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Revision to yesterday’s blog; HIIT workout: bedding in new brake pads.

Thursday, April 26, 2012 by  
Filed under Daily Blog

April
26
2012
A brand new Avid Elixir organic brake pad: 4mm

A brand new Avid Elixir organic brake pad: 4mm

I made a couple of incorrect assumptions in yesterday’s blog, and I need to follow up on that with some new information that has come to light.

Yesterday I received my replacement brake pads, and I decided to measure a brand new pad with my digital caliper. As you can see in the photo, the the new pad + pad backing is exactly 4.00 millimeters thick. The backing is 2.20mm thick, and so that means a brand new pad is 1.8mm thick. This puzzled me, because Avid recommends that the pads be replaced when they are worn to 3mm. Clearly the recommendation applies to the entire assembly (pad + backing), and not just the pad. This important distinction was not made clear in the recommendation, and I made an incorrect assumption that Avid was referencing the pad alone.

Obviously this new information alters the theory I put forth in yesterday’s blog. Specifically, it turns out my brake pads were very close to the end of their life, but still within the manufacturer’s specs as a “good” pad.

So why were my brakes screwing up?

Well, this morning I took a look at the used pads once again, measuring each of them. Turns out one side of the pads were worn more than other side (this was true of the front and the rear brakes). I think my brake issue could have been corrected by simply adjusting the calipers so the pads were properly centered over the rotors. Again, while the pads were all near the end of their life, they were still within specs. I no longer believe that pad wear caused the braking loss/increased lever travel I experienced on Tuesday.

I’ve updated yesterday’s blog with the new information about how to properly measure pad wear. The main points of yesterday’s blog still stand: check your brakes for proper operation on a regular basis, and don’t ride on a bike that is not functioning properly!

So with the new pads on the bike, the lever travel is back to where it should be. In the future I’ll be more diligent about maintaining my brakes.

Unfortunately with my injured calf I could not bed in the new brakes. Bedding in a new set of disc brake pads is an excellent HIIT cardio workout! Avid recommends that you bring the bike to about 12-15 miles per hour, then brake firmly until the bike is traveling at about walking speed. Repeat this 20 times. Then you have to accelerate the bike to 15-20 miles per hour, and brake firmly until you are traveling at walking speed. Repeat 10 times. Wait ten minutes, then do the other brake. I’ll have to wait until my calf is feeling better to tackle this.

As for my calf, it’s still hurting, but definitely on the mend. When I first get up in the morning or rise after sitting for a period of time the pain in my calf is pretty bad. Once my calf warms up a bit, however, the pain is not nearly as bad. I expect to be back on the bike by Saturday. 🙂

John Stone Fitness Comments

14 Responses to “Revision to yesterday’s blog; HIIT workout: bedding in new brake pads.”
  1. John,
    A big part of the problem is that the outboard pad doesnt get the same amount of hydraulic pressure as the inboard pad, its very common in most disc brakes. Even if you keep them adjusted the outboard pad will wear at a much slower rate, if you have ever seen a caliper opened up, the fluid passages are so small going to the outboard pad, its impossible to get the same hydraulic pressure on both sides of the caliper.

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    • Thanks for the added info Craig.

      So while the uneven pad wear is unavoidable, is keeping the pads centered on the rotor through a basic caliper adjustment the way to go in order to avoid the excessive lever travel I experienced?

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  2. Another VERY common problem with avid calipers is that over time one piston will quit fully extending. No one that I know has definitively figured out why but the best theory so far is that dust collecting on one of the pistons while extended is getting past one of the seals. Overtime build up of material causes enough friction to cause one caliper to not fully extend.

    I had a pair of elixirs that did this to me. Rotor kept getting warped because of it. Had it warrantied and was replaced by an elixir CR. Couple months later same thing happened. It was again warrantied and was replaced with an XO. Only rode on them for about a month before I sold the bike.

    If I still had that bike I would replace them with shimano SLX or XT. I have XT on my new bike and they are vastly superior to the various avid brakes that I had to slog through. About the same modulation/stopping power but I never have to adjust them. They were also VASTLY easier to bleed on initial installation.

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    • I’ve heard of the piston problem before, too. Some people seem to suggest lubing the pistons by braking with the pads out, lubing (some controversy over what kind of lube to use seems to exist), pressing the pistons back in and repeating that a couple times. Any thoughts on that?

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      • Yeah, I tried various lubrication methods but none really helped. I even went so far as to completely disassemble the calipers, clean them out with solvent, relube, assemble and put back on the bike. It would help for a little while (for a couple of weeks I would get full piston throw). I think that once material gets between the piston and its housing it scratches up the surface which makes them much more prone to sticking in the future. This might be a sign of bad seals on avid brakes.

        It’s pretty easy to diagnose if this is happening to your brakes. If your rotors are getting out of true it’s happening. There are very few things that warp a rotor minus a catastrophic crash.

        Also, overtime this problem makes it progressively more difficult to center your caliper on your rotor. The amount of piston throw of each lever pull starts to become somewhat random. So you loosen your caliper, pull your lever, and then tighten your caliper. But now when you release the lever your look and you can visually see that your caliper isn’t centered over the rotor! This is incredibly frustrating!

        The area I live in is typically very dry and dusty. Everyone running avids is switching to SLX now because this year they’re so inexpensive and work just as well as XT/XTR this year.

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        • Solid information, thanks, man.

          I’ve got new Magura rotors on the way (with luck they will be here tomorrow), so it will be interesting to see if they stay true. I’m not quite ready to toss the Elixirs in the bin just yet (I quite like them), but if they start having caliper sticking issues or rotor problems I’ll definitely move on–probably to another manufacturer.

          One final note: I don’t find the Avid bleed procedure difficult, and everything has always gone really well for me. Admittedly, I do take a lot of care to make sure there is no air in the system, and that does take a fair amount of time. If the Shimano bleed is even easier/faster to perform, well that’s pretty cool.

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  3. Hi John, first post but a long time lurker…I always enjoy reading what you have to say, even more so since you started mtbiking as it’s what I am into the most..so maybe I can give you a clue about the malfunctioning you was experiencing with your brakes: very often the spongy feel of the lever is caused by air bubbles in the circuit, all you have to do is a bleed. Buy the avid bleed kit with the two syringes, make sure you use the bleed blocks so that the amount of fluid you put in the system is exactly what the manufacturer indended. Adding more fluid to compensate pad wear is a very bad advice as that way, when you put new pads on, you would have to re-open and re-bleed the system.
    About squealing, the only avid brakes that are helpless are the old juicy 3’s. On all the newer models, fixing the squeal is very simple: slightly loosen the two caliper bolts, and while keeping the lever pulled, tighten them again. It has to be done every now and then because pad wear does not occur uniformly. Keep up the good work John, and happy trails!

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    • Hi, and thanks for de-lurking! 🙂

      I’ve got the Avid bleed kit (and have done a couple of trouble-free bleeds using it), but the problem this time around is not air in the system. I confirmed this when I put the new pads in place and the levers were just as they were a week ago.

      That caliper adjustment you described is what I alluded to in today’s blog as a measure to mitigate the uneven pad wear. I’ve done that many times before, but not recently as I’ve not experienced any rubbing or squealing (except when the brakes are wet, but that seems to be uncorrectable). I think I’m going to start doing a caliper centering as part of my weekly maintenance procedure.

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