Good day all,

While working on other broken parts of my 1966 Olds Toronado, I thought I would start planning my dual master cylinder upgrade and am looking for input on a couple things, if possible. Now, I have decided to go with a simple dual circuit upgrade rather than front discs, etc as I would like to try to keep everything as simple as possible.

Sizing everything up, and going with some excellent suggestions on here, I have decided to go with a mid-60's Cadillac Raybestos master cylinder (MC36373) as it should bolt right on to my original power brake booster. The only problems I see relate to the junction block under the hood where all the brake lines come together. I plan to plumb one port of the master cylinder to the junction block, remove the rear brake connection, and plug the hole. Front brakes done!

Now the problem I see here is making the connection from the second port on the master cylinder to the rear brake connection. How am I going to connect here without fouling on the junction block? There's not a lot of room to work on the rear brake line so I'm looking for suggestions. See my pics below, hopefully I am explaining this well and it makes sense.

The connection from the old master cylinder to the junction block is 1/4" line.......I am hoping the new master cylinder also uses 1/4" line as that will make it much easier to connect to both the junction block and the rear brake 1/4" line. I am unsure of the sizes on the new MC.


Brake junction block.

Rear brake line. Not much wiggle room!l

 

The GM dual circuit M/Cs typically use a 3/16" line to the front brakes with 3/8-24 threads and a 1/4" line to the back brakes with a 7/16-24 thread. Those are the "standard" inverted flare nuts that come with those size lines if you get them at an auto parts store. GM also used non-standard threads at some locations to prevent incorrect line connection on the assembly line, but that only applies to the distribution block or combo valve. You don't need those for your conversion.

Simply use a 1/4" line with the 7/16-24 nut for the rear brakes and a 3/16 line with the 3/8-24 nut for the front brakes. Get a three port tee fitting to split the one outlet on the M/C into separate lines for right and left. Done. Don't overthink this.

 

Thanks Joe....I'm definitely trying my best to not overthink the setup. A couple questions though to make sure I'm understanding. Are you saying that the Caddy Master Cylinder I'm sourcing will have two different size fittings on it? 3/16" line for the front and 1/4" for the rear?

​​​​​​​I'm reusing all the lines that are currently installed on the car so I guess my main concern is how to make it all fit where all the existing lines come together.

 

Well, apparently this one doesn't, as the specs on the Caddy M/C show 1/2-20 for both ports. That doesn't sound right so verify once the M/C shows up. You aren't going to be able to reuse all the old lines. You can keep the original junction block and use an inverted flare plug in the port that formerly connected to the rear brakes. Then you simply need to make up a new line from that block to the M/C for the front brakes. You can use an inverted flare coupler to connect the old rear brake line to a new short section that runs to the M/C. The risks here are that 1) there will be additional connections that are potential leak locations, and 2) if the old lines aren't in the best shape, you'll eventually need to replace them anyway.

1/2-20 inverted flare nuts are normally used on 5/16" tubing, but you can get 1/2-20 inverted flare nuts for both 3/16" and 1/4" tube. This assortment for 1/4" line is less expensive than buying the nuts individually. There is also this assortment that covers the full range of different nuts for both 3/16 and 1/4 tubing.

 

Right, got it.

I just don't see how I'm going to hook up that rear line with a coupler.......the old junction block is in the way. I guess I could cut it back a bit and re-flare it in situ.

 

Just bend it to where you need it to be.

 

Ok yeah, I'll see if I can manipulate it a bit to get it to fit.

My Toro also has the Bendix brake system........I guess I should have checked earlier. The 65 Caddy master cylinder will work with the Bendix booster correct?

 

My master cylinder showed up today. Looks like both fittings are 1/2". Rather than change things significantly, would it be ok to run short 1/4" lines from the master cylinder for both the front and the rear with 1/2" fittings designed for 1/4" line?

The line coming off the old master cylinder is 1/4" and goes to the junction block that I will reuse for the front brakes. I guess I could run that as a 3/16" instead of 1/4".......will that make any difference? I'm not really sure what I should do honestly.


That's a 1/2" wrench.

 

Just updating this project as I'm getting a bit closer to starting the dual master cylinder project on my 66' Toro. I guess my first question would be which ports on the new dual circuit Raybestos master cylinder goes to the front and rear brake connections?

 

It doesn't matter. The piston sizes are the same for a drum/drum system

 

Ok thanks again Joe, that's good info.

 

Have you attempted this yet? I'm hoping this bolts right up to the booster as predicted. I'll be doing this mod to my 66 toro as soon as I get some confirmation this will fit. Might even jump ahead of you! (and promise I'll take pictures if so). I've done the same mod on an early mustang.

 

I haven't gotten to the point where I can upgrade the brakes yet. I'm still dealing with some really bad rust at the rear of the car which is currently being repaired.

I probably won't get to the brakes until next year, honestly as I've got a lot to do with the car and the brakes work really good right now anyway. So, I'm really interested in how you make out. Pictures would be great! Good luck!

 

I ordered the acdelco part, looks the same but has a gold cover. Should be here in a few days then I'll get the pieces I need to plumb it, from the auto store.
MC replacement always opens a can of worms, because you need to bleed all 4 corners.

 

Looking forward to seeing how you make out. Hopefully you don't run into too many hassles. I know those bleeders can give you trouble!

 

Very intresting , would be nice with a dual mastercylinder and keeping the drums in our -65 98.

 

Looks snazzy. I'm distracted by carburetor currently but will get to this soon.

 

I did this same thing on a 65 several, repeat several years ago, been a while and the car is gone now. I had no trouble at all. I did something not mentioned here, I used what I call an adapter where the lines did not fit each other, or didn't fit the port on the master cylinder. I used an adapter, a brass fiting to fit one end to the master cylinder and the other end of the adapter fit what I needed to on the line. I got them at autozone. By the way the brake lines and brass fittings use the same size and thread count as a regular bolt, so you can use the bolts you have around to decide what size and thread count you need on the adapters and lines.
The adapters made it so easy, it was a great.

 

I mounted the dual MC on the booster, and have all of the parts ready to plumb it in, but have hit an obstacle. I can't get the line to the rears to budge...

Have alternated between penetrating spray and MAPP torch for a while now. Sigh... If I break this off, I need to flare that line in a pretty tight spot, or re-plumb it all the way to the back. This one fitting has me seriously considering leaving it as a single...

 

Will the other lines come out? Might be the same situation possibly but If you can get those off, you could unscrew the block from the rear line.

 

Interesting. If I can get the two front lines off, I'd plug them and use the block as a union.

 

So far they seem to be as frozen as the rear one. Granted I didn't give it hours to penetrate. Making brake fluid boil out the disconnected line from master is ... interesting. I suppose I need to make it a LOT hotter than just enough to boil brake fluid though (400F). Brass melts at 1700F.

 

Ok upon closer examination, there's room to flare that rear line. Once it's cut off, it can be popped off the clips and swung down into a more convenient area. I'll still need to get that fitting out, however, it should be easier once the tube is out of the way and I can put a socket and breaker bar on it. I have a very solid grip on the existing block, so something will have to give... . Given this experience thus far, I think I should check if all the wheel cylinder bleeders can move. A lot of bleeding will need to happen after this.

 

I never use heat on brake lines. I use a hammer and gently tap in as many directions as I can manage. I liberally soak with PBBlaster, Kroil or the like (WD40 is useless). I try to tap parallel to the brake line (perpendicular to the threads) using a way to small open end and tap on the open end. I very gently tap the same open end on the brake line (perpendicular to the brake line) where it goes into the fitting all around (to free up the line rusted to the fitting). And then using the proper open end or line wrench, I tap into all the flats I can get access to (all around) of the fitting. This is to free the threads of the fitting to the junction block. I repeat the process a number of times. Then using a line wrench I try to loosen it. I am very careful to watch if the fitting loosens, but the line is stuck inside the fitting. In that case I stop and try to spin the junction block off of the fitting, holding the fitting in position so it doesn't kink the brake line. Patience and repetition are the keys.

 

Sorry folks, i was hoping to document a nice DIY here, but its not going to work out that way. None of these fittings will loosen! I'm not going to hack off and re-flare everything. Not worth it. I'd rather make the emergency brake 100% dependable and take my chances with the single circuit. Abandoning and returning everything. If anyone wants a perfect fit dual master cylinder, let me know. I've never, in all my restorations, modifications, upgrades, etc, encountered something quite this ridiculous.

 

Can almost smell the frustration.......That's too bad, sorry it was such a fight. Re-plumbing the entire front brakes doesn't appear to be a huge undertaking though. You could probably replace the whole front end lines with nice, easy to work with, nicopp lines and even flare em on the bench. That way, you could still unscrew the block from the rear line.

 

I have no doubt it's possible and easy if the fitting cooperates. I have a personal limit of one car per year for a complete brake replumbing, and that limit has already been met on a car that desperately needed it (looking at you, dodge!) I'll eventually post a full parts list/plan for those who hopefully have better luck with the fittings than I did. It would be a VERY easy job if just that one line would come loose! I have a new single MC on hand already to install as the old one leaked.

Step #1 for anyone who wants to do the easy upgrade: See if the flare nut for the rear line can be loosened. THEN buy parts.

 

Good grief that rear line connection! I've been wrasslin' with mine for a few hours now and it's still frozen solid. Had the same issue with the 1/4" supply line from the master cylinder to the junction block. I heated it and cooled it about 30 times before I finally got it to break free. Currently I have all but the rear line connection broken free.

I've got an induction heater on the fitting and have been hitting it with that and alternating with freeze spray + penetrant over and over. It's gonna break free right??

 

Progress so far. Just doing some test fitting, things seem to be fitting alright. Just got to tackle that rear connection.

 

Only took about 30 heating and cooling cycles, but I got it free. I had to make up a little 1/4" line with a fitting on it, threaded into the other 1/4" location at the junction block so I could slip two sockets (1/2" socket + 19mm socket) and an extension over the line to help brace the junction block as it kept wanting to bend when I was reefing on the rear fitting. Those induction heaters are quite handy, there is a warning on the side that it's "professional use only" though .

 

Looks great , nice you got the fittings loose.

 

Progressing well so far. Making up a brake line for the rear connection was tricky as the exhaust pipe is right in the way and I didn't want the line too close to it. I may shorten up the tail on the connection to the rear union as it came out a little longer than I wanted but otherwise it wasn't too bad. I'll also be securing the old rear brake line to the frame with a clamp.

Then I'll be taking all the new lines out and cleaning them out with some brake clean and adding a dab of anti-seize to the fittings. Then on to filling the system with fluid, bleeding it, then leak checks.

 

All done,

Finally finished up today. Bled the master cylinder, bled all four corners, started the car and pumped up the brakes to check for leaks and all seems good so far. Went up and down the driveway to check for braking power and it seems exactly as it was before the upgrade. Can't really drive it around yet as we still have snow and salted roads here. I've bent the lines away from the exhaust where they're at least an inch away from it (although it looks closer in the pics - it's not). None of the lines are rubbing on each other as the clearances are more than adequate. The last thing I'm going to do is to attach a clamp to the frame for the rear line to give it a little more rigidity. While I was bleeding the brakes, some of the fluid splashed out and ate off some of the paint I did the master cylinder with. I'm going to touch that up as well.

Thanks to all involved, especially Joe P. who gave me excellent tips and advice on this upgrade along the way.





Clamp to be attached.



Before anyone says it......that's not thread tape! It's some debris sitting on the frame. No thread tape here.

 

Nice upgrade , congrats