Brakes

[oprn]

I just found these and want to share. Very informative!

https://www.youtube.com/watch?v=yAyovvseQ4c
https://www.youtube.com/watch?v=iJ7bf20phWc
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[EVfun]

I would recommend the second video first, as some of the graphs being used in the first video are explained in the second video. I also found his information from the second video on a web page, complete with text and graphs. I did not find a formula to calculate the "Ideal Brake Curve." I suppose ours would look more like the Porsche example given, being a tail heavy car.

The first video goes into showing the car brake balance, the effects of changing it, and how the strait line fits against the ideal max brake curve at different G forces. Most other sources seem to suggest that the maximum braking force that most drivers can control is about 0.6 G, something to consider if you adjust brake balance. Without seat belts could I stay in my seat above 0.6G? The second video shows the effect of a brake proportioning valve. If you put one on the front it should shift brake force line up (instead of down when installed in the rear brake line) as it would be shifting braking toward the rear instead of toward the front.
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[oprn]

I put them that way around because the second one is a bit dry (attention span?) but yes it really should be seen and understood first.

Agreed on the Porsche curve and the way the PV works. He also goes into peddle pressure issues which I am very interested in for my present project. He explains things very clearly considering his education and experience level. I hadn't given the effects of wheel base much thought, that was good too.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[EVfun]

This make me look at braking distance and G-force. 60mph to zero braking distances are often quoted for cars. G-force to distance is easy to compare.

60-0 distance of 120 feet is 1G.
60-0 distance of 200 feet is 0.6G.

30-0 distance of 86 feet is 0.35G.

I included that because that is roughly the upper limit of "gentle braking." It gives you an idea of a normal city traffic light stop.

Roughly:
MPH^2 / 30 = 1G stopping distance
MPH^2 / 30 / G = stopping distance
MPH^ / 30 / stopping distance = G
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[oprn]

Good stuff, thanks!
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[oprn]

Here is an in-depth discussion that looks to be pretty informative too for our cars. I haven't got through and digested it all yet...

https://germanlook.net/forums/showthread.php?t=4595
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[Busstom]

I am currently revamping the braking system on my '64 Bus, and using Wilwood's remote tandem master cylinder with their combination proportioning valve and Wilwood 4-pot calipers on all four wheels with 944 rotors all around. The nice thing about their remote master is that it is the same design as VW dual circuit masters, but comes in 1.0 and 1-1/8" bores (albeit a larger mounting flange, it is a somewhat larger MC). I'll report back with how it works, but it will be quite a while.

If you end up needing a larger MC, it might fit the bill, although maybe spendy for some people.
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My name's Steve and it's pronounced "Bust 'em" (cuz people think I'm Tom) 😏

[oprn]

I managed to get through this thread and the additional threads referenced in it. https://germanlook.net/forums/showthread.php?t=4595 As per usual there is plenty of personal opinions and arm chair speculation but... that's all part of the process is it not? Discussion and ideas? Food for thought? Some really solid ideas in there too. I especially liked that those fellows were calculating the mechanical bias ratios and comparing them to similar factory cars.

This is a pretty involved subject and as pointed out by many in the threads, there is no perfect answer because there are so many variables and every car we modify is different in some way.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[oprn]

[oprn]

I just stumbled onto this one. Worth a listen I think.

https://www.youtube.com/watch?v=dIqaOo83rGQ
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[EVfun]

I have some experience with master cylinder bore size, wheel cylinder size, and resulting pedal effort to stop. First thing I noticed, in the early '90's, is that swapping to the "buggy master cylinder" (really it was a '66 down Bus master cylinder with screw on reservoir) greatly increased pedal effort. Not an issue on a 1100lb. Buggy, but noticeable. Next I drove a '65 Bug -- wow less pedal effort than even my first car, a '60 Bug. Later I bought a stock oval window Bug -- more pedal effort like my Buggy with the Bus master cylinder but more noticeable since the Bug is heavier. I have a rough formula for calculating the pedal effort using the stock Bug pedal assembly.

Front wheel cylinder bore squared plus rear wheel cylinder bore squared divided by master cylinder bore squared will get you a number around 2. The lower that number the greater the pedal effort, the higher the number the lower the pedal effort. Here are a couple examples:
'58-'64 Bug stock: (484+361)/361= 2.34
'65-'66 Bug stock: (484+361)/309.76= 2.73
'57-down Bug stock: (361+289)/361= 1.80
early Bus master '64 Bug brakes: (484+361)/484= 1.75
current buggy brakes: (306.25+361)/361= 1.85

I have no information about disc brakes as I have not used disc brakes on any VW I've owned (except a Rabbit Pickup I had between around '96-'00).

Most of my effort has been around adjusting brake balance for my buggies with wheel cylinder bore sizes, and looking at the different VW stock choices.

'57 down Bug: 55-1/2% front
'58-'64 Bug: 57% front
'68 up US spec Bug: 61% front

This is a little different than the ratio used in the initial videos posted. I am using the front wheel cylinder area divided by the total front and rear wheel cylinder area to create a front percentage. Remember that if you are running different wheel sizes that also effects brake balance. The smaller tire is turning faster and doing that much more braking. My current buggy has about 50% front braking and about 33% of the vehicle weight on the front tires. The stock Bug is carries about 40% of its weight on the front wheels.
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[oprn]

Here is a question that I have not found the answer to yet. In a case where you would want to replace a single master cylinder with 2 master cylinders (in parallel) and a balance bar and maintain the same peddle pressure the new M/Cs then must be smaller.

The example I worked out is to replace a single 19mm M/C with 2, the new ones need to be 13.44 mm to maintain the same mechanical advantage and peddle pressure. Two 13.4 mm cylinders will be the same area as a single 19mm one.

Is my math correct on that? I have yet to find any discussion to this effect.

...or on the other hand does it even work that way?
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[EVfun]

That much is true IF the pedal leverage is the same. Usually the pedal gives a mechanical advantage of between 4:1 and 6:1 to increase travel and reduce effort. A tape measure guestimate from my buggy is that VW chose 5:1. Perhaps the balance bar pedal assembly gives more (or less) mechanical advantage than the stock VW pedal cluster.
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[oprn]

I don't know what peddle ratios come with the commercially available balance bar assemblies. Then I had my peddle cluster out I lengthened the brake peddle by about 2.5 inches so I suppose I am closer to 6/1 now.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[oprn]

This is from vdub engineering's website.

"Custom Brakes – Guidelines
by Lanner Khan

With custom brake kits in Type 1’s (T1), it is important to take into consideration and understand all the factors.

Why brake upgrades?

In my opinion, there are three reasons; brake fade, changing wheel bolt pattern and bling factor.

Brake fade is when your brakes are getting too hot and the brake compound in the pads are gassing out and no longer effective. The temperature of the brakes is exceeding the thermal properties of the friction pad. Your rotors are not cooling because they don’t get a chance to dissipate the heat between brake applications. If your brakes fade, then you need more thermal mass via larger and thicker rotors. For performance applications, vented rotors are a must. Solid rotors are for motorbikes and go-carts in my opinion. If you currently have solid rotors and are experiencing brake fade, switch to a vented rotor. If your vented rotor fades, then you need to improve the cooling or increase the thickness of your disk. Brake fade can also occur from boiling the brake fluid. This condition is not typical of street vehicles. The caliper pistons need to be insulated to prevent this, via titanium pistions or ‘pucks’ inside the existing pistons.

With brakes from other vehicles, your choice of wheels increases dramatically. The 4-130mm bolt pattern isn’t very popular with aftermarket wheel manufacturers. And let us all agree, that the wheel offerings available for the 4-130mm wheel pattern are outdated.

Got 17’s on your car? Got stock drums? Hmm…not very sexy. Big brakes behind big wheels.

Brake Hydraulics

Basic hydraulic theory states that 1) liquids are incompressible and 2) the pressure of a given closed system is the same anywhere within the system.

Pressure[P] (psi) is force [F] (lbs) over area[A] (square inches). If a 1 inch diameter piston is depressed with a force of 150lbs, this will generate a pressure of (150/3.14*.5*.5) = 190.98 psi. If a hose is connected to another piston that has a 0.5″ diameter piston we will see some force multiplication. The force would be the pressure multiplied by the piston area. (190.98psi*.25*.25*3.14)=37.50 lbs. So we see that a smaller piston will generate a smaller force given the same pressure. To summarize for a closed system:

P1= P2 (pressure 1=pressure 2)

F1/A1=F2/A2 (same as above since P=F/A)

So far so good. According to the above, just increase the piston area and you can increase the piston force for the same pressure.

If only life were so simple.

Since hydraulic theory states that liquids are incompressible, the fluid must be displaced. A displaced volume [D] is equal to a movement [M] times ares [A]. So if the same 1 inch diameter piston is depressed by 1 inch, we will displace .785 inches cube of fluid (.5*.5*3.14*1). If a second piston of .5″ diameter was connected, we would see the second piston move by 3.998 inches (.785/(.25*.25*3.14)). So, bigger pistons require more volume. To summarize for a closed system:

D1=D2 (displaced liquid 1= displaced liquid 2)

M1A1=M2A2 (movement1*area1=movement2*area2).

Understanding brake torque

Brake torque is what stops the wheels. The brake torque (ft-lbs) of a wheel is the clamping force (lbs) of the caliper times the disk radius (ft), times the coefficient of friction for the brake pad. The disk radius is measured to the centre of the brake pad.

Clamping force (lbs) is the brake line pressure (psi) times the total piston area of the caliper (square inches). The total piston area of a fixed caliper is the total of all the pistons areas. In a sliding caliper, the total piston area is the total of all the pistons times 2.

The brake line pressure (psi) is calculated from the force applied at the pedal. The pedal force (lbs) is multiplied by the pedal ratio, and divided by the master cylinder piston area (square inches).

If you’re following the story so far you will notice that rotor thickness has nothing to do with brake torque. The rotor thickness is related to the thermal capacity. Also, note that the pad area does not play a part either. Increasing the line pressure is possible by either stepping on the brake pedal harder, or decreasing the master cylinder size.

The system in action

A master cylinder is depressed which pressurizes a fluid. This pressure is transferred to the caliper pistons which in turn push the brake pad onto the disk. Adequate volume is required to insure that the master cylinder does not bottom out before the caliper can generate sufficient brake torque to stop the vehicle. The actual movement of the piston in a caliper is about 0.010″-0.015″. When the force is removed, the square seal in the caliper retracts the piston to remove the clamping force from the rotor. The above two hydraulic laws are ideal. In practice other factors must be considered; swelling of brake hoses, caliper deflections, caliper mounting deflections, compression of fluid, air inclusions in fluid etc.


Brake Bias

Also, some consideration must be paid to brake bias, that is the front to rear braking distribution. Depending on the size of your front and rear caliper pistons, you may alter the existing brake bias of your master cylinder (MC). If you understand brake torque, you will notice that rotor diameter, friction material, caliper piston size all factor into the brake bias equation. Other factors include weight distrubution of the vehicle, center of gravity of the vehicle and tire size. Weight distrubution and center of gravity factor in the dynamic weight transfer during braking. Typical rear static brake bias is only about 20-35%. Remember regardless of all the brake factors, the final word is between the tires and the pavement. With that said, you can use these factors to fine tune your vehicle’s braking characteristics.

If needed, use a proportioning valve to tame your beast. A prop valve is basically just a hydraulic pressure regulator, except that it only kicks in at a certain pressure (knee point). Up to that point, the proportioning valve does not exist (hydraulically speaking). Prop valves only reduce existing pressure. You want to set up the brake system so that under panic braking all wheels lock up the same. Then bias is SLIGHTLY to the front so that the front brakes lock up a LITTLE sooner than the rear ones. (Easier and safer to remedy understeer then oversteer in panic situations).

Depending on your brake setup, it is possible that you will have to add a prop valve to the rear circuit if you have a brake system that is biased towards the rear (rear wheels lock up before front wheels in a panic situation). Prop valves only reduce existing pressure.

Prop valves can be found at any hot rod shop. Wilwood makes a nice little unit that you can purchase directly from them. You will also need some adaptor fittings to accept metric bubble flare lines for installation. Please check local laws regarding prop valves on front circuits."
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[EVfun]

You don’t have to use brake line adapters to add an adjustable proportioning valve to your VW. Check out this from Wilwood. Going back to your original post in this thread it might make better sense to install that proportioning valve in the front on many tail heavy buggies. It would bend the braking curve UP when it kicked in. At last check my buggy weighed 370 lb over the front and 730 lb over the rear tires.

I don’t see any reason for disc brakes to stop an 1100 lb buggy when starting with brakes designed to stop a 1700 lb Bug. I rarely fly down the road over 70 mph in my plastic fantastic. If you want the style points then go for it. I just don’t see how it’s needed in a light street buggy.
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[oprn]

A couple of things, first I won't get into the proportioning valve front/rear debate as it's been covered many times before. There is nothing new to add to that subject.

The next is that I seriously doubt there are very many Buggies on the road today that are 1100 pounds, yours being one of the exceptions. Ours was 1423 pounds empty before the type 4 engine and the extra weight of disc brakes. Now add a couple of 200 pound people and enough luggage for a week or two on the road. Then add a tank of fuel, a little 150 pound trailer, a tent and an 80 pound canoe with paddles, life jackets, an electric motor and a deep cycle battery. With a jerry can of gas, suddenly we are pushing 2450 pounds without a 100 pound glass roof or roll cage made out of 300 pounds of pipe. Now take that on a 10 mile 8% down hill grade in a mountain pass at 70 mph in heavy tourist traffic and some clown up front jams on the binders to get a picture of a couple mountain sheep...

That sets the scene for some fancy driving I had to do on the shoulder of the road because all the 4 wheel power disc brakes around us were out braking us big time.

If the only thing we ever did with this Buggy was to go for ice cream in town on Sunday afternoon I most certainly would not be upgrading anything, not even the engine.

Then there are the guys that go with Subaru, Toyota, GM water pumpers, full competition grade roll cages, nurf bars and side pods, full roof, roof racks with several jerry cans a jackall and spare tire or two. Then they have dual rear shocks, long travel aftermarket suspensions front and rear, 30" tires and rock proof rims, mega decibel sound system, fire extinguisher. I would be willing to bet they easily tip the scales 3000 pounds or more.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age)

[EVfun]

If you make it weigh more than a stock Bug then you may want to upgrade the brakes. I'd be disappointed if I built a beach buggy that weighed in over 1500 lb. About that point I think I'd switch to building a baja bug. A full roof (one that will even withstand a rollover) is pretty handy in western WA. Disc brakes tend to require a little more pedal effort because with drum brakes the leading shoe is partially self energizing.

To make the brakes easier to apply (more stopping power per pound of pedal effort) you want to either make the master cylinder bore smaller or the bore at the wheel larger. This increases mechanical advantage, but it also increases pedal travel. There comes a point where this tradeoff will render dual circuit brakes pointless, with the pedal bottoming out in a half brake failure before you have any meaningful braking force on the other 2 wheels. You will notice that VW went to the low effort 17.5mm master cylinder in 1965 but just 2 years later when they switched to dual circuit brakes they jumped back up to a 19mm master cylinder.
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[oprn]

[EVfun]

If you have a full roll cage you could look into a reverse swing pedal assembly, seen most often in street rods. Combined with a 7 inch brake booster you could arrange for power brakes. It would put the booster and cylinder under the dash going reward from the pedal bracket/pivot location, not interfering with the stock gas tank.

All of this goes beyond my vision for a buggy, I’m very much of the less-is-more mindset. I drove the Mini-T around for a year with no turn signals, the headlights (no high beams) turned on with the ignition switch. The dash featured a speedometer and an ignition switch.
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