WHEN A CHANCE REALLY ISWORTH TAK­ING

911 Porsche World - - Practical Porsche - With 911 & Porsche World’s con­sul­tant ed­i­tor, Chris Hor­ton

As many of you will prob­a­bly know by now, I am not at all keen on im­pro­vised fixes to any car, and least of all to a Porsche – espe­cially when gen­uine brand-new spare parts are read­ily ob­tain­able. Do it right, do it once, and all that. Some­times, how­ever, you sim­ply have to make the best of the re­sources avail­able to you at the time – par­tic­u­larly when it’s a bill­pay­ing cus­tomer call­ing the shots. And even more so when he and his car are booked on a ferry to France the fol­low­ing day, and the new com­po­nents wouldn’t be avail­able un­til some time the fol­low­ing week.

My friends at Auto Um­bau, Robin Mcken­zie and Terry Parker, told me re­cently about a rather un­usual re­pair they’d had to carry out on a 996-model Car­rera 4. The owner, per­haps a lit­tle op­ti­misti­cally, brought it in the day be­fore his hol­i­day com­plain­ing of a rhyth­mic grind­ing sound from the vicin­ity of one of the rear wheels. Try as they might, though, they couldn’t iso­late it. Tem­po­rar­ily tak­ing out the brake pads and spin­ning the wheel soon elim­i­nated those or the disc as the cul­prits (quite of­ten you can get a noise like that if a stone be­comes trapped be­tween the disc and the caliper or the back­plate) and, although it then seemed to be com­ing from in­side the hub, it didn’t sound at all like a bear­ing.

But then ea­gle-eyed Robin spot­ted it. Look­ing more closely into the in­ner part of the hub assem­bly, where the con­stant-ve­loc­ity joint passes through it, he re­alised that the slot­ted ring upon which de­pends the ABS for its wheel-speed sig­nals had been forced out of round by cor­ro­sion on the un­pro­tected metal sur­face be­neath it. The sound, un­sur­pris­ingly, was the sin­gle high point on the ring hit­ting the hap­less sen­sor – and ob­vi­ously wear­ing it away in the process. Oddly, though, the ABS light had not switched on – had it done so the di­ag­no­sis would surely have been a lot quicker.

But what to do about it? The sen­sor, as­sum­ing that the fix­ing screw came un­done with­out break­ing, would at £140 from Euro Car Parts be an easy re­place­ment – if not ex­actly in­ex­pen­sive. But plainly there was ab­so­lutely no point fit­ting a new one un­til the cause of the prob­lem had been fixed; it would soon be de­stroyed by the dis­torted ring. Un­for­tu­nately, how­ever, you can­not buy the ring separately, but only as an in­te­gral part of a com­plete brand-new drive shaft. To you, sir, that will be around £650 plus VAT.

Af­ter a bit of thought and dis­cus­sion, our he­roes hatched a cun­ning plan. By care­fully bead-blast­ing the out­side of the CV joint (with any sen­si­tive ar­eas masked off with tape), they dis­persed enough of the rust to be able to slide off the ring. Fur­ther blast-clean­ing of both items re­moved all re­main­ing traces of cor­ro­sion, and by heat­ing to cherry-red and then rapidly quench­ing the ring alone they were able to shrink it back down to more or less its cor­rect in­ter­nal di­am­e­ter. It was still a lit­tle over­size, of course, and thus not quite a tight enough fit on the out­side of the CV joint, but that was solved by se­cur­ing it with an epoxy ad­he­sive. A thin but still use­ful coat of paint, and it was (al­most) as good as new.

But would it work? The short answer is yes. Per­fectly. There is no guar­an­tee for how long, and if it does later fail for any rea­son then the cus­tomer will prob­a­bly have lit­tle choice but to buy a new shaft (or per­haps a good sec­ond-hand item, if one can be found). Ei­ther op­tion brings with it the ob­vi­ous fi­nan­cial risk of hav­ing to pay twice for the re­quired labour, but if it saves the thick end of £800, even for a year or two, then I reckon that’s a chance well worth tak­ing. PW

The car en­thu­si­ast’s con­stant en­emy, cor­ro­sion, strikes at Porsches – which fa­mously have rust-re­sis­tant, zinc-coated body shells, of course – in the odd­est of ways. Here, rust on the body of the con­stant-ve­loc­ity joint be­neath the ABS ring on a 996 Car­rera 4 had grad­u­ally forced the ring out of round. This had caused the high spot (ar­rowed) to hit and ob­vi­ously wear away the sen­sor, mounted on the hub car­rier (right). The ‘fac­tory’ re­pair would have meant fit­ting a com­plete new drive-shaft – you can­not buy the ring separately – but at nearly £800 for the shaft, and a de­liv­ery date sev­eral days af­ter the car was due on a ferry, that wasn’t an op­tion. Time for some ‘desert en­gi­neer­ing’, then

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