Fitting the axle to the car
New screws or use old?
The Audi manual states that all bolts, screws and nuts, relating to this job, are use once only. It is important to replace all self-locking nuts, however some A2OC members suggest that the bolts are not Torque to Yield bolts, more commonly known as stretch bolts, and are therefore safe to reuse. Stretch bolts must not be reused, all bolts stretch but a stretch bolt is stretched beyond the elastic zone into the plastic zone.
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The advantage provided is that the stress strain curve is much flatter in the plastic region so the clamping force is better controlled. The clamping force is set by a characteristic that is manufactured into the bolt; it is not variable depending on the friction felt by a torque wrench. The friction felt by a torque wrench is dependent on the condition and lubrication of the threads and so can be quite variable. Finally a stretch bolt provides a greater clamping force for a given bolt size. Stretch bolts when removed cannot return to their original length and strength and therefore must not be reused. If you have any doubts replace your fasteners as advised in the manual. For others I summarise a debate regarding stretch bolts here on A2OC.
A standard bolt stretched within the elastic zone generally has a single torque figure specified, ie 55Nm. The torque wrench can only respond to friction felt which in turn will be influenced by cleanliness of the threads, lubrication etc. The actual amount of bolt stretch achieved therefore can be variable along with the associated clamping force.
If tighter tolerances are required for the clamping force required from a standard bolt stretched within the elastic region then a lower initial torque followed by an amount of turn can be specified, ie 30 Nm + 90 degrees. A portion of the stretch is determined accurately by an angle of turn after a possibly less accurate torque wrench setting. As the stretch is tighter controlled overall then so too is the clamping force. A torque wrench setting followed by an angle of turn does not necessarily confirm a bolt is a stretch bolt. A screw is unlikely to be a stretch fastener because there is no thread free portion where necking can occur.
A torque wrench only setting cannot be specified for a stretch bolt. A torque wrench that takes a bolt to the point of necking will never click. It will continue stretching the bolt to the point of failure. Torque specifications for stretch bolts specify and initial clamping force followed by an angle of turn. A stretch bolt can generally be identified by a slightly reduced diameter unthreaded portion of its length between the head and the thread. This is a head bolt set supplied by Elring:
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In the future I will be making a judgment based on this information and only replacing bolts that are likely to be stretch bolts.
Fitting the axle and associated components.
This is a reversal of the assembly process position the axle under the car on a lifting device and lift it up to the car. At this stage consider if the axle could fall off and if additional straps are required. Go under the car and insert the screws / bolts. Nip the axle up to the space frame. Check that both rear springs are seated correctly and insert the damper lower securing screws and nip up the nuts.
Stub axles were fitted and torqued, brakes assemble, brake pipes connected and ABS sensors fitted:
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Wheel bearings fitted with a new nut and torqued, drums were fitted, the brakes bled and the car lowered to the ground, the hand brake was then adjusted.
Get a volunteer to sit in the rear of the car, yes this is in the manual, I went for two of less than average weight to keep things balanced. Torque the 6 mounting to space frame bolts then torque the 2 long through bush bolts:
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Finally torque the damper lower securing bolts:
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I want this repair to last as long as possible so underbody sealing wax was applied to the whole assembly, excluding the drums:
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If you have removed the axle including the mounting castings it is now time to arrange for 4 wheel alignment.
Enjoy the new smooth ride at the rear.