Differential issues are pretty rare, but certainly not impossible. Most manufacturers use the more reliable tapered style roller bearings in their differentials, while BMW likes to use ball bearings. We don’t know why they did this, but it means they are more prone to wear, and can begin to whine at speed. This noise isn’t the immediate end of the world, the vehicle can still be driven while this is happening, but it is a huge nuisance, and will eventually need to be either rebuilt or replaced before it begins to affect the drivability of the vehicle.
There are a few options to go about remedying a situation like this. The first option is to rebuild the diff, and replace the faulty bearings. The differential assembly is something that needs things to be done with a very high level of precision and tooling that most shops do not have, and is a job that is best outsourced to a differential specialist. As you can imagine having your differential cracked open, rebuilt and put back together is not a cheap endeavor, and most would say you’re better off to replace the whole thing. What you add in parts costs you will save in labour, and by replacing the entire assembly you minimise the risk of a repeat problem.
A used unit with low kilometers is the option our customer opted for with this 2014 BMW 435Xi that was brought to us with a differential whine. We sourced a used unit with 50,000 km on it, brought the car in, replaced the differential with a new pinion nut, and we were done!
Or so we thought.
To our surprise and disappointment, the used differential turned out to have a whine of its own. We first needed to verify it wasn’t a misdiagnosed wheel bearing or driveshaft support bearing failure, and there were no signs of play in either of those. Our next plan was to fit our “chassis ears” tool. This uses an array of sensors mounted underneath the vehicle to accurately pinpoint the source of elusive noises and vibrations in a vehicle. This procedure verified that our original diagnosis was correct, and it was still the differential making noise.
With this in mind, we immediately set to work sourcing yet another differential. This time around, we opted not to go for another used unit. Though it could very easily be attributed to rotten luck getting a bad one the first time around, our customer’s timeline could not allow for the downtime that could come from another bad unit, not to mention there would be little peace of mind left for the customer after having both the original and the used differentials fail. It is obvious to us that there are some inherent issues with the OEM differentials, so as usual when OEM falls short, we looked towards the aftermarket.
We sourced a rebuilt differential that uses new bearings, and reconditioned gears. All fresh and ready to install. We ordered one of these assemblies, bolted it in, and to our delight, the noise was gone! The 435Xi is driving like brand new once more, and the customer can drive with peace of mind not wondering if his differential is going to start whining again.
Every vehicle that comes into our shop receives this same dedication to solving the problem at hand. Our service technicians are confident in their diagnosis, even when the parts seem to tell a different story.