juice brakes questiones

[larry harding]

i am slowly rounding up the parts to put juice brakes on my speedster project and have a couple of questions.
1. what solid king pin or king pin kit do i need to replace the original hallow king pins?

2. what type or year master cylinder should i use?

i have the les andrews books as well as the "how to build a traditional ford hot rod" both books have a lot of info on the juice conversion, but i don't see any specifics on the king pin and master cylinder.

[Mike Peters]

Our 31 slant window sedan had hydraulic brakes from a 46-48 Ford when we got it three years ago. I just finished converting it back to the original mechanical brakes. It still used the original hollow king pins and spindles, which I reused. The master cylinder was 46-48 Ford, as well as backing plates and wheel cylinders. It also had a spacer to adapt the later backing plates to the Model A spindles.

[nkaminar]

In my opinion, the later master cylinders, with two cylinders, is safer than the old ones that had only one cylinder. The tubing is run so that there are really two separate brake systems. I think is is right front and left rear and left front and right rear. Use the synthetic brake fluid that does not attract water.

I would look for solid king pins on the hot rod sites. But the hollow ones are probably strong enough. If you have a lathe and tool post grinder, you can machine your own king pins out of drill rod.

[larry harding]

i know ford went juice brakes in the late 30's which would have the solid king pin. were the later king pins the same size in all the straight axles or did they change over the years. i'm at a toss up on weather to go with the old style master cylinder go to the dual type which has added safety but a bit more plumbing.

[denis4x4]

Use a two chamber Mustang MC under $50 at any NAPA store

[Jim Brierley]

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I've always used the early Ford M/cyl, 1940 or so, 1" in diameter. I also use DOT 5 fluid, silicone. It repels water, so the cylinders last maybe forever.

[Jim Brierley]

Clings aftermarket makes a kit to install hydraulics, and everything fits nicely.

[midgetracer]

My experience is using a dual master cylinder, the MC bore must be at least as big as the original ford (40-48) master cylinder or the pedal travel will be excessive to activate the brakes I believe the correct MC bore is 1 1/8 inches. Clings takes the guesswork out, but the cost is substantial.

[Gene F]

I am guessing a kit from a trusted supplier is the way to go.

[40 Deluxe]

If you go the dual master route, do you know the necessity of proper pedal travel? It has to be the same as the original application of the cylinder or you will have NO braking if one side fails! The pedal will go almost to the floor before activating the remaining brakes, so if the pedal travel is shorter than designed by the OEM, it's crash time!

[30Murray]

The later style solid or hot rod king pins will not work with model a spindles and axles. The thrust washer sits above the model a spindle so it's kingpin is essentially carrying the weight of the car. With later style spindles the thrust washer sits under the upper spindle flange so the kingpin has a thin top flange not designed to carry weight. Hope I described this clearly, just look at drawings to see what i mean. I learned this the hard way after buying some later style kingpins for my hydraulic setup - they are now paperweights.

[ThosD]

"If you go the dual master route, do you know the necessity of proper pedal travel?"
Just went through this exercise in the past year. The single reservoir MC that came with my hydraulic conversion kit had a cylinder with specified diameter of 1". When measured, the dia was 1 1/8". I hated that MC. The pedal travel was short and required excessive force to stop. After reading serval conflicting posts about MCs on various forums, I sought advice from an experienced mechanic. A smaller dia cylinder allows for more pedal travel and thus yields better brake modulation and less force required to fully apply brakes. Also installed a dual reservoir MC so the front brake circuit is separate from the rear brakes. The beauty of the dual system is that a complete drain of fluid from one circuit does not affect the performance of the second circuit. Do not fear hydraulic brakes and do install a dual reservoir MC.

[Randy in ca]

Originally Posted by 40 Deluxe

If you go the dual master route, do you know the necessity of proper pedal travel? It has to be the same as the original application of the cylinder or you will have NO braking if one side fails! The pedal will go almost to the floor before activating the remaining brakes, so if the pedal travel is shorter than designed by the OEM, it's crash time!

This is exactly true. If the available pedal travel in the custom application is not at least as much as in the original brake cylinder application, in the event of a failure in one side of the cylinder you could easily find the pedal hitting the floor or firewall before any braking pressure can be generated.

Originally Posted by ThosD

"If you go the dual master route, do you know the necessity of proper pedal travel?"
Just went through this exercise in the past year. The single reservoir MC that came with my hydraulic conversion kit had a cylinder with specified diameter of 1". When measured, the dia was 1 1/8". I hated that MC. The pedal travel was short and required excessive force to stop. After reading serval conflicting posts about MCs on various forums, I sought advice from an experienced mechanic. A smaller dia cylinder allows for more pedal travel and thus yields better brake modulation and less force required to fully apply brakes. Also installed a dual reservoir MC so the front brake circuit is separate from the rear brakes. The beauty of the dual system is that a complete drain of fluid from one circuit does not affect the performance of the second circuit. Do not fear hydraulic brakes and do install a dual reservoir MC.

In the event of a failure in one part of a dual system, the pedal will typically have to be pushed a long ways down before any breaking pressure is created in the other part of the system. If your custom application does not have enough pedal travel available to reach this point you will effectively have no braking pressure in either part of the system. A smaller cylinder diameter will increase the amount of pedal travel and increase the likelihood of this happening. Dual systems are not near as fail-proof as most people assume.

[ThosD]

[QUOTE
In the event of a failure in one part of a dual system, the pedal will typically have to be pushed a long ways down before any breaking pressure is created in the other part of the system. If your custom application does not have enough pedal travel available to reach this point you will effectively have no braking pressure in either part of the system. A smaller cylinder diameter will increase the amount of pedal travel and increase the likelihood of this happening. Dual systems are not near as fail-proof as most people assume.[/QUOTE]
For my installation, I needed more travel to provide feel and modulation; the smaller cylinder MC solved the problem.
If the MC is working properly, a leak in one circuit will not prevent the second circuit from safely applying brakes.
Please review this file for an explanation of the operation of a dual reservoir MC:
https://shop.wilwood.com/blogs/news/...he-rear-brakes

[40 Deluxe]

Originally Posted by ThosD

[QUOTE
In the event of a failure in one part of a dual system, the pedal will typically have to be pushed a long ways down before any breaking pressure is created in the other part of the system. If your custom application does not have enough pedal travel available to reach this point you will effectively have no braking pressure in either part of the system. A smaller cylinder diameter will increase the amount of pedal travel and increase the likelihood of this happening. Dual systems are not near as fail-proof as most people assume.

For my installation, I needed more travel to provide feel and modulation; the smaller cylinder MC solved the problem.
If the MC is working properly, a leak in one circuit will not prevent the second circuit from safely applying brakes.
Please review this file for an explanation of the operation of a dual reservoir MC:
https://shop.wilwood.com/blogs/news/...he-rear-brakes[/QUOTE]

Keep in mind also, if a failure occurs in the front system you will only have rear wheel braking which means a huge increase in stopping distance and if you lock up the rear wheels, you will arrive at the crash site backwards!

[ThosD]

Originally Posted by 40 Deluxe

Keep in mind also, if a failure occurs in the front system you will only have rear wheel braking which means a huge increase in stopping distance and if you lock up the rear wheels, you will arrive at the crash site backwards!

Same possibility when mechanical brakes are not properly adjusted. When I purchased my A, the mechanical front brakes were not touching the drum and only the mechanical rear brakes were stopping the car. The front shoes looked like they just came out of the box; no wear at all.

[Randy in ca]

Originally Posted by ThosD

For my installation, I needed more travel to provide feel and modulation; the smaller cylinder MC solved the problem.
If the MC is working properly, a leak in one circuit will not prevent the second circuit from safely applying brakes.
Please review this file for an explanation of the operation of a dual reservoir MC:
https://shop.wilwood.com/blogs/news/...he-rear-brakes

Kind of hard to see, but I think if you look really close at the animation in that link you will see and appreciate the effect of a failure in either the primary or secondary system. Below are a couple more images. Couple that with the significant pedal travel increase accompanying a change to a smaller diameter master cylinder and one needs to be very sure that pedal will indeed be available in the event of any failure. Normal piston travel can easily be 1 to 1.5" and a typical brake pedal ratio is in the neighborhood of 6:1 (i.e. the pedal will travel 6" to move the primary cylinder 1"). In addition to the increased pedal travel resulting from any system failure, changing the master cylinder diameter by 1/4" from 1-1/8" to 7/8" will also increase pedal travel by about 40%.

If nothing else I think you may want to verify how your system will operate in the event of a failure the next time you change your fluid.

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[MickyD]

My 31 Tudor has hydraulic brakes I believe from the 40's and I use dot 5 and no problems.

[nkaminar]

True story: A friend of mine had "spongy" brakes. The repair shop he took the car to said that was normal and sent him away. The brakes failed resulting in a serious crash where he broke his neck. He did not die but is in serious rehab with problems that will last the rest of his lifetime. Brakes are important. No place to cut corners or experiment with unproven technology.

[ThosD]

My system works just fine. The MC must be matched to the braking system. Slightly more pedal travel if a complete, catastrophic failure occurs in primary circuit. Brakes are functional. Over and out.