magura cut 3It’s springtime and that means it’s time to hit the trails. Dragging your bike out of the storage locker and freshening it up for this season’s duties is a ritual in many parts of the country.  One thing is for certain…any issue that you had with your bike when you parked it at last season’s end…if you had a season ending…any issue you had will still be there. If you had a braking issue like mushy lever feel, howling pads, etc…this points to a problem for sure and one that needs to be solved before you get back out there, but what kind of problem is it?  Do we need a bleed or new parts or what?

I have a pretty vivid memory from long ago where I am descending a steep and loose trail.  I am waaay back over the saddle with arms outstretched, butt barely off the rear tire, on a loaded for camping MTB.  The brake levers are pretty much pulled to the grips, overheated cantilever pads pressing for all they are worth on hot rims, barely scrubbing enough speed to retain control.

Ah, memories!

But now we have disc brakes on pretty much anything that has any pretense of off road use.  Bully, I say, bully.  I am not going back to rim brakes for off road as discs are so superior as to render rim brakes an anachronism at best.  Yes, they were simpler for the home-based wrench wielders among us, but that is about it as far as things on the plus side for the average rider.

But as good as a modern hydraulic MTB disc brake is, they can still perform poorly.  And that poor performance is nearly always related to improper set-up or maintenance.  However, a bad performing brake pretty much looks like a great performing brake, so determining what is wrong is often a bit of a mystery.

At twentynineinches.com, we have come to appreciate the line of brakes that Magura has for MTB use, finding them reliable and easy to work with, and the newer models blend power with excellent modulation.  We even used two sets of brakes to upgrade two bikes that had less braking force than we would have liked.  The first was a full suspension 29er that was converted to e-bike use for a rider that wanted to use it as an exploration and bow-hunting based rig.  The stock Shimano lower level brakes were not up to the task of stopping the heavy bike, so a set of 4 piston MT7s on 180mm rotors were a huge improvement.  Although we did learn a lesson along the way, and we will talk about this later, the conversion allowed for one finger stopping once we got it right.

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The next bike we upgraded was a Fat Bike used by a pretty stout rider who was cooking his stock OE brakes and rotors.  They were a nice shade of blue. We added a set of four piston MT5 brakes here and that was a great choice for the application. So we have installed, cut lines, bled,etc, a few sets of brakes on some test bikes.

http://twentynineinches.com/magura-mt4-hydraulic-brakes-first-impressions/

http://twentynineinches.com/magura-mt7-brakes-mid-term/

However I also have had some Magura brake sets that were problems for me, and all of them were related to my own set-up issues such as a bad bleed or contamination (I typically have to cut to length and bleed brakes when we install them on a test bike), or from mixing and matching rotors from another company’s brakes with the Magura calipers.  And it has pointed out to me that it is all too easy to mess up a perfectly fine performing brake with a lousy install. I am a shade better than the average home mechanic in this regard.  If I can do it wrong, so can you.

I bet that most of the brake issues that folks have are not related to an inherent design flaw in the brake or poor engineering, although that can happen, but rather they are due to poor set-up or something like that.  And along the path to resolving these issues that arose, I would typically call the Master-Blaster of brake knowledge at Magura USA, Jude Monica, and he would walk me though my woes.  In the process, I learned a lot about brake set-up and what to look for; how to assess the issue and get to a solution.

That got me to thinking.  If I am clueless as to these things, how is the general readership doing?  Could you folks gain some understanding in how to diagnose brake issues?  I bet you could.  So we going to spend some time in the virtual garage and hopefully what we discuss will help you through your next hydro brake challenge with a bit more information then before.


42-MAGURA-MT7TNI:  Jude, I have heard you say that there are two main sources of brake woes:  Pressure and friction.  Can you begin to unpack that for us?  What is the difference?

JM: Of course, I would enjoy the opportunity to explain.

When helping someone with a brake issue, I start by questioning whether the problem is a “friction” issue or “pressure” issue and by that I mean simply, does the lever blade have a good pressure feel and contact point? If no, then I suspect air in the system but not always, as the issue could be a caliper alignment problem which is more commonly overlooked than not.

If the lever blade has a good contact point, then I immediately suspect a friction issue at the brake pad. Friction issues can include contaminated brake pads, rotor (possibly from a messy bleed) or more often overlooked, alignment of the caliper.

TNI:  Ok…so we have a pressure issue.  How can we know that is the problem?  What would be those symptoms that would point to that?

JM: Excessive lever blade travel or movement while applying the brake pads to rotor is the first sign there could be air in the system.

  • First question – did you recently service or bleed the brake (knowing its history?)
  • Are you competent and comfortable with the procedure?
  • Did you follow the instructions? Are you sure? Once asked to relay the details, they can reveal critical variations of the process.
  • Did you move enough fluid in the process? Are you sure? A common mistake is to move too little fluid and effectively see-saw the air back and forth instead of out of the system.
  • Did you thoroughly clean up after yourself…caliper, pad area, rotor area…for any residual fluids that can find its way onto the pad or rotor?

Friction issues can be disguised as pressure issues too. Instead of stopping the rotor when the pads make contact, little or no friction can equal flex at the lever blade assembly (including all small parts in the system), etc!

Example: Try any disc braked bike on the local bike shop sales floor by applying the brake lever to the contact point. Now with the bike stationary, go ahead and pull the lever blade hard all the way to the grip. Possible? Indeed. If there were a friction problem, you could interpret the lever travel as a bleed issue.

Ok…good. If all of the above were performed properly, you can eliminate yourself, the mechanic as part of the problem.

Next advice is to STOP re-bleeding the brake and look elsewhere for the problem. The caliper/pads/rotor and alignment of the caliper are also part of the system and therefore suspect.

magura cut 1TNI:  What are the most common mistakes mechanics make when bleeding a brake that will lead to poor performance?

JM: Even seasoned mechanics want to quicken the process by avoiding removal of the caliper. This is the first mistake one can make in eliminating themselves as potentially being part of the unsuccessful bleed.

Removing the caliper allows manipulation of the physical caliper while bleeding to assure the passages are angled in a way to allow air to gravitate upward toward and out of the bleed port location.

Secondly and just as important, closure of the port after the bleed is easier and eliminates the potential of residual fluids hiding NEAR the pads and rotor.

Now if fluids have gotten where they should not be, and if you apply heat while riding and braking, then the messy residual fluids become lighter in viscosity and can flow easily onto pads/rotors. Now quickly the problem becomes a friction issue disguised as a pressure issue.

Main point: not removing the caliper only lengthens the process and complicates the outcome.


 

MAGURA MT NEXT BRAKE BLEED from MaguraUSA on Vimeo.

 


 

TNI:  Friction.  If that is the problem, how might I know that and what can I do about it?  I have had pads and rotors get contaminated by either brake fluid or other chemicals, sometimes I can salvage them other times not.

JM: Pads can become contaminated from the usual suspects like errant chain lube applications, residual soaps and cleaners left on rotors, attempts from mechanics to re-lube caliper piston seals and as mentioned before, messy bleed attempts, myself included. After thousands of bleeds I still get surprised by the amount of mess I can make. Therefore, I must admit that I have an Isopropyl alcohol use problem and consume copious amounts!

All of the above types of contamination typically look similar with a mirror like glazing or shiny appearance to the brake pad face. Basically, you are polishing the pad face by using a lubricant combined with the friction of the rotor, the results being a slick combination of the two and drastically reduced friction!

Salvaging contaminated pads is an emergency-only procedure and is never recommended by any pad manufacturer!

TNI:  Is it important to keep the ‘system’ correct, such as not mixing other brand’s rotors with Magura calipers, etc?  I know on the E-bike conversion we upgraded, we had very so-so results until we swapped to Magura rotors over the existing Shimano rotors (which were a bit low end…older Deore brake).

2-MAGURA-MT7-brakesJM: That is exactly right. Obviously the mixed combinations will fit and will work to some varying degree, so the main problem is that the performance tested results (and failure data) on the manufacturer’s dynos are compromised.

The different manufacturer’s rotor alloys can be drastically different and the varying pad compounds from different aftermarket pad manufacturers will affect the heat and wear rates of the pad and rotor and ultimately the resulting performance.

Remember that a brake set is a “system” and all of the components have a scientific, known, performance capacity. Those important components in question include rotor width (thickness), rotor alloy composition, pad compound, pad steel back plate width, thickness, and shape, the fluid concoction, the mass of the caliper for heat control, etc.

TNI:  Getting it straight – Alignment.  Something I did not realize was so critical, is the alignment of the caliper in relation to the rotor.  In fact, you point out the tolerance here for excellent performance is surprisingly tight, even beyond what the eye can see.  That seems almost hopeless.

JM: Disc brakes require precision mounting in order to operate as designed so it is easy for a shop or home mechanic to suspect and blame the brake unknowingly, especially if they are new to the idea.

Firstly and historically, mounting tabs on all manufacturers frames are suspect for alignment accuracy. This is nothing new and has been a problem for over a decade or since the acceptance of bicycle disc brakes. Therefore there are several manufacturers whom produce disc tab facing hand tools.

The manufacturing process welds, bonds, or connects (via hardware in drop-out form) the brake tabs onto the frame which allows huge variations of mounting tolerances from heat expansion/constriction, curing or tolerance stack-up. In many cases the brake pad/caliper misalignment will correct itself with pad wear but you need a couple scenarios to accomplish this.

  • Modest elevation changes combined with heat aid in wearing the brake pads into the subtle, perfect, pairing or “bias.”

Remove the elevation component, which, in turn, removes potential braking heat and it can take a long time to correct pad alignment. The kind of one, single, ride that would produce great pad bed-in results in Colorado/New Mexico could take three months of riding and brake pad wear in Austin or Orlando!

magura cut 4With the popularity of the 4 piston caliper today, the potential for caliper misalignment is exaggerated over a 2 piston caliper’s pads. The reasons are due to the increased amount of brake pad surface area that contacts the rotor and that difference is mostly due to the pads leading and trailing edges. Think of a fraction of a millimeter measured at the leading edge translating to 1 plus mm difference at the opposing edge of that long pad.

This example would most certainly produce a “spongy” feel at the lever blade.

Do I re-bleed it or is it something else?  You tell me!


Thanks to Magura USA and Jude Monica for his time in getting us started on the path to better brakes.  Educate yourself, get the right tools and supplies, and if there is any doubt at all, let the pros at the local bike shop do the work.  Brakes are something to take very seriously.

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