bleeding our brakes

[MFrunkerOG]

I've never seen that with a pressure system unless you were using too high of a psi when pumping it up. It happens to me every time because I prefer using a vacuum pump.

When doing mine the other day, I went through 2L, which is too much, but wanted to make sure that trash fluid was 100% gone.

Did you do braided lines, or just a fluid change? You may want to grab one of those master cylinder braces as well. It gets rid of that initial pedal slop and bites as soon as you touch it.

Yep have the MPP cylinder brace as well. Yes I went with UP braided lines.

As for using too high pressure, I was using 15psi. But I have a feeling that the reason it only happens on the rears is because the pressure actually reduces in the lines due to line resistance.

It’s sort of like a beer line calculation (those who homebrew and keg know). A 1/4” steel beer line has an active line resistance of 1.2lbs per foot. That means if you apply 1.2psi at the inlet of a 1ft pipe of 1/4” diameter, the line resistance will cause 0psi at the outlet. Fluid will still flow, but at no pressure.

Now while replacing the car’s brake lines with the braided ones, I saw the feeder steel lines being much much smaller in diameter - almost 1/8”. I suspect the line length of the feeder lines at the farthest corner (rears) is probably a good 8 feet of line. The line resistance is also exponential with decreasing diameter - i suspect at least 3lbs per ft. So 24psi is the loss on the farthest corner. Neglect the 1psi of pressure added due to gravity for this explanation.

So essentially, bleeding at anything less than 24psi on the farthest corner from the reservoir means a Venturi effect is going to happen as there is no positive pressure left at the bleed valve.

I think this is why Tesla recommends 30spi on the bleeder pressure as you need to overcome that line resistance on the farthest corner, and still have a few psi at the bleeder valve.

 

[MFrunkerOG]

I was looking at stahlbus bleeder valves to make brake bleeding a snap without introducing any air (Venturi effect or pedal induced).

Stahlbus doesn’t have the dimensions for the new 2021+ model S bleeder valves.

Anybody here know this?

 

[Cal1]

I didn't see why you are bleeding. How many miles?

 

[Sam1]

I was looking at stahlbus bleeder valves to make brake bleeding a snap without introducing any air (Venturi effect or pedal induced).

Stahlbus doesn’t have the dimensions for the new 2021+ model S bleeder valves.

Anybody here know this?

Honestly that's a bit overkill unless you're doing regular track days and exhausting the fluid. It only takes a few minutes to hook up a pressure or vacuum bleeder.

 

[NarTaX]

Just replaced my brake lines with stainless steel ones. Then used a motive bleeder (pressure, not vacuum).

The rear brakes were doing tiny bubbles unendingly! I must have cycled 4L of brake fluid total through just the rears. What the heck!

Then I pumped the brake pedal 3-4 times per corner - no bubbles for 20 seconds, then back! WTF!

How did you resolve this? Were you able to rebleed the rears properly at 30psi?

 

[MFrunkerOG]

Yes, worked just fine at close to 30psi

 

[Mash]

I wonder why service manual doesnt call for reverse bleeding? Pushing fluid through the bleeding valve up to master cylinder. It has a few advantages:
1. ABS pump air goes out easier.
2. Guaranteed fresh fluid in the caliper without any mix.
3. 3x lower pressure
4. Easier to connect and run - no long tubes with tons of fluid inside.

Any ideas?

 

[SteelClouds]

If I recall, ABS systems have check valves or solenoids that would prevent that. Not to mention many seals in brake systems are flanged so when you apply pressure, the flange is pressed against the housing it’s in. Reversed pressure would force pressure past that flange and ruin the seal in all likelihood

 

[Mash]

If I recall, ABS systems have check valves or solenoids that would prevent that. Not to mention many seals in brake systems are flanged so when you apply pressure, the flange is pressed against the housing it’s in. Reversed pressure would force pressure past that flange and ruin the seal in all likelihood

Right, bad idea. Plus I don't see how to avoid air introduction into the line this way when you connect the tube.

 

[fholbert]

Right, bad idea. Plus I don't see how to avoid air introduction into the line this way when you connect the tube.

I've never bled Tesla brakes, but bleeding from the bottom up usually works best. The air in the system is trying to go up and if you're bleeding from the top down you are fighting the bubbles. Bleeding from the bottom up pushes bubbles they way they want to go and it's a one man job.

 

[Sam1]

I've never bled Tesla brakes, but bleeding from the bottom up usually works best. The air in the system is trying to go up and if you're bleeding from the top down you are fighting the bubbles. Bleeding from the bottom up pushes bubbles they way they want to go and it's a one man job.

That's why I always vacuum bleed.

 

[SteelClouds]

The service manual calls out pressure bleeding which is what I do

 

[bkcyk]

Is the brake bleeding procedure for the track pack brakes documented anywhere that end users can access?

 

[Mash]

I've never bled Tesla brakes, but bleeding from the bottom up usually works best. The air in the system is trying to go up and if you're bleeding from the top down you are fighting the bubbles. Bleeding from the bottom up pushes bubbles they way they want to go and it's a one man job.

I thought so for a second and then remembered that:

A. Bubbles appear at the caliper and bleeding them up is impossible. Only the total flush and throwing away totally healthy fluid.

B. Brake lines are very narrow - surface tension completely overpowers gravity in such tight space and now you have a much longer road pushing bubbles up.

Tesla said don't do it. They know details which we don't know.