Article by: Paul Axford
Applies to: All models with the M30 big six engine (this article was written with a 730i). The 730 and 735 big six automatics all have the ZF 4HP22 4-speed transmission, which is installed on hundreds of thousands of various European cars. Additional models with the M10, M20 ,M21, and M40 engines also use the same transmission.
All current wisdom suggests a simple “drain and fill” is much less risky than a full flush. It seems that new oil tends to loosen debris and, unlike in the engine, fine particles circulate around the system rather than become trapped in a filter.
Occasionally refreshing the oil to dilute the circulating particles over the service life seems to be the key, and for this reason I see no need to spend money on a synthetic unless you are towing or live in a mountainous area.
By the way, the dipstick is removed by tilting the base of the cap in the direction of the arrow on the top – no doubt a clever idea in the designer’s eye, but somewhat of a joke from an ergonomic point of view.
It may not be necessary to replace the filter screen unless the oil has not been replaced for 160,000 km (100,000 miles) or more. The screen doesn’t retain particles like a paper filter but it may be slightly clogged.
If you do decide to replace it (and I did,) you can save effort (and a potential leak) by leaving the dipstick tube attached to the pan during removal – just remove the tube support clamp 1/3 the way up.
Best to supply them with the “Getriebe Nr.” on the manufacturing plate, in my case 1043010726. Be sure to also purchase a new rubber gasket and note also that the two magnets present in the sump are not glued down, just “stuck” there in the dimples.
The ZF 4HP22 has a sump drain plug, opened with a 5mm hex key. If you drain over 1/2 hour you will get about 3.3 L of the total of approx 7.5 L. If you drain overnight you will get 5 L.
In any case, measure precisely what you remove and replace with the exact same amount of Dexron III, carefully poured through the dipstick opening.
Editor’s Note:
Another product that seems to have a positive effect on longevity is Lubegard. It has additional friction modifiers that can drop the transmission operating temperatures by up to 40 degrees Fahrenheit! I literally called Lubegard to ensure that this product is compatible with the ZF 4HP22 transmission.
~ M. Oswald
If you buy the filter from a ZF agent rather than the dealer be aware that the filter is a “deep pan” type, not the low profile type, unless your build date is pre-March 1988.
The “filter” in this case is actually a fine wire mesh screen. Ferrous particles would eventually be captured by the sump magnets and larger particles are stopped by the screen, but not normally captured by it.
A 10mm socket with extensions will remove the six pan fasteners. You will need a high-quality Torx T27 bit with a socket handle drive to remove the filter screws – don’t improvise here, they are quite tight as they also retain the valve body.
I replaced my magnets with a couple of the powerful rare-earth type just because I had them available.
The ZF 4HP22 has a sump drain plug, opened with a 5mm hex key. If you drain over 1/2 hour you will get about 3.3 L of the total of approx 7.5 L. If you drain overnight you will get 5 L.
Last item to note, unless you have a steady hand and incredible patience you will need to fabricate a method of attaching a small funnel to the dipstick tube such that the new oil can be easily poured in.
A short piece of rubber hose will do the trick.