Bleeding Breaks and master cylinder

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Booky1
Posts: 28
Joined: Thu Jul 06, 2017 4:54 pm

Bleeding Breaks and master cylinder

Post by Booky1 » Wed Jan 03, 2018 7:20 pm

Can you bleed the brakes with out bench bleeding master cylinder?This is a totaly rebuilt system and new master.Can you use one of the vacuum bleeder system to bleed system and master?

Ol'fogasaurus
Posts: 14055
Joined: Tue Nov 14, 2006 1:17 am
Location: Just north of Seattle

Re: Bleeding Breaks and master cylinder

Post by Ol'fogasaurus » Wed Jan 03, 2018 8:11 pm

Discs or "can brakes"?

Everybody seems to have their own way of bleeding brakes, especially "can" or drum brakes but since I started playing with VWs I learned of a good way of getting the best out of the bleeding process. I am going to be very basic on this.

On drum brakes start by adjusting the brake shoes to fully lock up the wheels at all four corners. You should not be able to rotate the wheels at all on all four corners. The reason for this is that you make sure that all the brake shoes are centered within the drum as it is easy to not have that happen. You might get the right sound when the adjusting is done but the shoes are not centered and can cause several reactions that you can feel in your foot or steering wheel.

Asssuming that the soft lines were changed at the same time as a complete rebuild is done: next you start filling the system by working on the wheel farthest away from the MC; the right rear corner. As the fluid goes down from the MC into the line you keep the MC full so no air bubbles or air is allowed to enter the brakes lines. Once the slave/brake cylinder is full and no air bubbles come out close the valve and start on the left rear corner. Also, keep an eye on the joins as you go through this. No leaking and make sure no air is getting back into the system. Getting air into the system is a hard thing to figure out but, from experience, it can happen.

Continue this process up to and through the front wheel cylinders. Then you can start adjusting the brake shoes at all four corners. As you start loosening up the shoes you listen for a slight contact/drag of both shoes on the brake drum; kind of a "swish, swish sound as you rotate the wheel. On new shoes you will get some wear at first as the ends of the brake pads wear to the shape of the wheel so a follow up adjusting might be necessary; again, lock the drum then back off on the shoes.

Disc brakes are simplier but still being careful of not allowing any air in the lines; this is important.

Some people do a "gravity bleed": this is where you open all four corners and, keeping the MC cylinder filled to not allow air in the lines. Once the slave cylinders are full then readjust the brakes. I have never done this before but a lot of people swear by/at it.

I haven't had much good luck with the vacuum bleeders on a VW while some people seem to. The basics are the same but I think they work better when the brake lines have already been filled. There are also the "pressure" bleeders with their own brake fluid drum that makes sure that the MC doesn't go dry but will they tightly hook up the opening in the MC (I've never used one on a VW).

Again, this is my opinion on this and it is just one in a million different way as I have already said.
Lee

My opinion is worth slightly less than what you paid for it.

Booky1
Posts: 28
Joined: Thu Jul 06, 2017 4:54 pm

Re: Bleeding Breaks and master cylinder

Post by Booky1 » Wed Jan 03, 2018 9:34 pm

Thank you for the reply. I no the basics of how to bleed brakes I was just not sure about master cylinder and bench bleeding cense the resivor is separate from master.

Ol'fogasaurus
Posts: 14055
Joined: Tue Nov 14, 2006 1:17 am
Location: Just north of Seattle

Re: Bleeding Breaks and master cylinder

Post by Ol'fogasaurus » Wed Jan 03, 2018 11:59 pm

Booky1 wrote:
Wed Jan 03, 2018 9:34 pm
Thank you for the reply. I no the basics of how to bleed brakes I was just not sure about master cylinder and bench bleeding cense the resivor is separate from master.
Booky1: sorry, but I wasn't sure so I went through the whole thing start to finish... maybe someone else will benefit from it.

Bench bleeding gets the MC primed but the rest doesn't change; just make sure that no air gets into the system during mounting of the MC and the reservoir; air in the system is an easy thing to do in some cars.

The idea of locking everything up wasn't taught back in the late 50's but what I learned in the 90s, when I starting to play with VWs, is still the best way to do it no matter what kind of a drum brake car you are working on; you get a good go the first time.

Lee

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