Single to Dual Brake System Conversion
This conversion was installed in a drum/drum vehicle with no power brake booster. No proportioning valve and no residual valves were fitted. The vehicle is factory designed with 57% output to the front and 43% to the rear. The cast iron dual master cylinder (MC36237) was chosen for the ports being in the inside of the engine bay. Prior to this change another consideration was a readily available bracket with pivoting arm that enables the installation of power brake booster in which the assumption is that you would not modify the chassis for this fitment. The new setup was for safety of splitting the brake system into two which will be seen during bleeding post assembly(conversion.jpg).Parts Needed:
Brake Master Cylinder Part#MC36237(Raybestos) 1"bore. Front and rear ports on the inside, on engine side. 1/2-20 on both primary and rear. No port for brake switch. This master comes with a special crown washer that is used on power brake booster installation. Fits on 1966-74 Jeep and other makes and models.
Brake lines: Rear 3/16" brake line with 1/2-20 adapters to 3/8-24 from master to brass block Tee. Front 1/4" brake line with 1/2-20 adapters to brass block 7/16-24.
AGS BL3, AGS BLU3(Brake line union 3/16" line), AGS BL4(BL-430), AGS BL3(BL-312), AGS BL3(BL-308), BLAG360, BLAS420, BLF-44B (1/2-20,1/4 in.)
Brake Light Switch: OEM 1171742,
KEM EG1050(fitted on this build), SLS30, S199, SL139, SL528, SL37, SW13
Brake fluid type 3 is good enough, type 4 will be better.
Optional: Brake pedal pushrod.
5/16" box wrench for rear brake line bleeders
3/8" box wrench for front brake line bleeders(front bleeders are angled so need socket to break free)
3/8", 7/16", 1/2" pipe wrench
Vise grips and heat for seized lines as needed
Vise to hold lines for flaring
Dedicated Flaring kit for 3/16 in. and 1/2 in. (No chewing kit)
Soapy spray bottle and rags
Teardown
During disassembly the brake lines were seized at the front distribution brass block. I was able to brake one line free but ended up having to cut two of the lines to remove on a vise. I used heat on the brass block so that the expansion of metals would give the brake line nut room to break free. It was necessary to use large vise grip pliers on the brake line nut (seized brake lines.jpg). The brake line nuts are not hardened so it doesn't take much to round them out with a pipe wrench specially if seized from rust. My parts list does not have included brake line for the replacement of the right front line. Seems like lots of parts, but you will have some bad flares and poor bends. After the do overs you will have used up this supply I used. The brake lines came with nuts, and it was least costly to get nuts this way than buying by themselves. Also, I ended up getting the brass T-block for the brake switch from local parts store.
By observation you can see that the front distribution block has different sized paths between the front and the rear. It has one 7/16-24 thread with 1/4 in. pipe on the top and three 3/8-24 thread with 3/16 in. on bottom sides. This factory brass block located on the chassis adjacent to master cylinder was reused but the port to the rear was plugged with a 3/8-24 steel inverted flare (not seen in images). That rear port on the master was plumbed to the rear brake line using a brass union and inverted flares with nuts. Within the rear brake line is the brake switch on a brass tee with 1/8-27 NPT on all three. It was necessary to add NPT inverted flare nuts to fit with the brake lines.
Flaring Brake Line
The flaring tool with the horseshoe shaped tool and threaded shaft with the point grabs the pipe with threads. It will leave chewing on the brake line and the flares can come out shifted off to the side. This happens because the pointed part does not a have a guide. In my case the metal was too soft, and it was deforming during the first step of flaring, so in order to clean up the point I lost the guide. I completed the flare lines with two different flare kits, one was solely used for the 3/16 in. lines(kit in blue box) and the chewing kit for the 1/4 in. line. The kit I used on the 3/16 in. line has a guide and it is difficult to making bad flares with this tool. In order to finish my 1/4 in. flares, I made another tool (on a lathe) to go in between to shape the flares with the "chewing" tool. 
Frame Trim
It is necessary to modify the frame to allow the MC36237 to fit. There is a factory cut out there for the single master, but it is further back. You remove material ahead of this area. There will be a factory weld at this location on the frame. After I removed the necessary material, the frame snapped and opened up less than a 1/32 in. I had it welded in this the same location grounded it down smooth and painted. Keep in mind that weld and paint will add more material so consider when fitting for clearance(frame modification.jpg).
Studs To Mount
The studs that come out of the firewall are a bit on the short length if anyone is familiar with the 63 Skylark/Special you will have already noticed this. The use of thinner nuts is highly discouraged. The dual master cylinder's mounting thickness will not be any thinner than the original single master. To correct you remove the support from behind the firewall under the dash for access. I did not try to remove the studs from risk of damaging the support. Instead drill and tap for allowing to screw in bolts with longer length(studs.jpg).Brake Pedal Pushrod
You will need a brake pedal pushrod if you do not modify your original to fit. To modify the original pushrod, you would use a Dremel to remove material (while wearing respiratory protection) to reduce the outer diameter (OD) on the non-removal washer that keeps into the master by the snap ring. There is two changes you make, inner diameter of the hole in the master(MC36237) is just a hair too small and the washer is too thick. If you use the thick washer, it may be possible that the brakes would be a bit applied, how much? I don't know, but I didn't want to take the risk. You are removing enough of the washer thickness on the inside so that the snap ring goes into retaining channel and there is no preload on the master's piston. Achieving this is accomplished if you hold the pushrod at the end with a rag and angle the Dremel with mandrel and fiber metal grinding disk on the washer it will rotate and remove material evenly. It will be trial and error until you get there being careful not to remove too much material. You leave in the crown washer that is in there for power brake booster otherwise the pushrod is making that contact direct on the piston. Also, you would not need to put inside the channel the bullet spacer that is available under some other applications.
Location Of Components
I decided to place the brake switch at the top near the original location and within the rear brake circuit. I felt that placing it lower could expose it to more exhaust heat, the harness connection would need to be extended and wanted to avoid it in the front circuit which does 57% of the stopping. I originally started to flare the line on the vehicle going to the rear to add a union right by the brass block where I cut it? After the "chewing" tool produced (with my help) multiple bad flares, several trims later I ended up next to the steering column at a tight squeeze. With this in mind it was probably the easiest selection for the rear line. From the union to the switch the line was shaped to avoid contact with the brass block bracket(brake lines.jpg). 
Testing
There were many leaks after the conversion. Two of them were at the distribution brass block and the other was at the brake switch threads. I used some of the extra brake line nuts as thread chasers. This is easily done by using your Dremel to grind out three cuts evenly separated around the threads. Once I verified that the lines would thread in properly, I used Prussian Blue on the flanges to check for contact due that I was having issue with sealing. Some of the AGS brake line flares were questionable, but I still attempted to bleed the setup with no success due to leaks. My assumption was that they have the equipment to properly flange these lines, but after repeat leaking, I ended up redoing the flares that AGS delivered on the lines and leaks were resolved. I added Blue Loctite on the brake switch threads to prevent leaking along with retorque to the block, but it did not seize. The switch and block are NPT threaded yet the fluid was getting through (this is a good topic of discussion), so I decided to add Hylomar to the threads which did stop the leaking.Summary
This is not a one-day project. Consider some time for cosmetic, because there will be rusty parts. As you can see, I painted the new master with hardened paint, and it started to blister at the edge meets the lid from the brake fluid just in this short time. Also, I originally put in a coated 1/4 in. line for the front, but with the leak do overs and flaring that was a waste of additional cost on that one part. I installed all steel brake lines which is a bit more challenging but doable using the correct tool on a vise. In regard to losing the original look I considered that many of these cars are no longer on the road. To be on the safe side, I went with this change.Testdrive
Pedal feels the same to when it had the single master cylinder. Upon TestDrive intermittently the brake lights were working and eventually seized to work. In this conversion I installed a new OEM switch and jumped to the conclusion that it was failing from long shelf life. Before I went to replacing it with the good used working switch, I trouble shoot the lights using basic methods. If you observe in the image the switch can sit in such an orientation to disconnect the 2-way pigtail connector. I found the connector was in, but not all the way home because it was partially bumped out by the wheel well adjacent to it. The correction was just to give the connector more space with mild adjustment at the switch and brake lines. There was no need to open the system or switch replacement. Brake lights are working now.Additional reference on this topic.
63 skylark single to dual master conversion
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