Them the brakes
In the last past, I discuss how often projects on this car are presented here linearly but in real time occur over weeks, or even months, with many interruptions. The brakes are a great example.
I began working on the brakes in May and have slowly, meticulously, going through almost ever component. After putting the “new” suspension in the car, I noticed a weird sound coming from the passenger side, seemingly the front. I identified it as a metallic brake squeak.
And chasing that down became a game of wack-a-mole, somewhat intentionally.
I could have simply replaced and rebuilt everything and avoided the wack-a-mole approach. The brakes looked old, the calipers were probably original, 40 year old units and wouldn’t suffer from rebuilding. The brake lines had been replaced with thinner ones covered with blue nylon; presumably stainless steel lines underneath the blue nylon. While brake squeal is often addressed by changing pads, there was plenty of reason to go through the whole brake system. And since I wanted to know what was causing the squeal, I decided to going through the brakes one component at a time.
Because the calipers were hanging on bungee cords for months while waiting for the suspension rebuild, and the car didn’t make that noise before, I thought maybe the flexible brake lines got stressed and brake fluid was not flowing freely. So, I decided to change those out for some new stainless steel lines.
Changing the brake lines was more of an ordeal than I’d like. Most of the old lines came off easily (and fitting the new ones was a breeze) but some of the nuts were over-torqued when the (non-stock) lines were installed by one of the previous owners. I did some on-line research and consulted with Rob Siegle (The Hack Mechanic) and several mechanic friends about the best method to use for uncooperative brake lines. The challenge is that the nuts are made of a somewhat soft metal (brass?) and too much force can result in rounding off the corners of nut. I settled on using a specially designed vise grip but even that was marginally successful. But, after many trips to the garage, and a lot of persistence, the old lines were off and new ones on.
The finished product was nice but, regretfully, did not cure the noise.
So, I decided to change the pads and rotors. As alluded to in the last post (Alpina Archaeology), changing the rotors was not a straight-forward exercise of ordering parts and swapping them. Not because changing a rotor is a challenge but because finding the right rotor at a reasonable price is a challenge. I won’t re-plow those fields, but a fair summary is that Alpina used custom front rotors but stock BMW rotors from an e32 7-series fit on the hubs and inside the pads—not perfectly in terms of visuals, but they work fine. While the offset of the BMW rotor vs. the Alpina rotor was slightly different, as was the thickness, they bolted up, the pads had more than sufficient contact and they stopped the car.
With the new rotors and pads on, it was time for another test drive. Early indications were excellent! There was no unusual noises for a long spirited drive. But, when I was going up the hill to my house I could hear the same old sound at slow speeds. On the final, slow entry into the garage, it was louder than ever. This was particularly befuddling. I really thought the noise was being caused by the pads.
If it’s not pads what else could it be? I wondered if the calipers were hanging up and needed to be rebuilt. They were 40 years old. The car was not pampered; it hadn't been given nothing-but-the-best maintenance. I’ve never rebuilt calipers before. This all added up to trying that next.
Worried about how the piston is removed from the caliper, I watched several youtube videos about BMW caliper rebuilding. The method I copied suggested using the power of the hydraulics to push out the pistons: taking the caliper off the strut but lines still attached and, after putting a 2x4 in the place of pads and rotor, push down on the pedal. I tried something similar—removing the pads but leaving the caliper on the strut and rotor in place—with partial success.
The rest is supposed to be easy: remove pistons from the caliper, clean it up, replace the seals, and reassemble. Reality was a bit different. Not all the pistons were protruding from the calipers. The ones that were, didn’t move freely. None of the videos showed this situation and I didn’t know how to force them out. But, the pistons had a recessed shoulder that I could grab with my big-assed plumber’s wrench. Some moved, slowly. Others didn’t at first. But spraying a liberal amount of brake lubricant and slowly wiggling the piston around in the cylinder got more and more movement until they popped out.
Once out, I took stock of the pistons and bores. Forty years and (guessing) infrequent brake fluid changes left a fair amount of residue on the pistons. Some came off with brake cleaner and rubbing but some needed some time with the wire-wheel.
Eventually, they all got cleaned and were ready for reassembly.
There’s not much to a caliper. The rubber seal—much like a ring on a piston—and the boot on the end keeping crap out of the bore. When taking out and replacing the rubber seal, you gotta be careful not to score the bore but the hardest part was replacing the retaining clip that holds the rubber boot on the caliper.
Once completed, the calipers went back on and it was off for another test drive. Of course, the sound remained. The only things left were the parking brakes and rear brakes.
For the rear brakes, I decided to do something weird: Instead playing my wack-a-mole game of replacing one component at a time, I ordered pads, rotors, and caliper rebuild kits. Some of the parts had to come from Germany and that took over a month. Once here, I torn into the project almost immediately, eager to finally silence the brakes.
Spoiler alert: the rear brakes started and ended with disappointment. The good news is the middle part of rear brakes (rebuilding the calipers) was a success, meaning the calipers got rebuilt and work as intended.
The disappointment at the start of the rear brake project was that the rotors did not fit. This was weird, as Alpina (and other B7 owners) told me that the rear brakes were stock BMW parts and the rear brakes for a 3-liter e9 and early 6-series coupe were the same size (19mmx272mm) so I assumed those were the correct parts. But the hat was deeper on the new rotors and they would not fit on the hubs; indeed, if you lay them next to each other, the new rotors sat taller.
Adding to the weirdness was that, unlike the front, there were no unique Alpina markings, further indicating the rear rotors were a stock BMW part. Instead of puzzling over this and trying to find the right rotors, I pressed on; the existing rotors were old but not too thin to keep using and that mystery would have to wait for another day.
Replacing the pads, of course, was easy. And rebuilding the calipers was too it turned out. As with the front brakes, getting the pistons out of the calipers was the hardest part, with one of the four pistons so uncooperative that the caliper was brought to a local shop that is willing to help me out on some of my DIY projects. They used heat to help convince the piston to exit the caliper and it was simply a matter of changing out the rubber parts, lubing the piston and bore, and reassembling. It went swimmingly, even the retaining clip on the dust boots (which was much easier than the front calipers).
So, what was the disappointment at the end of the project? It wasn’t bleeding the brakes. That took two attempts for some strange reason, but that was hardly a disappointment—more like a minor annoyance. No, the disappointment was that the test drive revealed that the noise remained. Perplexed, I mentioned it to Stu, a mechanic friend who is helping me with the e21 C1 2.3 I’m restoring (www.alpinac1.com) and he causally said “yeah, half of them make that sound regardless of what you do.”
Is Stu right? Is there no cure for the squeaking/squealing? I don’t know, but for now that mystery will just have to wait, like the rear rotor mystery. I mean, the brakes work and I’ve pretty much exhausted the possibilities….