Brakes
From Crankshaft Coalition Wiki
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==Preamble== | ==Preamble== | ||
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. | 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. | ||
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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== | ||
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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. | 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. | 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. | ||
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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. | 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=== | ||
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==Resources== | ==Resources== | ||
*[http://www.mpbrakes.com/technical-support/overview.cfm Technical support] from MP Performance Brakes. Includes FAQ, Configurations, Troubleshooting, and Installation Guides | *[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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