Hot Rods USA Tech Blog

September 22nd, 2006

Welcome To The Hot Rods USA Tech Blog

Posted in Uncategorized by Tech Support

This Blog was created to help supply our customers with the technical information that they request. As well as giving each of you a chance to ask questions or leave comments about each post. You must be registered to leave a comment however this service is free.

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September 18th, 2006

How do you determine the pressures output of the master cylinder?

Posted in Brakes by Tech Support

I have been asked hundreds of times how do you determine the pressures output of the master cylinder. The following information will help you determine the proper size master cylinder:

To figure how much pressure your master cylinder is putting out:
C = pedal ratio
D = pounds of pressure apply by your foot
E = area of you master cylinder
F = pounds of pressure out of the master cylinder
C X D /(divided by) E = F

Example: If you have a 1″ master cylinder the area equals 1/2″ x 1/2″ x 3.14 = 0.785 Square Inches. So, 100 pounds (of applied foot pressure) X 6 (pedal ratio) divided by 0.785 = 764 pounds of pressure.
If you have a 1-1/8″ master cylinder, 100 psi X 6 (pedal ratio) divided by 0.9935 = 604 pounds of pressure.

Here is some info on master cylinder with “constant” of 6 to 1 pedal ratio and 100 psi being applied.
3/4″ master cylinder = 1359 psi
13/16″ master cylinder = 1158 psi
7/8″ master cylinder = 998 psi
15/16″ master cylinder = 870 psi
1″ master cylinder = 764 psi
1-1/8″ master cylinder = 603 psi

DO NOT Try to use a OEM master cylinder smaller than 1″ without calculating the volume requirement. It is like choosing between jump off a cliff or a plane, how do you want to die? Remember you can not do anything after you run out of brake fluid, but you can still press on the brake pedal harder.

If you are upgrading you brake system check the following about your master cylinder:

1. Does it have a built in residual valve? If yes, replace it with a disc/disc or disc/drum master cylinder that matches your calipers.
2. When replacing the master cylinder ALWAYS buy new. Determine the size bore based on the caliper design and piston sizes being used.
3. Master cylinder used with a booster will generally have a dimple in the back of the bore. This dimple will mate to the flush mounted rod on the booster.
4. On installation be sure to check for a small amount of free play so the master cylinder is not preloaded.

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September 18th, 2006

Ride Height: You need to pick out your wheels and tires!

Posted in Chassis by Tech Support

Ride Height–Is the height of your car when it is sitting and the suspension is at the optimum setting (location). I can not stress how important setting ride height is on a chassis.

First, you need to pick out the wheels and tires you will be using in the front and in the rear. The diameter of the tire determines the ground clearance, frame angle, engine angle, shock length and correct angle to weld the front suspension.

After establishing the diameter of the tires, find the front spindle location based on the manufacturer’s specifications. The car manufacturers all have specifications on this. If you plan to install a front end kit, the manufacturer should also be able to provide you with this important information.

Take the radius of the tire diameter and use these measurements to set the distance from the ground. In the front measure from the center of the spindle and in the rear measure from the center of the axle. You now have “ride height” and everything should be relative to the ground. Of course the ground or suspension jig should be perfectly level as all your measurements will be made from this origin.

No chassis builder can build a chassis that is tuned with optimum suspension without knowing proper “ride height”. How did they know your “ride height” without asking you what wheels and tires you are going to use? Maybe they do not want to know so when your car does not handle correctly they can sell you some additional parts. Remember to ask a salesperson these questions when you are buying. Do they sound credible or just out to make a buck?

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September 13th, 2006

Brake Fluid

Posted in Brakes by Tech Support

Brake fluid is the liquid that transmits the force through pressure for the brake pedal to the brake lines. Basically the brake fluid does not compress so it transmits this force (pressure) without lost.
One of the worst enemies of brake fluid is heat. If the brake fluid boils or there is a leak in your system there will be a lost of this incompressibility and your pedal travel will increase. Not all brake fluids are the same. Most brake fluid has ethylene glycol as it main ingredient. Ethylene glycol has lubricating capability for the rubber parts and has a high boiling point.
Moisture is another enemy of brake fluids. All brake fluids will absorb moisture form the atmosphere, this moisture lowers the boiling point of the fluid drastically. This moisture also can effect the balance of the system casing corrosion. A perfect example of moisture getting your system is the early Corvette brakes where it was common to change the calipers on a regular basis due to contamination and corrosion.
Silicone brake fluid has a higher boiling point (around 700 degrees F.) than the ethylene glycol base fluids, but the major disadvantage is not “hygroscopic”. Hygroscopic? “Altered by the absorption of moisture” What this means is since it is not a glycol based, when moisture enters the system it is not absorbed by the fluid. This results in beads of moisture moving through the brake line, collecting in the calipers. Since it is not uncommon to have temperatures in excess of 212 degrees F. (the boiling point of water), this collection of moisture will boil causing steam and vapor lock, this in turn will cause system failure. Silicone (DOT 5) is also highly compressible due to aeration and foaming under normal braking conditions.
If you are changing from a glycol based fluid to silicone or the other way around. The two types do not mix so your system should be completely purged, disassembled and dried out. When the two fluids are mixed you will get a gummy substance and it will really mess up your system.
We recommend using a good DOT 3 fluid. Wilwood makes a hi-temp fluid with a minimum dry-boiling point of 570 degrees F Dry-boiling point is measure in its virgin non-contaminated state. Wet-boiling point is the temperature a brake fluid will boil after it is fully saturated with moisture. DOT 3 fluids have a minimum wet boiling point of 284 degrees F.
Brake fluid should be changed periodically due to contamination. Never mix different DOT brake fluids. Under racing condition you would change these fluids like changing your oil.

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Welcome To The Hot Rods USA Tech Blog

How do you determine the pressures output of the master cylinder?

Ride Height: You need to pick out your wheels and tires!

Brake Fluid

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