Brake Master Cylinder
 

Hi all, recently, as I continued repairs on deer damage, I've had to replace my brake master cylinder and reservoir. At the moment, the brake pedal falls all the way to the floor, and provides zero braking power, even at little speed. Before I go through the process of bleeding this used master cylinder, is this normal? Should I buy a new OEM master cylinder instead? Or should I just bleed the brakes completely?

Hello Corn,

The master cylinder is not too expensive and is one of the things you may want to but new because IMHO, if you install a used one you will not know how soon the used one will start to leak (old seals..) and you will have to start over again.

Good luck with your repair!

Thank you! For now, should I just pull it and order a new one? Or can I afford to drive on it for a little while and bleed it now?

+1 on the new master cylinder, unless you know the history of the replacement. New or used you will end up doing a complete flush and bleed down of the brake system

Yes, it is normal for an un-bled master cylinder to lack braking pressure. Power brakes can very easily compress air bubbles inside the system. I'm guessing you have at least some pedal pressure with the engine off? Without the power assist, it is harder to compress the air.

You'll have to bleed a new MC too, so why not bleed the one you have on there already? If you get good braking, great. If not, you have practice for when you bleed the new one.

Brake fluid is (relatively) cheap.

(I'm assuming you got the used unit in good shape from a reputable source.)

The master cylinder I sent you should work fine. New, old, or remove and reinstall will require you to bleed the entire brake system.

As a coincidence, for your reference just ran into this link (not related to seller whatsoever..)

OEM Master Cylinder For Sale PMK 628 997-355... | Panjo

Okay thank you. I was worried that there was a problem because there's no brakes whatsoever

If you use a power bleeder such as the Motive you can just bleed the brakes. BUT if you are going to attempt to pump the brakes with the master cylinder to bleed, then you will need to bench bleed the master cylinder first.

Buy new OEM or quality aftermarket. Then yes, you must bleed the brakes. It sometimes takes awhile, but stopping is worth it.:D

So as it turns out, you're supposed to bleed the master cylinder before you put it in. Brakes have been bled profusely, but zero braking power is available because there must still be air in the master cylinder. To prove this, I switched cylinders with my old one, same story. I could bench bleed the cylinder, but all the fluid spills out before it's able to be put on the car. Should I put the master cylinder in and attach a pressurized bleeder to the reservoir and bleed it that way? Would that be faster than bleeding for hours by having a buddy pump the brake pedal?

Hello Corn,

You should try one of these, and you will never go back to the buddy system...

https://www.ecstuning.com/ES3474/?gclid=CMyix5GZ_M0CFYJqfgodbx0GDQ

What Gilles said...
The power bleeder pushes the brake fluid through the system. Just crack open the valves on the calipers one at a time until there is a clean, solid flow. Start with the rear, then do front. Doing a two man bleed is horrible in comparison.