# Replacing a master cylinder

**URL:** <https://community.cartalk.com/t/replacing-a-master-cylinder/55315>\
**Category:** Maintenance/Repairs\
**Created:** [September 19, 2010, 11:55am UTC](https://community.cartalk.com/t/replacing-a-master-cylinder/55315 "2010-09-19T11:55:13Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![mrbean](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@mrbean](https://community.cartalk.com/u/mrbean)\
**Post date:** [September 19, 2010, 11:55am UTC](https://community.cartalk.com/t/replacing-a-master-cylinder/55315/1 "2010-09-19T11:55:13Z")

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Last year I bought a pressure bleeder for flushing and replacing brake fluid (well worth the $50).  
  
  
  
 I’m going to be replacing a master cylinder soon and will use it to bleed the system. I’ve replaced M/Cs many times before and I have always bench bled the cylinder first and then bled the system the old fashioned way.  
  
  
  
 My question: Is it necessary to bench bleed the cylinder first if I’m using a pressure bleeder? I vaguely recall reading somewhere that it is not, but I’m not sure.  
  
  
  
 Thanks!

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**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\
**Post date:** [September 19, 2010, 12:26pm UTC](https://community.cartalk.com/t/replacing-a-master-cylinder/55315/2 "2010-09-19T12:26:50Z")

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If the master cylinder is properly bench bled and installed no further bleeding is necessary.

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**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\
**Post date:** [September 19, 2010, 2:50pm UTC](https://community.cartalk.com/t/replacing-a-master-cylinder/55315/3 "2010-09-19T14:50:18Z")

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No. The master cylinder doesn’t require bench bleeding before it’s installed. That’s one of the advantages of using a pressure bleeder.

Tester

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**Author:** ![Xebadaih](https://avatars.discourse-cdn.com/v4/letter/x/d07c76/32.png) [@Xebadaih](https://community.cartalk.com/u/Xebadaih)\
**Post date:** [September 19, 2010, 3:36pm UTC](https://community.cartalk.com/t/replacing-a-master-cylinder/55315/4 "2010-09-19T15:36:01Z")

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What about the air you introduce into the lines when you disconnect them from the old master?

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**Author:** ![meaneyedcatz](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/meaneyedcatz/32/692_2.png) [@meaneyedcatz](https://community.cartalk.com/u/meaneyedcatz)\
**Post date:** [September 22, 2010, 2:00am UTC](https://community.cartalk.com/t/replacing-a-master-cylinder/55315/5 "2010-09-22T02:00:16Z")

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As long as you do not crack open any other bleeders its no problem.

After installing the m/c and connecting the lines you can bleed them and all will be good.