420A Bleeding the master cylinder

[Keola916]

I'm about to replace my master cylinder because the seal that goes through the firewall leaks a lil. I know how to put it in I just need a little guidance on how to bleed it after replacing it. A step by step or video would be very helpful
-thanks

 

[Dericsh]

First you need to bench bleed the master cylinder. This video is not dsm specific obviously but it should give you an idea.

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Then you just need to bleed your brakes like regular. You either need a friend or a vacuum pump.

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[TCB91GSX]

And if you don’t bench bleed it, you will 100% need the vacuum bleeder to get it correct. Recently did mine without bench bleeding and went through two vacuum bleeders cause the Advance Autoparts brand did not work. I would bench bleed if I had to do it again.

 

[1990TSIAWDTALON]

I do both then manually squirt the last 2 on every line to be sure.

 

[Keola916]

First you need to bench bleed the master cylinder. This video is not dsm specific obviously but it should give you an idea.

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Then you just need to bleed your brakes like regular. You either need a friend or a vacuum pump.

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Is It ok if I just bench bleed it and then install it or will I have to bleed it again after installing it?

 

[Dericsh]

Is It ok if I just bench bleed it and then install it or will I have to bleed it again after installing it?

Bench bleed it, install it, then bleed all four calipers

 

[BLACK'98DSM]

Bench bleed it, install it, then bleed all four calipers

Or since it's an N/T he'll probably be bleeding the wheel cylinders on the rear, but everything still applies.

Also I wasn't sure at first if O.P was asking about the brake master cylinder or the clutch master cylinder.

 

[Dericsh]

Or since it's an N/T he'll probably be bleeding the wheel cylinders on the rear, but everything still applies.

Also I wasn't sure at first if O.P was asking about the brake master cylinder or the clutch master cylinder.

Good catch!

 

[AWD-Tony]

Highly doubt brake booster is leaking inside

 

[Keola916]

Highly doubt brake booster is leaking inside

its the clutch master, should have clerified

 

[Dericsh]

its the clutch master, should have clerified

Yeah so the same principle applies to bench bleeding before install and then bleed it at the slave after install.

 

[CKOPOCT]

OP - Just pouring brake fluid into the master cyl won't purge the air that is trapped inside the plunger/piston portion (the business part of the master cyl). If all you do is install, pour, and go you'll spend a lot of time working that trapped air out through the system. Bench bleeding saves you time, effort, and mess.

Upon installing the master you're still going to get air in the top side of the lines even though you bench bled the master cyl. Because of this bleeding the system is a must to purge the system of air. For the clutch it should be pretty quick as the length of the clutch lines is short, but it is still necessary.