Related links: 1000q: how to adjust your shifter mechanism.
17mm allen wrench
gravity pump (siphon), or compressed air tank, hose and nozzle, or some other pump
2.0 Liters of gear oil (the transmission and differential share the same oil)
Basic kitty litter or driveway spill absorber
VW is constantly changing their gear oil spec for whatever reason and contradicting themselves so just use whatever you want as long as it's GL-4. The part number for G70 is G 070 726 a2. Most VW manual transmissions should only use a GL-4 gear oil, not a GL-5 gear oil like 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 OEM VW synthetic and found that I prefer Redline MTL since it's slightly thinner and makes shifting easier, especially in the winter. Here is a link where you can get Redline MTL.
If you want to play with different gear oils, below is a chart of gear oil viscosities from tdiclub showing index, at 40C, and at 100C. OEM VW gear oil for the mk4 is outlined in red and Redline MTL is outlined in dark green.
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, chock the wheels, jack up the car using the factory jack points, rest car securely on jack stands, and make sure the car is safe and secure before doing anything else. Note that the car must be level, otherwise the fluid level will not be accurate. I use wheel blocks to raise the car as an extra level of safety in addition to jack stands as suggested in 1000q: mechanics tips or 1000q: making wood blocks.
Engage the parking brake and put the car in gear, 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. Remove the plastic splash shield under the engine. If your car is lowered or you want an extra level of protection for the aluminum oil pan you can add a metal skid plate. See 1000q: skid plate for more details.
Clean the area around the fill and drain holes or else dirt can get into the transmission fill hole.
Use 17mm allen wrench to loosen the fill hole plug, circled in yellow below. Always loosen or remove the fill hole first to make sure that you can refill the transmission after draining.
Loosen drain plug, circled in green. Put a catch pan under the drain
plug, remove the plug, and let drain.
Here is another angle.
Below is another picture from a different view on a mk3 VW. It's the
same basic transmission except the power steering line is routed differently.
Clean the drain plug and put it back. Torque to about 20-23 ft lbs.
Refill with 2.1L. Once you have added enough gear oil, it should start to drip out of the fill hole (assuming the car is level). Stop and put the cleaned fill plug back. Torque the plug to about 20-23 ft lbs. If you foamed the oil at all, add slightly more fluid to the transmission to compensate for the foamed oil (the foamed oil 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 on the TDI 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. (*your car may
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.
If you spilled some gear oil during this procedure, wipe it up with paper towels. Then sprinkle kitty litter or driveway spill absorber and step on it to grind it into the stain. After it sits and absorbs the oil, sweep up the gravel/dust. Most local auto shops or garages will accept used engine oil or gear oil for free but if you can't find a local disposal, earth911.com can search for a local waste disposal. You can also use a large piece of cardboard to act like a placemat to avoid small stains from leaks.