BMW DIY – Manual Transmission and Differential Fluid Change How To
Changing Manual Transmission & Differential Fluids: Easier Than You Think, More Important Than You Know.
While all of us know the importance of regular engine oil changes – and the penalties of neglecting this common maintenance task – there are two other important fluid changes that we tend to ignore. Perhaps the two most neglected maintenance tasks on most vehicles, including our BMWs, is the regular changing of fluids in the differential (rear-end) and the transmission.
Like engine oil, the fluids in your BMW’s differential and transmission perform two tasks. They not only lubricate and prevent wear to the parts that are moving against each other, they also help cool the assembly by removing heat from the metal parts and transferring it to the case. Air moving over the outside of the iron or aluminum case then removes the heat from the case. Unlike engine oil, however, these fluids do not build up contamination from engine combustion. But they do break down from heat and “shear” (the fluid’s molecules being broken down by the grinding action of the gears and bearings). Additionally, these fluids do become contaminated with minute metallic particles that are the byproducts of metal-on-metal wear.
The best way to assure that your BMW’s differential and transmission oils are doing their jobs (anti-wear & cooling) and protecting their respective assemblies is to replace them annually. This is a relatively simple task; if you are already changing your own engine oil, you should be able to change your differential and transmission fluids. Here’s an overview of the basics, followed by a step-by-step guide:
The fill plug is in the rear aluminum differential cover. (See Figure 1 below.) Note that some later model BMWs have the drain plug on the passenger side of the main differential housing. The drain plug will be in either the rear cover, below the fill plug, OR in the passenger side of the differential housing. Both plugs are internal hex (Allen type). The drain plugs on early BMWs are removed using a 10mm hex tool; most later BMW drain plugs require a 14mm hex tool (see our 10mm, 14mm, 17mm shorty hex tool kit). In most applications, two quarts of fluid will be required, though you may not use it all. Check the applicable Bentley or Haynes repair manual for fill quantities on specific models.
Manual Transmission Basics:
On a manual transmission case (Figure 2) there are both a fill plug and a drain plug. The fill plug is normally on the passenger side of the transmission case, near the middle of the side of the case. The drain plug is on the bottom of the transmission, typically at the rear. There are two types of fill and drain plugs: one has an external 17mm hex head; the other has an internal 17mm hex (Allen type). Again, two quarts of fluid will do the job in most applications. Check the Bentley and Haynes manuals for model specific fill quantities.
Changing The Fluids:
The following procedure is applicable (in general) to both the differential and the manual transmission.
NOTE: For both of these tasks, the vehicle must be raised and safely supported so that you can access the underside of the vehicle. If you are not using a vehicle lift, you must jack up and securely support the vehicle on jack stands. Be sure to wear safety glasses while working under the vehicle. Before raising the vehicle, drive it for a few miles to warm up the fluids.
Since the filler hole for the differential and the manual transmission are under the vehicle, you can’t just pour the fluids in to them as you can with the engine. You will need a fluid transfer pump (see list of parts and tools).
Below, we will show the procedure on a typical BMW differential. Follow the same steps in performing the drain and fill on a manual transmission.
1 Remove the fill plug. We do this first for two reasons; to assure that the plug can be removed, and to prevent a vacuum in the gear-case housing as the fluid drains.
2 Remove drain plug.
3 Drain the old fluid into a suitable container (see our self-contained drain pan) by removing the drain plug and allowing the fluid to empty completely.
4 Clean the drain and fill plugs of any accumulated sludge and/or metallic particles.
5 Replace the drain plug. We suggest replacing the drain plug with our Super Magnetic Neodymium drain plug. These plugs offer superior ability to remove metallic wear particles from the fluid.
6 To fill the manual transmission or differential, use a fluid transfer pump (see our 1/2 liter fluid transfer pump) to add fluid through the filler hole until the level reaches the bottom of the hole.
7 Replace the filler plug.
That’s all there is too it! If you have any questions about these procedures – or anything to do with your BMW – please give us a call at 800-535-2002 or visit our web site at www.bavauto.com
Click below for Liqui-Moly synthetic 75w-90
manual transmission and differential fluid (non-limited slip):
Click below for Red Line synthetic 75w-90 differential fluid (all differentials):
Click below for Red Line synthetic 75w-140 differential fluid (all differentials):
Click below for Red Line synthetic manual transmission fluid:
Click below for self-contained fluid drain pan: