When was the last time you serviced your transmission and differential in your BMW? If you can’t remember, it’s probably time to do them both. This edition of Tuned In Weekly is a special one, since the main focus was on VW/Audi Haldex service, we decided to offer you BMW guys a little something too. So, here’s your reminder for drivetrain service and a few options we have to make your life easier.
First things first, whether you have an automatic or manual transmission BMW, servicing the fluids regularly is critical for transmission performance. For the differential to last hundreds of thousands of miles, it also needs regular fluid replacements. While the drivetrain fluids are intended to be ‘lifetime’ fluids and often do not carry a service interval from BMW, we owners tend to find that not to be the case, especially with auto cars. You don’t need to replace gear oil as frequently as engine oil, but it’s a proactive service that should be completed with some regularity. You’ll read differing opinions online about recommended service intervals ranging from 30k miles to never, but there isn’t an exact ‘perfect’ interval. In my experience, balancing cost and regularity equally tends to point me to a 60k mile interval for drivetrain fluids. I generally service the transmission and differential(s) every tenth oil service, or roughly 50k miles on a 5k mile oil service interval. This way, I have peace of mind that my gears are happy, lubricated, and healthy. It also gives me the chance to inspect old fluid relatively frequently to spot any impending disasters.
It’s that inspection of the old fluid that I find most important. You need to know what’s happening inside the mystery boxes that are transmissions and differentials. Ok, they aren’t all that complicated, but still. If an easy service allows me to spot something bad before it happens by finding an unusually high concentration of metal flakes, I’m better prepared to budget for and tackle that critical repair when the time comes. Just like regular engine oil service, drivetrain fluid service gives you the chance to stay ahead of problems rather than react to them when they happen unexpectedly. It’s just best practice to be proactive.
Now that you know the importance of regular drivetrain service and inspection, let’s talk fluids (and filters for you automatic drivers.) We’ve made your life a bit easier when it comes to these essential services by piecing together complete kits that include the fluid, filter (when applicable), fill plug, drain plug, and crush washers so you don’t have to hunt for the right stuff. With Genuine BMW options as well as quality aftermarket options, you can pick the kit that’s right for you and know it’s exactly what your car needs, too. But that’s not the end of it. If you’ve never performed one of these services before, you could benefit from a few handy tools we also recommend.
A Schwaben Fluid Pump is effectively necessary for refilling your differential and manual transmission. Auto guys have it a bit easier with their trans fluid refill, but they’ll still need a way to fill up the differential, so this applies to both variations.
Another essential tool is a drain pan. I don’t like to mix fluids in my drain pans as that can make it difficult to inspect the fluid after it’s drained. If you mix coolant and oil, you get that gross milkshake substance. So you can inspect the fluid, it’s a good idea to have a separate drain pan or dedicated bucket for each fluid. We have a few that make catching and disposing of the fluid easy for you that you should include if you don’t have a few laying around unused.
Finally, you’ll want to ensure your drain plug and fill plug are both torqued to spec when you’ve completed the service. This is critical. You don’t want to over-tighten these plugs, as the cast metal differential and transmission can crack when the fill or drain plugs are installed too aggressively. We don’t have to tell you how bad that can be. A 3/8in drive torque wrench and 1/2in drive torque wrench are both necessary to have in your toolbox for nearly every job. Depending on what transmission and what differential(s) you have, there are a few different specs across the range for torque. Remember, the bigger the torque wrench, the less accurate it is at lower values, the opposite is true for smaller torque wrenches. So, it’s a good idea to have at least a 3/8th drive and a 1/2in drive around to make sure you’re installing those plugs correctly.
The last little bit of advice we have to make this job happen flawlessly is to always crack the fill plug open first, then try the drain plug. If you do this in reverse and open the drain plug first, in the off chance that your fill plug is seized or rounds off, you will end up stuck with no way to refill your transmission or differential. This is obviously less than ideal, so make sure you can open the fill plug first, then go for the drain plug.
That’s pretty much it! When you refill the fluid, you’ll know it’s full by seeing fluid begin to pour out of your fill hole and by double-checking the amount of fluid you’ve filled. Remember, there will likely be a little old fluid left in the system, so it may take less than the total amount required to fill it, so don’t be scared if it doesn’t take all the fluid included in your service kit to fill the transmission or differential.