Misc. Braking Questions FAQ
compiled & edited by Kristian #562
Please read the
Disclaimer before attempting any work in this FAQ.

Problems & Solutions

Aftermarket Brake Parts

Misc. Brake Questions

Other (Separate) Brake FAQs:

Bad master cylinder, caliper or brake fluid?

Problem: I recently bought a 2000 F650 and after about 50 miles, the front brake lever went all the way to the bar. I could pump it up, but after that first occurrence, it frequently, but not always, went to the bar. Took it back to the dealer and they said the master cylinder needs replacing (after the technician originally thought they were OK, because of the intermittent problem). While waiting for the part, I read the brake FAQ and decided to change the fluid in both front and rear brakes, as the brake fluid was the color of coffee ... actually more like espresso!. Now, I've ridden the bike about 10 miles and the brakes seem nice and tight. Is it possible that I really do have a bad master cylinder, or could changing the brake fluid fixed the problem? Also, if the brake lever goes to the bar, how would one know if it's a bad master or front caliper?

Solution: Well, after changing the "espresso" brake fluid to "gin" color, I went out and practiced panic stops from 25 to 45 mph, and brakes are still working fine, so I'm inclined to think it was bad fluid and not a bad master cylinder. Phoenixtoohot


Rear Brake Failure?

Change your Fluid REGULARLY! Check your Brake Hoses!


Brake Mount Failures?

Only ever heard of ONE instance. ed.

Instance 1

OK, right to the point here. I have just had the sh*t scared out of me by a brake mount failure that caused a total loss of the front brakes at speed on my 98 F650ST. I went to brake at 30-40mph and there was a CRACK followed by the clunk of my entire front brake caliper assembly rotating out of place on its remaining mounting bolt resulting in no brakes and a floppy brake lever. On examination the lower of the two caliper mounts (where the caliper is bolted to the fork leg) had fractured vertically through the bolt hole, leaving the caliper hanging on via the upper mount and the break pads totally dislodged and hanging loose.

Q1. Has anyone heard of it happening before?
Q2. Is this a known issue?
Q3. Is this something that BMW should know about?
Q4. Is this a weld repair or a new lower fork job?

I would advise anyone to take a close look at the brake mountings on the forks and check for cracks just in case. This was really sudden and with no warning. Had it happened at motorway speeds I would not be here to make this post. I have just had all the covers off this and taken a look in the cold light of day. The good news appears to be that the mountings to the fork leg are ok. The bad news is that it is the caliper mounting plate that has failed. This plate connects the caliper to the forks and mounts two pins that allow the caliper to move. The mounting for the lower of these pins has fractured vertically. You can see a diagram above of the brake assembly. The mounting that has fractured is just below the lower of the two bolt holes on fig. 3 (see above). As you can imagine, my BMW dealer is taking a real interest in this and will be looking at this ASAP with a view to kicking it up the BMW ladder if there is no sign of external forces at work. MrWolf, Dave-O'C-98 F650 ST

Leaking Brake Line?

Leaking Front Master Cylinder?

If it leaks, it will quickly corrode metal parts, including allows and strip paint. Clean it up quickly and fix it!


  1. Reservoir Overfilled.
    Solution. Take out some Fluid with a CLEAN Turkey Baster or Better yet, BLEED some fluid out.
  2. Seal Problem #1: There is a bit of rubber, from one of the punched holes on the diaphragm, that is still attached, but on the inside, so you can't see it. It raises the lip of the seal enough to cause leaking. btw, CHECK for splits or defects in the sealing lip of the Diaphragm first. If there is a defect, that's where it's weeping from, and you will need a new diaphragm. No amount of sanding of the lid will help you if the Diaphragm is split or has an extrusion (manufacturing) defect.
    Solution. Undo Screws, Check Diaphragm, Reinstall. Do NOT Overtighten the Screws. If the Seal is good, it will seal just fine. One thing you should always do is to coat the threads of the master cylinder lid screws with anti-seize compound. If there are any screws that are going to corrode on your bike it is going to be these screws. (Richard #230). If all else fails, replace the diaphragm and make sure that the vent grooves in the top of the master cylinder cover are clean.
  3. Seal Problem #2: Rubber diaphragm under the lid was not re-installed or tightened (most likely too tight) correctly, or if there is a problem with the vent holes under the cap.
    Solution. Undo Screws, Check Diaphragm, Reinstall. Do NOT Overtighten the Screws. If the Seal is good, it will seal just fine. If all else fails, replace the diaphragm and make sure that the vent grooves in the top of the master cylinder cover are clean.


Front Master Cylinder Rebuild?

Q. The front brake plunger on my '94 Classic F is sticking. Does this mean that it is shot and really should be replaced or can it be stripped and greased up. I saw on the Motobins website that they only supply the master cylinder and throttle assembly as one unit. Is this correct? Pat#1210

According to the GS Manual this item should be replaced (Front/Rear Master Cylinder Cup) every 40,000kms for Bikes WITH ABS. This Boot can be replaced.

The BMW part #'s:


What about Sticky Pistons/Dragging or "Binding" Brakes

by Andy #982, Mark #403 & Kristian #562

Severity: It can be dangerous, so fix it soon! Here are some examples:


  1. The brakes drag (slightly) to stop anything getting between the pad and disk that might cause scoring. Its simpler for the OEM than fitting any other sort of protection to the pad/disk.
  2. If the wheel spins freely for maybe 10 seconds (or less, even a 3-4 good rotations) after a good shove, all is OK despite some slight rubbing (not squealing) noise.
  3. If it is dragging, in other words it gets hot to touch even if you do NOT use the brake, check the fluid level before anything else and see if removing some helps. Stay within the sight glass limits, but you'll find half full to low may be better than full.
  4. If you've played around with your forks/axle lately, you may have put the bike together with a slightly different wheel position. There's a surprising amount of variation in how the forks will come to rest with everything loosened up, and how they will end up when you tighten the triple clamps, axle pinch bolts and fork brace. If you tighten things up with a slightly different angle than you had previously, you can get additional brake drag until the pads "seat" themselves again to the new position. See the  Front Wheel Removal FAQ for tips on how to put the forks back properly and the Rear Wheel Removal FAQ for the rear.
  5. For the Rear Check the Brake Plunger moves freely. For the Classic, Undo the The Allen Key Screw (i.e. the Brake Pedal Bolt). Take it off the Axle and Grease the Axle, and the Plunger and connections. Put some Vaseline or Grease in the rubber boot.
  6. Next check Check the Rotor is not Warped. They warp easily if they get too heat for too long or they are dropped when you do a wheel change or any maintenance work e.g. Bearings. Here are some New Rotor sources.
  7. Next idea is to replace the fluid and bleed. Old fluid with water in it can expand under heat before it all goes spongy.
  8. Next idea is to check the Pistons are CLEAN. What often happens is that as the pads wear the pistons extend further and further out of the caliper until you change the pads. Then with new pads you push 'em back in again. But if you didn't clean the piston's at all, all that gunge ends up going back into the seal and can cause the piston's to "stick" somewhat.
  9. Don't forget to ALSO check whether or not the master piston returns completely!
  10. After that its strip down and new seal time at which point you'll want to check the FAQ or maybe see a mechanic. If a seal kit is available, just get a clean place to work and replace every seal in the kit. Clean everything as you go, you are looking in particular for anything that might prevent fluid getting back to the master cylinder. Lift the rear wheel up an check if the brakes are slightly on even if you're not breaking. If they are, this often causes over heating and you have to overhaul your brakes, which isn't very hard. If you find any inside dirt coating the brake cylinder or piston then polish it away using a light rubbing but never polish in and out, go around and around or you may cause leakage through micro scratches. Then use new gaskets/o-rings.


Other reasons for Brakes heating up

Caliper out of Alignment

Problem: Caliper torture. I already have a warped rotor, I confirmed I have a minor hub warp (.05-.06mm) problem, and I don't want to tighten the rotor any more than I have to, as I have had previous problems with rotors warping due to overtightening. I'm trying to shim the mounting points (actually, just 1 or maybe 2 spots) on the hub as flat as possible, before I tighten the rotor to it, and the rotor starts going thru heating and cooling cycles. I'm tempted to go for Loctite 243 (for removal without heat) and maybe 10Nm. But I did measure, and it looks like the longer GS will fit the Classic, and if I ever have to do this again I will order the longer bolts. I've been looking at those seating clearances also. They might be affected if the spacer were the wrong thickness (unlikely), if the wheel bearings weren't fully seated (mine are fully seated, crushing/holding the wheel bearing spacer in place, OR if the rotor mounts cut into the wheel hub are machined too deeply, causing the rotor to be seated farther inboard, which is what I'm think may be my problem, but is much harder to check without disassembly. If that was the case, I could make the axle spacer on that side a few mm thinner to shift the rotor outboard. As it is, for my caliper to fully release off the inboard side of the rotor, the caliper has to slide inboard EVERY SINGLE BIT that is available, including compressing/crushing the slide pin guide bellows. When the bellows expands/pushes ever so slightly (we're talking about less than a millimeter), as is it's rubber nature, the caliper binds that tiny bit.....actually the front caliper releases even less, and binds more, but has never even gotten warm to the touch, despite the rotor getting hot when used hard. If the rear caliper weren't so consistently too hot to touch, to the point where I worry about the rubber seals, I'd ignore it. The brakes have always worked perfectly, except for the heat. And without actually dissembling the caliper (which I won't do unless I have spare seal rings) I've tried all my tricks - I've flushed the caliper 4-5 times, expanded out the pistons and cleaned/sprayed them, removed the slide rubbers, cleaned them and tried 3 different hi temp caliper greases (synthetic and non synthetic) on them, crushed them shut and bled out the excess air and grease from the sliders, used older thinner pads which give me an additional mm of clearance, used new OEM pads with new clip and pin hardware, checked the release freeplay on the master cylinder, and retracted the pads, filled the master cylinder halfway, sealed it, and then pumped the pads down, creating a minor vacuum in the m/c. I've serviced plenty of disk brakes, but I'm at a loss on this one..... maybe a stupid question - I'm not used to Brembos. I've been reinstalling my cleaned greased slide rubber bushing by forcing it into the caliper hole, and then installing the base plate slide pin, then bleeding the bellows as I crush the caliper. You aren't supposed to place the slide rubber on the pin and THEN force the rubber thru the caliper hole are you? Seems hard to do without lubing the outside of the rubber to go thru the caliper hole, like you'd tear the pin thru the rubber. I dunno - no hurry, but clever ideas are welcome. Otherwise, I just freakin love my bike! HsN

Solution: None.

Brakes work for about 50 applications and then it grabs the disk.

Problem: I got a 2001 F650GS, as far as I am concerned it is a lemon. Any way, was riding to work yesterday, stopped at the light and I can smell this sharp burning odour. looked at my rear brake and my calliper has smoke coming out of it. I did notice earlier that the bike is kind of sluggish, but did not think much of it at the time, riding in city traffic and all... My rear calliper seized I thought, so I took the screwdriver out of the bike kit and to my surprise I was able to spread the shoes with little effort, that goes for the calliper itself, it was free to move. I do have excessive travel on my brake pedal, brakes work for about 50 applications and then it does the same thing (grabs the disk), ABS work. One thing I noticed that when I apply and release brake I can see the piston move back and forth about 1/16".There is no way it should move that much, at the time when brakes will not release the brake pedal feels solid, like it was from new. Any thoughts? I think it might be the master cylinder, or some kind of check valve in ABS system. Pooshkin '01 F650GS, Winnipeg, Canada.

Solution: Just about a month later, I finally got all new rear braking system:), dealer had no clue what to do, did not care about what I had to say. I got new disc, caliper, shoes, master cylinder, they had to take parts off a brand new bike. It was getting pretty strange what it was doing, the bike was applying rear brake by itself. Pooshkin '01 F650GS, Winnipeg, Canada.


Brake Calliper Retaining Bolt Warning

IMPORTANT: If you ever remove the Front Brake Calliper for any work, Steering Head Bearings, Fork replacement, whatever, make sure the Bolt threads are clean and there are absolutely NO bits of Aluminium or any other dirt or swarf jammed in the threads. If there is, use a fine screwdriver and a wire brush to clean them thoroughly. In addition check there are no bits of Aluminium in the threads of the Calliper itself. Test that it can be wound all the way in BY HAND before tightening. If it jams going in by hand, take it out and check it and clean it again until you CAN screw it in BY HAND.

The reasons should be apparent, however any small amount of Aluminium in the thread will start the bolt jamming. If you tighten it further with a socket or spanner, it can't screw in any more and starts ripping threads out. Then with more Aluminium now jammed in the threads, as you back it out it rips even more Aluminium out. You do not want this to happen. Really Bad Karma. Do not exceed the specified torque.

Why Does my Brake Pedal Pulse ?

3 Reasons:

  1. Loose Brake Pedal Axle.
  2. Worn Roller. See The Chain Roller FAQ
  3. ABS Activation

Loose Brake Pedal Axle (Most Common)

Missing lower chain roller.

ABS Activation

Front Brake Play

See the Cable FAQ

Sources of Aftermarket Brake Calipers, Rotors, Brake Lines


Floating rotors are not "attached" to the rotor carrier. There are "half holes" in the rotor and the carrier and there are rivets that keep the rotor positioned in the carrier. They have a slight amount of wiggle room. The REASON is so that when they get hot, they can expand without warping because nothing is NAILED down. They are free axially only. Draw two concentric circles. On the inner circle, draw a set of six or eight tiny circles, spaced equidistantly. Now, cut out the tiny circles. Then cut on the inner circle. The piece from the outer to the inner, with the tiny circles, is what the actual ROTOR part of a floating rotor looks like. Now loosely rivet it to the inner circle at the tiny circles and figure out how to mount the inner circle to your hub and you have a floating rotor assembly. Get it? Floating calipers are free to move across the thickness dimension of the rotors, to adjust their position as the pads wear. The two "floats" are orthogonal and therefore can be used in concert or individually, as you like. Flash #412

OEM Brakes:

Our front Brakes are 30/32 mm Two Pot Brembos and the rear is a single pot 34mm Brembo.
The Caliper No's are F 22.5553, R 22.5546.

OEM F650 Classic Part#:
Disc Part # 34 21 2 345 323
Brake Caliper # 34 11 2 345 319
Disc Part # 34 21 2 345 314
Brake Caliper # 34 21 2 345 312

OEM F650 GS/Dakar Part#
Disc Part # 34 11 2 345 824
Brake Caliper # 34 11 2 345 854
Disc Part # 34 21 2 345 314
Brake Caliper # 34 11 2 345 856

Frenotec has OEM Brembo Parts, but doesn't specifically list the BMW F650. It does say "New cast caliper with 4 individual pads. Provides better braking pressure and feel than older style calipers. Will upgrade most Ducati, Aprilia, Moto Guzzi systems". If you find one that fits, please let us know , ed!

Aftermarket Brake Parts Sources:

Brakes - Aprilia:

Brakes - Braking: www.braking.com

Brakes - Ducati:

Brakes - EBC: www.ebcbrakes.com

Brakes - Galfer: www.galferusa.com
by Todd#389

Q. Can one use a floating rotor (which Galfer offers as an option ) WITH a floating caliper (like we have on the F650)? I always thought it was either/or, but I ain't owned any fancy bikes.

Brakes - Harrison: http://www.billet.co.uk/

Direct Links to Harrison's F650 Specific Pages

"Thanks for your mail Kristian. Apols for the delayed reply. The caliper that we make specifically for the F650 (front only) is the #235. It has 54mm spacing on the mounts. As far as we know the fitment is the same for the "Classic" f650 and the newer F650GS, but would like to have a confirmation of any differences if any of your riders are knowledgeable on the subject. Our caliper is direct fit, and designed to work with the factory disc.

We will be updating the website shortly, but the fitment is currently posted on the 'new products' page.

Prices are (GBP excluding courier and VAT if applicable):

Billet Original facia design:
6-Piston Polished 239 each
6-Piston Clear or black anodised 259 each

'2k1' or New 'Signature' facia design:
6-Piston polished 271 each
6-Piston Clear or black anodised 289 each


Brakes - MAP Engineering: www.map-engineeering.com

Brakes - Motorworks:

Brakes - Nagesti:

Brakes - Spiegler:

Feedback on Aftermarket Brake Parts

AM - Calipers

AM - Rotors

AM - Rotor Bolt Sizes & Torques

AM-Brake Lines (or Are Steel Braided Brake Hoses Better than the OEM Rubber ones?)

This subject is like discussing OIL. There are 1001 differing opinions. Like the OIL discussion, a cross section of these opinions is presented here. You choose which camp you fall in.

Note: BMW already (and only) installs steel brake lines on the F650 bikes that come with ABS and then ONLY the front.

Contact Area & Front Wheel vs. Rear Wheel

Q.  So, because I'm very curious (its good I'm not a cat), I did some research on MC Dynamics and believe I can summarize what I have read so far. Please correct me if I am wrong.

Given an unlimited coefficient of friction at the front tire contact patch and given that the COM (center of mass) of the rider/MC system is higher than the center of the front wheel, the MC will eventually tilt forward after shifting 100% of the mass to the front wheel. For optimal braking the COM should be as low and as far back as possible. I'll give a link for the source of this info below.

So, assuming that the COM of the bike is a constant (ignoring brake dive for the moment), then the rider's addition to the calculation for COM comes at the pegs, handlebars, knees/thighs, and bottom. Clearly, if we could get 100% of our mass while braking at 1g on the footpegs (lower than the center of the wheels) that would be great (its impossible of course). So, the best we can hope to do with COM is limited by how far back we can sit on the bike and still operate the brake lever while trying to keep as much force off the handlebars as possible (get yourselves a thighmaster). You need to sit as far back as possible to counteract as much as possible the effect of the force put on the handlebars (trying to tilt the bike over). The more weight you can keep on the rear tire the more you can use its coefficient of friction in addition to the front. Hopefully, I've gotten most of this right...here's the link I mentioned: 
http://www.dinamoto.mecc.unipd.it/ Chris in Santa Cruz, CA #782 - 19-Mar-02

A.  The basic answer is Yes!

Weight transfer needs to be balanced against what a brake can absorb in terms of energy which is a combination of down force, tyre contact area and the brakes ability to generate heat and then get rid of it. Brake balance changes weight transfer during the stop.

If things are uneven, you get events such as ABS activation of a lifted wheel that will change weight transfer again and upset the whole vehicle calculation.

Instrumentation consists of wheel speed sensors (like ABS), vehicle speed (via radar) and pressure transducers in the brake lines. Everything is plotted against time, so you can get vehicle deceleration, wheel angular deceleration etc. Temperature transducers are useful to sort vehicles that don't work as the disk or drum temperature pretty much tells you how much work a brake is doing. This calculation is pure energy, so must be basically true, especially if both axles have the same airflow etc. Kinetic energy becomes heat, first law of thermo dynamics applies.

Temperature kit is cheap if anyone wants to play. All you need is a couple of rubbing thermocouples and a voltmeter with two channels and you can pretty much measure your own brake split for a given ride or manoeuvre." Andy Leeds UK #982

2-Up Braking

Brake Links