If you retain one piece of information from this story, it should be that universal joints are an essential part of the drive system on front-engine rear-drive vehicles. The driveshaft is responsible for transferring energy from the transmission to the rear differential and, in turn, supplying power to the wheels. U-joints enable the inflexible driveshaft to move as the vehicle encounters bumps on the road and as the engine twists on its mounts. The reason the drive shaft needs to have some upward and side motion is because the engine is attached to the chassis via engine mounts (We speak the truth.—MAX). The amount of engine torque is dependent upon the power output of the engine and the material the engine mounts are made of, where the differential is separate from the engine and does not twist with it. One of the things that keeps the driveshaft from ripping apart the rear differential and transmission as all this twisting and shaking is occurring are the u-joints. I’d call that an essential part of the driveline system.
The MAX Power BMW began shaking when the engine turned more than 3,000 rpm, and that led us to believe the u-joints might be wearing. When u-joints wear, the driveshaft begins rotating off center, causing driveline vibration. We headed out to BMW specialists (And new home to ex-staffer Edandy.—MAX) Race Marque Systems in Van Nuys, California, for its professional opinion. The company’s professional opinion was actually a little worse than we hoped. They informed us the BMW u-joints did need replacing, but, unfortunately, BMW u-joints cannot be serviced. Instead, an entire new driveshaft with u-joints must be purchased from BMW at freakishly high costs. RMS placed a call to Wenco Industries Inc., a trusted name in driveshaft components, hoping they would know some other option. Luckily, Wenco knew of an upgrade for the BMW driveshaft making the u-joints serviceable. We knew that serviceable u-joints would be better in the long run, so we told them to dive in.
After dropping the BMW at RMS, they stripped the old drive shaft from the car and placed it in the hands of Wenco. The OEM u-joints on the driveshaft cannot be lubed or removed, so when any part of the driveline fails, the whole unit must be replaced. Wenco cut the old u-joint from the driveshaft and placed a new one in its place, but instead of staking it to the driveshaft as BMW does, the company allows the u-joint to be removed. Wenco also adds a point where the owner can lube the u-joint every 15,000 miles. Wenco then balanced the driveshaft at 3,000 rpm, average revs for a BMW at highway speeds, and returned it with assembled u-joints to RMS where the improved unit was reinstalled.
A stock BMW should be able to achieve somewhere between 80,000–90,000 miles before the u-joints wear enough to be replaced. However, when you add in factors such as a lowered suspension and gains in horsepower, the lifespan of the drive components are massively decreased. Having a driveshaft fail can virtually ruin a car, so we recommend this upgrade for anyone with a lowered or high-output vehicle.
Converting the u-joints to serviceable parts runs somewhere in the neighborhood of $300 plus labor, but that is a lot cheaper than replacing the rear end of the BMW, not to mention the headache of trying to track down an entire driveshaft. Now our project BMW is back on the road, and thanks to RMS and Wenco, we are capable of having the u-joints rebuilt if the problem ever arises again.