The brake fun just keeps on comin!

A few weeks back I found brake fluid in the engine bay below the master cylinder and the rear system's brake fluid reservoir was bone dry. I noticed the bolt that screws the rear-wheels' brake line into the bottom of the master was wet and could be tightened a good 3/4 turn, so I tightened it, bled the master, and the pedal felt great. Noticing both wheel cylinders were leaking, I replaced those this past week.

I tried to take the car out tonight to test the brakes and noticed I needed to pump the pedal up to get the car to stop when coming out of the driveway. I checked in the engine bay and a fair bit of brake fluid was sneaking out between the brake line's bolt and the bottom of the master again despite tightening that bolt a few weeks prior. Is there a plastic/rubber seal there that has failed indicating I need a new master brake cylinder, or is that metal on metal which is now leaking for some reason?

The car has been sitting for the better part of 9 months while I redid the floor's sound deadening/carpeting and it's odd that the entire rear brake system seemed to die at the same time.

The wheel cylinders were last changed in 2016 and the master was changed in 2019.

Edited 16 hours ago16 hr by chaseincats

If the paint on the booster below the mounts of the MC has been eaten away sounds like the master is bad. Start there. Seating the lines on the master cylinder can be tricky.

The nut on the brake line into the master cylinder is a metal on metal seal. If you have factory lines or CuNi lines then you should be able to get it to seal. If they're stainless, they can be much harder to get sealed

4 hours ago, Patcon said:

The nut on the brake line into the master cylinder is a metal on metal seal. If you have factory lines or CuNi lines then you should be able to get it to seal. If they're stainless, they can be much harder to get sealed

Wow that's weird then. Since it's metal on metal and has been connected/not touched for years, why would it start leaking now? I did notice whenever I take the cap off that reservoir it does make a pop as if it's pressurized.

15 hours ago, chaseincats said:

A few weeks back I found brake fluid in the engine bay below the master cylinder and the rear system's brake fluid reservoir was bone dry. I noticed the bolt that screws the rear-wheels' brake line into the bottom of the master was wet and could be tightened a good 3/4 turn, so I tightened it,

15 hours ago, chaseincats said:

a fair bit of brake fluid was sneaking out between the brake line's bolt and the bottom of the master again despite tightening that bolt a few weeks prior.

15 hours ago, chaseincats said:

the master was changed in 2019.

2 hours ago, chaseincats said:

has been connected/not touched for years, why would it start leaking now?

Maybe it was never properly tightened. As soon as you started using the brakes you started pushing fluid out. When it was sitting for years there was no pressure.

Regardless, it's leaking now (maybe). Are you sure that the fluid is not running down the bottom of the MC from a leak inside the bore? Might depend on how the car sits if the bore tilts forward or backward.

16 minutes ago, Zed Head said:

Maybe it was never properly tightened. As soon as you started using the brakes you started pushing fluid out. When it was sitting for years there was no pressure.

Regardless, it's leaking now (maybe). Are you sure that the fluid is not running down the bottom of the MC from a leak inside the bore? Might depend on how the car sits if the bore tilts forward or backward.

It was sitting for ~9 months being driven maybe monthly during that time period and hadn't leaked since I installed the new master in 2019 so it's weird that all of a sudden its tightness became an issue. It was driven weekly before 9 months ago so it wasn't sitting that long in the grand scheme of things.

That said, it was leaking after being tightened and the pedal needed to be pumped up to work which is new. The car sits flat.

Is the reservoir making a pop noise when the cap is opened (being positively pressurized inside it) an issue? This is exclusive to the rear reservoir I believe.

Edited 1 hour ago1 hr by chaseincats

You shouldn’t hear any noise other than the booster actuating. I don’t think you mentioned if it has leaked between the booster & MC. If you did I missed it.

4 minutes ago, Yarb said:

You shouldn’t hear any noise other than the booster actuating. I don’t think you mentioned if it has leaked between the booster & MC. If you did I missed it.

No leak between the master and the booster. It only seems to be coming down near the areas where the brake lines screw in to the bottom of the master.

I just thought it was odd that the rear reservoir (for the drums) has positive pressure on it when you take the lid off and the one for the calipers opens without a pop of pressure.

Is there a pressure release valve in the reservoir cap that could be blocked forcing brake fluid to be squeezed out of the bottom when the pedal is pressed or something?

Edited 47 minutes ago47 min by chaseincats

46 minutes ago, Zed Head said:

Are you sure that the fluid is not running down the bottom of the MC from a leak inside the bore? Might depend on how the car sits if the bore tilts forward or backward.

It's more likely that your MC seals have blown.

7 minutes ago, Zed Head said:

It's more likely that your MC seals have blown.

I bought a new one which should be here tomorrow(ish). When the master's seals go out, does it take the wheel cylinders out too? It's just odd everything started leaking/misbehaving at once.

It's also possible that the metal to metal seal of the brake line was damaged when you changed the MC the first time. Pretty common for the tube to twist with the fitting when the fitting is loosened.

The only way to be sure is to examine the parts. A magnifying glass and bright lights help. Take a close look and you'll see where the actual sealing surface is. A spec of foreign matter can screw things up. Something to be aware of if you do change the MC. The threads don't do the sealing, they just do the clamping.

You can see the cone that fits inside the end of the tube in this image from Rockauto. That's the sealing surface.

5 minutes ago, Zed Head said:

It's also possible that the metal to metal seal of the brake line was damaged when you changed the MC the first time. Pretty common for the tube to twist with the fitting when the fitting is loosened.

The only way to be sure is to examine the parts. A magnifying glass and bright lights help. Take a close look and you'll see where the actual sealing surface is. A spec of foreign matter can screw things up. Something to be aware of if you do change the MC. The threads don't do the sealing, they just do the clamping.

You can see the cone that fits inside the end of the tube in this image from Rockauto. That's the sealing surface.

Interesting. I'll give it a look when I change it out, but it's odd that it started leaking 6 years after being installed if the connection there was originally poor.

Is the rear reservoir being internally pressurized unlike the front not a concern?