Anywhere between 60,000-100,000 miles is a good gear oil change interval. Related links: 1000q: adjusting your shifter mechanism. (A common problem is mixing 1st and reverse gear).
17mm allen wrench
gravity pump (siphon), or compressed air tank, hose and funnel, or some other way of getting the oil into the transmission
2.0 Liters of gear oil (the transmission and differential share the same oil in the manual transmission) 75w90 synthetic gear oil
(VW# g 005 000 is the .01 liter size) (VW# g 005 100 a1 is the 0.5 liter size), this is aka G50 gear oil
paper towels and basic kitty litter or spill absorber
Note: your transmission should use GL-4 for best results. Refer to your owner's manual for the most precise answer. Older VW transmissions should only use a GL-4 gear oil, not a GL-5 gear oil which includes Mobil 1 75-90. Many people have success with Redline MTL or MT 90, or Royal Purple Max gear. I have tried a few different gear oils including the VW synthetic, I prefer Redline. If you want to play with different gear oils, below is a chart of gear oil viscosities from tdiclub. G50 is outlined in red.
VI Vis@40C Vis@100C
128 159.0 18.3 = AMSOIL CTL SAE 50 Powershift GL-1
..............16.7 = Motul MOTYLGEAR 75-90 GL-4/-5
..............15.6 = VW G50/G51 GL-4
185 90.0 15.6 = Redline MT-90 75-90 GL-4
..............15.2 = Mobil 1 Synthetic 75W-90 GL-5
..............15.2 = Motul Gear 300 75-90 GL-4/-5
..............15.0 = Elf Tranself Synthese FE 75-90 GL-4/-5
132 116.0 14.9 = AMSOIL AGL 80W-90 GL-5
177 84.5 14.7 = AMSOIL MTG 75-90 GL-4
..... 76.6 14.2 = VW G052-911
133 76.2 11.0 = AMSOIL CTJ SAE 30 Powershift GL-1
183 56.2 10.6 = Redline MTL 70-80 GL-4
194 47.1 9.6 = AMSOIL MTF Synchromesh Trans fluid (GM/Chrysler) GL-?
208 41.6 9.1 = Penzoil Synchromesh trans fluid GL-?
198 34.0 7.5 = Redline D4 ATF Dexron III / Mercon / API GL-4
138 40.5 7.1 = AMSOIL CTG SAE 10W Powershift GL-1
..... 31.2 6.5 = VW G-052-171-A2 GL-?
..... 35.1 6.4 = VW G-055-726-A2 GL-?
..............6.3 = VW G52 (part numbers G052726A2 / G05272601)
Engage the parking brake, jack up the car using the factory jack points, rest car securely on jack stands, chock the front and/or rear wheels as necessary, and make sure the car is safe and secure before doing anything else.
Make sure that the car is level so that the fluid in the transmission is level. Important: if the car is not level then the fluid level will not be accurate.
Remove engine plastic under cover.
Clean the area around the fill and drain holes - don't skip this step or else dirt may get into the transmission!
Use 17mm allen wrench to remove the fill hole, circled in yellow. Always loosen or remove the fill hole first to make sure that you can refill the transmission.
Loosen drain plug, circled in green. Put a catch pan under the drain plug, remove the plug, and let drain.
Below is another view (from a later generation TDI, it's pretty much the same thing).
Do not dump used gear oil onto the ground or into the water! If you can't find a dump for used coolant/antifreeze, engine oil, gear oil, or other car fluids, here's a search for your local waste drop off: earth911.com search.
If some gear oil spilled onto the driveway, first wipe it up with towels. Then pour some driveway spill absorber or basic kitty litter on the spill. Step and grind the litter into a fine gravel or dust and then let it sit to absorb the stain. When the dust is wet, sweep it up and throw it out.
Clean the drain plug and put it back. Torque to about 20-25 ft lbs
Once the gear oil comes out of the drain hole (assuming the car is level) or you have added enough gear oil, stop and put the cleaned fill plug back. Torque the fill plug to about 20-25 ft lbs. If you foamed the oil at all, add slightly more fluid to the transmission to compensate for the foamed fluid (the foamed fluid contains air).
There are a few ways to get the fluid back in. You can use a gravity
pump or siphon, where the bottle is higher than the fill hole and connected with
a hose. You can also use a hand pump designed to force fluid out of a
container. The easiest method is to use a funnel and hose, and snake it
into the transmission fill hole from above. I feel that this also
wastes the least fluid. Below is a picture of the yellow tube going into
the fill hole, sorry that it isn't that great but it's not terribly interesting
and if you got this far you know where the fill hole is.
If you spilled some oil on the ground, first wipe it up with towels. Then pour some driveway spill absorber or basic kitty litter on the spill. Step and grind the litter into a dust and let it sit for a while. It needs time to soak up the stain. When it's saturated, sweep up the gravel/dust.
Another method is to use compressed air to force the fluid into the fill hole. It's not possible to use a funnel on many cars so I originally made this for my Audi and on other cars. To use the compressed air method of adding fluid, take a compressed air tank and regulate the pressure down to a reasonable amount, just enough to get the fluid flowing. If the pressure is way too high, the bottle could pop, so start low and then increase the pressure if the fluid isn't moving fast enough.
Use a short length of hose, just longer than what is needed to go from the bottom corner of the bottle to the transmission fill hole. Make sure the hose has at least 1/4 diameter, otherwise the fluid will have a hard time flowing through the hose. If you can't breathe through the hose, it's too thin.
Poke a hole slightly smaller than the hose in the cap (smaller is better for
a tight air seal), and a small hole (again, smaller is better) in the top of the
bottle, marked by the green arrow in the below picture. Obviously the air
input hose has to be above the fluid level or else it will leak out. Now
stick the hose into the cap, making sure the hose goes all the way to the
bottom. Make sure that the hose goes all the way to the bottom of the
bottle otherwise you will get just foam instead of fluid. Too much foam
will fool you into thinking there is more fluid than is actually in the
transmission. If this happens, let it settle down and overfill it
slightly. Also make sure the hose has a large enough inside diameter
because thin hoses will transfer fluid at a snail's pace. Since a picture
is worth a thousand words, here you go.
Now press the compressed air nozzle into the hole in the top of the bottle marked with the green arrow in the picture above. Warning! Do this step last because you may accidentally press the trigger on the compressed air nozzle before the hose is in the fill hole. If this happens, your expensive fluid is now all over the ground. Apply gradually increasing amounts of pressure until the fluid is gone. If the bottle stretches a little that is okay. If you think it's going to pop, stop applying pressure. I put my gloved hands around the bottle cap and nozzle to prevent any fluid from hitting me in case the bottle cap blows off. As always, wear protective safety goggles.
Like this tip? There are many more tips for the mechanic at 1000q: mechanics tips and garage organization.
Note that the fill hole end of the hose has a coat hanger bent into an s-shape (so it stays in place) with a hook at the end. I did this so that I could use the same hose for both manual and automatic transmissions and to minimize dripping at the end of the hose. Some Audi transmissions have a cap on the fill hose which requires a 90o bend at the tip.
Once the gear oil comes out of the drain hole (assuming the car is level) or you have added enough gear oil, stop and put the cleaned fill plug back.
When you go to the next bottle, just poke another air intake hole in the next bottle and transfer the cap. Don't let the hose touch the ground because it will collect dirt. If it gets dirty just thoroughly wipe it off.
When putting the fill and drain plugs back, you can wrap the threads once or twice with teflon tape to help ensure no leaks.
After you're done, hang the hose with a paper towel or two on the end and let it drip dry.
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