The shockabsorbers on the A35 are double acting lever arm units. They normally give little obvious trouble and consequently tend to be ignored. Their condition is important not only to give a comfortable ride but also has a big effect on the road holding of the vehicle. Worn shockabsorbers, especially at the front of the car, can make the steering vague and make the car wander or jump about on a wavy or bumpy road. Roll will be excessive on bends with the feeling that the car wants to go stright on. The front shockabsorbers are particularly important. It should not be assumed that because the car passes the MOT that the shockabsorbers are satisfactory. The A35 seems to require firmer damping than many other cars. Furthermore the MOT test is usually done on a cold car when the shockabsorbers are at their best, and problems are often only revealed on a long hot journey. Shockabsorbers should be replaced in pairs.
Testing the Units
Shockabsorbers are best tested on a warm day after a run so that they are
warm and at their weakest. At each corner of the vehicle, press down on the
bodywork and release. If the car rebounds and then settles down againjust
a small amount after reaching the top of the rebound the unit is satisfactory.
If there is any more up and down motion the unit either needs filling with
oil or renewing. Inspect for leaks. These usually occur from the oil seal
round the short axle to which the arm is attached. If the leaking is very
minor it is only necessary to maintain the oil level by filling with oil
at every service. Shockabsorber (or hydraulic jack) oil is injected through
the hole at the highest point on the shockabsorber after removing the screwed
plug. This is accessed from under the wheel arch in the case of the front
units, and from under the rubber plugs under the rear seat squab in the case
of the rear units. Do not confuse the filler plug with the much larger plug
which contains the valves, of which more later. If the leak is bad the unit
will need replacing. If there is no apparent leak but the performance was
poor, the oil has probably all leaked away! Finally check for play in the
axle pivot. This is particularly important for the front shock asborbers
because they form an important part of the front suspension and any looseness
is dangerous as it affects the steering geometry. The symptoms are that the
steering can become vague and variable, with the vehicle pulling to one side
when the brakes are applied and to the other when accelerating. Take hold
of the arm and try to move it from side to side. Any looseness requires immediate
replacement of the unit. Note that this failure can happen to new and
reconditioned units almost immediately, and if so they should be returned
under guarantee.
Refilling a Shockabsorber with Oil and Expelling the Air
The only long term cure for a failed shockabsorber is a new or reconditioned
unit. But if the reason for failure is lack of oil but the seals are not
too badly damaged then the oil can be replaced, but the air within the unit
must all be displaced. This must also be done when fitting a new unit. With
the unit fixed in a vice in the position it will be in when fitted, move
the lever up and down to the extremes of its travel. (This is difficult if
not impossible to do with the unit on the car.) This removes the air. Add
oil and continue the process until no more air is being expelled and the
oil is up to the bottom of the filler hole.
Modification of Lever Arm Units
The only modification for the lever arm shockabsorbers is to increase the
rebound damping rate. Unscrew and remove the large plug on the shockabsorber
body and carefully remove the small stick like valve which sits in the middle
of the exposed hole. This has a nut screwed on one end which compresses a
spring which holds the valve closed. The nut is soldered in place. To uprate
the rebound rate, this nut should be screwed clockwise to compress the spring
more, a full turn being sufficient improvement as a rule. Experiment until
you find the rate which suits your car and the way you drive. The nut can
be resoldered in the new position. It is important that shockabsorbers are
modified in pairs, so that the response is the same on both sides of the
car.
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(c) R H Johnston, 1998. Material may not be published for profit
without permission.
Whilst great care is taken to ensure that the technical information and advice offered is of the highest standard, neither the author, nor The Austin A30/A35 Owners Club, or the Officers of the Austin A30/A35 Club accept any liability at law for any death, injury or loss whatsoever arising from the use of advice contained in this article.