How it Works: Torsion Bar Suspension

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Torsion Bar Suspension

The torsion bar is basically a length of metal rod anchored at one end to the car body and at the other end to the suspension lower link. As the wheel passes over a bump the bar twists. It returns to its original position when the bump is passed and restores the car to its normal drive height. The resistance of the bar to twisting has the same effect as the spring used in more conventional suspension systems. A certain amount of load is permanently applied to the bar to maintain the car's ride height. The torsion bar may be mounted either longitudinally or transversely in the system. One of the most useful things about this system is that the torsion bars are adjustable. Two older cars (we won’t say classic, because the Marina is certainly not considered one) that used torsion bars were the Morris Marina and Chrysler Valiant, which mounted the bars longitudinally.

Removing A Torsion Bar

Before starting to remove faulty torsion bars it is important to remember that the components are handed - that is, they are not interchangeable from one side of the car to the other. If you are removing both torsion bars you should therefore keep the two sets of components separate. You will also need a special tool - a universal ball joint separator which you can probably find online. First remove the road wheels and support the car on axle stands. Disconnect the battery. Next, unscrew and remove the grease nipple from the lower link of the swivel pin. You will then need to find some way of supporting the weight of the suspension. One method is to lower the car on to a wooden block about 20-21 cm (8ins) thick. This block should be placed as near as possible to any disc brake dust shields under the lower suspension arm. Replace the axle stands so that they give additional safety at this height.

The next step is to lift away the lower bush and raise the shock absorber arm away from the ball pin. To do this, first unlock the lock nut on the reaction pad and use a self-locking wrench to hold the upper bush housing as you remove the nut. Then remove the upper bush housing with the upper bush. You can now clear the shock absorber arm away from the ball pin and remove the lower bush. You will next have to separate the steering rack and lever from the suspension mechanism. To do so, first undo and remove the nut on the steering rack rod ball pin. Then use the ball joint separator to release the ball pin from the steering lever.

Before starting to remove the torsion bar itself, jack up the car slightly to relieve the load on the torsion bar, while still resting the lower suspension arm on the wooden block. Then release the reaction lever from the chassis by undoing and removing the bolt, spring washer and reaction lever washer. Move the reaction lever forwards along the torsion bar. Next, slacken the nut holding the eyebolt through the chassis member until the suspension lowers by 12 mm Qins). Finally, remove the torsion bar by gently pulling the shoulder from the chassis housing. The reaction arm is still attached to the torsion bar. Remove it by taking off the circlip and sliding the reaction arm free.

Fitting A New Torsion Bar

Re-fitting a torsion bar is the reverse of the removal method, but the following points should be noted. A new torsion bar can be fitted to either side of the car, but a used one can be fitted back only on the same side of the car. This is because used torsion bars always have a slight "set", which causes them to remain slightly twisted in one direction. Any corrosion or scoring in the bar affects its reliability, and it should not be re-used. The adjustment screw on the reaction lever should be set half in and the lock nut tightened before re-fitting the reaction lever. Make sure that you set the eyebolt nut to the specified torque, which is normally around 6.9-7.4 kg/m (50-541b/ft). Similarly set the bolt holding the reaction lever to the chassis to the correct torque of 3.0 kg/m (2.21b/ft), and also the track rod ball pin nut, to 3.3 kg/m (2.61b/ft). Make sure that you renew any damaged nuts, bolts and bushes when re-assembling. They must all be in excellent condition. When you have fitted the new torsion bar, adjust the suspension trim height.

Adjusting Suspension Trim Height

Whether you have fitted a new torsion bar or just dismantled it for inspection, you will have to re-adjust the trim height. There are two stages to the trim adjustment, coarse and fine. For coarse trim adjustment you have to shift the reaction lever on the torsion bar splines. To do this first place the swivel strut base on a block of wood and disconnect the damper arm (shock absorber arm) as described above. Then scribe or punch alignment marks on the reaction lever and bodywork and undo the reaction lever securing bolt. Slide the lever forward to the end of the splines, taking careful note of its position as it comes off the spline. Move the lever up or down one spline and slide it back into place. Re-assemble the suspension and check the car height. Repeat this procedure until the trim is correctly adjusted. You can now make the fine adjustment. First remove the reaction lever securing bolt, then slacken the adjusting bolt lock nut. Then, with the wheels off the ground, turn this adjusting bolt either clockwise to increase the trim height or anti-clockwise to lower the trim height.
Torsion Bar Suspension
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