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Remove and Replace the Master Cylinder

Does your pedal slowly sink to the floor when you push on your brakes? Have you checked your brake lines and wheel cylinders for leaks and found none? Do you notice the level of brake fluid in your reservoir dropping after relatively few miles of driving? If so you probably need to replace your master cylinder. Here's what you need to do. Disconnect the ground strap from the battery. Brake fluid is a very effective PAINT REMOVER so CAREFULLY drain the brake fluid reservoir using a bulb syringe.

The master cylinder can be accessed by way of the left front finder well or, on standard beetles, you can also get to it by removing the gas tank. (This gives you a little more room to work)
Place a piece of card board and a rag under the master cylinder to catch any brake fluid that might run out of the lines.
Pull the line(s) that feed the master cylinder out of their rubber plug(s)
On 67 and later bugs use the same method.
Unplug the wires or plugs that go to the stop light switch(s). 66 and earlier bugs have 1 stop light switch, 67 and later bugs have 2 since they started using a dual circuit master cylinder half of which fed the front of the car and half fed the back. It doesn't matter which of the wires goes to which side on the stop light switches that only have two terminals. The stop light switches that have 3 terminals usually have a plug that only goes on one way. In 1968 they came out with a warning light that told you if half of the dual master cylinder wasn't working. This light was turned on by a third switch in the middle of the, now obsolete, 68 & 69 only master cylinder. This can be replaced with a later model master cylinder just tape up the wires that would go to the center switch. If you want your warning light to work you'll need to use the later model stop light switches that have three terminals and modify your wiring. We show you how to do this in Vol. 9 Wiring of our instructional video series.
The 1967 and later dual switches used on the master cylinder are shown here.
Take loose the metal lines. You may have to turn the flare nut back and forth a few times until the metal lines no longer turn with it. This may save you the cost of new lines and the time and effort it takes to replace them.
Move to the inside of the car and remove the two 13mm bolts that hold the master cylinder in place. The old master cylinder can now be removed.
Note: There should be a tube like metal spacers over each bolt. If yours aren't there you need to get/make some so you can tighten the bolts without their head disappearing through the hole in the double panel. This will make it much easier the next time you replace the master cylinder.
Swap the stop light switches from the old master cylinder to the new one. Of course now is a good time to replace them if they are old and rusty. If the new master cylinder doesn't come with rubber plugs these will also need to be swapped or new ones bought.
Put the new master cylinder in place lining up the push pin as you slide it into the hole. There should not be any pressure on the master cylinder caused by the push pin if the brake pedal is all the way back. If there is then the push pin needs to be centered in the master cylinder or readjusted.
Start the metal line fittings by hand to prevent cross threading. Then tighten them the rest of the way with a flare nut wrench.
Plug in the stop light wires and pop the feeder lines back into their rubber plugs.
Move to the inside and tighten the two 13mm bolts, with their spacers, into place.
Refill the reservoir and bleed the air out of the master cylinder by having someone on the inside pump the pedal a few times and then hold it down as you loosen and tighten the top line fitting. Repeat until no bubbles come out with the brake fluid.
On 67 and later bugs both circuits (front and rear) will need to be bled using this same method.
If at this point your pedal feels spongy it means you've got air in the lines that go to your wheel cylinders and these will also need to be bled. Note: While bleeding the brakes make sure you maintain a good level of brake fluid in the reservoir. Reconnect the battery ground strap and you're done. Replacing the master cylinder, as well as the rest of the brake system, is shown in detail in the video Vol.4 Brake Maintenance available from Bug Me Video.

Rick Higgins and Crew
Bug Me Video, Inc

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