Category: Mechanical

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Replace Rear Differential Mount

From day 1, the M5 had a strange vibration in the driveline. I tried to diagnose it and had several possible root causes. There was some also possibly unrelated clunking coming from the rear. Before I knew what the subframe bushings entailed, the rear differential mount was discussed a lot. By its positioning and function, it seemed to be a likely candidate for replacement.

Rarely is the consensus on the internet, but one thing that was suggested often was to use the part from the Euro M535i (33171129786), which was more robust and less expensive than the OEM M5 part. I sourced a Lemforder part from FCP Euro. It was a pretty easy procedure, but unfortunately did not eliminate the clunking.

Around this time, my speedometer was intermittent. I found that the speedometer cable was rubbing on the differential output and shorting out. I taped it up and the problem was fixed. I was thankful it wasn’t anything more serious.

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Repair Front Passenger Window Regulator

I knew the front passenger window wasn’t working before the car even arrived, so I very early on sourced a replacement window regulator from eBay. After it arrived, I realized that the main failure were the contacts on the window switch, which once cleaned up, demonstrated that the regulator was indeed working.

What wasn’t working well was the fact that the window went up and down very slowly compared to the driver’s side window. During the interior project, I removed the door card and the vapor barrier to remove the window regulator. I degreased all of the old, dried grease in the tracks and lubed it up again using white lithium grease. It goes up and down beautifully now.

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Replace Antenna Mast

I had mentioned that my bent antenna was a possible suspect to my battery issue, which really turned out to be my alternator. In any case, the antenna was annoying, so I started looking for a replacement. The motor was fine and I found that the whole unit was pretty expensive, but the mast itself wasn’t too bad. I had sourced one on eBay months ago and then finally got around to installing it, which was actually pretty fun.

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Replace Billy Boat Exhaust with Stock Exhaust

The M5 came with an aftermarket Billy Boat exhaust. It looked nice, but I found it to be very loud. Because I didn’t put it on, I didn’t have any experience to compare it to the stock exhaust. I took it to a muffler shop and they assured me there were no leaks. After a while, I learned that I had to coast into my driveway with the engine off to avoid disturbing my neighbors at night. This was not sustainable.

The decision to go back to the stock exhaust was the first of many to return the M5 to as original as possible (and avoid the slippery slope of euro mods or other “improvements”). It took me a while to source one, as new units or NOS by then were not available. Eventually, one turned up on mye28.com and after figuring out how to get it delivered with reasonable shipping costs, it arrived and I had the B&B swapped out. It was sold later to another board member.

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Replace Battery, Alternator and Belts

Even after my no-start trouble-shooting, I was chasing a battery/charging issue for a while. After a lot of reading, one hypothesis was the bent/broken antenna, which was not allowing the mast to fully retract and draining the battery. After replacing the battery didn’t solve the problem, I looked into the alternator.

It was suggested that it could have simply been the diode, which was relatively easy to swap out. I decided to just R&R the alternator with a remanufactured unit. I also took this opportunity to replace the belts, as they had to come off anyway for the procedure. I also got a new air flow meter to intake boot, which also had to be removed anyway.

This was my first “major” DIY repair (major would be redefined many times during my ownership). It was also the first time experiencing frustration of not being able to readily (i.e., today) get the parts I needed. The gear and teeth on the alternator adjusting bracket were stripped, so I ordered the parts I thought I needed. It turned out (as often the case in my early ownership), the one I needed was different and unique to the M5. The actual part was several days out, but I was impatient so I modified the one I had to work. I tried to bend it, but ultimately cut it in half to fit, which I actually think is stronger than the original part.

This was my first truly gratifying project and I haven’t had a battery or alternator issue since.

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I’m Running to the Store … Be Right Back

My first hiccup with vintage car ownership happened when I ran to the grocery store (an hour before guests were to arrive). Upon starting the car to return home, it didn’t. I contemplated the no start situation. It cranked fine, until it ran out of crank. I didn’t have time to deal with it, so I took an Uber home and returned later in the evening with gas (just in case I hadn’t learned what empty was) and jumper cables.

After it still would not start, I called a tow truck. The guy, being helpful, suggested maybe it was the ignition coil or distributor, the former he advise was easy to change. So, instead of towing it, I left it overnight and returned the next day with a new coil. I swapped it out in the Safeway parking lot, but still no start. Then, I had it towed in earnest to one of the independent shops in town that I let work on our cars.

They called and advised that there was “power to the coil but no reference signal.” They found the reference sensor connector was “broken and had vibrated loose.” Because the speed sensor is wrapped together in a loom along with the reference sensor, I was encouraged to just replace them both because there was no additional labor. I approved this because I didn’t know any better. $606.17 in parts and labor later and I was back on the road.

Several weeks later, I was working on the car (thankfully right in the driveway) and when I went to turn it on to put it away in the garage, it again wouldn’t start. It was getting dark, so I just left it there. I researched some things and then had an “ahah” moment on my way home. I went straight to the car, followed the reference sensor wire to the firewall and sure enough, I found it unplugged. I plugged it in and the car fired right up. I was relieved, but then I thought about the first failure. Was it as simple as my current situation and did I pay all that money when they could have just plugged it back in? I’ll never know, but for better or worse, that second-guessing started me on my DIY adventure with the M5. I’m thankful for it, but my wife may not be.

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Procure Bentley Manual and Miscellaneous Parts

Even before the car arrived, I preemptively started ordering items for the car. Once it arrived, I found more items that needed attention. All of these items were sourced from eBay.

  • The day I won the eBay auction for the M5, I preemptively sourced a new window regulator for the front passenger door, which I knew from the seller to be inoperable.
  • A couple days later, I purchased the Bentley Manual for the BMW E28.
  • I needed some extra keys, so I ordered a couple OEM lighted key blanks.
  • I found one of the seat adjustment switches to be a little sticky and intermittent. In hindsight, it was probably from too liberal application of leather conditioner. I bought a replacement just in case, but cleaning up the connections made it work perfectly.
  • The “M” seat badges were all a little worn out, so I found 4 replacements for the front and rear seats.
  • Finally, the Check Control Unit near the sunroof switch wasn’t working. I purchased a replacement and when I went to install it, I found that the original was simply unplugged, seemingly to preempt the known issues with intermittent brake lights. I plugged it back in and the original worked perfectly.