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Old 02-07-2013, 03:18 AM   #1
Hearse OP
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Handle bar MC upgrade

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
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Old 02-07-2013, 04:03 AM   #2
chasbmw
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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.
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Old 02-07-2013, 06:11 AM   #3
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Quote:
Originally Posted by chasbmw View Post
I prefer 13mm used on my 75 R90/6. Some people use 12mm, and I'm sure that 14 would work as well.
Chasbmw is right. 12, 13, or 14 are all good, but smaller is better; see http://roadstarclinic.com/content/view/89/95/ . I used a 14 mm and it works great, see post #125 here http://www.advrider.com/forums/showt...=741179&page=9 .
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Old 02-07-2013, 06:18 AM   #4
chasbmw
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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...........
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Old 02-07-2013, 06:55 AM   #5
Stan_R80/7
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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.
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Old 02-07-2013, 07:50 AM   #6
chasbmw
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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
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Old 02-07-2013, 08:30 AM   #7
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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.

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Old 02-07-2013, 09:00 AM   #8
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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.
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Old 02-07-2013, 11:01 AM   #9
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Quote:
Originally Posted by chasbmw View Post
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...........
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.
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Old 02-07-2013, 12:17 PM   #10
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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!
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Old 02-07-2013, 12:18 PM   #11
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Quote:
Originally Posted by craydds View Post
Chasbmw is right. 12, 13, or 14 are all good, but smaller is better; see http://roadstarclinic.com/content/view/89/95/ . I used a 14 mm and it works great, see post #125 here http://www.advrider.com/forums/showt...=741179&page=9 .

dude i love everything about your bike! thats a sweet setup

what grips are they? they look nice and wide...im looking for some bigger grips as well (big ass gorilla hands)
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Old 02-07-2013, 12:25 PM   #12
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This is the complete deal

Just need to check that's a 13mm

http://www.motobins.co.uk/bmw-parts....20valve%20Twin
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Old 02-07-2013, 12:30 PM   #13
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Quote:
Originally Posted by chasbmw View Post
This is the complete deal

Just need to check that's a 13mm

http://www.motobins.co.uk/bmw-parts....20valve%20Twin
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-Motor...84505f&vxp=mtr

or this one because it has that orange factor too...(bikes orange)
http://www.ebay.com/itm/BWS-ZUMA-JOG...4b9fa7&vxp=mtr
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Old 02-07-2013, 01:09 PM   #14
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Quote:
Originally Posted by Hearse View Post
dude i love everything about your bike! thats a sweet setup

what grips are they? they look nice and wide...im looking for some bigger grips as well (big ass gorilla hands)
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/fic...1&rnd=08102012
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Old 02-07-2013, 04:03 PM   #15
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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.
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