Brakes
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==Preamble== | ==Preamble== | ||
| − | This article will introduce you to brakes and the components that are involved | + | This article will introduce you to brakes and the components that are involved in a hydraulic brake system. We will try to break down the brake system in to its proper categories so that you can understand them better and apply that knowledge. |
Many people ask frequently about braking systems, and what is better and what is usable. Everyone wants to go faster, handle better, braking is often ignored, mainly due to the price of major upgrades. After research and some experience most people will find that big brake kits, slotted, cross-drilled rotors have not made a huge dent in 60-0 or 70-0 stopping distances. | Many people ask frequently about braking systems, and what is better and what is usable. Everyone wants to go faster, handle better, braking is often ignored, mainly due to the price of major upgrades. After research and some experience most people will find that big brake kits, slotted, cross-drilled rotors have not made a huge dent in 60-0 or 70-0 stopping distances. | ||
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==Drum brakes== | ==Drum brakes== | ||
| − | [[ | + | [[File:Brake leading trailing and duo servo.jpg|frame|none|Leading/trailing shoe drum brake left; duo-servo type on right]] |
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| + | ===Dou-servo drum brakes=== | ||
| + | When replacing drum brake shoes, if you have one shoe with less friction material than the other, the shoe with '''''less''''' material covering the steel shoe | ||
| + | goes towards the '''front''' of the vehicle. This is commonly found on duo-servo type drum brakes. Because of how the brakes work in a duo-servo, the rear shoe sees more wear than the front. On the diagram above this can be seen. On the duo-servo drum brake, the front shoe is called the "primary" shoe, the rear shoe is the "secondary" shoe. | ||
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| + | ===Leading/trailing shoe drum brakes=== | ||
| + | These are seen in lighter duty applications such as the rear brakes of a front wheel drive vehicle. On them, the bottom of the shoes are solidly held against a pivot point, and only the tops of the shoes expand out to contact the drum. This design has less braking ability than a duo-servo type brake because only one shoe has a self-energizing effect. In this setup, the front (leading) shoe may be the same as the rear (trailing) shoe as far as the amount of friction material covering the steel backing shoe, but the material may be thicker on the front (self-energizing) shoe. In other cases the front shoe will be smaller like the duo-servo type. | ||
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| + | There has been years of confusion on the issue of which position the longer lining shoe goes in. The reason for the confusion is the Willys Overland company and it's successive owners. Ask almost any mechanic who works on vintage cars and they'll tell you "Bigger goes in Back" - B = B.<BR> | ||
| + | But<BR> | ||
| + | Old Willys vehicles are the major exception to this rule. All old Willys (Jeep) vehicles - CJ-2A, CJ-3A, DJ-3A, M-38, CJ-3B, early CJ-5, M38-A1, Wagon, Truck, Forward Control call for the longer shoe to be placed to the front. Any factory manual will confirm this. Don't trust aftermarket manuals, they may tell you to follow the convention that the rest of the automotive world followed for decades. | ||
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| + | ===Other drum brakes=== | ||
| + | *Two-leading-shoe drum brakes were used on motorcycles before disc brakes became popular. Also seen on large trucks. | ||
| + | *Single-servo type brakes are used on trailers, etc. On them the brake cylinder plunger extends only from one side, bearing on the leading shoe. | ||
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| + | ===Self adjusters=== | ||
| + | On vehicles having self adjusting brakes, the self adjuster mechanism (link or cable depending on the type) goes towards the ''rear'' of the vehicle. | ||
==Brake system== | ==Brake system== | ||
| − | The picture below shows a typical | + | A high performance brake system will often use specific brake fluid for the application, stainless steel hard brake lines, teflon lined braided flexible brake lines, air ducting and venting, along with all the other necessary items to aid in controlling brake component temperatures. |
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| + | The picture below shows a typical hotrod brake system which utilizes an adjustable proportioning valve, residual pressure valves, a master cylinder, and a vacuum brake booster. This is an under-floor brake system setup. | ||
[[Image:Hot_rod_brake_system.jpg|border|450px]] | [[Image:Hot_rod_brake_system.jpg|border|450px]] | ||
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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. | ||
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| + | =====Pedal ratio/bore size vs. pressure output===== | ||
| + | <table border="1" cellpadding="2" cellspacing="0" width="595"><tr bgcolor="#CCCCFF"><td class="tdName" width="20%">'''Pedal Ratio'''</td><td class="tdName" width="20%">'''Bore Size'''</td><td class="tdName" width="25%">'''Pounds Input'''</td><td class="tdName" width="25%">'''Approx. PSI Out'''</td></tr><tr class="trLight"><td>6:1</td><td>1-1/8</td><td>75</td><td>450</td></tr><tr bgcolor="#eeeeee" class="trDark"><td>6:1</td><td>1 </td><td>75</td><td>575</td></tr><tr class="trLight"><td>6:1</td><td>7/8</td><td>75</td><td>750</td></tr><tr><td bgcolor="#oooooo" colspan="4"></td></tr><tr bgcolor="#eeeeee" class="trLight"><td>5:1</td><td>1-1/8</td><td>75</td><td>375</td></tr><tr class="trDark"><td>5:1</td><td>1 </td><td>75</td><td>475</td></tr><tr bgcolor="#eeeeee" class="trLight"><td>5:1</td><td>7/8</td><td>75</td><td>625</td></tr><tr><td bgcolor="#oooooo" colspan="4"></td></tr><tr ><td>4:1</td><td>1-1/8</td><td>75</td><td>300</td></tr><tr bgcolor="#eeeeee" class="trDark"><td>4:1</td><td>1</td><td>75</td><td>380</td></tr><tr class="trLight"><td>4:1</td><td>7/8</td><td>75</td><td>500</td></tr></table><p> | ||
===Brake boosters=== | ===Brake boosters=== | ||
In most cases the vacuum required to operate a power brake vacuum booster should be at least 18" for best results. In most cases anything less than 14" of vacuum will not be enough. Using a vacuum reservoir is not a very good substitute for inadequate vacuum. In cases where there's not enough vacuum, a vacuum pump may be used, or the system changed to manual brakes. | In most cases the vacuum required to operate a power brake vacuum booster should be at least 18" for best results. In most cases anything less than 14" of vacuum will not be enough. Using a vacuum reservoir is not a very good substitute for inadequate vacuum. In cases where there's not enough vacuum, a vacuum pump may be used, or the system changed to manual brakes. | ||
| − | If space is a problem, a dual diaphragm booster might be enough smaller in diameter to help. | + | If space is a problem, a dual diaphragm booster might be enough smaller in diameter to help, as long as the booster has sufficient pressure to do the job. |
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| + | ====Some guidelines from MP Brakes:==== | ||
| + | A midsize GM car with disc brakes in the front and drum rear brakes will require at least 900-1,000 psi to the wheels to lock them up. The pressure output of the booster is directly proportional to its diameter, the larger the booster the greater the power assist. | ||
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| + | The following assumes 18 in/Hg of vacuum at idle, and 120 psi of pedal force: | ||
| + | *Four wheel disc = 9" dual diaphragm (1200 psi) | ||
| + | *Front disc/rear drum = From the 9" dual (1200 psi) down to a minimum of a 7" dual (900 psi) | ||
| + | *The 8” dual diaphragm booster makes 1,000 psi | ||
| + | *9” single diaphragm 900 | ||
| + | *7” dual diaphragm 900 | ||
| + | *7” single diaphragm 800 | ||
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===Brake lines and fittings=== | ===Brake lines and fittings=== | ||
[[File:SM_brake_fitting01.jpg|border|300px]] | [[File:SM_brake_fitting01.jpg|border|300px]] | ||
| − | == | + | ==Power to manual brake conversion== |
| − | + | *[http://www.hotrodders.com/forum/manual-brake-conversion-g-body-212363.html Converting 1980 GM G-body] | |
| + | ==Resources== | ||
| + | *[http://www.mpbrakes.com/technical-support/overview.cfm Technical support] from MP Performance Brakes. Includes FAQ, Configurations, Troubleshooting, and Installation Guides | ||
| + | This may be one of the best brake articles I've ever seen.... | ||
| + | *http://www.pirate4x4.com/tech/billavista/Brakes/ | ||
[[Category:Brakes]] | [[Category:Brakes]] | ||
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