We got an interesting call a couple of weeks ago. A customer here in Ft. Lauderdale wanted to have a one-piece driveshaft made for his BMW E36. He had already purchased an aluminum adapter for the three-bolt flex disc at the transmission. At first, I wasn't sure it was something we'd be able to tackle, but I told him to bring the adapter and his old driveshaft by so we could take a look.
A couple of days later the customer stopped by with the aluminum adapter and the OEM E36 drive shaft. Because we were going to be replacing the two-piece shaft, he only brought the rear section of the drive shaft so that I could get a measurement of the flange pilot. Upon measuring, I noticed a problem: we didn't have any balance machine adapters to attach the drive shaft for proper balancing.
To remedy this issue, I went by our favorite metal supply store and bought some 1018 round stock so that I could machine an adapter for the driveshaft balancer. It's especially important to have proper fitting adapters so that the drive shaft runs perfectly concentric while balancing. Anything else can cause an improper balance which means the drive shaft will vibrate while driving.
Sizing the 47mm female pilot to accept the flange on the BMW driveshaft
With the brand new adapter ready to go, it was time to go collect parts for the actual drive shaft build.
Installing the aluminum adapter in the E36 meant that the two mounting surfaces for the drive shaft would be hard points with no flex. As you drive, it is essential that the driveshaft have some form of 'give' so that it can move back and forth as the suspension of the car moves up and down over the road. This meant that we would need to install a slip yoke and spline set up in the drive shaft itself. Lucily, the female pilot on the aluminum adapter was a common flange size for American drive shaft components. The differential side of the shaft used the 47mm pinion flange that we machined the balancer adapter for.
We needed the following drive shaft components to build the shaft:
- Weld-in spline
- Slip yoke
- Weld-in tube yoke
- 47mm flange for the differential end
- Flange for the transmission end (where the aluminum adapter was to be installed
Here we can see the build components for the one-piece E36 drive shaft. For some reason I left the 1100 series u-joint out of the shot.
We asked the customer to take a measurement between the two mounting flanges under his car. This would give us a flange to flange, running position measurement for us to build the drive shaft to the proper length. With this measurement in hand, we measured out the parts to determine our tubing length.
Now we knew the proper length, we put the drive shaft tubing in the lathe to cut it to size.
Usually we cut the driveshaft tubing to size in the cold saw. Since we were just cutting off a small piece though, I went ahead and trimmed it up in the lathe.
When preparing drive shaft tubing for the weld-in parts installation, it's best to chamfer and deburr both ends of the tubing on the lathe. While chamfering, we also cut back on the tubing to square the ends up. This makes it a lot easier to get our components machine straight before we weld up the seams.
We ended up using an 1100 series drive shaft tube yoke for one end of this shaft. We ran into a small problem though: the tube yoke was a little oversized for the 3"X.083" tubing that we purchased for the job. This was remedied by boring out the tubing to about .015" smaller than the diameter of the yoke. Machining it to this size allowed for a really nice press fit.
With the parts prepared and the tubing sized, we welded up the drive shaft and installed the u-joints.
This is an interesting u-joint in that the grease fitting is in the cap. Having a feature like this makes it really handy to grease the u-joint in a snap!
This is the end of the drive shaft that we had to custom size the tubing for the BMW tube yoke. As can be seen in the pic, we've got the u-joint and 47mm flange installed.
With the u-joints and flanges all in place, it was time to balance the drive shaft. We test fitted our custom machined adapter and everything fit nice and snug with no wobble or side to side play. This fitment is critical for an accurate balance. Anything less could lead you to a 'false positive' in your drive shaft balancer and the customer will still experience a vibration while operating the vehicle.
And that's it! We've got the shaft all balanced up and ready to go other than paint. Thanks for reading!