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Interceptor 650

Ah - G994PNH - where are you now - There follows a blow by blow account of the long struggle to get this car up together. This was originally written on a Psion 5 on successive evenings down the pub and published using the Serif Webplus service that is now discontinued so is now reproduced as a text file

In this episode we come to the Graunching and Ratchetting and difficulty with low speed turns. Is was becoming obvious that all the tyres were badly and unevenly worn so an appointment was made with Dave Pillinger Motors in Peasdown St. John who does four wheel tracking for racing cars and so is well qualified so set up road going AWD systems. He was most excited to encounter a car that was old enough to be programmed into his equipment - he sticks with a taut string and potentiometer system which can be calibrated with the jig that came with it instead of relying on an annual and expensive visit from the equipment manufacturers. With the car on the hoist the rear alignment was checked - Camber OK, toe in miles out on the offside. This was corrected by loosening the bolts and tapping the wishbone with a hammer - a Birmingham Vernier? and attention transferred to the front. Camber and castor angles both sides acceptable (in any case you can't do a lot with these) but the toe in - oh dear! 15mm out! no wonder it wouldn't steer straight! and the right hand track rod end seized up solidly. A halt was called to the proceedings, the job part paid for and the jouney home undertaken. The car steered nticeably better with the rear alignment done and some of the graunching had gone. A new set of track rod ends was ordered. and my long suffering local garage agreed to fit them when he was having a welding torch and Transit kingpin day. This done, it was noticed that the tyres were unfeasibly worn with canvas showing on one of the inner edges of the front tyre so new tyres were ordered from a well known, poupular and cheap local tyre chain - Stand up Bathwick Tyres - with the agreement that they would temporarily set the tracking before they fitted the tyres as the car was back with Dave Pillinger the following week. They ordered the tyres, I turned up with the car, and my allotted fitter said that he coudn't do the alignment as he couldn't reach the adjuster(!) - to no avail I said that the track rod ends were new and free and that I only wanted it approximate. The discussion was not helped by some young knowitall fitter suggesting that "it'd cost me £100.00 at Hi-Q mate".  We agreed not to proceed with the sale.  . I roughly set the wheels parallel using a couple of bits of Dexion, some cable ties and a tape measure and Bathwick tyres lost a (long standing) customer and about 5000 brownie points. New tyres were subsequently fitted by A1 tyres in Bath and the tracking adjustment completed. Car transformed but ratchetting still there. While at Dave Pillinger Motors the possibility of the ratchetting being caused by incorrect operation of the diff locks was explored but none of us really had any idea of how the V8 system worked so we couldn't really investigate apart from deciding that the rear Torsen diff appeared to be working. More research needed. From various sources (mostly internet and largely SJM Autotechnik - cheers to Scott Mockry who maintains a mine of information on various 4WD audis) it appeared that the rear diff was a purely mechanical stand - alone Torsen type with no external control over the locking, the front diff had no locking facility and the centre diff was incorporated into the auto gearbox and locked by a clutch fed from the gearbox high pressure hydraulics and operated automatically by the gearbox controller. The theory that the diff lock may be causing the ratchetting and difficulty in slow sharp turns was reinforced when it became obvious that normal behavior was restored over 15mph - at higher speeds than this the diff lock is overridden. The diff lock is triggered when the gearbox controller detects a difference in wheel speeds (it has feeds from the ABS controller for this purpose as well as a couple of accellerometers to modify the performance when cornering) so it seemed possible that a loss of a wheel speed signal due, perhaps, to an intermittent wheel sensor' lead, might be the cause of incorrect operation. The ABS seemed to work fine as far as the brakes were concerned but this may use different signal processing. or something.


 


Part Three



Part Four