Moto Guzzi National Owners Club
Moto Guzzi National Owners Club
Moto Guzzi National Owners Club
Text size:  A  A

You and Your Brembos

Spring is approaching and that means it's dead brake time for many Guzzi owners. Since the '70s, Guzzis have been blessed with wonderful braking systems, but they will croak from old age and neglect. If your brakes have crusted up, perhaps this article will help some. This is not the only way to do things; it's just what has worked for me.

What The?

Simply put, a hydraulic braking system is a piston (with rubber rings) in the master cylinder which compresses brake fluid, which then pushes out the pistons in the slave cylinder (which run in rubber rings) in the caliper which then press the brake pad's friction material against the rotor. When you release pressure on the master cylinder's lever, the pistons retract and the rotor is free to rotate again. Nothing to it.

Before You Begin

Cleanliness is next to Guzzliness, so have a clean work area and bear in mind that every component of the brake system MUST work perfectly. It also helps to have all of the necessary parts on hand. Check out the entire system before you delve in.

The Master Cylinder

Due to the ingress of dirt, contaminated brake fluid, or simply lack of use, these will require rebuilding, which is a piece of cake.

Remove the master cylinder, dump out the brake fluid, take off the lever and check to see if there's a circlip holding the piston in place. (Some have them, some don't). Remove the circlip, if applicable, and insert a slender drift into the fluid's exit orifice (where the line connects), and smack out the piston. While Brembo offers a special drift for this, an old motorcycle spoke of the correct diameter will suffice.

Put on some rubber gloves (as brake cleaner is nasty stuff) and flush out the master cylinder. Take a good look at the cylinder's bore to make sure that it's not scored or pitted, and if all is well, as it most likely is, let it dry. Some people use a hone for the cylinder bore but I've done a couple hundred without one, so I don't think that's necessary. All the manuals say not to use compressed air, but I've always used one with a drying chamber to take the moisture out, so who knows?

Grease up the new piston seals with the supplied grease, take out your Brembo drift, and then gently smack the new piston into place. Most models use a brass collar for this job, although some also use a circlip. If you don't have the correct drift, a deep socket can be employed, although I've never tried this route.

Reattach the lever and pay attention to the lever adjustment. Each master cylinder has a means for adjusting the free play in the lever: it's either an eccentric Allen secured by a 6mm nylock nut, it's built into the lever itself utilizing either an Allen or flat head screw, or it is controlled by one of those dippy spring-loaded stoplight switches.

The owner's manual will give the exact clearance required (1000SP says .05-.15mm ), and this is important because if there is insufficient clearance between the piston and lever, the piston cannot draw in a fresh supply of fluid, which means no brakes, especially when things heat up. This could prove to be exciting!

Pour in fresh fluid, put your finger over the fluid exit orifice, and pump it three times. It should build up pressure and should squirt like a garden hose. So far, so good.

Check the condition of the bellows on the cap, the sealing ability of the reservoir, the sealing ability of the 900 nipple if applicable, and if you have a remote reservoir, check the state of the brake line. If any of this stuff isn't perfect, replace it now. Nothing is more aggravating than having to go back to square one with brakes.

For the rear master cylinder, check the condition of the lever's return spring. This one will fatigue and act as a parking brake, which can be quite puzzling the first time you encounter this problem.

Oddly enough, the old round reservoir master cylinders work better than the later models with the 12mm trapezoid fitted to the front of the LeMans IV, this being an especially forgettable number. However, round master cylinders aren't quite as stylish!

Stoplight Switches

Brembo uses a lot of different types, but only the old hydraulic ones are worth buying. They come in Short, which just screws into a junction block by itself, and Long, which has a shank long enough to attach a line.

If you need to replace one of these, put a wet rag underneath the dud switch, hold a little pressure on the lever, unscrew the old one and screw the new one (complete with new crush washers) in most of the way, pull the lever in fully to push out the fluid, tighten up the switch fully, go pump-pump- pump with the lever, and then use the stoplight switch as a bleeder nipple three or four times. With any luck, you won't allow air into the system. Failing that, see the bleeding dry lines section at the end of this article and start at the master cylinder and work your way down. It helps to have a nubile assistant for this one.

Proportioning Valves

According to Greg Field's Guzzi Big Twins, the valves without the bleeder nipples are not really proportioning valves; instead, they're just junction blocks with orifices of a different diameter.

While I don't know of anyone who has dissected a proportioning valve, the logical assumption is the valving consists of a ball and spring arrangement. As brake fluid is hygroscopic (absorbs water), really neglected items are candidates for replacement due to rusted internals.


I have fished a few mud wasps and old spider webs out of these! One of the things that you should always check is the action of the caliper pistons. If they are not both pushing out and retracting freely and equally, they need to come apart because having a sluggish piston will only drive you insane as the project nears completion.

Year ago one gentleman suggested removing the calipers from the forks annually and then pumping them until the pads closed up to help lubricate the pistons with fresh brake fluid. Sounds like a good idea to me.

To rebuild calipers you first leave them on the forks, put a 10mm Allen socket on a breaker bar and pop the two caliper halve Allens loose. Remove the calipers, take the pads out and dump out the old fluid.

The early models came with two bleeder nipples per caliper, and before you even think about touching these, squirt them with WD40 or something similar, put a brass drift on them and give them a good smack. Carefully try to loosen them, and if they don't want to budge easily, give the heads another good smack. At worst, you might have to heat them with a propane torch to loosen them.

Should you manage to shear one off, you're going to have to put the caliper in a drill press and keep going up one size larger on the bit until you can twist them out with a screwdriver. If you own a set of E-Z outs, now is the time to throw them away as they have the tensile strength of a carrot (to steal a line from Carrol Smith). Once they're finally out, put in new ones with antiseize.

With the bleeder nipple(s) in place and the pads out, try blowing compressed air through the banjo's bolt hole at about 35 PSI. With luck, the pistons will pop out. Sure they will.

If your calipers are pre-LeMans III, they have chrome plated pistons and are unlikely to budge due to crusting onto the rubber seals inside the piston bore. When this happens you separate the caliper halves, dump out the brake fluid, remove the rubber piston gaiters (protective rubber seals) and the caliper halve sealing O-ring and stick them in an oven at 2500 until they start to smoke. What you're doing is softening up the piston seals. Take a pair of Vice Grips, grab hold of the piston's lip and twist them out. Remove the seals from the bore and let the calipers cool to room temperature.

Clean them out with brake cleaner and gently remove all of the grease and crud deposits. Slob up the seals and new pistons with assembly grease and insert them into the bores. Put some grease on the small O-ring which seals the two halves (to keep it in place), put some antiseize on the new Allens and tighten them up. Brembo goes berserk when anyone does this, but I chicken out at 25 foot/pounds.

Here's one thing you should know: some of the Allens which come with the rebuild kit won't have enough thread on the shank. If you're ever nearing the end of brake bleeding and notice a thin line of wetness where the caliper halves join at the front of the caliper when you apply pressure to the lever, you need to take the bolts out one at a time and either replace them or add another thread or two with a die as no matter how tight the bolts are, they're not fully pulling the halves together. Without the halves completely tightened, you'll never get all the air out of the system.

Brake Pads

The Brembo brake pads had (have?) a nasty habit of falling apart; the friction material would stick to the disc and shear off from the backing plate. Ferodo pads are the way to go. When brake pad manufacturers quite using, asbestos and changed to sintered metal, other manufacturers' pads were found to be too effective and would lead to rotor failure in severe (i.e.; racing) applications. Undoubtedly, this has been changed by now, but I prefer to stick with what I know will work.

If the pins are questionable, put in some new ones as it could save your life.


Rotors come in a few varieties: fixed, semi and full floating, drilled, undrilled, one-piece and two-piece. Guzzis have come with all types, and the Brembo items have always been cast iron as opposed to stainless steel. They went with cast iron as it affords greater braking power although the rust is unsightly and probably contributes to shortened caliper usefulness. Just because you have Brembo calipers on your Guzzi does not mean that the rotors are Brembo items. I'm not positive, but I believe that all of the full-floating rotors fitted to the Guzzis are Brembo items.

Returning to the cast iron for a moment, you can expect Brembo to get away from this in the near future and switch over to steel. (It's currently in use for their racing department.)

Whatever the manufacturer or rotor compound, be sure to check both the rotor thickness and rotor integrity (cracking) when you change pads, as a broken rotor would cause a really nasty crash. Probably happen at a bad time, too.

Be sure to put rotors on with a torque wrench and use new 10.9 Grade bolts, Belleville or hardened washers and a drop of Loctite.

Crush Washers

Two types are used, aluminum and copper. I believe that copper does a better job of sealing than aluminum does, plus copper is cheap enough. If you're caught short with copper ones, you can reuse them by annealing, which simply means heating them up until they turn red and letting them cool off again. I'd say using a new one is preferable but an annealed one will work in a pinch.

Brake Fluid

The elixir of life - brake fluid both serves to push the pistons out, and it lubricates the pistons and seals. Feels nasty, too.

The cap may say USE ONLY DOT 3, 3-4, 4 or 5 depending on which model you have. The cap says DOT 5 would be for Europe's DOT 5, which isn't the same as our synthetic DOT 5. Here in the US it would translate into DOT 5.1, which is available for around $20/pint.

The word from Brembo is that synthetic brake fluids cause the seals to swell, and Kevin Cameron notes that silicone isn't a very good lubricant. If the pistons do not retract properly, you either have no brakes or locked brakes - either way, you crash. This is one case where it's foolhardy to assume that the manufacturer is an idiot.

The 3, 3-4, 4 and 5.1 are all non-synthetic brake fluids which absorb water from the air, so pick a day when the humidity is relatively low or else you'll be putting in pre contaminated fluid. That's why they always instruct you to keep the cap on a fresh container.

Brake Lines

Keep the rubber lines if you're doing a 100% original restoration - everyone else should chuck them and put on steel braided ones. Over a period of time the rubber ones will harden, deteriorate and swell noticeably when you apply pressure to the lever. When yours go, "Wheeep-Wowwww!", chuck'em. I know, "Who cares, they only slow me down, har, har."

Banjo Bolts and Rigid Line Fittings

There's two styles of bolts, the Short one for connecting a single line, and the Long one for connecting two lines to a junction block. For the banjo bolts and rigid line fittings, I always use a light coating of Loctite PST. This helps to prevent leaks and also keeps the threads from corroding. As with all Loctite stuff, only use a little bit - one full, light turn on the threads will do the trick. If you blob it on, you risk blocking off a fluid orifice.

Brake Bleeding From Scratch

The fun part! Here's where you want to make somebody else do the job. Failing that, you do it yourself. There're all sorts of ways to accomplish this - pressurized master cylinder caps, pumps that suck air through the bleeder nipples, syringes that pump fluid up through the nipples. For what it's worth, I do it the slow and messy way.

The master cylinder(s) and caliper(s) have been checked and are functioning properly, the lines are in good shape and you've armed yourself with a gallon of cheap fluid and a few pints of real fluid. The body work is off; the calipers are hanging up in the air (with the pads in place) as high as you can get them with the nipples pointing upwards; you've got a supply of wet rags; you've got lines hooked up to the bleeder nipples with box wrenches attached; you've got a container with a little fluid in it and it's time to start.

Bleeding The Front, Dry Lines

The trick is to start at the master cylinder and use every junction point as a bleeder nipple. Put a wet rag under the master cylinder's junction bolt, pump it slowly a few times and then put pressure on the lever, open the bolt with a 14mm box end wrench, press the lever through its stroke and while the lever is held in, you tighten the connection back up.

Do this four or five times, until only fluid is coming out, and then move on to the next brake line junction until you've arrived at the caliper.

Once you've used the caliper junction as a bleeder nipple, you can use the bleeder nipples on the caliper and if all is well, in no time at all you'll be pumping through nothing but fluid.

If you have two discs working off the front master cylinder, go back up to the junction block and bleed the air from that connection back down to the other caliper. When all is well, you go back to the first caliper's bleeder nipples and bleed them again. If nothing but fluid comes out, go to the other caliper's nipples and bleed them. The pads will be closed up and the lever feel will be firm. If not, go back to the master cylinder and start over. If the lever's firm, it's onto the rear master cylinder.

Bleeding the Rear, Dry Lines

By fashioning a suitable tool, you can bleed the integrated brakes by yourself. You can use a monster box end wrench, but even a forked stick will do if it's long enough.

For the integrated brakes, you do it the same way as the front (every connection as a bleeder nipple) but get the air out of the rear caliper first. Once that's free of air, you work your way up to the front caliper, and then go back to re-bleed the rear at the bleeder nipples, re-bleed the front at the bleeder nipples and you're almost done. Yay!.

Break out the good fluid (Most everyone uses Castrol LMA4.) and pump the cheap junk out and throw it away. Don't even think of reusing brake fluid as it becomes oxygenated from being squirted through all of those little orifices. Gee, I don't understand why they feel so spongy... Figure on using two pints of the good stuff for all three calipers.

You can now take the calipers down and gently pry the pads apart with a clean screwdriver or whatever have you. This, of course, will push fluid back into the reservoir, so be prepared for the mess. This can also expel that last pocket of air that's been driving you crazy. Put the calipers on, pump the levers a few times, check the fluid levels and you're done until the next time.


You've done everything right and the feel still isn't firm. Either something has been missed in the rebuilding process, there's air trapped somewhere, a loose connection is letting air back into the system, or it's the lever itself.

Sometimes an air pocket will get trapped, and that's when you take a rubber mallet and bonk everything a few times (master cylinder, junction block, calipers, self) and that will help to dislodge it. A short spin on the bike will also have the same effect.

If the bike has a remote reservoir, try holding it below the master cylinder and then bleed it at the master cylinder. The air will rise into the master cylinder and you'll then be able to pump it out.

The lever itself can oftentimes be the culprit. I had a IV, for instance, on which the contact patch on the front brake lever had worn down to such an extent that it just would not push the piston in far enough. Once the lever was built up a bit, it was perfect. While you want sufficient clearance between the piston and lever, more is not better, so use a feeler gauge.

Brake work can be very aggravating at times so if it doesn't go right, clean up the mess, clean yourself up and come back to it the next day. It's not like it's going to go anywhere, and you'll be in a better frame of mind.

Regular Maintenance

Ideally, you want to bleed brakes twice a year. Annually is adequate, and 18 months is the longest you can neglect this. Extend this period and you'll find yourself swimming in a sea of brake fluid with it running up your nose. Pump fresh fluid through the bleeder nipples in the Spring and again before you put the bike away in the winter, just as your owner's manual suggest, and your brakes will last for years.