Brakes
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===Residual pressure valves=== | ===Residual pressure valves=== | ||
| − | A one-way valve that allows fluid to flow through it at any pressure, but limits the amount of return pressure to a certain amount by way of a spring loaded check-valve. Usually comes in 10 psi (red color) for drum brakes and 2-3 psi (blue color) for disc type brakes. These valves are mainly used in under-floor systems where the calipers are higher than the master cylinder reservoir and to compensate for the return spring tension in drum brake systems. RP valves eliminate excessive brake pedal travel in both systems | + | A one-way valve that allows fluid to flow through it at any pressure, but limits the amount of return pressure to a certain amount by way of a spring loaded check-valve. Usually comes in 10 psi (red color) for drum brakes and 2-3 psi (blue color) for disc type brakes. These valves are mainly used in under-floor systems where the calipers are higher than the master cylinder reservoir and to compensate for the return spring tension in drum brake systems. RP valves eliminate excessive brake pedal travel in both systems. |
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| + | On a normally functioning brake system having the MC above the calipers, there is no need for a RP valve. If there seems to be a need for a RP valve in a disc brake system having the MC above the calipers, look for the root cause, rather than putting a 2 psi band aid on it. | ||
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| + | The reason a RP valve shouldn't needed is because disc brake calipers have no retraction mechanism like a drum brake. A drum brake has springs that pull the shoes away from the drum, calipers don't. It would take 'vacuum' applied to the brake fluid to cause the caliper piston to retract- and that's what happens when the MC is BELOW the calipers and the fluid tries to run "downhill" to the MC. | ||
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| + | If you have a soft pedal w/a 4-wheel disc non assisted brake system it could be due to air in the lines- bleeder screws on the bottom (calipers swapped side to side) will cause air to be trapped and a soft or spongy pedal. A too-high pedal ratio, a defective MC, or too small MC bore will also cause it. | ||
===Master cylinders=== | ===Master cylinders=== | ||
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[[File:Pedal ratio1.jpg|thumb|700px|left|Pedal ratio guidelines from mpbrakes.com]] <br style="clear:both"/> | [[File:Pedal ratio1.jpg|thumb|700px|left|Pedal ratio guidelines from mpbrakes.com]] <br style="clear:both"/> | ||
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| + | The problem sometimes encountered when using a disc/drum manual MC on a 4-wheel disc system is inadequate volume to the rear disc brakes. Calipers take more volume than drums. If there's not enough volume, the pedal will bottom before the brakes are fully applied and the pedal will not be firm. | ||
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| + | To use a disc/drum MC on a 4-wheel disc system, the MC needs to be capable of about 1200 psi and has to have adequate volume to operate the rear disc calipers. The MC bore needs to be about 7/8" to 1", and the pedal ratio needs to be around 5:1. Be sure to remove the residual pressure valve to the rear drums. An adjustable proportioning valve can be used to adjust the front-to-rear brake bias. | ||
===Brake boosters=== | ===Brake boosters=== | ||
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