1955 Disc brakes with original master cylinder?

[83ragtop50]

The '55 I recently purchased was in the process of being converted to front disc brakes with an original power brake booster in place. The previous owner installed a dual master cylinder at the firewall. It looks very much out of place and is very close to the exhaust manifold. I would like to return to the original master cylinder. Has anyone accomplished this? If so how was it plumbed?

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[Tom Alpers]

The '55 I recently purchased was in the process of being converted to front disc brakes with an original power brake booster in place. The previous owner installed a dual master cylinder at the firewall. It looks very much out of place and is very close to the exhaust manifold. I would like to return to the original master cylinder. Has anyone accomplished this? If so how was it plumbed?

The way they were doing it is really the best way for what you are working with. With the dual master the booster works the front disk circuit only and the circuit to the rear brakes is un-boosted. If you convert back to the original set up with a single master cylinder you will be boosting both front and rear (or boosting neither if you get rid of the booster). Disks take more pressure to apply and with only one circuit it makes it more likely that in an emergency or on wet pavement you will wind up locking the rear tires and losing control. If you do want to go back you need to splitter block that was originally down on the frame. The single feeds that block and the block feeds the two front brakes and also feeds a line to the rear brakes. If you do it that way you could put an adjustable proportioning valve in the rear brake circuit to rebalance the system if/as needed. Technically, you could do a lot of brake line fab and split the output of the single master before it goes to the booster and feed one output leg to the booster and on to the front disks and the other splitter leg to the rear brakes. I have never heard of anyone doing that but it seems like it could be done.

 

[83ragtop50]

The way they were doing it is really the best way for what you are working with. With the dual master the booster works the front disk circuit only and the circuit to the rear brakes is un-boosted. If you convert back to the original set up with a single master cylinder you will be boosting both front and rear (or boosting neither if you get rid of the booster). Disks take more pressure to apply and with only one circuit it makes it more likely that in an emergency or on wet pavement you will wind up locking the rear tires and losing control. If you do want to go back you need to splitter block that was originally down on the frame. The single feeds that block and the block feeds the two front brakes and also feeds a line to the rear brakes. If you do it that way you could put an adjustable proportioning valve in the rear brake circuit to rebalance the system if/as needed. Technically, you could do a lot of brake line fab and split the output of the single master before it goes to the booster and feed one output leg to the booster and on to the front disks and the other splitter leg to the rear brakes. I have never heard of anyone doing that but it seems like it could be done.

Thank you for the thoughtful response. I plan to return to the original master cylinder. I had thought of splitting the line in advance of the booster with the nonboosted side feeding the back brakes. But I am thinking that the addition of a proportioning valve might be the better way to go. Either way I realize that the braking will not be on par with modern power brakes. But I drove without power assist until the mid 80s so I am aware of the differences. It will be a while before I get to implement this but will provide an update when it happens.

 

[Tom Alpers]

Thank you for the thoughtful response. I plan to return to the original master cylinder. I had thought of splitting the line in advance of the booster with the nonboosted side feeding the back brakes. But I am thinking that the addition of a proportioning valve might be the better way to go. Either way I realize that the braking will not be on par with modern power brakes. But I drove without power assist until the mid 80s so I am aware of the differences. It will be a while before I get to implement this but will provide an update when it happens.

I'm still running single master with original style booster and original drum brakes. They work fine in normal driving and feel little different than modern car brakes. In emergency braking you do need to be prepared for the car to possibly head off to the side a bit, you'll want to have the full lane available. Modern cars have had ABS standard for so long now that probably half the drivers on the road have never driven a car without ABS and don't realize how much stability it adds.

 

[83ragtop50]

I'm still running single master with original style booster and original drum brakes. They work fine in normal driving and feel little different than modern car brakes. In emergency braking you do need to be prepared for the car to possibly head off to the side a bit, you'll want to have the full lane available. Modern cars have had ABS standard for so long now that probably half the drivers on the road have never driven a car without ABS and don't realize how much stability it adds.

Previous owner started the disc brake conversion but health issues made it such that he could no longer perform work on the car. I now own his incomplete projects. I would have been fine with drum brakes on all four corners but all of the rotors, calipers and related parts are already in place. He no longer had the original drum brake parts. I decided to leave the discs in place but want to get rid of the dual master cylinder which looks SO out of place.

 

[Tom Alpers]

The thing that always catches my eye on those is that shiny yellowish cover. What about painting it dark grey so it's less noticeable?

 

[kerry a berg]

The '55 I recently purchased was in the process of being converted to front disc brakes with an original power brake booster in place. The previous owner installed a dual master cylinder at the firewall. It looks very much out of place and is very close to the exhaust manifold. I would like to return to the original master cylinder. Has anyone accomplished this? If so how was it plumbed?

I have been dealing with brakes on my 56 bird for a year and tried several ways of plumbing. I had front disc brakes installed approximately 20 years ago and found the braking to have a noticeable harder brake pedal. I was told back then that it was normal for disc brakes. Prior to that my brakes had good stopping ability with what I thought to be normal pressure. Fast forward to this year and I now do all of my own work, being retired. I have totally redone my brake system putting in all new brake lines, rebuilding the original power booster and the dual master cylinder. I tried several different ways to plumb the brakes. I even tried a portioning valve, also know as a compensation valve, an electric vacuum pump and plumbing several different ways. My end result as of this point in time was to stick with the dual master cylinder. Plumb the larger bowl (mine is the forward bowl) to the brake power booster, and from the power booster to a “T” splitter midway on front tubular frame, and out to the right and left front disc brakes. The rear, smaller bowl is plumbed to the brake switch light valve on the left side frame rail with a single line proceeding rearward to a “T” fitting and then out to the right and left rear brakes. This has produced the best braking performance so far but not as good as the original 56 Ford braking with 4 drum brakes and original power booster. I found little to no benefit with the proportioning valve or the electric vacuum pump. The bottom line is that the original ford power brake booster was not designed for disc brakes as it produces insufficient power making pedal pressure harder. This is with front disc brakes only. I can’t imagine it trying to work with four disc brakes. I know of several brake retro fits where disc brakes were installed on all four wheels, a dual master cylinder, a modern brake power booster, and portioning valve installed and that produced good power braking like newer card without or prior to ABS. This, however, requires moving the battery to the trunk. Good luck and let us know who it turns out.

 

[Ronaldo]

The '55 I recently purchased was in the process of being converted to front disc brakes with an original power brake booster in place. The previous owner installed a dual master cylinder at the firewall. It looks very much out of place and is very close to the exhaust manifold. I would like to return to the original master cylinder. Has anyone accomplished this? If so how was it plumbed?

Do not keep the original master. You want the dual master for safety . I have made the conversion and in addition to the original heat shield I used another one from another Ford application. Looks fine.

 

[Tom Alpers]

I have been dealing with brakes on my 56 bird for a year and tried several ways of plumbing. I had front disc brakes installed approximately 20 years ago and found the braking to have a noticeable harder brake pedal. I was told back then that it was normal for disc brakes. Prior to that my brakes had good stopping ability with what I thought to be normal pressure. Fast forward to this year and I now do all of my own work, being retired. I have totally redone my brake system putting in all new brake lines, rebuilding the original power booster and the dual master cylinder. I tried several different ways to plumb the brakes. I even tried a portioning valve, also know as a compensation valve, an electric vacuum pump and plumbing several different ways. My end result as of this point in time was to stick with the dual master cylinder. Plumb the larger bowl (mine is the forward bowl) to the brake power booster, and from the power booster to a “T” splitter midway on front tubular frame, and out to the right and left front disc brakes. The rear, smaller bowl is plumbed to the brake switch light valve on the left side frame rail with a single line proceeding rearward to a “T” fitting and then out to the right and left rear brakes. This has produced the best braking performance so far but not as good as the original 56 Ford braking with 4 drum brakes and original power booster. I found little to no benefit with the proportioning valve or the electric vacuum pump. The bottom line is that the original ford power brake booster was not designed for disc brakes as it produces insufficient power making pedal pressure harder. This is with front disc brakes only. I can’t imagine it trying to work with four disc brakes. I know of several brake retro fits where disc brakes were installed on all four wheels, a dual master cylinder, a modern brake power booster, and portioning valve installed and that produced good power braking like newer card without or prior to ABS. This, however, requires moving the battery to the trunk. Good luck and let us know who it turns out.

You have nailed it. When I was researching new boosters that could be used to replace my original midland. one of the things I found was the amount of pressure the boosters could generate. The original booster and a suitable replacement booster THAT FITs only generate on their output port about 800 psi. That is fine, more than enough, for drum brake systems. Disk brake systems, as a general statement, can require up to 1400 psi to produce their maximum effort. Which obviously means that, again, as a general statement, the factory style booster will not produce enough pressure to properly power a disk brake setup. That's not to say you can't get more than 800 psi from a system with the factory booster, but you won't get it as "boosted", you'll have to generate it by pushing hard on the brake pedal after the booster had done all the boosting it's capable of. Since there are many conversion kits people use, many ways to plumb them, several choices of parts to use, I would not say that its impossible to get the right mix of parts where the disk setup works well enough even with the original booster. It may be that with dual piston calipers it takes less pressure or some other variation on parts people might use. I've seen posts from more than one person saying they were disappointed in their disk conversion because it didn't seem to work any better than the drums as far as how hard they had to push the pedal to stop the car. But the needed psi is the reason the most complete and successful kits relocate the battery to the truck and use a larger diameter modern directly connected booster. Just going from the 8" midland to a 9" booster represents a huge increase in booster power.

 

[KULTULZ]

Think of it this way -

The OEM SGL RESVR MC will not generate the proper pressure/volume to operate a front disc changeover. The front disc changeover needs at a minimum 1,000 PSI and needed volume (dependent on style calipers used) to initiate properly. You can also go with a smaller bore MC to increase output pressure but will experience greater needed pedal effort.

The rear drum brakes are self-energizing unlike disc and do not require high pressure. Once the primary shoe expands and makes drum contact, you have very aggressive braking in the rear (using quality friction materials).

Be certain that the replacing dual reservoir has a RESIDUAL PRESSURE VALVE in the drum circuit. If not one will have to be installed in-line externally or there are special wheel cylinder kits available to not use a RPV.

You might also consider a front disc circuit METERING VALVE that will hold off front disc application until the rear drums are energized giving better vehicle control.

It is best (IMO) to run the front disc circuit through the OEM MIDLAND BOOSTER and the rear drum circuit unassisted. You can also increase rear wheel cylinder diameter to make the vehicle more aggressive. You MUST use an adjustable PPV with a modified system(s) to prevent rear wheel lockup on panic stopping and to some degree front and rear brake ends bias balancing.

There is a heat shield available to shield the MC from exhaust heat and banjo fittings to make the install easier with left side MC outlet lines (to clear the BATT heat shield).

If you retro-fit the rear drums with self-adjuster kits, the brake pedal will remain at correct height and will not fall due to brake shoe wear (or adjust regularly). As rear shoes wear, the pedal height will drop resulting in the front disc doing more work and most people will not notice.

 

[83ragtop50]

KULTULZ - Thank you very much for the great information regarding disc brakes and braking in general. I would convert back to drum brakes all around if the previous owner could have provided the parts he removed. But I find myself with a brake conversion project that was almost completed without the previous owner being of help due to a major health issue. I am bumbling my way through completing a few other almost completed work items on the Tbird. I am experienced on classic Mustangs, but this is my first Tbird. I purchased the Tbird for my wife. It is her dream car.

 

[KULTULZ]

You are more than welcome, hope it helps.

This is a problem in the hobby the discarding of take-off parts as there are no quality replacements. Most everything is off-shore junk.

If you did want to go back to the original drums, take-off parts should not be that hard to find with everyone seemingly doing the disc swap.

What problem(s) are you having with the conversion?

And what the wife wants, she gets, as it should be ...

 

[83ragtop50]

When I got the car the previous owner, who was suffering the aftereffects of a severe stroke, told me that the disc conversion was complete expect for bleeding the system. I realized immediately that was not correct because the booster was missing the check valve and the associated vacuum line was plugged with a bolt. As I studied at the engine compartment I found several non-original looking maintenance parts. I would truly like for the engine bay to appear more like the original (not looking for perfection but the dual master cylinder stuck out like a sore thumb. I was looking for a way to replace it with an original style part. That is why I started this thread. I appreciate your thoughtful comments. BTW my shop is chocked full of take-off parts from my other vehicles. I save virtually everything original.

 

[KULTULZ]

In other words, you want to more or less restore the mechanicals (under-hood) to appear as original assembly and return to drum brakes all around?

Is the changeover MC a FORD style or a GM CORVETTE style? Are the disc front a take-off from another FORD vehicle (or kit) or an aftermarket GM kit ? Can you provide photos?

- 55 BIRD w FORD MC -​

- GM 'CORVETTE' STYLE MC -
​

 

[55birdman]

I have most of the original brake parts available as I did a 4 wheel disc conversion.
All new wheel cylinders, etc.
Interested?