Article reproduced with kind permission from Mike Fishwick
The older BMW gearboxes were filled with either normal 75-80 EP gear oil or automatic transmission fluid, this being denoted by the use of either a brown or orange label near the filler plug, and owners of such cars therefore accept the need to change the oil from time to time. Many have found that the use of a more modern synthetic lubricant improves their gear change action, but if following this route, first find if your gearbox requires the use of GL3/GL4 oil only, or the modern GL5 standard.
Owners of classic cars should be aware that GL5 oils contains additives which will rapidly attack any copper alloy components such as selector forks and bushes. The older GL3/GL4 lubricants are now becoming difficult to obtain from local suppliers, but are still available from oil specialists such as Opie Oils.
It is amazing how many rational people accept the BMW claim that gearboxes bearing a yellow sticker near their filler plug contain ‘Lifetime’ oil! This simply means (in BMWSpeak) that it will be satisfactory for the three year New Car warranty, and a couple of years afterwards for the benefit of the BMW Approved Used Car warranty. As with any oil, it gradually becomes contaminated with moisture and tiny particles of metal, and degraded as the polymer viscosity improvers become minced between the gears and splines.
While those who buy a new BMW and run it for a short period will not be concerned by this, those of us who buy used, and/or plan to keep the car for a long time, should remember that the gearbox will benefit from regular oil changes at a maximum of five years or 50,000 miles, whichever comes first. These figures could advantageously be reduced to three years or 30,000 miles, but anything less would really be a waste of time and money.
BMW dealers, of course, are not exactly keen to change this gearbox oil, and often quote a very high price for the task. This is probably due to a discount structure which does not does not provide their usual profit margin, and the slow rate of use which a drum of gearbox oil would have due to the majority of owners accepting the propaganda that BMW have discovered an immortal lubricant!
There are, however, several sources of suitable oil for those who have managed to reject the notion that only Castrol lubricants, being the only BMW-approved oils, can be used. Although Castrol are one of the foremost lubricant manufacturers, the fact that they seem to share a bed with BMW probably owes less to the unparalleled excellence of their products than it does to the level of discount at which they supply BMW!
A glance at the Opie Oils website (opieoils.com) will show that several other manufacturers produce suitable gearbox oils, such as Fuchs Sintofluid SAE 75w-80, which was the original factory fill, and similar American products from Amsoil, Redline, and Royal Purple. These are supplied in 1 litre or 1 US pint (956 cc) quantities and will be delivered to your door the next morning, for roughly £15 per litre.
I use Amsoil MTF in the ZF gearbox of my Z3 for, and have no complaints. For some reason the Americans use the SAW engine oil viscosity scale, which translates to 75-90 as a gear oil.
Draining the gearbox is easy enough – place a suitable container below the drain plug (the capacity is 1.3 litres) unfasten the level plug on the RH side of the gearbox, and then remove the drain plug. As with an engine, it is best to drain the gearbox while it is warm.
On the ZF gearbox used by most 2.8 litre and M3 engines, both plugs are of the tapered thread type, and are attacked with a 17 mm ring spanner. When replacing these plugs, carefully degrease the both threads, and lightly coat them with a thread sealing compound, such as the Loctite product which is available in small tubes from Halfords. Tighten the plugs with one hand at a radius of about six inches and you will do not harm. The ‘dry thread’ torque figure is 52 N-M or 35 lb-ft.
The Getrag gearbox used by the smaller engines uses plugs with an 18 mm hexagon socket, but the same procedures apply. Their filler and drain plugs, however, have a lower ‘dry’ torque setting of 35 N-M or 25 lb-ft, but one hand at a radius of four inches will suffice.
Always remember that manufacturer’s torque settings are for the benefit of production line robots, who are working on oil-free components – application of these figures to lubricated threads in an aluminium casing will result in expensive damage! Mechanical sympathy is a skill worth developing.
Refilling either gearbox can be a problem, as there is insufficient space alongside to hold a one-litre oil bottle. On my Z3 I find that the upper half litre from each container can be squeezed in, after which a large syringe must be used for the rest, although a garden syringe and a length of plastic pipe would be easier. Another option would be to use a pressure bleeder. The ZF gearbox takes 1.3 litres, and the Getrag slightly less.
The final drive unit is not exactly filled ‘For life’ being included in the service schedule for an oil change at every second Inspection 2, but in the ‘Capacities’ section of the Owners Handbook it is listed as being ‘Filled for Life.’ It is therefore often overlooked.
When planning to change the final drive oil, it is essential to first find if your car is fitted with a limited slip differential, the fitting of which depends mainly on the market for which the car was ordered. For example, in terms of the Z3, all UK-market cars were fitted, but not so in Japan. To be sure, simply quote the last seven digits of your VIN code to any dealer, and ask for a printout of the car’s options list.
If an LSD is listed in the ‘Standard Options’ area, described as a ‘Sperredifferential 25%’ it will require the use of a special oil, due to the use of a multi-plate clutch pack in many models. In most applications this has been superseded by a Torsen (TORque SENsing) differential, so the time-honoured method of jacking the rear wheels off the ground, and seeing if when one is turned the other rotates in the same direction (LSD present) or the reverse direction (no LSD) cannot be relied upon as an indicator.
Although the Torsen LSD contains only gears, some are of a sufficiently specialised worm type to also require a particular lubricant, both LSD types being satisfied by Castrol SAF-XJ. A non-LSD final drive will be happy on most hypoid lubricants, such as Castrol SAF-XO. Both are available from Opie Oils.
Although the final drive capacity is listed as being 1.5 litres, when I first changed mine I drained exactly 1 litre, and filled it with 1.75 litres to the level plug! Perhaps BMW had found that only 1 litre was ‘Acceptable’ and therefore saved the cost of 0.75 litre per car . . .
Changing the final drive oil presents no problems, the plugs requiring the use of a 14 mm hexagon key, ideally in socket set form. On many mocels, such as the Z3, removal of the spare wheel provides greatly improved access.
It would, however, be wise to first obtain a pair of the solid aluminium sealing washers (07.11.9.963.355) and ideally a replacement ‘O’ ring seal for the speed sensor (126.96.36.199.166) as this can sometimes fail. If changing this seal, take care to replace the ‘O’ ring on the curved step of the sensor, rather than the square step. While it is removed, carefully wipe the sensor head to remove any fine metallic debris, which can eventually prevent its operation.