The pin in the Brembo

Bronze Coast, Alameda , CA
California US

It’s way past time for the rear brake pads on the Guzzi to be replaced. I’ve been putting it off for too long thinking that I don’t really use my rear brake that much anyway. Of course, that’s terrible reasoning for at least three reasons.

First, it’s terrible reasoning because I ought to use my rear brake. The front brake is always going to do more work, but why not let the rear brake do its part too? Novice riders frequently rely too heavily on their rear brake, which can lead to nasty high-side crashes. Intermediate riders who like to pretend that they are better than they really are frequently show off how little the novices know by going to the other extreme: never using the rear brake at all. Well, OK. So the front brake has (depending on who you ask) between 75% and 85% of a motorcycle’s braking power. Well, that means that using both brakes yields between 18% and 33% more braking power. That’s nothing to sneeze at.

The second reason it’s terrible reasoning is much the same as the first. Even if I don’t routinely use my rear brake, I may encounter emergency situations where that extra braking power is not just nice, but necessary. Even the guys sitting in Starbucks drinking lattés while wearing full leathers know that there are times when grabbing some rear brake is necessary. If I need it, I want the brakes to be there.

Third and perhaps most importantly, it doesn’t matter if I’m not using my rear brake. The brake calipers have small springs that hold the brake pads against the brake rotor all the time. The springs hold the pads only lightly against the rotors but they are still always touching the rotors. This prevents the brakes from needing greater travel when the pads are worn down. This is a problem that’s easy to see on a bicycle: adjust your brakes so that the brake shoes have just a millimeter clearance on each side, then ride for a few hundred miles. If you’ve been using your brakes the brake shoes will be worn down a couple millimeters each. Instead of 1mm clearance, your brake shoes will now be 3mm away from your rims and you’ll have to pull harder on your brake levers just to get the same braking power. It’s not a huge problem, but motorcycle (and I assume automobile) brakes avoid it by making sure the brake pads always lightly graze the rotor.

ImageThat means that once the brake pads are worn simply avoiding the use of the rear brake doesn’t help. The pads will continue to wear until there’s no brake pad material any more and you have metal on metal, which will quickly damage the brake rotor.

So it is high time I learned to replace my brake pads. The rear brakes are the best place to start anyway, because on my bike I have two sets of pads on the front and only one set on the rear.

The instructions for replacing the rear brake pads in the Guzzi shop manual (yes, I keep the shop manual on my iPad) are fairly clear. One pops off a cover shield, extracts a pin by hitting it with a push rod and a hammer, then removes a retention spring, slides the old pads out, the new ones in, and puts it all back together. Piece of cake, except when it isn’t.

The trouble came when the pin would not budge. Heeding my father’s advice (don’t force it, get a bigger hammer) I set down the rubber mallet and screwdriver I’d been using and retrieved a five pound hammer with a flat-head tapered punch. The pin withstood some mightier blows without budging so it was time for me to utilize the universal tool for finding solutions to problems other people have probably encountered: Google.

Unfortunately, though a Google search led me to several accounts of people with exactly the same problem with Brembo brakes, most of the forum responses were the same: reiterating the standard instructions. The unspoken message was clear: though you’re doing what we say you should do, you must be doing it wrong, because it always works this way. Some of the solutions offered involved dremel tools, blowtorches, and replacing the entire brake system. The one good piece of advice was to hit the pin with a very small amount of a penetrating oil and go at it again in a few minutes. While this did not free the pin to pop through under the force of the hammer, I did find that I could rotate the pin easily with a pair of pliers.

I had tried hitting the pin from the right side of the bike rather than the left, but the majority of the time I was working from the left. From the left the brake is more easily accessible, but also the photo in the shop manual shows the brake from the left side of the bike. After finding that I could rotate the pin with pliers, I tried pulling on it. To my surprise, it came out easily about 2mm (see picture at the top of this post) though I could not pull it any further than that. This proved that the pin had not seized but further it was obvious that the pin had a head on it that would prevent it from going farther through the hole it sat in.

When hit from the right side (perhaps for the first time since applying the penetrating oil) the pin slid easily out the left side after just a few taps, just like it was supposed to.

Someone, whether the last owner or the shop I usually take the bike to, had put the pin in from the wrong side1. On reflection it seems like an easy mistake to make. After pushing the pin through from the left, one might easily not think to circle to the other side of the motorcycle to push the pin back in from the right when done. The pin-hole would be right there, an obvious place to return the pin to what seems like its original position.

More important is to get this information out where future searchers with the same problem can find the solution, especially because most of the forums that have threads about «stuck Brembo pin» are automobile forums. The design of the brakes themselves may be similar, but on an automobile it is not anywhere near as convenient to simply walk around to the other side to try and tap the pin out from the other side. I imagine the temptation to replace the pin from the side one is looking at would be greater as well, and for the same reason.

Yes, get the penetrating oil (but use it very sparingly—you don’t want oily brakes!) but before you fire up that blowtorch or start to dremel the pin out, try tapping the pin from the other side to see if it was put in from the outside. And a reminder: when you are done replacing your brake pads, put the pin back from the side opposite from the side facing you. It’s going to be a little awkward, but much easier than trying to hammer the pin in a direction that it won’t go next time you have to replace the brake pads.


  1. Whether there is such a thing as a wrong side in this case seems somewhat subjective. I’m calling having the head of the pin on the left side of the motorcycle «wrong» only because it is opposite of what is expected after reading and looking at the photographs in the shop manual. The pin will do its job equally well inserted from either side. ↩︎

Comments

Are there really springs pressing the pads against the disks in Brembo brakes? I have never seen a disk brake system that used anything like that. Usually the pads just rest against the rotors unless something pushes them away. Subarus used to have pistons that screwed themselves in as they were used, but that is the only case I have ever seen where the pistons weren't free to retract under pressure.


Dad

…but something is keeping tension on the pads. Once I got the pads out of the calipers, the pistons closed down to where I couldn't fit a business card between the bare piston and the rotor, never mind fit the new pads in. Once I removed the calipers entirely I was able to push the pistons back in using a flat piece of metal and pushing with both thumbs. It was a little tricky (sort of a situation that requires three hands but in the space I could fit two fingers) but with some patience I did eventually get the new pads fitted.

It's nice to know that I can do this myself. The first time may have taken a few days, but the second time will take an hour or so. I'm very glad my first attempt was on the rear brake. The front brakes may be a bit easier to get to, but there are two of them and each one is a four-piston brake instead of a two-piston model like my rear brake. Now that I've done the rear brake the added complexity of the front brakes won't be a big deal. But if I'd tried the front brakes first that would have been a lot more frustration. 

Every disc brake I have seen simply relied on the hydraulics to keep the pads from pushing back. If they closed up by themselves when you removed the pads, they must be different from anything I have seen. Unless, of course, you hit the brake pedal by mistake while the pads were out. Or perhaps you have a booster system that retains a little hydraulic pressure. (I have never seen one like that, but it certainly is possible.) The reason that the pads are hard to retract is because the design of the hydraulic system gives you mechanical advantage when applying the brakes, and that means mechanical DISadvantage when pushing fluid the other direction.


It is always very satisfying to me to fix things. It isn't just about the money, but more about understanding how things work. Of course, you get to save a bunch of money, too.


Dad