there is a third; improper shifting habits, ignoring worn shift linkages and bushings. but these are characteristics of an oaf, and that's beyond the scope of this article because changing the gear oil is the least of your problems.
that sit alright with you?
OK, put another way, they also suggest oil and filter changes at 20,000 km (12,000 miles) for the same models.
do you see where this is going?
never mind that it's synthetic oil. if you can afford to own a car like this, cutting those intervals by a quarter for the engine and about half for the gears is a pittance if you're going to keep the old girl around for a while. so forget the suggested service intervals, the company whose cars we lust after prefer to see you in their newer models; and there's no faster way there than by slowly killing the obsolete ones.
if you don't drive your bubble Porsche often enough—do you at least start the poor thing a couple times a week, give her some throttle and get 'er hot enough to kick on the fans? careful old boy; improper preservation is as bad as clay barring the paint...microscopically speaking, of course.
"some engine and gear oil formulas contain chlorine and sulfur, and when these mix with water moisture, some bad shit begins to happen."
rust on steel and iron acts as an abrasive that will quickly wear away when engines and gearboxes are started up again. if they've been allowed to sit for several months, rusty surfaces will leave behind pitting on the metal surfaces...no so problematic for the hardened gears, it's the bearings you've got to worry about — pitting on the balls, rollers and the races they glide on will never get better with use. by the time they begin to whine or rattle, driving the thing will quickly make gearbox replacement supersede rebuilding it.
will every gearbox be vulnerable to these extremes? difficult to say. there're too many factors to consider like climate, altitude, geography, oil composition, and the like for anyone to formulate concrete answers. drive it and drain it often — prevention is preservation and preservation is prevention, so let's get on with the oil change.
you don't need a lift for this job; a hydraulic jack, an axle stand, and a sheet of 1000 mile paper (cardboard in hobo parlance) will do nicely. being that the 968 doesn't have a lift point in the middle like the 944 does, jack up the driver's side (LHD car, passenger side RHD) front high enough to get an axle stand on the rear jacking point...or you could jack up the rear and place an axle stand on the torsion bar tube closer to the aluminum bearing flange it comes out of.
grab a drain pan, a 1/2" drive breaker bar, 1/2" drive 10mm allen head socket and slide underneath her tail. there, behind the rear axle, is the massive Getrag hanging down. now look on the driver's (LHD car, passenger side RHD), to the right of the axle flange is the fill plug (green arrow labeled 1)...loosen and remove this one first. why? because if you loosen the drain plug first and find that you can't break the fill plug loose without resorting to violence, you're fucked and have just turned a simple job into a complex one with no plot. make sure you clean the area and the cavity where the socket fits using a hammer to lightly tap the socket in—you want to be sure that sucker is driven fully home before taking a crack at it.
now place a catch pan under the drain and do the same for the drain plug (red arrow labeled 2); clean out the cavity, insert the 10mm allen head socket, pound 'er home, loosen, remove and let her piss out the old gear oil. you'll want to lower the car back down on level ground while it drains. if you're feeling a little horny, jack up the opposite side to drain out nearly every last drop. keep the fill and drain plugs in separate places; you don't want to put the wrong one in the wrong hole...remember the drain has the magnet in the middle.
when the last of the oil is two or three drips away, clean out the drain/fill plugs paying special attention to the drain plug's magnet. what did it attract? small chunks like flies on a turd or a viscous paste made with fine particles? this is a pretty good indication of what kind of party's been going on in there while the doors where closed.
you may or may not notice that the plugs also have aluminum crush washers; the same as on your engine oil drain plug — 27mm OD/22MM ID part number 999 123 118 30 (see image above). the Porsche parts catalog doesn't call them out for the 968...unsure why, but mine had these washers on them. and since I always have a bunch of these on hand, I decided to replace them.
do your research on the oil brands. call the manufacturer, talk to the goddamned professionals, but resist the urge comb the forums—it only takes a few inconclusive pieces of advice, opinions, and rants to confuse and further frustrate the uninformed — ask 10 different people and you'll get 36 different answers. and forget your local Porsche dealer, they get some generic shit in bulk without a clue who makes it...I called a few out of curiosity. so much for the source; stateside, anyway.
when you're ready to fill the gearbox, raise the car back up and rest it on the axle stand, clean the area around the drain, and make sure you have the right plug; remember, the drain plug has the magnet. insert your freshly cleaned drain plug wearing a fresh aluminum crush washer by twisting it counter clockwise a twitch until you feel the threads disengaging. I prefer doing this to ensure that the plug is ready to start the threads, minimizing the chance of a cross-thread. the service manual calls for 35 Nm (22 ftlb) of torque on the drain and fill plug.
you have two options in order to accomplish this. one is the redneck method of using 1" clear PVC tubing sticking into the fill hole and out of the driver's side wheel well topped with a funnel, or the method I have pictured above using a much cleaner "fluid transfer pump" mechanism. I've used the former method but went with the latter this time 'round because I felt like changing my routine. now this "fluid transfer pump" can be bought at any variety auto parts joint or Harbor Freight. it screws over most gear oil containers and comes with two lengths of pick-up tubes to suit their depths. the best part of this contraption is the barb at the end of the tube that inserts into the fill hole and stays in place while you pump.
since the 968 takes 2,75 liters, I kept the car's driver's side (passenger side for RHD) elevated and pumped in about half a gallon (roughly 2 liters), and then brought 'er back down to level ground to feed in the remaining ,75 liters. the second and third shot from bottom shows how the pump handle fits nicely into a nook between the spare tire hump and muffler when the car is down on level ground leaving enough space to squirt the oil in.
"6mm seems insignificant, like fly pussy, but if you've psychological issues stemming from being caught masturbating in your formative years, I suppose you're hardwired to follow instructions to the letter."
owners of early production 968s, take note; your gearbox was manufactured with the fill hole 6mm (1/4") too high. these gearboxes are tattooed with the number 6 followed by the plus sign ( 6+) above the fill hole as shown in the illustration below. the service manual insists that you must fill the gearbox 6mm (1/4") below the filler bore — how they expect one who may not have the creative capacity to do this beats me. here's a suggestion; take a 90° pick tool, make sure it's clean, insert it into the fill hole angling the tool parallel to the ground, quickly but carefully remove it, and measure the distance between the fluid mark and the 90° bend...or use your finger and measure from your first knuckle.
6mm seems insignificant, like fly pussy, but if you've psychological issues stemming from being caught masturbating in your formative years, I suppose you 're hardwired to follow instructions to the letter.
remember to note the service in your log book with date and mileage along with a note reminding you of the next service interval.