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Old 03-19-2010, 10:25 AM   #1
davemon OP
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Airhead Rear Disc Brake

Anyone have a retrofit for a replacement of the stock rear brake caliper of a 77 R 100 S. I've seen fronts replaced but have yet to see the rear changed. The old Brembo single piston just doesn't get it. A dealer told me it was the first anti lock brake system which isn't far from the truth. Ideas anyone
Dave
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Old 03-19-2010, 11:21 AM   #2
Rob Farmer
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Dave,

The caliper is fine it's the linkage to the master cylinder that's the problem there just isn't enough travel to get the caliper to work properly. If you sort the linkage out it's actually a decent brake. I'm about to start sorting my R100RS rear out, I'll post some pics if you don't get yours working before I finish mine.

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Old 03-19-2010, 11:39 AM   #3
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I want to see how you do this!
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Old 03-19-2010, 12:56 PM   #4
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me too- very interested.
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Old 03-19-2010, 06:34 PM   #5
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The rear brake system is a poor design all around. I had to rebuild the caliper and M/C to get a base line of abysmal performance, then try to improve it from there. Creative bleeding helped the most, as the rear line is a bendy bubble trap. At one point I was so frustrated, I was ready to convert to a drum, which is another option for you.
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Old 05-31-2013, 01:37 PM   #6
Jeremiah
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78 r100s

Ok -I am new to this R100S. And I have spent my time dialing things like the timing - carbs- getting rid of the pinging - and the old girl is running great. Stopping is another issue.
It is now time to look at the rear disc. I have heard stories about how bad these early rear discs are - but REALLY? I cannot believe I can't make this work better. It is a true anti-lock brake but anti-stop is not making me comfortable.
I have been scouring the internet to find out what I can do and this thread was the first that even had a hint of the problem.

I will change the pads - clean the disc - but will reworking the lines and actuator help?

Any other advice would be appreciated.

Here is a picture of my newest love: Stopping to wave at the cows.

[/img]
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Old 05-31-2013, 03:56 PM   #7
DaveBall
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I have "fixed" many rear disk brakes on airheads by first checking and cleaning the master cylinder, rebuilding if necessary, then replace the flexible rubber hose with a braided one. Next check and rebuild the caliper. Once that is done, reverse bleed it in place. You do NOT have to remove the caliper and raise it to bleed it. It will work just fine in place. You can reverse bleed the system to get a good solid pedal a whole lot faster than it takes to remove the caliper.

I hear all these weird so called fixes for something that just needs to be bled properly. I have yet to find any rear disk airhead that I could not make into a very good and reliable brake. I can lock it up or modulate to get the best stopping possible.
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Old 05-31-2013, 05:33 PM   #8
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Originally Posted by DaveBall View Post
I have "fixed" many rear disk brakes on airheads by first checking and cleaning the master cylinder, rebuilding if necessary, then replace the flexible rubber hose with a braided one. Next check and rebuild the caliper. Once that is done, reverse bleed it in place. You do NOT have to remove the caliper and raise it to bleed it. It will work just fine in place. You can reverse bleed the system to get a good solid pedal a whole lot faster than it takes to remove the caliper.

I hear all these weird so called fixes for something that just needs to be bled properly. I have yet to find any rear disk airhead that I could not make into a very good and reliable brake. I can lock it up or modulate to get the best stopping possible.
+1 I might even prefer a softer lever for better modulation.
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Old 05-31-2013, 05:41 PM   #9
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Great!

Thanks for the good news! I will clean things up and see if that helps.

But I have never "reverse bled" a system. How do you do that?

Thanks for the reply.


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Old 05-31-2013, 06:10 PM   #10
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Originally Posted by Jeremiah View Post
Thanks for the good news! I will clean things up and see if that helps.

But I have never "reverse bled" a system. How do you do that?

Thanks for the reply. Roy
here's what I use for problem bleed jobs.. pumps brake fluid in reverse or conventional direction Phoenix Systems#596-2001

here's a pic of a new one, mine's all beat up. they also make plastic versions that's much cheaper.




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Old 05-31-2013, 11:47 PM   #11
Plaka
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Originally Posted by davemon View Post
Anyone have a retrofit for a replacement of the stock rear brake caliper of a 77 R 100 S. I've seen fronts replaced but have yet to see the rear changed. The old Brembo single piston just doesn't get it. A dealer told me it was the first anti lock brake system which isn't far from the truth. Ideas anyone
Dave
I just got rid of mine. Even when working poorly I could lock the rear wheel under heavy braking anytime. The rear just isn't worth a lot no matter the type of brake. And I just don't use the rear brake a lot anyway.. Holding the bike on hills and heavy braking. The disk is heavy, complicated and a service hassle several ways. For what? Apparently it was a dumbass styling move on BMWs part. 100% stoopid. They got rid of it too. The drum is lighter, vastly simpler, just as strong, almost zero service, easier rear wheel service, etc. Only downside is if the rear seal leaks it can oil the shoes.

Interestingly, the drum I'm fitting shows a lot of wear for very little spline wear. Only 40K on the wheel. It belonged to one of those rear brake types afraid to use the front (or maybe a hand problem?). All they did was stomp that rear.
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Old 06-01-2013, 06:47 PM   #12
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OK, Plaka, I understand where you are coming from. Basically, you don't like using rear brakes on bikes. I have also heard some people hate using a front brake because it could lock up and cause a loss of steering. Give me a freaking brake and I will use it.

Fine, but there are a lot of us that learned how to adjust and use rear brakes to the point we know how they should feel and work. The rear disk on an Airhead will work just fine, and greatly helps at slowing down the bike when used properly and in conjunction with the front brakes.

And,

I have posted this before, more relating to rear disk brakes, but it works the exact same on front brakes.

I see that everyone wants to bleed the brakes using the most time consuming and difficult methods.

1. Leave everything mounted as it should be.
2. Go to local pharmacy / drug store and purchase 2 large syringes that hold at least 30cc of fluid. and purchase some clear surgical tubing from them as well, about 2 feet is more than enough.
3. Use 1 syringe to suck all the fluid out of the master cylinder and dispose of it in a disposable container.
4. Using the 2nd syringe attach about 12 inches of tubing and suck up some new brake fluid.
5. Attach the tubing and the 2nd syringe to the bleeder on the caliper, and crack the bleeder.
6. Slowly inject the fluid in thru the bleeder while having someone hold the brake pedal slightly depressed, or hold the brake handle part way in. I just put a 1 quart paint can on a brake pedal or use a zip tie on the handlebar.
7. Close the bleeder and refill the syringe.
8. Repeat steps 5 and 6, watching the master cylinder for bubbles and remove excess fluid as required.

I have done the above procedure on a lot of friends bikes with "useless non working rear disk brakes" and every one of them has ended up with an excellent rear brake. This procedure is simple and once you do it, you will be very surprised how easy it is to get a good solid pedal, and a brake that will actually stop the bike.

I also use this same procedure on front brakes if I have had to remove any lines, or I just can't get the spongy feeling out of them using the normal methods. This is especially useful when you have replaced any lines.

Now class, please take notes on the above as it will be on the test.
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Old 06-01-2013, 07:48 PM   #13
Plaka
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Originally Posted by DaveBall View Post
OK, Plaka, I understand where you are coming from. Basically, you don't like using rear brakes on bikes. I have also heard some people hate using a front brake because it could lock up and cause a loss of steering. Give me a freaking brake and I will use it.

Fine, but there are a lot of us that learned how to adjust and use rear brakes to the point we know how they should feel and work. The rear disk on an Airhead will work just fine, and greatly helps at slowing down the bike when used properly and in conjunction with the front brakes.

And,

I have posted this before, more relating to rear disk brakes, but it works the exact same on front brakes.

I see that everyone wants to bleed the brakes using the most time consuming and difficult methods.

1. Leave everything mounted as it should be.
2. Go to local pharmacy / drug store and purchase 2 large syringes that hold at least 30cc of fluid. and purchase some clear surgical tubing from them as well, about 2 feet is more than enough.
3. Use 1 syringe to suck all the fluid out of the master cylinder and dispose of it in a disposable container.
4. Using the 2nd syringe attach about 12 inches of tubing and suck up some new brake fluid.
5. Attach the tubing and the 2nd syringe to the bleeder on the caliper, and crack the bleeder.
6. Slowly inject the fluid in thru the bleeder while having someone hold the brake pedal slightly depressed, or hold the brake handle part way in. I just put a 1 quart paint can on a brake pedal or use a zip tie on the handlebar.
7. Close the bleeder and refill the syringe.
8. Repeat steps 5 and 6, watching the master cylinder for bubbles and remove excess fluid as required.

I have done the above procedure on a lot of friends bikes with "useless non working rear disk brakes" and every one of them has ended up with an excellent rear brake. This procedure is simple and once you do it, you will be very surprised how easy it is to get a good solid pedal, and a brake that will actually stop the bike.

I also use this same procedure on front brakes if I have had to remove any lines, or I just can't get the spongy feeling out of them using the normal methods. This is especially useful when you have replaced any lines.

Now class, please take notes on the above as it will be on the test.
please specify the drugstore/pharmacy where I can buy 300CC syringes and clear vinyl tubing. Also the ID of the tubing so it will fit the nose of the syringe available AND fit the bleeder nipple.

before you can even get to tyour rather involved procedure you hav to assemble the bits. Actually grocery stores can be a source for taper nose syringes (for injecting meats and vegetables,) or a feed and grain for a big luer lock nose or even really big taper noses (for giving oral meds to animals). The tubing might be a hardware store or hobby shop. I've got everything, syringes of all types and sizes from big spinal tap jobs and veterinary to old school all glass ones. Boxes and boxes of every type and size tubing. Putting that rig together I bet I still have to source something.

And then I gotta dick with it. You got 8 steps with 2 that repeat an unknown number of times (x times), so 8+2x steps. I got one with a drum. As an exercise for the graduate students, what positive value (including 0) for x satisfies 8+2x=1? Riiiight.*

Dealing with the drum?? Every 15,000 miles I reach down and give the thumb screw a turn. Then go riding. bet I can make 75 miles before you are done screwing with a disk that isn't any stronger than my drum. (I been dreaming about getting rid of that ^&$#ing disk since I got the bike, and collecting the parts)

Getting on the fronts is a lot faster, for me, than getting on the rear. Has to do with boots and foot position. I keep the pedal as low as possible which requires the brake to be set up perfectly, disk or drum, but still it is very slow to move my foot over to it as opposed to simply clenching my hand. This was very apparent recently when I blew a front brake line. I didn't run into the intersection (low speed) before I could get on the rear, but I went past the stop sign. I use the rear, just not a lot. (and I have crashed twice due to locked up front brakes). Under heaving braking modulating the rear is very difficult. There is so little traction at the back tire it just wants to slide out, and usually does and I need to back off. I wouldn't mind anti-lock back there.

To bleed my fronts I use a power vacuum pump and reciever. It's a snap, and quick. No screwing around injecting fluid backwards with syringes. (you can use vacuum from the top too). Works fine for the rear and I get a hard pedal, but getting to the bleeder bolt on the RS is stupid. I got the last part off a couple days ago and it's wunnerful.

You can build a gizmo that beats your syringe. Start with a piece of tubing that fits the bleeder nipple. Then get a 12" length of brass tube (maybe copper-plumbing isle) from the hobby shop that fits that and a tire valve off an old tube with both nuts (or a valve from an HVAC supply, bolts in a hole). Take a canning jar and drill a hole for the brass tube in the lid and solder the tube in so it reaches the bottom of the jar---maybe pick a quart jar. Just sand or wire brush to bare metal and use whatever solder---stay away from the red rubber on the edge. Then make another hole and install the tire valve, maybe use some silicone. Now fill the jar with clean brake fluid and gently pressurize with one of those little bicycle pumps (whatever you got). it'll push a quart of fluid backwards if you want. Crack the lid when you close the bleed nipple to release the pressure. Solder two brass tubes into the jar lid and you can fill both front calipers from the bottom at once (if the system was fully drained for instance).

Personally, I got a Gast vacuum pump and an old two jar medical reciever. As good as it gets. (and the pump will run an airbrush or air eraser, double benefit)




* as a side note. I been having a yard sale to raise money to fix my truck. I had a big cardboard box full of styrofoam I wanted to ditch so I put a price on it of -$1.00. And added parenthetically "I pay you". Know how many people 'got it' out of the dozens and dozens that came by? 1. (and he was cracking up)

Finally a little girl comes by, mid teen or so. She wants the big box and the purple crumple velvet scrap book. Asks how much the scrap book is. I say $1.00. Says she wants the box for -$1.00. I say fine. She starts pulling out money. I ask her if she has had negative numbers in school. She nods, with hesitation. I ask her what -1+1 is. She starts thinking hard. Smell of wood burning. I tell her to put her money away, take both and keep thinking about it.

Some days I feel like an asshole, other days I just figure the world needs to go screw itself. I suck at math, but I can get that one.

Plaka screwed with this post 06-01-2013 at 08:04 PM
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Old 06-01-2013, 08:09 PM   #14
supershaft
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Quote:
Originally Posted by DaveBall View Post
OK, Plaka, I understand where you are coming from. Basically, you don't like using rear brakes on bikes. I have also heard some people hate using a front brake because it could lock up and cause a loss of steering. Give me a freaking brake and I will use it.

Fine, but there are a lot of us that learned how to adjust and use rear brakes to the point we know how they should feel and work. The rear disk on an Airhead will work just fine, and greatly helps at slowing down the bike when used properly and in conjunction with the front brakes.

And,

I have posted this before, more relating to rear disk brakes, but it works the exact same on front brakes.

I see that everyone wants to bleed the brakes using the most time consuming and difficult methods.

1. Leave everything mounted as it should be.
2. Go to local pharmacy / drug store and purchase 2 large syringes that hold at least 30cc of fluid. and purchase some clear surgical tubing from them as well, about 2 feet is more than enough.
3. Use 1 syringe to suck all the fluid out of the master cylinder and dispose of it in a disposable container.
4. Using the 2nd syringe attach about 12 inches of tubing and suck up some new brake fluid.
5. Attach the tubing and the 2nd syringe to the bleeder on the caliper, and crack the bleeder.
6. Slowly inject the fluid in thru the bleeder while having someone hold the brake pedal slightly depressed, or hold the brake handle part way in. I just put a 1 quart paint can on a brake pedal or use a zip tie on the handlebar.
7. Close the bleeder and refill the syringe.
8. Repeat steps 5 and 6, watching the master cylinder for bubbles and remove excess fluid as required.

I have done the above procedure on a lot of friends bikes with "useless non working rear disk brakes" and every one of them has ended up with an excellent rear brake. This procedure is simple and once you do it, you will be very surprised how easy it is to get a good solid pedal, and a brake that will actually stop the bike.

I also use this same procedure on front brakes if I have had to remove any lines, or I just can't get the spongy feeling out of them using the normal methods. This is especially useful when you have replaced any lines.

Now class, please take notes on the above as it will be on the test.
+1 on the braking. Especially if you ride two up. Personally I rarely use the back brake hauling the mail on smooth fast roads and I make time on most my friends while braking but . . . . If I was road racing I would use the back brake. One trick is to use it just a little right as/before you get into the front brakes. All the fast guys do it. The rear brake squats the back of the bike so that when you get heavily into the front brakes that nano second after you have settled the front end into the braking dive so that the front end doesn't SLAM down, the bike dives less because the back of the bike was lower to start with for having just lowered it via rear brake squat. Let me warn everybody that blowing brake lines and clumsy feet are not going see anything close to that idea happen!

Drum versus discs??? There are reasons why all bikes have have disc brakes now. Vintage trails bike classes are separated between drum/disc because having discs is a HUGE advantage over drums. Trails is NOT about braking power. It's all about modulation. That is MOST of the advantage of disc brakes.
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Old 06-02-2013, 05:28 AM   #15
boxerboy81
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please specify the drugstore/pharmacy where I can buy 300CC syringes and clear vinyl tubing. Also the ID of the tubing so it will fit the nose of the syringe available AND fit the bleeder nipple.
Know any Nurses?
Ask for 60cc catheter tip syringe and some smooth bore oxygen tubing that'll fit.
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