Quantcast

Frankenbrakes and brake improvement discussion

Discussion in 'Downhill & Freeride' started by Udi, Sep 2, 2015.

  1. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

    Rep/Likes:
    70 / 558
    Joined:
    Mar 14, 2005
    Messages:
    4,367
    This is an open ended thread for anyone who has problems with current production brakes and wants an alternative solution. If you are 100% happy with your brakes then great, this isn't the thread for you, be happy. I think it's safe to say that every brake out there currently has notable flaws though, unlike a lot of aspects of bikes that are currently very polished in their function - like frames, suspension and drivetrains.

    Braking has developed many new issues over the years. If we go back 12 years, with the Hayes HFX/Mag era we had relatively reliable hydraulic braking with modest power. Shimano extended on this with their M800/M756 brakes which were supremely reliable but also not that powerful. Many people had issues with glazing and destroying pads from having to drag them excessively.

    Then we saw a big jump in power with servo wave and larger 4-pot calipers, which decreased stopping distances and glazing issues, but lever throws grew as a result of the increase in hydraulic leverage ratios on these brakes, and lever inconsistencies became a bigger issue as well. There seems to be a 50% chance that any given brake will experience lever throw fluctuations over a run, commonly reported on all the big brands like Avid/SRAM and Shimano - but not necessarily on every single brake, which makes the data very patchy. For example, Mike Levy for years raved about Shimano in his Pinkbike reviews while sometimes unfairly ripping Avid/Formula to shreds, but in reality, we were seeing numerous warranty cases with XTs leaking / fluctuating in throw / occasionally having complete MC seizures here concurrently with his raving. Now with the new M8000 and M9000 Pinkbike is reporting these problems like they are new, but in reality it was just their luck of the draw.

    I think there is a common theme with problems being proportional to power, so brakes with less leverage tend to be more reliable - possibly unrelated directly, but rather because lever throw variations are much more of a problem when they happen on an M810/M820 for example (where the throw is so long that your lever engages near the grip) compared to an old Hayes brake where you had a larger safety margin.

    Finally, with the switch to 650b, we've reduced stopping power by a very clean ~4%. Simple lever arm calculation here, bigger wheel = need bigger brakes, which we don't actually have.

    On top of all this, an ongoing issue is that pad compound changes due to heat affecting the friction coefficient over the wear life of the pad - i.e. brand new pads start off with good bite after break-in, but then deteriorate over time as the surface hardens and experiences molecular changes. Shimanos heat-sink pad and rotor ideas are probably the only thing that actually address this issue, so points to them for that. Larger rotors also do the same thing.

    So, solutions?
    • In my book the best solution is a bigger rotor, but these died out due to lack of popularity. The key benefit is that they increase braking force "cleanly" - i.e. without any cost in lever feel like servo wave, or lever throw distance like mechanical/hydraulic leverage, or reliability. Both Hope and Formula offered 220/225mm options, with Formula being quite good with rotor weight optimisation so a 220 option from them would have been quite viable. Are there any good options left for this?
    • Lever throw fluctuation - what actually causes this, is it heat driven from fluid expansion, or more likely to be from seal expansion? I feel the fluids aren't the problem. I suspect the problem may be caused at the caliper end, thus being a fault of the caliper - since the lever doesn't see force or temperature fluctuations under constant deceleration - but am open to correction.
    • Excessive lever free stroke - this is purely a function of hydraulic and mechanical leverage, which is why brakes like the M820 have mountains of power but awful stroke distance. Servo-wave helps, but I think in this case they should have changed the leverage curve a bit to cut some stroke. Free stroke is also wasted by internal lever design, particularly lever stroke distance between u-cup seal meeting and crossing the primary port. I've found this is internally modifiable on most levers with careful thought, and something that can also change with lever age/wear - which has been part of the reason I've used my particular brake set very happily for 5 years now. The reason for this thread is that I want more power without extending stroke.
    • I see an ideal solution as finding a combination of lever and caliper that offers good power and free stroke while eliminating individual products (levers and calipers separately, not entire brakes) that cause dynamic stroke variations - and possibly bringing some larger rotor options into the mix, so that the increase in power can be shared between the lever's leverage (= more stroke, unavoidable), and the caliper's leverage (clean).
    • I've been putting together a database of lever and caliper piston sizes along with resultant hydraulic leverage, perhaps people would be willing to take measurements of their brake levers so we could add mechanical leverage into the equation and have a good bank of mix/match options.
    • I know I haven't mentioned every brand here but I've tried pretty much everything. If simply buying Hope/Formula/Magura actually fixed these issues I'd have just done it, reality is everyone has their flaws, but by opening up some compatibility options, it might be possible to generate better optimisations. Obviously DOT and Mineral need to stay with their own kind, unless seals are standard sizes that can be changed.
    So with the reasoning out of the way, I've been collecting data and very briefly slapped it into a spreadsheet below. The mechanical component needs formulas inserted still (and must be considered), but the hydraulic component is already working. I will make it editable in future and add a "sandbox" section that allows you to calculate the results of mixing and matching various items from the collection. :)

    https://docs.google.com/spreadsheets/d/1sjPSmOYbhjDBFxcvXVw1ufKfowEBu1AKh8sB6T8e24Y/edit#gid=0

     
    #1 -   Sep 2, 2015
    Last edited: Sep 2, 2015
    • Like Like x 7
    • Useful Useful x 6

    Please register to disable this ad.

  2. kidwoo

    kidwoo Celebrating No-Pants Day

    Rep/Likes:
    134 / 1,233
    Joined:
    Aug 25, 2003
    Messages:
    20,917
    Location:
    In my pants
    v-brake levers, avid BB7s + whiskey.

    That's what I've learned from RM.

    Would you even need to have identical piston area/volume displacement between brands to mix and match? I like shimanos levers but if I could just throw someone else's calipers on the end that don't leak and let air in, I'd be happy. I know you won't get the same 'feel' as either in a mismatch but does it really matter?

    When you get a good one, it's good forever it seems.
     
    #2 -   Sep 2, 2015
  3. troy

    troy Monkey

    Rep/Likes:
    31 / 296
    Joined:
    Dec 3, 2008
    Messages:
    722
    I'm using Shimano Deore Servo-wave levers with Magura Louise BAT (2008+) calipers and 8" Magura Venti discs + steel braided hoses.



    IIRC Those calipers have 22 mm dia. pistons, just like a current SLX/XT/etc. calipers from Shimano. It seems like the lever throw is reduced a little bit (just like I wanted) and the power remained almost the same. IIRC Magura master cylinder is 10 mm for Louise and 10.5 mm for Shimano stuff.

    About the inconsistency of the shimano brakes: I think that the problem is with the master cylinder sealing. While I was bleeding my frankenbrakes some day, I've noticed, that something is off with one of the levers. When I was pumping it very fast, the lever was sucking some air into the system (don't know where from, but my guess would be - bladder area). I had no problem with the other lever. Next time I will switch the levers and check if the seal is faulty or what. It wouldn't surprise me tho, I've kinda overfilled those brakes slightly, to test something, and the excess oil kinda leaked slowly from the lever (under the bladder cover thingy) during the next couple of rides, so it is a weak spot for sure.
     
    #3 -   Sep 2, 2015
    • Dislike Dislike x 1
    • Useful Useful x 1
  4. HAB

    HAB Chelsea from Seattle

    Rep/Likes:
    68 / 591
    Joined:
    Apr 28, 2007
    Messages:
    9,897
    Location:
    Seattle
    No, within reason. You'll change the lever feel and power a bit, but it'll work.

    Look at it this way: There's a cylinder in the lever. It displaces fluid, of a volume equal to the cross sectional area times the stroke. Then there are some number of pistons in the caliper (be it 2,4,6, whatever) that sweep out a volume equal to the amount of fluid displaced by the master cylinder (less any expansion of the hoses, etc). The smaller the ratio of master cylinder area to piston area, the longer the lever throw will be, but the more power you'll get out of it.
     
    #4 -   Sep 2, 2015
  5. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

    Rep/Likes:
    70 / 558
    Joined:
    Mar 14, 2005
    Messages:
    4,367
    @kidwoo
    Yep I agree - the bad ones seem to show their issues within a month or two, if you get one that's lasted 6 months to a year it's probably going to be good for many years. I'm not sure if the Shimano issues can be isolated to the caliper or the lever though - eg. I know for a fact that M785 calipers develop leaks easily, but M820/M640 calipers don't seem to suffer from that, so I think the varying throw may not be from an actual leak - rather I suspect it comes from reversible heat expansion of something within the system.

    No you definitely don't need a match in hydraulic leverage, but you do need a rough match in terms of the combined mechanical and hydraulic leverage. The cool thing is that if you have a complete dataset on this, you can tailor the match to try and improve something you didn't like about the original brake - for example if you had an M820 and liked the power but didn't like the huge throw, you could possible find a lever with slightly less leverage like the M800 (for example) and trade off a small amount of the power for a shorter throw, and possibly also more reliability if the older lever was less prone to variance in throw. It also means you can be aware of exactly what difference your proposed mismatch will result in - i.e. if it'll give you more power with a throw increase, or vice versa.

    I just threw together a quick spreadsheet which loosely combines all aspects of a brake system, will edit it into the original post if anyone is interested. I'll make it editable once I've finalised the formulas, particularly for the mechanical leverage.

    @troy
    I've noticed the same thing as you on various Shimano levers. The leaking after overfilling is normal though, as basically in any brake the reservoir side of the system is sealed weakly on purpose to remove the possibility of pressurising the system and turning an open system brake into a closed one. This is why people who try to fix excessive stroke issues (as a result of leverage) by overfilling the system experience a reversal of their efforts within a day of riding. I will try and add some Magura data soon too, as it will be useful for Shimano blends.

    Does anyone have a confirmed master cylinder diameter for the Hope Race and Tech3 lever?
     
    #5 -   Sep 2, 2015
  6. kidwoo

    kidwoo Celebrating No-Pants Day

    Rep/Likes:
    134 / 1,233
    Joined:
    Aug 25, 2003
    Messages:
    20,917
    Location:
    In my pants
    Right. The only scenario I see it being a problem is too little fluid pushed for the caliper piston volume that might extend the lever throw too far to be reasonable.

    I want to try what troy's got going on. I'm kinda over having DOT fluid around grabbing water out of the air so a shimano magura combo would be good.

    I've warrantied enough brakes now, calipers and levers both, that I'm pretty sure the problem most people are getting from the shimanos are what keeps getting said......leaking around the pistons. I know it's happening because my pads get fouled if I don't ride my bike for a few days. And a bleed fixes the weird bite point after leaned g-outs so I'm pretty sure the leaks just let air in that accumulates over time.
     
    #6 -   Sep 2, 2015
  7. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

    Rep/Likes:
    70 / 558
    Joined:
    Mar 14, 2005
    Messages:
    4,367
    I've seen scenarios that don't fully agree with that - eg. while I've seen m785s with varying lever throw and leaking / weeping caliper pistons, I haven't (personally) seen m820s with caliper pistons weeping or leaking - but I have seen m820s without those problems that do still suffer from dramatically varying bite point over a single run. So if one of these is "leaking around the pistons" then it's drawing air without losing fluid, which isn't impossible, or the fault is caused by something else.

    I'm as interested as you in figuring out the actual cause, but I think it's wise to not eliminate any options until they are 100% guaranteed to not be a factor. Do keep posting your thoughts though, more pieces of the puzzle are always good.

    On fluids, I've never found water ingress on DOT brakes to be a problem, and neither have I had any issues with the boiling point of Mineral Oil, or even using fluids with lower boiling points. As I hinted at, most brake faults are design issues rather than fluid issues (unfortunately often blamed on fluids!) so personally I don't think there is any need to choose between glycol and oil (except avoiding DOT5 silicone fluid which has higher dissolved air content, but no one uses that anyway).

    I'll add some Magura data to the list, can someone share the piston sizes of all current Magura brakes?
    @troy perhaps?
     
    #7 -   Sep 2, 2015
  8. kidwoo

    kidwoo Celebrating No-Pants Day

    Rep/Likes:
    134 / 1,233
    Joined:
    Aug 25, 2003
    Messages:
    20,917
    Location:
    In my pants
    Well the inconsistent bite point is air. Because every time I've gotten it, a completely neurotic bleeding session fixes it. Whether it's caused in an individual case by leaky pistons or a bad initial bleed/hole in hose/whatever is going to differ.

    I just know in cases where I've had a really good dialed brake work well for a long time, and then not, barring something stupid like a hose breach, it's always been the pistons leaking. First I notice the slick brake pads that need to be burnt off, then two or three rides later I start getting the bite point variations. But no, I'm not saying you need leaky pistons to get to that point. They just also do that, and that can be the source.

    A friend of mine who reps shimano had this clear plastic hose and caliper demo setup he takes around to shops. It's insane how many little nooks and crannies are in the caliper and lever housings there are that can hold bubbles.
     
    #8 -   Sep 2, 2015
  9. StiHacka

    StiHacka Compensating for something

    Rep/Likes:
    262 / 2,112
    Joined:
    Jan 4, 2013
    Messages:
    7,407
    Location:
    i͓̽t͓̽ i͓̽s͓̽ fu͓̽l͓̽l͓̽ o͓̽f s͓̽t͓̽a͓̽r͓̽s͓̽
    Shall we bleed them in ultrasonic bath?
     
    #9 -   Sep 2, 2015
  10. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

    Rep/Likes:
    70 / 558
    Joined:
    Mar 14, 2005
    Messages:
    4,367
    Yeah I have no doubt. But the question remains about what's happening on brakes that have the bite point variations when they don't have a leaking caliper, perhaps there is an air ingress point on the lever too like troy suggested (which would make sense since he's not running Shimano calipers, and Magura calipers have a 5 year leakproof warranty)? It would be cool to find the problem and a permanent solution, since the Shimano levers seem to have a good functional design apart from the fact that half the time they cause the brake to suck.
     
  11. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

    Rep/Likes:
    70 / 558
    Joined:
    Mar 14, 2005
    Messages:
    4,367
    For a giggle, the first frankenbrake I made was back in 2003. It was a Grimeca System 12 caliper (bigger pistons than M755, similar to M810/M820) with the MC from the smaller System 8 brake. Coupled it with EBC Red pads and Goodridge hoses, to this day was probably the most powerful brake I've owned. Had a really long throw as expected, just bearable, but could flip you OTB on command.



     
  12. maxyedor

    maxyedor <b>TOOL PRO</b>

    Rep/Likes:
    18 / 177
    Joined:
    Oct 20, 2005
    Messages:
    2,998
    Location:
    In the bathroom, fighting a battle
    I've always thought the variation in bite point was partially due to the lack of a residual valve like an automotive set-up has. That valve keeps the tinniest bit of pressure in the system and keeps the pads ever so slightly rubbing the rotor, no big deal with 250hp, but a huge deal when you're just some spandex clad wanker on a bike.

    The pads never seem to retract consistently on any of my brakes, the worst were my Magura Louise FRs when they got dirty, pistons would stick and usually result in uncertain bite point until I took the 5 minutes to clean them. Noticed the same thing on my Shimanos, while neither my XT or XTR brakes ever get quite as bad as the old Maguras, there's nothing I've tried that will make them work as well either. I also have worse issues with the rear than the front, always, and the rear is always dirtier, be it dirt or brake dust. Again leading me to believe that inconsistent pad retraction, exaggerated by dirty brakes makes for weird bite point problems.

    Another random thought I've had, why are brake MCs seemingly universal across a brand, it makes sense with Deore/SLX/XT/XTR as they all run the same caliper pistons, but Zee and Saint are totally different calipers with different piston surface area (I believe it's different anyhow), why do they run the same levers? Another take-away from auto racing is that your MC should be matched to the calipers, biggest cause of spongy brakes with shit modulation is people running the wrong MCs. Why would mountain bikes be any different?
     
  13. kidwoo

    kidwoo Celebrating No-Pants Day

    Rep/Likes:
    134 / 1,233
    Joined:
    Aug 25, 2003
    Messages:
    20,917
    Location:
    In my pants
    I think that's going to be the problem.

    There's more than one problem. :D
     
  14. shirk007

    shirk007 Monkey

    Rep/Likes:
    5 / 27
    Joined:
    Apr 14, 2009
    Messages:
    220
  15. kickstand

    kickstand Turbo Monkey

    Rep/Likes:
    44 / 388
    Joined:
    Sep 18, 2009
    Messages:
    3,445
    Location:
    Fenton, MI
    I think the shimano inconsistency can also be due to difficulty to get a good bleed on. Mine were done by the shimano guys themselves and the same issue remains. My problems stem from the brakes changing after taking somewhat large hits, huck to flat, squared edged rocks you smash into, etc. Which leads me to believe that air is somehow getting stuck in the system during the bleed, or being allowed into the system some how and then being jarred loose on a big hit.
     
  16. kickstand

    kickstand Turbo Monkey

    Rep/Likes:
    44 / 388
    Joined:
    Sep 18, 2009
    Messages:
    3,445
    Location:
    Fenton, MI
    I always felt like the process to bleed avids seems to pull the bubbles out of the system better.
     
  17. StiHacka

    StiHacka Compensating for something

    Rep/Likes:
    262 / 2,112
    Joined:
    Jan 4, 2013
    Messages:
    7,407
    Location:
    i͓̽t͓̽ i͓̽s͓̽ fu͓̽l͓̽l͓̽ o͓̽f s͓̽t͓̽a͓̽r͓̽s͓̽
    I had a pair of MT-8s and they were the weakest brakes ever. The flexy carbon-ish master cylinder and levers (flexy as hell) not only felt like crap but also leaked like a sieve. The calipers looked OK, perhaps I should frankenlever them as well.
     
  18. xy9ine

    xy9ine Turbo Monkey

    Rep/Likes:
    3 / 51
    Joined:
    Mar 22, 2004
    Messages:
    2,614
    Location:
    vancouver eastside
    a batch of the mt8's were replaced on recall due to said lever leaks (mine did that as well). considering the super light weight of these units (xc brakes, really), they worked pretty well for me. fragile levers however, yes. I broke a carbon lever, and when i saw what the replacement price was opted to retire them & buy xt's instead.
     
  19. kidwoo

    kidwoo Celebrating No-Pants Day

    Rep/Likes:
    134 / 1,233
    Joined:
    Aug 25, 2003
    Messages:
    20,917
    Location:
    In my pants

    I absolutely agree with this.

    There's a phenomenon that happens where you'll do a really hard leaning turn, straighten up, then nothing. Every shimano brake I've had a problem with does this. It's terrifying.

    But then they go back to normal, work fine, until that scenario happens again. Which is why I agree. Air in the lines will still allow the brake to work. But when it gets jarred into the pressure feed, shit gets dangerous. How it gets there is up for debate in each case but it's absolutely air.
     
    • Like Like x 2
  20. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

    Rep/Likes:
    70 / 558
    Joined:
    Mar 14, 2005
    Messages:
    4,367
    You're absolutely correct, it's not ideal and it shows poor attention to detail. Something that mightn't be clear to you is that you do need *some* change in this hydraulic leverage to make a more powerful brake (car brakes are a little different with a booster in the relationship) - i.e. if you took a Saint/Zee and linearly scaled up the MC piston diameter from XT/SLX to suit, you'd have a brake that had no extra power while being heavier for no reason.

    On the other hand, if you make no change at all, you end up with a really long throw. In my opinion at the very least, the Saint/Zee needs a different leverage curve on their SW mechanism to compensate for the fact that the greater hydraulic leverage is going to cause a longer throw. To be more precise, there would ideally be a decrease in the mechanical leverage during the first 2/3 of the free stroke to generate more piston displacement before reverting to the regular ratio soon before contact point. The levers would feel a bit different but that's better than a large throw difference which is what they currently have.
     
  21. maxyedor

    maxyedor <b>TOOL PRO</b>

    Rep/Likes:
    18 / 177
    Joined:
    Oct 20, 2005
    Messages:
    2,998
    Location:
    In the bathroom, fighting a battle
    True, the larger M/C piston would increase volume to move the pistons earlier, but decrease pressure, thus costing you the extra stopping power of the Saint/Zee calipers.

    IMHO, what's needed is an entirely new lever body, change the length of the lever blade, M/C bore, and pivot point so that you get more travel of the M/C piston with the same travel on the lever blade. Now that shifters mount to the lever, you should be able to move the lever body all around and not effect cockpit ergonomics as long as the clamp doesn't move in relation to the grip.

    I have had the same problem as Kidwoo and Kickstand have, my XTRs feel mushy mid-ride, maybe even leak, then after a scary decent with no/minimal brakes, they work fine again. Comes down to poor design, brake calipers need a smooth inner surface and good flow, no point in a bitchin' looking exterior if the inside is full of trapped air. The problem seems to be magnified by frames with internal routing where the caliper can't always be moved around freely while bleeding.
     
  22. johnbryanpeters

    Rep/Likes:
    199 / 1,699
    Joined:
    Sep 27, 2001
    Messages:
    21,980
    Location:
    Making moss sad in New Haven, Vermont
    I don't follow your line of argument. Irrespective of the position of any air, pressure throughout the system is going to be constant at any point of time, same in the master cylinder, line, and caliper.
     
  23. kidwoo

    kidwoo Celebrating No-Pants Day

    Rep/Likes:
    134 / 1,233
    Joined:
    Aug 25, 2003
    Messages:
    20,917
    Location:
    In my pants
    Right. But there's fluid in the system that's not in the 'active part'.

    There's a reservoir at the top. Air in there won't do squat because the master piston closes it off.

    I think it makes it up to there (which is good) but then makes it back into the piston in the lever assembly.
     
  24. johnbryanpeters

    Rep/Likes:
    199 / 1,699
    Joined:
    Sep 27, 2001
    Messages:
    21,980
    Location:
    Making moss sad in New Haven, Vermont
    That makes sense.
     
  25. wood booger

    wood booger Monkey

    Rep/Likes:
    3 / 73
    Joined:
    Jul 16, 2008
    Messages:
    670
    Location:
    the land of cheap beer
    Shimano Zee almost killed me a few times last weekend in Downieville.

    Front was perfect, rear bite would move much closer to the bar basically giving zero brake (like big bubbles in the system).

    A pump or two "fixes" it, but it took some time for me to develop the skill to only pump the rear when grabbing both brakes in cases where massive braking was needed.
    Pumping a front Zee with 203mm rotor by mistake is scary when blasting through rocks!
    Rub the belly and pat the head.....

    I found that even the slightest pressure on the brake and it stayed consistent. Air is entering from the lever somehow when it is fully open.

    I hope someone finds a permanent solution! I love everything else about Shimano brakes.
     
    #25 -   Sep 2, 2015
    Last edited: Sep 2, 2015
    • Like Like x 1
  26. Jm_

    Jm_ Turbo Monkey

    Rep/Likes:
    114 / 636
    Joined:
    Jan 14, 2002
    Messages:
    6,833
    Location:
    AK
    Damn, this all ended for me when I got rid of the formulas for the XTs
     
  27. TrumbullHucker

    TrumbullHucker trumbullruxer

    Rep/Likes:
    74 / 486
    Joined:
    Aug 29, 2005
    Messages:
    2,077
    Location:
    shimsbury, ct
    ITT: school

    this is my honest opinion.. if you ride the brakes (as do I) with whatever bleed/ brake combo/ brake company you have; they will start feeling like shit ( inconsistent bites, faded power, levers to the bars randomly ).

    The heat generated must be insane( i honestly think it is the prime suspect to shitty brakes ).. and these are all relatively small parts. I do "enjoy" seeing shimano's ice rotors, because aluminum itself sucks heat out pretty damn good. the brake pads with the wings? idk about that

    i would love to master how to bleed my zee brakes..i feel like i always fuk up somewhere. i even tried using my fukking beard trimmer to vibrate the bubbles up out of the knooks and crannies the system has (inb4 dildo jokes)
     
  28. StiHacka

    StiHacka Compensating for something

    Rep/Likes:
    262 / 2,112
    Joined:
    Jan 4, 2013
    Messages:
    7,407
    Location:
    i͓̽t͓̽ i͓̽s͓̽ fu͓̽l͓̽l͓̽ o͓̽f s͓̽t͓̽a͓̽r͓̽s͓̽
    Regardless how well I bleed my Zees (if you bleed them with the pistons extended and then push them back, the levers will leak from the reservoir), they always develop a leak somewhere and inconsistent bite point after a few rides. The "fast berm -> WTF happened to my brakes" combo is way too familiar.

    Perhaps we could disassemble the calipers and make the oil paths smooth with sandpaper?
     
  29. troy

    troy Monkey

    Rep/Likes:
    31 / 296
    Joined:
    Dec 3, 2008
    Messages:
    722
    MT5/MT7 calipers have 4x17 mm dia. pistons. There is a possibility that I was wrong, and shimano uses 11mm MC and Louise had 12mm MC, and the Gustav had 10.5mm MC, cant measure it without destroying the levers...

    According to Magura technician MT master cylinders are not compatible with Louise calipers, so they probably have some different dia. piston in there (or they are just saying that for safety reasons)

    Here are some Shimano cutaways (no wonder they are so hard to bleed properly):




     
    • Useful Useful x 1
  30. kickstand

    kickstand Turbo Monkey

    Rep/Likes:
    44 / 388
    Joined:
    Sep 18, 2009
    Messages:
    3,445
    Location:
    Fenton, MI
    This explains my experiences to a T. I have the same issue on my rear SLX as well.
     
  31. Sandwich

    Sandwich just shake your rump
    Staff Member

    Rep/Likes:
    50 / 443
    Joined:
    May 23, 2002
    Messages:
    14,537
    Location:
    01776
    Couple questions, on mobile so don't freak out.

    Would different diameter rotors make a difference in shimano brakes due to different cam action?

    Does anyone else bleed their shimanos top-down, moto style? That's the way I've done it and have had few problems with a set of 810s and 785s in dh conditions.
     
    • Like Like x 1
  32. toodles

    toodles Turbo Monkey

    Rep/Likes:
    17 / 238
    Joined:
    Aug 24, 2004
    Messages:
    1,839
    Location:
    Australia
    Stolen from Worlds thread.


     
    • Like Like x 1
  33. toodles

    toodles Turbo Monkey

    Rep/Likes:
    17 / 238
    Joined:
    Aug 24, 2004
    Messages:
    1,839
    Location:
    Australia
    Has anyone had much time on the guide ultimates? I know SRAM/Avid don't have a terribly good reputation for durability (my old Codes were the best brakes for the first few days after pads/bleeding, but always developed issues) but SRAM has made a big deal of the modifications to the lever and caliper to prevent air ingress and to facilitate ease of removing any trapped air.

    Keen to know if its all talk, or whether they've succeded. Hopefully they shift their focus to revamping the Codes next.

    The Hope V4 sounds terrific from what I've read, but they're too expensive for me to consider running them just to try. I'm also a bit concerned by the spares availability on both Hope and Magura compared to the two big S brands.
     
    • Funny Funny x 1
  34. kickstand

    kickstand Turbo Monkey

    Rep/Likes:
    44 / 388
    Joined:
    Sep 18, 2009
    Messages:
    3,445
    Location:
    Fenton, MI
    I can't much discuss the feel, but my wife has the guide RSC and likes it. Has had zero complaints about the brakes over the course of the season, they still feel brand new to me when I play with them from time to time, but I have never ridden them.

    I'm planning to get a set over the winter.
     
  35. Kanye West

    Kanye West 220# bag of hacktastic

    Rep/Likes:
    14 / 136
    Joined:
    Aug 31, 2006
    Messages:
    3,409
    The exact issue that KidWoo is describing is an issue that any brake that isn't syringe bled is prone to having. This is due to the air pocket up in the reservoir near that worthless "bladder" thingy. When you lean over, the air pocket covers the port that goes to the MC piston, and it has to cycle once or twice to purge the air back up into the reservoir. Moto brakes have this perforated plastic "dome" kinda thing at the bottom of the reservoir to prevent, or at least delay this. Seems to work relatively well on those, and the Shimanos especially seem to allow very free passage of that air pocket into the active part of the line. Lean the bike over or flip it to fix a flat, turn rightside up, dead brakes, 5-10 cycles and good to go again. That tells me the air pocket is living up at the top of the system and is only briefly introduced before being purged again.
     
    • Like Like x 1
    • Useful Useful x 1
  36. kidwoo

    kidwoo Celebrating No-Pants Day

    Rep/Likes:
    134 / 1,233
    Joined:
    Aug 25, 2003
    Messages:
    20,917
    Location:
    In my pants
    I've exclusively used syringes to bleed brakes for the last 18 years.

    It's shimano, not a syringe.
     
  37. Kanye West

    Kanye West 220# bag of hacktastic

    Rep/Likes:
    14 / 136
    Joined:
    Aug 31, 2006
    Messages:
    3,409
    Well, I mean any brake where you aren't purging every last bit of air from the reservoir against that bladder with a syringe or way of burping the air. Should have been more clear. I was half involved in a discussion about inva-, er, "annexing" Canada.

    If the air exists up there and there's not a great way to keep it from flowing freely into the active part of the line, then yeah, that'll happen.

    I've got a couple extra moto MC's in the garage. I'll get some shots of that baffle that's over the MC port.
     
  38. Nick

    Nick My name is Nick

    Rep/Likes:
    226 / 1,626
    Joined:
    Sep 21, 2001
    Messages:
    11,353
    Location:
    behind you, don't wait up.
    Not sure that's moto style, but yes. Always.

    Other than a leaking saint 810 I've excellent bleeds. I don't mind spending "extra" time bleeding brakes, don't wait until just before a ride, bleed top down, move shit around, seal the mc and bleed the caliper, top off. VIOLA! Cheat death another day.
     
  39. Nick

    Nick My name is Nick

    Rep/Likes:
    226 / 1,626
    Joined:
    Sep 21, 2001
    Messages:
    11,353
    Location:
    behind you, don't wait up.
    I have a pair of old 755 levers and a pair of old Magura Julie calipers that I'm tempted to experiment with, just for kicks + this thread.
     
  40. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

    Rep/Likes:
    70 / 558
    Joined:
    Mar 14, 2005
    Messages:
    4,367
    I've added Magura and Hope hydraulic data to the spreadsheet.
    If anyone could help and measure their lever dimensions for me it would be helpful, I will draw up what needs measuring a bit later.

    Could someone tell me what the Hope master cylinder diameter is in the current Race and Tech3 levers? @Hacktastic maybe? I emailed Hope but they have ignored two emails so far. @troy can you confirm the master diameter on the new Magura levers, and Gustav if you know?