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Old 12-05-2013, 11:16 PM   #1
dm635 OP
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Dual output under tank Master cylinder

Just found out these were made and could use one to hook up the 2nd (right) Brembo caliper. I picked up a dual brake setup for the better braking. Have only been using 1 Brembo caliper for a while and even 1 Brembo caliper pulls better than the single ATE.

With the setup it seems I have all that's needed to install duals with some modification. Would like to keep the '78 R80/7 as stock as possible especially if it comes to wiring. The problem I have is setting up a line from my single output master cylinder to the splitter in available space. Seems that a dual output MC would be the easiest stock looking setup for my problem that fits correct as well as functions. Lines match up perfectly going this direction.

Anyone have one to sell? Going with a bar mount MC you'd have to change the controls and match up wiring, RIGHT? Have also seen a crossover line. Hook up a line from the bleeder on the left to the input on the right. Hope this makes sense, it's late,

Dave
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Old 12-06-2013, 12:43 AM   #2
disston
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The under tank ATE master cylinders were all 17mm I believe. (just so you know)

They turn up regularly on Ebay. Are sometimes reasonably priced. A rebuild kit w/piston is not cheap.
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Old 12-06-2013, 02:00 AM   #3
Steve W.
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Quote:
Originally Posted by dm635 View Post
Just found out these were made and could use one to hook up the 2nd (right) Brembo caliper. I picked up a dual brake setup for the better braking. Have only been using 1 Brembo caliper for a while and even 1 Brembo caliper pulls better than the single ATE.

With the setup it seems I have all that's needed to install duals with some modification. Would like to keep the '78 R80/7 as stock as possible especially if it comes to wiring. The problem I have is setting up a line from my single output master cylinder to the splitter in available space. Seems that a dual output MC would be the easiest stock looking setup for my problem that fits correct as well as functions. Lines match up perfectly going this direction.

Anyone have one to sell? Going with a bar mount MC you'd have to change the controls and match up wiring, RIGHT? Have also seen a crossover line. Hook up a line from the bleeder on the left to the input on the right. Hope this makes sense, it's late,

Dave
Unless you are going to show in a concours event. You and the bike will be much better served going with the handlebar MC. I replaced my (78 S) undertank with a MC from a R65 with 13mm bore. Much much better brakes. Your current switch pod will go right on the MC mount. Just get a splitter from a later model bike or run two lines down from the MC. Do a search there is plenty of Pics and info on Advrider.
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Old 12-06-2013, 02:16 AM   #4
dm635 OP
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I'm not sure how to tell what size mine is. But I'm sure I still have plenty of lever action left for another caliper.

It was in fact ebay that I saw a 17mm dual output yesterday. Don't remember what it was going for. Of all the reading I've done here I was not aware they were available. I'd rather try to find one here and hopefully get some history on it on its condition.

Or check again to see if I can run a short line from my MC to the splitter. If I can get the splitter properly positioned & secure I can go with it. Found out though that the rotor bolts I picked up are for a single rotor & not dual. Not a problem, I'll get the correct ones.

Edit: Steve we were typing at the same time. My bike is not or will it ever be concours. Is definitely a rider. I will look into the bar mount MC as an option. As I get older I've gotten past modding too much, already been through it. To me the simplicity of stock is where it's at for my own purposes.
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Old 12-06-2013, 03:05 AM   #5
AntonLargiader
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As I get older I've gotten past modding too much, already been through it. To me the simplicity of stock is where it's at for my own purposes.
I wouldn't think of it as modding; it's just updating. It's stock for the later bikes, which is better than stock for the early bikes.
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Old 12-06-2013, 05:57 AM   #6
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That's the way I see it too. It's a safety upgrade. Just need to get the right side on to complete. All parts added are stock factory parts.

I understand wiring, but not going to mess with what's original if I can help it. If I make any changes at all it will be completely documented in my service logs and manuals so I know what's been changed or touched. I keep an ongoing log on each machine in the fleet.

Got an old Bimmer I did an auto to 5sp swap and have over 2 pages of just wiring touched. Any change is clearly marked in the ETM. Electrical Troubleshooting Manual. Probably spent over a month reading that manual front to back knowing every circuit involved. Could be considered a mod, but to me it is an upgrade along with proven better factory bolt on big brakes from bigger heavier cars requiring the correct master cylinder as more fluid is being moved, limited slip and more. In the end it's all completely reversible and as an upgrade it's staying. Wasn't just mechanical, plenty of electrical too.
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Old 12-06-2013, 07:55 AM   #7
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I'm sure you will find lots of dual output 17mm MCs on EBay. This is because they are crap and you will be undoing all the good you have done by fitting Brembos.

The real problem with the old ATE brakes was that BMW cocked up the ratio between the slave and mastercylinders, Norton did the same and the route to more powerful controllable brakes for both bows and Nortons from the 70s is to fit a smaller MC.

Connect BOTH Brembos to your existing under tank MC, various methods described here and elsewhere, or as discussed use a 13mm handlebar MC.
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Old 12-06-2013, 08:30 AM   #8
dm635 OP
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Thanks for that. I've read the smaller MC's do work better when going to duals. I take it the stock ATE MC is 13-14mm. Are there any markings on the MC to indicate piston size??

Unless something comes from this post I'll either run a small line to the splitter or run a crossover.

I'm searching for working opinions here.

Thanks Dave
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Old 12-06-2013, 08:45 AM   #9
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I've got a dual output version here if you need one. It came off of a running r100rs and it good to go if a little dirty. I'd be willing to let it go for ya if you need it. Shoot me a PM if you'd like.
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Old 12-06-2013, 09:02 AM   #10
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There used to be a chart somewhere on the Net that listed all the popular combinations of MC vs. caliper area. You get a number, like the final drive numbers, that tells you what the ratio is between MC and caliper. I can't give you the numbers or the formula for that matter either but if you decrease the size of the MC you get more force, stronger brakes, but give up short travel. The small MC lever has to move farther. You can get the same advantage by increasing the area of the calipers. Dual calipers are an increase, twice the area if they were 38mm units. But BMW dual systems use 40mm units so it's bigger still. Then with the dual system MC they messed up they made it 17mm. Add to all this the under tank system has a cable that will stretch putting some softness into the system and the OEM brake hoses add a little more because they stretch.

It gets expensive if you improve every single aspect involved but it has been done. Maybe eventually you would like to improve several of these areas? But the number one improvement has been for a number of years to get a smaller handlebar MC. I don't know what size to say will be best. I see in print here that 13mm is popular and recommended for a single caliper. But I also see a 13mm recommended for a dual set up? It just seems to me that eventually you have more travel needed than the lever can provide.

I don't need two finger brakes on my Airhead. I have a dual set up that is not completely installed but as soon as I figure out which MC will work and what size I may get around to finishing this.

Does anybody know the Web site I mention with the chart of MC vs. caliper sizes?
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Old 12-06-2013, 10:31 AM   #11
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Quote:
Originally Posted by disston View Post
There used to be a chart somewhere on the Net that listed all the popular combinations of MC vs. caliper area. You get a number, like the final drive numbers, that tells you what the ratio is between MC and caliper. I can't give you the numbers or the formula for that matter either but if you decrease the size of the MC you get more force, stronger brakes, but give up short travel. The small MC lever has to move farther. You can get the same advantage by increasing the area of the calipers. Dual calipers are an increase, twice the area if they were 38mm units. But BMW dual systems use 40mm units so it's bigger still. Then with the dual system MC they messed up they made it 17mm. Add to all this the under tank system has a cable that will stretch putting some softness into the system and the OEM brake hoses add a little more because they stretch.

It gets expensive if you improve every single aspect involved but it has been done. Maybe eventually you would like to improve several of these areas? But the number one improvement has been for a number of years to get a smaller handlebar MC. I don't know what size to say will be best. I see in print here that 13mm is popular and recommended for a single caliper. But I also see a 13mm recommended for a dual set up? It just seems to me that eventually you have more travel needed than the lever can provide.

I don't need two finger brakes on my Airhead. I have a dual set up that is not completely installed but as soon as I figure out which MC will work and what size I may get around to finishing this.

Does anybody know the Web site I mention with the chart of MC vs. caliper sizes?
13mm will work very well with twin discs, the lever pull is longer and much more progressive, it comes fairly close to the bar, but continued to work well, during a test by doing several crash stops from about 70 mph.
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Old 12-06-2013, 10:53 AM   #12
dm635 OP
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Thanks Disston. With the setup I got I'm not using the rubber lines. They are stiff Luftmeister lines. They start at the splitter and go to the hard connecting line at the Brembo caliper. Guy told me they were easily over $100 for the pair. I need a short hard line from the single output MC to the splitter going to each caliper with proper mounting.

I'm all ears for a better setup if anyone's got it. Let me know how to better what I've got. At this point I'm held up making the junction from the MC to the splitter. Gotta get duals run over the single bringing this baby to a stop.
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Old 12-06-2013, 11:05 AM   #13
Stan_R80/7
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For the Master cylinder to caliper cylinder ratios (these guys also sell the FDB155 Ferodo brake pads for ATE calipers):

http://www.vintagebrake.com/mastercylinder.htm

I have a set of lower fork sliders from a /6 which had dual front brakes, along with an ebay used ATE caliper, caliper rebuild kit, and a brake line bubble flare tee. I may try assembling a second disk using my current 14 mm under tank MC this winter. All that remains is getting a short piece of bubble flair brake line and another stainless brake hose.

Although, I have gotten used to the single ATE caliper brakes and by loosening the cable a bit - to get a full hand grip on the lever - feel better about stopping. The build in ABS is not so bad. I would not feel comfortable two up riding with the single disk.

Stan_R80/7 screwed with this post 12-06-2013 at 11:21 AM Reason: grammar
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Old 12-06-2013, 11:42 AM   #14
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I'm all ears for a better setup if anyone's got it.
We're telling you: handlebar-mounted MC. All you have to do is extend the brake switch to the lever. It's not stock for your bike, but neither are the Brembos and neither is the hybrid splitter thing. 100% reversible. You say you are good with electrics, but if this is a stumbling block for you than either you're not good with electrics or you don't realize how straightforward this is. Kludging the plumbing together and retaining the under-tank MC so you can save your existing brake switch connection makes no sense to me.
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Old 12-06-2013, 02:41 PM   #15
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Originally Posted by AntonLargiader View Post
We're telling you: handlebar-mounted MC. All you have to do is extend the brake switch to the lever. It's not stock for your bike, but neither are the Brembos and neither is the hybrid splitter thing. 100% reversible. You say you are good with electrics, but if this is a stumbling block for you than either you're not good with electrics or you don't realize how straightforward this is. Kludging the plumbing together and retaining the under-tank MC so you can save your existing brake switch connection makes no sense to me.
Anton
I don't think you even have to move the wiring to the HB. The hydrulic pressure switch mounts on the undertank splitter same as under tank MC .On the splitter it screws in the back.On the MC it screws in the front.Under tank MC has wires to a level indicater that can be eliminated. HTH
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