PULLING THE PLUG ON A 944 TRANSAXLE CASING
Arguably the most awkward problem facing any DIY Porsche owner – and many professional technicians, come to that – is galvanic corrosion. The process by which, over a long period (and sometimes a very short one), ferrousbased components effectively weld themselves into any surrounding light alloy. Many is the time I have stood beneath some disappointingly recent and so still high-value example of Stuttgart’s finest, raised on a lift, while the hero of the relevant how-to story drills out the remains of a broken screw or bolt before tapping the resulting hole and/or fitting a suitable threaded insert. It can add many hours to the job – and significant cost.
It strikes in unlikely places, too. On each of the three transaxle cars I have owned (a 944 and two 924Ss) the filler plug for the combined gearbox and final drive required some pretty heavy-duty hardware (and heat) to shift, with the added complication in the first 924S of the hexagonal key simply rounding out the matching recess in the plug. It looks as though my recently acquired Mercedes-benz Vito might have the same issue, too, although fortunately that filler plug not only has a much deeper recess for the key, but also appears to be made of much better-quality material, and so has not already been damaged.
What to do, then, if your filler (or drain) plug won’t budge, or becomes so damaged that you can’t grip it properly? (And obviously you need to make absolutely sure you can shift the filler plug before draining the oil, not when the contents of the transmission are in a bowl beneath it. Turning the car upside down to refill the unit is more than just a little inconvenient…) First, wirebrush the plug and the surrounding area to loosen as much surface corrosion as possible, and then give the exposed threads of the plug a generous squirt of penetrating oil – this last step ideally a few days before you need to do the job, and perhaps repeated several times. I always wonder in these circumstances how much of the penetrating oil, if any, will genuinely enter the necessarily minuscule gap between the plug and the casing, but every little helps – and it can’t do any harm.
Next, clean out the recess in the central part of the plug to eliminate as much corrosion and good, old-fashioned dirt as possible – a straight or angled pick is probably the best tool for that job – and then make sure that you have a good-quality key that is as tight a fit as possible. Don’t worry if you have to tap it gently with a hammer to drive it fully home– unless, of course, that comes as the result of not cleaning out the recess sufficiently (see above) or, perhaps, that the key is actually not quite the right size. The correct key for the 944 transmission plugs is a 17mm job. Finally, make sure that you have sufficient room beneath the car to get a good purchase on the plug via a suitably long bar that will give you the necessary leverage. I would hesitate to use an impact wrench on something as potentially fragile as this (although you might have to if all else fails), but there is no doubt that a short, sharp pull (or push) on something as tight as this is always more effective than a gradual increase in pressure.
Don’t panic if your key does start to round out the recess in the plug. Well, not quite yet, anyway. Snap-on – among others – sells sets of special reverse-fluted sockets designed to grip the outside of rounded-off bolts and nuts and, unlikely though it might seem, they can usually make remarkably short work of even something that started off completely circular, such as one of these plugs. Choose the socket that’s as tight a fit as possible over the threads, perhaps tapping it home over the relatively soft material with a few short, sharp blows from a heavy hammer – you are in no position to pull your punches here. Again give yourself a fighting chance by using as long a bar as possible, and perhaps land the knockout punch by getting the area round the plug as hot as possible, with either a DIY- style gas torch or, better still, an oxy-acetylene set-up. Just be careful not to start melting everything in sight, and bear in mind the obvious fire risks, not least due to the proximity of the fuel tank. Have an extinguisher ready, in case.
It would, of course, be a good idea to buy a couple of new plugs before you start – the part number for both is 111 301 127E; they cost a mere £2.76 apiece plus VAT – and it’s obviously only sensible to protect any remaining exposed thread, once they have been fitted, with a squirt of some wax-based preservative. That should help prevent any water working its way down the thread, and creating further corrosion in future.