(on 740 with 5HP30)
By Ralph (Dutch740)
Applies to: cars with A5S560Z / 5HP30 transmission (ie 740) maybe 730 V8 as well (?)
Problem: Automatic transmission leaks fluid from the selector shaft, and you slowly lose your (very expensive) transmission oil.
Fix: Replace seals (there are two), top off transmission afterwards.
Tools needed: I'd strongly suggest having the car on a lift, getting the seal out took me 15 minutes of fidgeting and prying with half a dozen different tools, crawling halfway under the car would have made it much more frustrating Also, the car needs to be level to top off the transmission. However, the car will need to cool for about two hours before the transmission can be touched without burning your hands. Also, the seal in question is about 5cm away from the exhaust. So have plenty of time (I changed the brake pads while waiting for the car to cool)
To top off the transmission, you will need a 17mm hex drive socket and good leverage (I used my torque wrench). The fill opening is in the bottom of the pan. To top off the transmission, you will need some sort of pump (I used a very cheap squeeze type plastic transfer pump, worked fine) and the correct oil. Other than that, you just need some prying tools for the seal (some small flat screwdrivers) and a 13mm offset ring wrench or 1/4" drive ratchet with an undeep socket.
5HP30 transmissions use special gear oil, do NOT use Dexron or such. For E32 cars, you should get Shell LA-2634. If you want to double check, look at the transmission identification plate on the right hand side of the transmissions:
The plate will be black with silver if the car uses the Shell oil; if it is green you have a newer transmission which uses Esso LT71141 oil. For more details and numbers on those, check here.
The oil is expensive and as far as I know can only be bought from the dealer. It is €17.70 excluding tax per liter, and it comes in 5 liter conainers. The seals are only €2:
I only bought one seal, I hadn't realized there is one on each side of the transmission (they are identical). I'd suggest you buy two (or maybe three if you are afraid you might damage one)
Raise the car and secure it with the handbrake and/or blocks. Don't rely on the parking pawl on the transmission, you might well accidentally disengage it while working on the shaft.
The selector shaft can be seen on the side of the transmission. It goes through the entire transmission and sticks out on both sides. The selector shaft is rotated by a short arm, which connects to a cable. The cable connects to the selector handle inside the car. The picture below shows the arm after I cleaned it, it was covered in transmission oil before.
Below, you see the other side of the transmission. The shaft is exactly the same, just has a plastic cap over it. I assume that on a right hand drive car, the selector cable connects to this side.
Remove the arm by removing the 13mm nut. There's not that much room between the nut and the exhaust. The other nuts you can leave alone, just swing the arm out of the way.
Pry the old seal out. This wasn't as easy as I had hoped it would be, since you have to be very careful not to scratch the area around the seal. In the end, I found a small flat screwdriver worked best, use the flat area of the shaft for leverage (the part where the arm sits)
Old seal tore when I removed it, it was completely dried out and brittle. The new seal has letters on one side, this side has to face out. The side you see on the picture faces into the transmission.
Be very careful when installing the new seal, it's easy to cut it on the sharp edges of the selector shaft. Some vaseline on the shaft and on the outside of the seal will help a lot. Be sure to clean out the area around the shaft, if there's dirt or oil in there, the new seal won't seat properly.
Reinstall arm and 13mm nut. To top the transmission off, it should be cold or handwarm at most. Undo the 17mm nut in the pan:
Some oil will trickle out as you remove it, but if it's really pouring out it's probably quite full and you should skip to the part where you fill it with the engine running.
Use the transfer pump to pump oil into the pan. Some will come back out, but it won't be full until old, dark coloured fluid comes gushing out as you pump in new oil. As you can imagine, this process is rather messy, have a drip pan and rags available. If you're driving the car back, some clean clothes might be a good idea too.
One full, start the engine, move the selector lever through all gears, and back into park. Now, top off the transmission again with the engine running. Once you get old dark fluid gushing out again, clean the fill opening and reinstall the plug. My car took about 2.5 liters in all, the previous owner must have driven with this (very slow) leak for quite some time. Transmission shifts smoother now (shifts when cold had been pretty harsh, much better now, also kickdown had been pretty rough) and it also took care of the '3rd gear whine' when cold.
Prices excluding sales tax.
If you would like to add any comments, remarks and/or corrections to this procedure, feel free to email Mike Oswald and we'll put it on our site. Share your experiences with us so others may benefit from it.