master cylinder question

[76bonanza]

Anyone have detailed instructions on how to replace the brake master cylinder? Bench bleeding and such?


Thanks

[Frank-id]

Changing a master cylinder is NOT a tough task. Some planning is required. Open the hood and decide the wrench sizes needed, get a quart of DOT 3 brake fluid, and have a roll of paper towels near. My method is first remove all fluid in master cylinder. Find correct line wrenches for lines and loosen fittings but resnug fittings to prevent fluid from leaking.
Check replacement cylinder for correct replacement. Put new cylinder into a vice or have helper hold cylinder upright. Add new fluid half full. Use an old pushrod and slowly push piston to front of stroke. Watch fluid being drawn into cylinder piston bore, and fluid will push out discharge past fingers held over line holes. Fluid will begin to be forced from line connections.
Remove old cylinder and replace with new cylinder quickly as to not loose fluid. Use papter towels to absorb any spilled fluid, as fluid can remove paint. Connect the lines first, with just a little tightening. Tighten the 2 nuts holding master cylinder to power booster. Add brake fluid to 3/4 full. Replace master cylinder cover loosely to prevent fluid from spurting out of top. Helper should slowly pump brakes. Pedal should become firm and solid. While helper holds pedal down under pressure, mechanic can slightly crack open line fittings to release any air and to note fluid pressure. Crack open fittings slowly and only about 1/4 turn of wrench. Open front fitting then rear, several times. Allow brake pedal to be at rest for a minute. Now apply brakes and note pedal position. If pedal is low toward floor, another round of line bleedings is necessary. The best pedal height is often after a brake adjustment. Be sure to top off fluid but allow about 3/4 inch air space at top.
Some times a complete bleeding of all positions is needed. Discard any used fluid. Do not reuse. The best fluid is DOT 5 synthetic but some special procedures are required.......

[76bonanza]

Thanks So I should just use dot 3 brake fluid?

[Frank-id]

Brake fluid is some unusual liquid. The DOT ratings have to do primarily with , the boiling point of fluid under pressure. Braking materials can achieve some very high temps. The Dot 3 fluid is great for most auto and truck use. One of the bad characteristics of most brake fluids is that of being hydroscopic. Hydroscopic describes any fluid that will/can absorb water. Water is not good for braking systems. The fluid does not attract a gallon a week but about 1/2 ounce over several years. This water is one cause of brakes systems to develope corrosion at the pistons at each wheel. Fluid should be changed about every 5 years. Usually the brake systems demand shoe and pad replacements and the fluid is replaced......
Dot 5 or 6 fluids are very costly and must not be mixed with any other type brake fluid. Dot 5-6 do not absorb water and have a very high boiling temp. Most aircraft and high performance equipment use the best. The fluid is also a synthetic blend....