Master cylinder

Ask Andy › Category: Brakes › Master cylinder
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Admin Access Staff asked 2 years ago

I had all my brakes lock up today and got my beetle towed home. It seems that the master cylinder went out. The pedal went very hard, couldn’t push it more than a centimeter when applying the brakes.

When I got it aligned the alignment tech said he thought the rear brakes were dragging. This is a AC industries kit on all four wheels

Parts go out, have issues, no big deal, but I was curious if you have seen this happen and if you have a suggestion on a new master cylinder for this setup. I was never a fan of the ambidextrous one.

Specifically should I be adjusting the brakes in any special way, etc.

1 Answers
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Andy Shouse answered 2 years ago

Hi Kenn,

I’m sorry to hear of this trouble you have had.  Unfortunately,  the  #59192 is not a good invoice number for me to look up, so I have nothing here to go one.

As for a master cylinder locking up, there is several questions to have answered.

I am assuming you are using this master cylinder as it is designed to be used with 4-wheel disc brakes.

Questions:

  1. Is this a new build that you haven’t driven before?
  2. When this happened, did you try to open a bleeder valve to see if there was residual pressure in the brake system?
  3. Once the brakes cooled down, did the brakes unlock?

With all of the Air Cooled VW master cylinders for Bugs, Super Beetles, Ghias, Things, Type 3s and 1966 and older Buses, there is no way for residual brake pressure to hold in the master unless the piston is not returning completely to rest.

As the piston comes back to rest when the brake pedal is released, there is an orifice that aligns internally in the master and allows brake fluid to return to the brake fluid reservoir.  This is mandatory because as the temperature rises in the brake fluid, the brake fluid expands.  As the brake fluid expands, the excess has to go somewhere.  If it cannot go back up into the reservoir, the excess fluid pressure will push on the pistons in the wheel cylinder or caliper, causing the brakes to lock up.

The biggest cause of this is that the master cylinder pushrod is not adjusted correctly and it is too long.  This will keep the piston in the master cylinder from coming back to rest.

Thanks, Andy

andys@socalautoparts.com

/by