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Old 04-06-2011, 09:19 AM   #1
davemon OP
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Airhead Rear Disc brakes

I realize the brakes on the airhead leave a lot to be desired but anyone figured out how to make the rear disc on a 77 R100S work? Caliper change?
Master cylinder change? Mine won't lock the rear wheel if I stood on it with both feet. Not really willing to go to drum but looking for a fix.
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Old 04-06-2011, 11:47 AM   #2
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77 R100S with a rear disc?

The "S" bikes were manufactured with drum rear brakes.
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Old 04-06-2011, 01:01 PM   #3
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Quote:
Originally Posted by mymindsok View Post
77 R100S with a rear disc?

The "S" bikes were manufactured with drum rear brakes.
Until 78.
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Old 04-06-2011, 07:53 PM   #4
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It is a REAL job to get all the air out of that system. I suspect that is your problem. That and/or a shot rubber line.
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Old 04-06-2011, 07:57 PM   #5
bmweuro
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It could have been made from 9/77-12/77. The only way to get the rear disc to work is a smaller bore master cylinder like a 12mm. Modify the mounting to use an earlier K100 with ABS, R1100 or R1150 rear brake master cylinder.
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Old 04-06-2011, 08:05 PM   #6
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New brake hose is a must on these old Airheads. The originals have all swelled up and choked the hole down the centre by now.

And that rear brake is a bitch to bleed for some reason. Taking caliper off and hanging it so rubber hose is vertical helps, as does a vacuum bleeder.

Can't remember exactly but I think there were two sizes of master cyl bore, the later ones being smaller and more effective. You can get the old ones sleeved to fit the later piston/seal.
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Old 04-06-2011, 08:47 PM   #7
supershaft
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Good advise you guys! Yea, the master cylinder bore is too big on those but still . . . the smaller MC's don't work well with junk lines full of air either! I really was going to say something about that but I though about first things first.

supershaft screwed with this post 04-06-2011 at 10:08 PM
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Old 04-06-2011, 08:53 PM   #8
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I never liked the rear disc on my 78. Seemed like way too much crap not doing 1/2 what the drum could do. Plus it made getting the wheel off more difficult.

But it sure looked good.
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Old 04-07-2011, 08:17 AM   #9
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Had the same priblem with my 81 RT a few years back.I ended up replacing the master cylinder,new steel line,and a steel braided line to replace the rubber line.I then added a little wxtra line off the fluid resivoir so I could rise up above the master cylinder and then pumped the hell out of the pedal till I had a real brake..It was apain in the asss but it worked.Your right it does look good
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Old 04-07-2011, 01:03 PM   #10
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what have worked on my RS :
I put old break pads, a crew driver between break pads.
I pupm on break pedal
Twist the larg flat screw driver, brake fluid and air goes back in brake fluid tank.
I do again and again that
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Old 04-08-2011, 02:22 PM   #11
davemon OP
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The bike is a 78 from the engine number
I have replaced the rubber hose with a top grade one from a place in Ohio. New pads and bled the hell out of the system. Roughed up the rotors a bit with some emory cloth and cleaned out the cooling holes. So it looks like a rebuild of the master cylinder and getting the rotor turned
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Old 04-08-2011, 08:49 PM   #12
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Quote:
Originally Posted by davemon View Post
The bike is a 78 from the engine number
I have replaced the rubber hose with a top grade one from a place in Ohio. New pads and bled the hell out of the system. Roughed up the rotors a bit with some emory cloth and cleaned out the cooling holes. So it looks like a rebuild of the master cylinder and getting the rotor turned
Whats wrong with your rotor?
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Old 04-08-2011, 11:08 PM   #13
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Two mates of mine replaced their rear steel brake line and rubber hose with a custom one long stainless steel brake hose.

Both are very happy with the solution. This comment was as significant for the rear brake as it was for the front.


Quote:
I finally got around to having a good ride on the RS today after fitting the new braided brake lines front & rear...Should of done it years ago as it made a world of difference, just amazing really ........
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Old 04-10-2011, 05:59 AM   #14
davemon OP
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The hose I put on was from Spiegler and the rotors are running straight but pretty polished.
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Old 04-10-2011, 11:41 AM   #15
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You can waste as much time and money and thought on this as you want. Unless you go to a smaller bore master cylinder nothing will really change. These things were crap when they were new.
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