Handle bar MC upgrade

Discussion in 'Airheads' started by Hearse, Feb 7, 2013.

  1. Hearse

    Hearse Project n'gagi

    Joined:
    Nov 7, 2012
    Oddometer:
    148
    Location:
    sydney
    Hey guys,

    There are lots of threads on this upgrade from under the tank to handle bar MC's

    Bike: r90/6 75 model

    But....

    1) what size MC, 14mm should be ok?

    2) can I use any MC or does it have to be off an /7 or the like, i.e. can I use a Honda handle bar 14mm MC? I am replacing all switches/brake lines etc anyway so that's no issue

    Thanks guys
    #1
  2. chasbmw

    chasbmw Long timer

    Joined:
    Feb 19, 2006
    Oddometer:
    2,797
    Location:
    Bath Uk
    I prefer 13mm used on my 75 R90/6. This is a twin throttle pull M/C as used on some later airheads, your switches and throttle cables will transfer seamlessly. You can fit a front brake switch to it as well. This is still available new from BMW or from eBay?

    You can use any 13mm M/C. The only advantage of using the BMW unit is that it is a no hassle modification. I use a splitter under the fuel tank as per the later bikes, so I have a single hose to the splitter, then twin hoses to the lower hard lines.

    In terms of use 13mm works well to give you both power and control of the brakes, there it's lots more lever travel, but this is a good thing. I did a series of panic stops from about 70mph, fully loaded just to ensure that I would not run out of brakes coming down a mountain pass. Some people use 12mm, and I'm sure that 14 would work as well.
    #2
  3. craydds

    craydds Long timer

    Joined:
    Aug 3, 2010
    Oddometer:
    1,178
    Location:
    Las Cruces, NM
    #3
  4. chasbmw

    chasbmw Long timer

    Joined:
    Feb 19, 2006
    Oddometer:
    2,797
    Location:
    Bath Uk
    Cray. Iv seen that chart before but can't work out how to use it

    Eg with dual discs with single slave cylinders of 38mm each...........
    #4
  5. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

    Joined:
    May 12, 2012
    Oddometer:
    2,484
    Location:
    VA
    My '78 (manufactured in '77) under the tank MC is 14mm. I expect your /6 under tank MC is also 14mm (but am not certain). Smaller is better and would go with 12 mm if it were the same cost and availability as a 13 mm.
    #5
  6. chasbmw

    chasbmw Long timer

    Joined:
    Feb 19, 2006
    Oddometer:
    2,797
    Location:
    Bath Uk
    Stan, I would guess that yours is a single disc bike?

    I reckon that having a full hydraulic system is better than BMWs strange mix of mechanical and Hydraulic
    #6
  7. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

    Joined:
    May 12, 2012
    Oddometer:
    2,484
    Location:
    VA
    Yes, my MC is for a single 40 mm caliper and rotor. I know mine is 14 mm because the bore was measured before sending it out to be sleeved and subsequently installing a kit. The lack of a cable and linkage provides an advantage to the handle bar MC, compared to the under-tank approach.

    Based on hydraulics, the smaller the piston diameter in the MC the more mechanical advantage. But there must be enough volume to operate the brakes. Considering volume, a pad movement of 0.5 mm for dual 38 mm ATE caliper pistons requires a 12 mm handlebar MC piston to move ~10 mm. Although, I don't think pads would normally move that much.
    #7
  8. JonnyCash

    JonnyCash turd polisher

    Joined:
    Jan 22, 2011
    Oddometer:
    1,802
    Location:
    Midcoast, Maine
    When I switched mine over, I used a 13mm, and I'm really happy with it. If I were going to do it again though, I might consider a 12mm.
    #8
  9. craydds

    craydds Long timer

    Joined:
    Aug 3, 2010
    Oddometer:
    1,178
    Location:
    Las Cruces, NM
    Let's see, dual calipers with single pistons... got it. Across the top of the chart is the MC size in mm, e.g., 13 mm. If you had a 13 mm (put in your MC number) then follow that column down to the piston row; piston size and number of pistons is the on the left side of the chart . Let's look at the left side and follow it down to 38 mm; listed is 38, 38 (2), and 38 (4). The number in parenthesis, e.g. (2), is the number of pistons. i.e., 38 (2) is used for our 38 mm dual caliper ATE's. So, follow the 38 (2) row across to the 13 mm column and there is your ratio; in this example it reads 17.09
    From that chart, see: Single piston calipers are much happier in the 14:1 to 12:1 range. Keep that in mind. I have the 14 mm MC, dual 38 mm ARE's, so my ratio is 14.73.
    #9
  10. Hearse

    Hearse Project n'gagi

    Joined:
    Nov 7, 2012
    Oddometer:
    148
    Location:
    sydney
    i love all you guys, yew!

    thanks heaps for the replys guys

    I am trying to find a 12mm MC but sweet jebus, perhaps my googling skills are lacking but its real hard, and 13mm is no better!

    I will get my search on...see what i can find

    thanks again guys!
    #10
  11. Hearse

    Hearse Project n'gagi

    Joined:
    Nov 7, 2012
    Oddometer:
    148
    Location:
    sydney
    #11
  12. chasbmw

    chasbmw Long timer

    Joined:
    Feb 19, 2006
    Oddometer:
    2,797
    Location:
    Bath Uk
    #12
  13. Hearse

    Hearse Project n'gagi

    Joined:
    Nov 7, 2012
    Oddometer:
    148
    Location:
    sydney
    wicked - just having a sneaky look now

    thanks for that

    300 pounds is pretty steep, hell yea.

    there are heaps of 14mm out there, and i love the 14mm ones i can find....just making sure it would work, peeps above all saying that its not ideal....hmm would there be much difference between having a 13mm to a 14mm?

    I am digging either of these:
    http://www.ebay.com/itm/NISSIN-Moto...Parts_Accessories&hash=item485084505f&vxp=mtr

    or this one because it has that orange factor too...(bikes orange)
    http://www.ebay.com/itm/BWS-ZUMA-JO...her_Vehicle_Parts&hash=item2a224b9fa7&vxp=mtr
    #13
  14. craydds

    craydds Long timer

    Joined:
    Aug 3, 2010
    Oddometer:
    1,178
    Location:
    Las Cruces, NM
    Hearse, thanks for the compliment! Are asking about the handgrips on the handlebars? They are a stock BMW item, part #32-72-1-237-811 is the grooved handgrip (the smooth grips are #32-72-1-230-407 , see if this works http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51891&rnd=08102012
    #14
  15. SamH

    SamH 90S on the bench

    Joined:
    Aug 14, 2005
    Oddometer:
    436
    Location:
    Tasmania, Australia
    I used a 1/2" mc on twin 38mm ate's and found that while they stopped well they never felt firm at the lever. I could always pull the lever to the bars.
    #15
  16. Hearse

    Hearse Project n'gagi

    Joined:
    Nov 7, 2012
    Oddometer:
    148
    Location:
    sydney
    so how would you better the feel in the brake lever?

    Would you up the bore size to say a 13mm?

    (im trying to understand front brakes well in my head - so forgive the multiple questions :1drink)
    #16
  17. JonnyCash

    JonnyCash turd polisher

    Joined:
    Jan 22, 2011
    Oddometer:
    1,802
    Location:
    Midcoast, Maine
    I used a universal fitment Magura 13mm. It was like $110 I think. It fit very well with the /5 style throttle, after I chopped off the old brake lever perch. I got it from Economy Cycle, but I know lots of places sell it.
    #17
  18. Hearse

    Hearse Project n'gagi

    Joined:
    Nov 7, 2012
    Oddometer:
    148
    Location:
    sydney
    links dude? please :)

    got it - http://www.economycycle.com/servlet/the-295/Front-Master-Cylinder-Kit/Detail

    $50 delivery form USA to AUS - HAHA...wtf?! man you guys pump us aussies
    #18
  19. craydds

    craydds Long timer

    Joined:
    Aug 3, 2010
    Oddometer:
    1,178
    Location:
    Las Cruces, NM
    If you achieve a good leverage ratio as described here http://roadstarclinic.com/content/view/89/95/ , and if the goal is to have the ratio somewhere around 14:1 to 12:1 as proposed in the article, then the "feel" should be good. To address the problems that SamH reports in his post above - it sounds like it could involve several issues. A few come to mind: 1) brake hoses - get new hoses, possibly the Spiegler type - http://www.spieglerusa.com/brake-line-kit-77.htm ; 2) get new bake pads; 3) align the calipers correctly; and 4) bleed the system and bleed it again and elevate the calipers above the MC and bleed 'em again. Also, did I mention... bleed the system?
    #19
  20. JonnyCash

    JonnyCash turd polisher

    Joined:
    Jan 22, 2011
    Oddometer:
    1,802
    Location:
    Midcoast, Maine
    #20