Drilling ATE MC for second brake line

Well after doing a fair bit of research I've settled on the idea of using the stock 14 mm under tank master cylinder for the dual disc conversion on my R90/6. I've already got a nice pair of stainless lines and think that the cleanest execution would be to drill and tap the blank boss to accept the second line. I have read of this being done but no straight up how to.

Have any of you had first hand success doing this? Can you offer any tips to reduce the chances of me turning my MC into a boat anchor? Looks like I'll need a 10mm by 1.0 pitch bottom tap. My biggest question is how accurate do I need to be matching the bevel angle of the drill bit to the new brake line to make sure it seats fine with no leaks.

P.S. I'm already aware of all the drawbacks to the UTMC and the various ways to upgrade to a handlebar MC so no need to try and sell me on that option.

Are you familiar with machining a 10mm bubble flare female fitting with reduced thickness? I don't think my 14mm under tank MC has enough wall thickness for more than a few threads. Of course, there is always the option of building up material through welding.

Personally, I plan running a short section of M10x1 brake line from the MC with a bubble flare tee as others have done. Some have used dual lines with a banjo fitting, which has also worked. I have yet to hear of someone making a single port 14 mm MC into a dual port. Good luck!

Instead of drilling a second hole I used a double banjo bolt on the original location.
You will have to machine the seal surface on the master cylinder flat since it was never designed as one. I filed mine flat and have never had a problem.

Here is what it looks like:



Before filing the seat:



After filing the seat.



BTW, the calipers may look the same but they are left and right. I didn't know that until I couldn't get a left caliper to seal on the right until I modified the seat for the brake line fitting. An easier optionwould have been a banjo like I did at the master cylinder.

I never had a problem with the calipers being on the left or right side. They've always sealed up for me. I have no idea why yours didn't seal.

I've had my machinist drill the second hole. I've had this done numerous times by at least four different shops and individuals. It's not rocket science, and the second hole always looks just like the first one - plenty of room for the job. I wouldn't attempt it myself as it does require precision, correct tools and the understanding. It's never cost me more than $20. So find a machinist who can do it for you - don't attempt it yourself. Not worth it.

Wow, thanks for all the quick responses!

Kai Ju, I've seen that photo of your set up before, looks great. Unfortunately I've already got a set of stainless lines with stock fittings, not banjo fittings.

I have considered running a tee or splitter but it seems the less pieces of plumbing the better.

Wirespokes, seeings how we live in the same neighbor hood do you have a contact for one of the machinist that you have used? $20 is much cheaper than I would have guessed.

I was mistaken about the wall thickness; the ATE under tank MC has a boss to drill and tap for a second brake line. Here is a link describing the bubble flare compared to other brake line flare configurations: http://www.hoseandfittingsetc.com/our-blog/bid/76614/Brake-Line-Fitting-Identification-How-to

Apparently, the DIN bubble flare used on ATE BMW motorcycle and VW car brake systems is also designated as ISO 45 degree. Apple Hydraulics in New York lined my old ATE MC and may drill and tap a new brake line port at a reasonable cost if queried. Good luck!

I am in the same boat as OG. I was planning to have my original twin outlet MC sleeved by apple for the smaller piston, but then I picked up a 14mm single disk under tank MC in great shape, and was planning to drill it for the second fitting. It looks like a simple process, assuming you can jig the casting up so that you get a near perfect 90 deg reference between the bit, tap, and the surface of the boss on the MC. I have not attempted this yet. I may check and see if a local machine shop can do it.

I'd wonder what kind of tooling the factory uses to cut the tapered bottom of the hole-- it has to be at a certain angle and has to have a the proper finish, else the fitting will leak. Would a simple drilled hole work?

I'd be inclined to fit an adapter to a drilled hole, with proper sealant or use the double-banjo fitting shown earlier.

I don't know for certain, just ruminating...

--Bill

I'm right in the middle of a dual drake conversion myself. I have my spare master cylinder on the bench and have been running through the possible work arounds mentioned here. The easiest is probably leave everything as is and run a brake line from one caliper to the other over top of the fender. Next would use a factory splitter but I can't find a used 4 hole one so I can use my brake light switch. The idea of filing a flat to use banjos seems doable but I already have lines with bubble flare ends. The perfect solution is the second boss drilled out but that requires finding a machine shop willing to tackle the job. I'm thinking I might go another route, drill the boss out for a 1/8 inch NPT tap which most already have and requires marginal precision and no seat angles then install one of these adapters
http://www.mooreparts.com/5850-CNC-F896/
The precision cut seat is solved by the adapter which would turn this into a workbench job instead of the hassle of a machine shop. Am I missing anything.

This is known as a "Drill Point Seat". In other words, the drill establishes the bottom of the hole. Handy.

That would certainly be the easiest and cheapest solution if you have an existing brakehose already. I didn't know that this type of fitting even exists.Good to know.

What makes sense to me, and what I intend to do, is install a short piece of M10x1 bubble flare line on the MC outlet: https://www.belmetric.com/bl10-cohline-p-1113.html?cPath=17_186

Then put a M10x1 bubble flare tee on the end: https://www.belmetric.com/blt10x1-c...d=7ingsk83rdo8s9ap66gd3iokt2&cPath=17_564_187

This addition of brake line and tee converts the single output MC to a dual. Also, and this is important to me, the process is 100% reversible. So, when the day comes and the bike is sold or willed to someone else it can be put back in factory original trim. Of course, coiling of the brake line and location of the tee are important details.

I think the same could be said for making a flat on the output and using twin banjo fitting brake lines. In some ways that approach is cleaner. But, I have new stainless bubble flare brake lines and don't want to spend more money.

Like many things, there are multiple approaches. Which approach depends on the owner. Machining another M10x1 bubble flare port to the MC will work just fine. However, as often found, the devil is in the details.

From a hobbyist perspective, I would appreciate the machining details to make the port. From aligning and holding the MC for drilling, the size of hole for the brake fluid, the tooling used to cut the seat, deburring, and the overall approach. While I expect someone could perform such work in a lathe, a mill would likely work better. Of course, that is not to say someone could use a HF drill press with a custom ground drill bit and make all this work - because I am certain someone can.

Regarding the bubble flare to NPT adapter: the brake calipers and lines are all M10 bubble flare, so going to NPT means converting back to bubble flare before connecting the brake lines. But, sure, that will certainly work with a few more fittings.

Well it's good to see that I am not the only one contemplating this. The adapter that johnwgy posted looks pretty simple but I would suspect that you would need to use some sealant around the pipe thread, like most pipe threads.

bmwwrench's comment about this fitting being known as a "Drill Point Seat" is exactly the info I was hoping to hear. This gives me encouragement to move forward with drilling and taping for the 10mm line.

Plan B in the event that I get a weeping seal at the flare fitting will be to machine flat the boss and utilize a copper crush washer on the line to seal it at the top much like a a banjo fitting.

By the way, I found some good brake line plumbing info at this link. http://www.dimebank.com/BrakePlumbing.html

I believe that the NPT method that johnwgy has in mind is to drill the right side of the MC casting, in the same location where the bubble flare hole would be, but with the benefit of simply drilling the hole and cutting the threads, no seat machining required.

Here is a link to information from brakeequip.com (which seems to be a legitimate company) for brake systems on making a drill point seat: http://www.brakequip.com/wp-content...al-procedures-reusing-fitting-bracket-etc.pdf . This article describes using a 118-125 degree point drill bit - which all standard hardware store drill bits are 118 degrees.

Also, as a note, "plumbing" is not in a car, aircraft, motorcycle, or other vehicle (i.e. http://en.wikipedia.org/wiki/Plumbing). As someone who has spent considerable professional time in hydraulics, pneumatics, and other pressurized pipe and tubing system work the use of "plumbing" is very annoying and demonstrates ignorance and incompetence (ahem). Best of luck with your endeavors!

Yes, you are correct. I misread the fitting. That approach would remove the need for machining a seat.

Personally, I am rather picky about brake system hydraulics. But, that approach is certainly an option. It doesn't remove most of the machining issues, but does resolve figuring out the angle to cut the seat.

Yet one more way to approach this issue!

The brake light switch is basically installed into the master cylinder just the same as the adapter, the only difference being the thread pitch so I can't imagine any hydraulic concerns going this route.

I think the brake switch uses BSPP (british standard parallel pipe) threads - which are very similar to NPT threads. The BSPP fittings have a flat surface and a seal. I threw away my defective brake light switch, so I can't measure the threads. BSPP and NPT for 1/8 fittings are very similar but not identical. It would be prudent to prove me wrong and ensure brake switch threads are NPT and not BSPP.

I've used 1/8 NPT fittings and BSPP fittings for high pressure pneumatics in air rifles. Professionally, always flare fittings or welded systems. Here is a hydraulic vendors reasons for not using NPT: http://www.hydraulic-supply.com/html/productline/prodcat/npt-fittings.htm

If I were going to machine a new port, it would be female bubble flare. I would take the time to figure out the seat angle and either buy the proper tool or make one. It is likely a 90 degree spotting drill may work: http://www.victornet.com/subdepartments/HS-Spotting-and-Centering-Drills/1216.html

The NPT to bubble flare fitting will work in theory with teflon tape on the threads. However, thread depth is a consideration. NPT uses tapered threads and a tapered tap to cut them. The seal is from the treads. I don't think they make bottoming NPT taps, so thread depth may be an issue. Practicing making 1/8 NPT threads on some scrap steel stock would be a good idea. Good luck!

Well I tackled this project today and it was a piece of cake. Clamped the MC into my drill press with a nice new 25/32" bit (closest I could find to 9mm), drilled blank boss to the same depth as the other side. Then I chucked in a couple of smaller bits to finish boring through to the MC bore matching the other side.

The cast was very easy to drill and tapped just as well with a 10mm x 1.0. I couldn't find a 10mm bottom tap locally so I just ground off most of the taper from the regular tap after tapping the the initial threads. It all seems to work well.

FTW, OG. Post up some pics.