Technical Air trap above ABS unit

judderbar · Oct 21, 2020

I noticed the highest point of the Punto braking system is the master cyclinder feeds 1 and 2 to the ABS unit, followed by the 4 exits from the ABS unit that go to each wheel.

That must mean that sometimes air will diffuse from the lower master cylinder reservoir to the higher and therefore lower pressure ABS pipes. Yes the pipes are under a huge pressure sometimes. But I am not sure what actually will happen.

I found an informed motor bike thread saying you can remove air by tying down the brake lever overnight. It was suggested this works because the air can escape thru the rubber hoses or connections which allow high pressure air to escape but do not allow liquid to escape.

I was wondering if you could get a harder brake by adding two bleedable valves to the highest point of the system. Or does the clean new hydroscopic fluid tend to dissolve a small amount of air anyway even over a year or more?

On the other hand its something else to go wrong and hardly worth bothering about!

But even so I just ordered a spare master cylinder and ABS unit from the scrap yard to get totally obsessive compulsive about it and see if i can find out if air does migrate there naturally with new fluid.

:idea:

judderbar · Oct 24, 2020

I got the abs and master cylinder unit and now it all looks too complicated for me to want to spend more money to get this connected and whatever mad scientist Ideas I was having have gone away.

At least I have some good spare parts.

judderbar · Oct 27, 2020

My mind is still a bit stuck on this idea.

But I have to confess I probably got side tracked into this thinking by not realising the brake booster naturally makes the brakes appear to pump up firmer as the vacuum power of the booster is consumed by the action of using the brake pedal.

I could be chasing shadows.

I changed over the master cylinder. The new one is like new. I took it apart and it looks as good as new inside and out. Supposedly 6000km from 2006.

But I noticed that some 1996 puntos have a remote brake reservoir so raising the brake reservoir is one possibility. or making the existing master reservoir cap air tight by taking out that white plastic thing inside the cap and then putting a t piece on the clutch master feed and having a higher remote reservoir which are commonly fitted on racing cars where you cannot reach the master cylinder.

At the end of the day I am not even sure any of this thinking is worth what I am doing................but I seem to be realising i am somewhat obsessive compulsive.........:idea:

chris3234 · Oct 27, 2020

The force of the fluid being pushed through the system should easier clear any trapped air in the pipe
If there was issues you'd see a lot of complaint's from people being unable to bleed them

judderbar · Oct 27, 2020

chris3234 said:
The force of the fluid being pushed through the system should easier clear any trapped air in the pipe
If there was issues you'd see a lot of complaint's from people being unable to bleed them

I am thinking what happens after the brakes are perfectly bled and the system is left for a year.

chris3234 · Oct 27, 2020

judderbar said:
I am thinking what happens after the brakes are perfectly bled and the system is left for a year.

And where would this air come from?
For that amount of air to get into the system you'd have to have a fluid leak someplace

judderbar · Oct 27, 2020

chris3234 said:
And where would this air come from?
For that amount of air to get into the system you'd have to have a fluid leak someplace

When you take your foot off the pedal there is an open connection between the outside air and the fluid in the braking system.

When the car is not used, air will travel thru the liquid to the lower pressure areas

https://upload.wikimedia.org/wikipedia/commons/3/38/Master_cylinder_diagram.svg

chris3234 · Oct 27, 2020

judderbar said:
When you take your foot off the pedal there is an open connection between the outside air and the fluid in the braking system.

When the car is not used, air will travel thru the liquid to the lower pressure areas

https://upload.wikimedia.org/wikipedia/commons/3/38/Master_cylinder_diagram.svg

If your system is open to the atmosphere there's something wrong with it

The only place there should be any air is the the is the fluid reservoir
And that's only there to to accommodate the extra fluid needed for when the brake system wears as the system

I'm.unsure why you think air will somehow work its way through the system and settle above the abs system?
When your foot is off the pedal the system isn't open to air? It's still sealed

judderbar · Oct 27, 2020

chris3234 said:
If your system is open to the atmosphere there's something wrong with it

The only place there should be any air is the the is the fluid reservoir
And that's only there to to accommodate the extra fluid needed for when the brake system wears as the system

I'm.unsure why you think air will somehow work its way through the system and settle above the abs system?
When your foot is off the pedal the system isn't open to air? It's still sealed

The cap on the master cylinder keeps the dirt out but is not air tight. With your foot off the pedal the outside air is able to mix with all of the braking fluid in the system.

roverp480 · Oct 27, 2020

I cannot see how "air " will migrate into the system. Some highly mobile constituent atoms of the various gases that make up air may do , but given the low pressure variance over a few cm's I cannot see it being of consequence. Most braking system are open to air and I would think if it were an issue we would know about it. Water is the biggest problem as the standard Dot 4 fluid is hydroscopic and that why its recommended to change every 2 or 3 years.

judderbar · Oct 27, 2020

I better test my theory.

At 20.45 27/10/20 I filled a test tube with braking fluid and it is standing in a cup of fluid. The tube is leaning slightly in the cup to create an opening at the bottom of the tube.

I am supposing:
1. in a few days there is going to be a tiny air bubble at the top of the tube.

2. After a month there will be a cm of air.

chris3234 · Oct 27, 2020

judderbar said:
I better test my theory.

At 20.45 27/10/20 I filled a test tube with braking fluid and it is standing in a cup of fluid. The tube is leaning slightly in the cup to create an opening at the bottom of the tube.

I am supposing:
1. in a few days there is going to be a tiny air bubble at the top of the tube.

2. After a month there will be a cm of air.

This isn't representative of a system in a car
Also there's has not been a single report of this happening on the car if it would happen in a month like you say there would have been thousands of complains of people having spongey brakes and needing the bleed the system all the time and there hasn't been

chris3234 · Oct 27, 2020

judderbar said:
I noticed the highest point of the Punto braking system is the master cyclinder feeds 1 and 2 to the ABS unit, followed by the 4 exits from the ABS unit that go to each wheel.

That must mean that sometimes air will diffuse from the lower master cylinder reservoir to the higher and therefore lower pressure ABS pipes. Yes the pipes are under a huge pressure sometimes. But I am not sure what actually will happen.

I found an informed motor bike thread saying you can remove air by tying down the brake lever overnight. It was suggested this works because the air can escape thru the rubber hoses or connections which allow high pressure air to escape but do not allow liquid to escape.

I was wondering if you could get a harder brake by adding two bleedable valves to the highest point of the system. Or does the clean new hydroscopic fluid tend to dissolve a small amount of air anyway even over a year or more?

On the other hand its something else to go wrong and hardly worth bothering about!

But even so I just ordered a spare master cylinder and ABS unit from the scrap yard to get totally obsessive compulsive about it and see if i can find out if air does migrate there naturally with new fluid.

:idea:

Two more things from your original post
You said the lines going to the brake calipers are the highest point is the system being above the abs unit
That how they are in virtually all abs system not seen one that isn't like this yet

Second you mention the air will escape through the brake hoses?
It won't if sir can pass through the hoses to exit it could also enter the brake system this way so your hoses would let air into the system when your car isn't being used meaning brake would need bleeding all the time

I'd say 99% of car made would need need the brakes bleeding in 20 years of life unless fluid gets changed or callipers/brake lines get changed

judderbar · Oct 27, 2020

chris3234 said:
Two more things from your original post
You said the lines going to the brake calipers are the highest point is the system being above the abs unit
That how they are in virtually all abs system not seen one that isn't like this yet

Second you mention the air will escape through the brake hoses?
It won't if sir can pass through the hoses to exit it could also enter the brake system this way so your hoses would let air into the system when your car isn't being used meaning brake would need bleeding all the time

I'd say 99% of car made would need need the brakes bleeding in 20 years of life unless fluid gets changed or callipers/brake lines get changed

Air will pass in both directions through an air permeable brake hose. The hoses are at the higher pressure end of the system. More air will pass from a hose at higher pressure than the surrounding air, than air at lower pressure entering the high pressure hose. The air permeability works in the direction of correction rather than worsening

It still seems a worthwhile question to me. Do you get a harder pedal if the master cylinder is at the highest point?

judderbar · Oct 18, 2021

just top close this thread off. After 3 months I did not get the tiniest amount of air appearing in the upturned test tube full of brake fluid.

So my idea is totally busted. Just as others thought it would be.

GrandePunto PL · Oct 24, 2021

1. There is something wrong with the education system in your country. Basics of physics, mechanics, hydraulics. Too much things to debunk...

2. If you are not using the car for 1 year it is considered "car abuse" (just like child abuse - someone should take it from you). There will be a problems with the car (with brakes too, possibly - but not for reasons you've made up).

PS
Moderators: move this thread to the spam section.

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