Replace Reverse Light Switch Wiring

When I performed my driveshaft and shifter assembly repair, I didn’t take enough care to secure the reverse light switch wiring. The excess slack quickly got tangled up in the driveshaft, causing it to wear and break. Thus, my reverse lights were rendered inoperable.

Also, when torquing down the guibo nuts, I had a feeling one was stripped as it kept spinning and the torque wrench would not click. My understanding was that these nuts and bolts were single use, so I went ahead and ordered new replacements for all of them in anticipation of dropping the exhaust and driveshaft (again) to repair the reverse light.

Sure enough when I tried to remove the stripped nut, it just kept spinning. It took me a while to figure out how to remove it, especially in the tight area with not many options. Eventually I used some vise grips to apply some longitudinal force on the nut as I wrenched the bolt. Again, these bolts can only point towards the front of the car, so there’s limited space between the guibo and driveshaft flange and the transmission. With this method, I was able to slowly back off the nut and remove the stripped bolt.

I only needed to move the driveshaft out of the way vs. removing it completely. While wrestling with it, the halves became separated and the front half ended up being removed. Thankfully, the two halves were already marked as maintaining its balance was important. I used those marks to extend the lines on the splines to get it lined up for reassembly.

One issue I had was that the replacement bolts, which were the correct part number, were too long. When inserted back to front (the only way), the bolts would not clear the flanges on the transmission and thus would not allow the driveshaft to turn. I could have used multiple washers to get the necessary clearance, but I decided to get the right length bolts locally with the correct strength grade.

I now had functioning reverse lights and my driveshaft was perfectly secured.

Replace Driveshaft, Guibo and Transmission Mounts

The main reason for my long list of holiday projects was the driveline shudder I had experienced since my first drive in the M5. It was very easy to replicate, so I was disappointed that the seller had not disclosed it, though they didn’t deny that it was occurring or an existing problem. In any case, it was my mission to fix it.

As stated in the shifter rebuild post, I didn’t want to deal with just the CSB, which was likely the root cause of the issue, so I bought a completely rebuilt and balanced driveshaft with a new CSB installed. I had already removed the old driveshaft to complete the other projects, so I was just waiting for the new one to arrive to install it. Aside from installing the new bolts and nuts both fore and aft, the key step to installation was pre-loading the CSB prior to tightening it down.

It was a no-brainer to also replace the¬†guibo (apparently actually “giubo” or flex disk) while installing the driveshaft. To avoid twisting the actual guibo itself, you really had to tighten the flange side nut, which also made torquing difficult. Finally, there were some posts online that indicated that it didn’t matter which way the bolts/nuts went, but I found that there was no clearance to insert the bolts towards the rear of the car, which would have made tightening and torquing a lot easier. This seems like it would only be possible by removing the flange from the transmission output first.

While it was all apart, I also replaced the transmission mounts, which was easy relative to cleaning the transmission support. With the “new” driveshaft, shifter assembly and transmission mounts, it was looking pretty good under the car.