1973 280 sedan

[aspbenz]

brakes question , brake pedal goes to floor, the reservior fluid holder has fluid in them. what is my issue ,

[BWhitmore]

Defective master cylinder, ruptured brake hose, leaky metal brake line, leaky brake caliber. Most likely defective master cylinder.

[Kofi]

if you see no brake fluid on floor then you most likely have air in the system that needs to be bled out

[Carpenterman]

If you can't pump the brakes up, this symptom indicates a bad master cylinder. The fluid could be leaking into the booster and you would never see it.

[Idle]

Look online for a cutaway view of a master cylinder. See those rubber cups that are in the cylinder tube? They push the brake fluid out of the master cylinder and into the brake lines to create pressure on the system.

That big brake booster can that sits behind the master cylinder is not your problem, but it could be what is making your problem come to light. This is because on the end of your Master cylinder, the end that bolts to the brake booster can, there is a seal. If that seal is blown the vacuum inside your brake booster could just be sucking the brake fluid out of your master cylinder.

But if that was the case you would see a loss in fluid from your brake fluid canister. In fact, if you are loosing brake fluid from anywhere in the system you would see a lose of fluid.

But if the fluid level is staying level then just about the only thing that can cause what you are describing is bad cups, also known as pistons, in the master cylinder. They do wear down, and the walls of the master cylinder do wear and get pitted. Either way you would not get the pistons to seal up enough to cause pressure in the system when you step on the brake.

And.... Do check on the ground, or the inside of your tires, for signs of brake fluid leaking out. If the leak is big enough then you are doing nothing but squirting brake fluid out when you step on the brake.

If you find a leak repair it. If you don't find a leak replace your master cylinder.

And pay attention to the instructions on how to bleed the master cylinder after you have installed it. This is very simple but it needs to be done slowly and it helps if you have a helper to keep the fluid from splashing out during the master cylinder bleeding process.

[Frank Reiner]

Oral Kaopectate