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Old 03-24-2008, 08:56 AM   #1
David_S OP
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Need advise on R90 /6 brakes or lack of

Well yesterday was the maiden voyage of my newly acquired 74 R90 /6 and other than the headlight falling out she did well. My concern is the front brake sucks. It's the stock setup, single solid rotor. The PO installed a new master cylinder, hose, and line (stock BMW parts). The pads & rotor look good and there doesn't appear to be any air in the system. It just doesn't stop worth a darn I can't even get enough braking to make the front dive a little. I'm curios what my options are to improve the braking without converting to a dual disk since that just isn't in the budget. Have any of you installed a drilled rotor, SS hose, and after market pads to achieve a noticeable improvement? I don't mind spending a few more $$'s on the old gal but would like to get a bit better braking for the money. Any input would be appreciated. TIA

DS
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Old 03-24-2008, 09:09 AM   #2
Cigars&Scotch
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2 things

First I guess you have the under tank master. You really need to work on it to get the air out. I would suggest you take the tank off, undo the aeroseal clamp that hold it and unmount the whole thing with the hose still connected. The problem is you get an air bubble in by the brake switch, its the silver thing on the end with the 2 wires comming out of it. Tilt the whole assembly with the brake switch down and tap it with a screwdriver. If there is any air in there, you will see a bubble come up through the tiny fill hole in the center of the reserv. You can take the cover off while doing this, just make sure there is enough fluid to cover said hole.

Second

There is a cap under the mount for the disc calliper. Take that off and insert a long flat screw driver. This is a cam that adjust the center of the caliper to the disc. When you turn it one way, you will see the caliper move to one direction. Find the center off the caliper with reference to the disc. Put the cap back on and you are ready to go.


Remember that this is a 30+ year motorcycle, it aint doing no stoppies!!
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Old 03-24-2008, 09:48 AM   #3
benway
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as said, correct adjustment of ate calipers is critical to brake performance

take a thick black marker pen and mark radial lines on both sides of the disc.

spin the wheel [or ride it a bit] and gently apply the brake

the idea is to get the fixed pad [inner] to remove the lines equally across the disc [ie pad parallel to disc], and hopefully the "floating" outer pad too. --depending how long its been out of alignment. that might take a little while.

remark the line and adjust the eccentric cam in the caliper [as above] until all the black line is removed evenly

also, if there are new pads in the caliper, they can take a while to bed in

but you should definitely be able to get the front to dive.

hope that helps
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Old 03-24-2008, 10:33 AM   #4
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Thanks for the tips. I'll check it out this eve but the pin that goes in the bottom may very well be the cause. The Clymer made no mention of adjusting it so I just stuck it in and screwed in the cover plug. I'm not expecting the brakes to be like a new dual disc power assist but I really think the way it was yesterday dragging my feet would be more effective. I knew something was amuck when the rear brake was more effective than the front. I'll post my results good or bad once I get another test ride.

Thanks,

DS
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Old 03-24-2008, 10:42 AM   #5
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If they are new pads, they may need bedding in. I've heard that some pads need to get really hot before working well. Make several panic stops from 35 o 40 or even faster. Check with the manufacturer to make sure.

As has been said, adjustment is important. A simple way to adjust them is to apply some pressure to the lever while adjusting the concentric adjuster that holds the caliper in and that it swivels on. As you turn the adjuster, you'll feel a spot where it turns easily. In the middle of that area is where it should be in adjustment.

You may also need to rebuild the caliper. With everything else replaced I'd suspect the caliper needs looking into. They're not difficult to work on, but what I suspect is that the piston has some corrosion and is hanging up in the bore.
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Old 03-24-2008, 10:43 AM   #6
dlrides
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Quote:
Originally Posted by GoodTill
2 things

First I guess you have the under tank master. You really need to work on it to get the air out. I would suggest you take the tank off, undo the aeroseal clamp that hold it and unmount the whole thing with the hose still connected. The problem is you get an air bubble in by the brake switch, its the silver thing on the end with the 2 wires comming out of it. Tilt the whole assembly with the brake switch down and tap it with a screwdriver. If there is any air in there, you will see a bubble come up through the tiny fill hole in the center of the reserv. You can take the cover off while doing this, just make sure there is enough fluid to cover said hole.

Second

There is a cap under the mount for the disc calliper. Take that off and insert a long flat screw driver. This is a cam that adjust the center of the caliper to the disc. When you turn it one way, you will see the caliper move to one direction. Find the center off the caliper with reference to the disc. Put the cap back on and you are ready to go.


Remember that this is a 30+ year motorcycle, it aint doing no stoppies!!
+ 1

Once they are bled and adjusted properly, you should not have a problem. A master cylinder and caliper rebuild may be required, but even that is very simple.
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Old 03-24-2008, 10:46 AM   #7
dlrides
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Quote:
Originally Posted by David_S
I'll check it out this eve but the pin that goes in the bottom may very well be the cause. The Clymer made no mention of adjusting it so I just stuck it in and screwed in the cover plug.

DS

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Old 03-24-2008, 11:12 AM   #8
benway
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Quote:
Originally Posted by David_S
Thanks for the tips. I'll check it out this eve but the pin that goes in the bottom may very well be the cause. The Clymer made no mention of adjusting it so I just stuck it in and screwed in the cover plug. I'm not expecting the brakes to be like a new dual disc power assist but I really think the way it was yesterday dragging my feet would be more effective. I knew something was amuck when the rear brake was more effective than the front. I'll post my results good or bad once I get another test ride.

Thanks,

DS
I read the replies on the micapeak/airmail list also and I think everyone just assumed that you had adjusted the cam/caliper and still didnt get any braking.

the cause is very very likely that you did not set the caliper

note that the cam need a very small adjustment/turn to make a big difference. it is in my Clymer on p630, chptr 11 on brakes

get the caliper adjustment correct and the brakes will work as intended-- for a 30+ yr old bike!
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Old 03-24-2008, 11:30 AM   #9
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The front brake on my R90/6 seemed to work pretty good even though it wasn't near a modern bike. I pulled mine of as I was replacing the fork seals. After installing it I tried doing the adjustment. I think I still need to do some tweaking, I like the marker idea. It also took a while to work out some air that got in the lines. It's getting better, but I know it can be better than it is. Although what I really need to do is re-build the master cylinder and put on a braided brake line.
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Old 03-24-2008, 12:19 PM   #10
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The ATE brake won't win any awards but it will work fine if every aspect of it is in good shape and adjusted properly. SS lines will help. Rebuild the master cylinder if you have any doubts about it and adjust the pull at the cylinder often. Rebuilding the brake is also easy. Also as mentioned the brake shoe has to be adjusted with so it contacts the disc correctly. I did all of these on a /7 I used to own and the brakes were alittle more than acceptable.
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Old 03-24-2008, 01:21 PM   #11
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Ferodo pads will make a nice difference. I always hated the under-tank M/C, especially when full loaded or on the track, so I swapped mine out for a handlebar-mounted unit. Much better feel, and no stretching of cables.
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Old 03-24-2008, 06:01 PM   #12
David_S OP
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SNIP I read the replies on the micapeak/airmail list also and I think everyone just assumed that you had adjusted the cam/caliper and still didnt get any braking. SNIP

Email has been all screwed up today and I didn't receive any replies. I found them by going into the archives. Thanks for mentioning it.

Thanks for all the other replies as well. I adjusted the cam and it seemed to help. I'm going to go with another set of pads since I really don't know anything about the ones on the bike and they are a bit glazed. Also I did the marker on the rotor and it wiped off in the center on the fixed pad side but not as wide a path as the pad which makes me think the pad may be worn uneven on the edges. I could strait edge it but if I'm going to remove them I'll just toss a new set on. The caliper was supposed to have been rebuilt by the PO and it appears good as far as piston travel with no binding. I'm also going to try bleeding it since once the brakes start to apply the lever does seem to come down quite a bit without the brakes actually being applied much harder. I'll be sure and tilt the master cylinder to remove the trapped air by the switch. Heck it's to cold here to ride much anyway so I may as well be tinkering and getting to know the machine a bit better.

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Old 03-25-2008, 06:39 AM   #13
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This is good info as I will be attempting this on a 76 /6 I am putting the fix on.
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Old 03-25-2008, 03:29 PM   #14
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I added a SS brake line, a new drilled rotor and better pads from Bob's BMW-WORLD OF DIFFERENCE
It stopped much better after the mods hands down. A common mod for the /6's was the double rotor set a la the 90/S but's thta's a bit more coin.
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Old 10-05-2008, 11:59 PM   #15
Humungus
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Quote:
Originally Posted by Cigars&Scotch

There is a cap under the mount for the disc calliper. Take that off and insert a long flat screw driver. This is a cam that adjust the center of the caliper to the disc. When you turn it one way, you will see the caliper move to one direction. Find the center off the caliper with reference to the disc. Put the cap back on and you are ready to go.


So guys what does this screw actually do. Manuals aint giving up a lot.

How does it move the pad & in what direction ? I can see that it changes the pads angle but how can that effect the inside pad ?
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