive cars, when accelerating hard, the car will steer one way, (usually to the right) and then on deceleration, the car steers in the opposite direction. The rear beam mounting bushes are also more prone to wear on two wheel drive cars due to the loading put on them during acceleration. If the rear beam mounting bushes are worn excessively, to the point of collapse, the rear suspension will run directly onto the harder mounting kit and transmit high levels of road noise at all times. If this is the case, then we would recommend the fitment of replacement urethane rear beam bushes. | ||
Why do GGR not usually recommend urethane rear beam mounting bushes? | ||
The rear suspension arms are fitted with metal flexible joints, and so, road noise is passed directly into the rear subframe. If soft subframe mounting bushes are not used, this noise will be transmitted into the bodyshell of the car. The use of urethane rear beam mountings does bring a noticeable improvement to the handling of the car, but the increase in road noise must be tolerated. | ||
Why do you always set Koni dampers on their mid way setting? | ||
The adjustment of the Koni dampers was originally intended to allow adjustment to compensate for wear in the dampers after thousands of miles use. With a new damper, this adjustment will allow the user to increase or decrease the damping effect (stiffness) of the shock absorber. The front dampers can be adjusted comfortably, without removing from the car, (it is not so straightforward with the rear dampers), so the damping balance can easily be altered by adjusting the front shock absorbers. | ||
Why do you not generally suggest the front strut brace for Escort Cosworths? | ||
We have found that with stiffer suspension fitted to the Sierra Cosworths, the front suspension top mountings will flex, and that there is a noticeable improvement in the response of the suspension with a strut brace fitted. The Escort Cosworth bodyshell was designed to have a higher level of torsional rigidity & therefore there is less flexibility in the suspension mountings. The front suspension mountings are more rigid for a couple of reasons, firstly, the engine compartment is shorter, so the transmission bulkhead that runs across the car is closer to the mountings, plus, the inner & outer wings are braced together at the strut top mounting area. | ||
The rear suspension tops are only usually the top mountings for the rear dampers, the rear springs are mounted independently so the springing loads are transmitted into another part of the bodyshell. If coil over dampers are used, (combined spring & damper units), or extremely stiff shock absorbers, then a rear strut brace would be advisable. | ||
I have heard that the rear suspension subframe is fragile, is this true? | ||
Yes, it can be bent very easily by subjecting it to unusual side loadings, bumping into kerbs, or bouncing into pot holes for example. The intricate shape of the rear suspension subframe (it looks almost like a metal coat hanger!), makes for a strong mounting against forces in the usual directions, but it will bend easily in other directions. Again, due to the shape of the subframe (or beam), it is often impossible to ascertain that it is definitely bent without replacing it. | ||
The suspension strut tops on the front of the Cosworth bodyshells are not parallel; the tops are closer together than the bottoms. As the strut brace is shaped to fit to the strut tops, it will not fit down over the top of the suspension towers without dismantling. As the brace fits to the front of the strut tops, you can usually mate the brace to the towers by bringing it in from the front of the vehicle. | ||
As the front suspension moves, the distance from the (moving) wheel hub to the (fixed) differential changes. When the ride height of the car is such to make the driveshaft straight, (parallel to the ground) the distance between these two points is the shortest, as the suspension moves (up or down) away from this, the wheel hub is moved further away from this point. There is obviously provision made within the driveshaft joints to allow for this movement on a standard car, but with significantly lowered suspension, this may not be sufficient. We can supply a specially made driveshaft that is slightly longer than the standard item; this will reposition the inner joint back into the original position. Please note that this driveshaft problem can also be caused by failed engine mounting rubbers, permitting the engine (and differential) to climb away from the wheel hub, allowing the driveshaft to break free from its joint. | ||
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