Apply pressure to brake pedal = no fluid lost on disconnect?

[_Mja_]

Hi,
I saw this technique whilst watching a YouTube video but can't figure out why brake fluid wouldn't squirt everywhere -

If you use a brake press tool to put pressure on the brake pedal and disconnect a brake connection you'll not loose any fluid or let air enter the system.

This sounds great but I just get how it works. Id have expected fluid to squirt everywhere.

Could someone explain it to me?

Cheers
Matt

[E-bmw]

Perhaps put a link to the video up as I can't actually really understand what you mean.

[Chris32345]

I don't see how it would work

If you out any pressure on the brake pedal it should force fluid through the system because that's how it works

Hence how you can press the pedal with a nipple open to bleed the system

[steveo3002]

with the pedal depressed the plunger/piston in the mc is in a place where its not allowing flow so the system doesnt drain

some fluid will escape

[_Mja_]

Cheers. I can't find the the link now. It was a chap doing the rear brakes on the car, he put a contraption on the brake pedal and disconnected the brake pipes and nothing really came out. I was impressed and thought it would save a job of full brake bleeding however in my head I thought squeezing the pedal would send fluid in the direction of the caliper.

I'm looking for a way that I could disconnect a brake pipe connector to flexi to do a rust repair around a bracket where the pipe comes through the engine bay to the front arch. Ideally i don't want to loose a load of fluid and leave it disconnected for a day or more whilst i repair.

[steveo3002]

ive made up a selection of male/female blanks for such jobs ...if you will be left with a male end sometimes a bleed nipple rubber cover will pop on a seal it while you mess around

or old flexi hole with vice grips on to seal it ?

[_Mja_]

Cheers Steveo. Yes this is the first time I'll be messing in an area like this. I do have a sealey pressure bleeder if all else fails but I've got a lot of jobs to do on the car and wanted to make it as simple as possible so i finish a job and move on to the next.

Perhaps making up some male/female ends is the answer - dumb quesiton time - which do i need for this job in the pic?

I need to disconnect the flexi so i can weld a repair. It's gone rotten around where the grommet used to be.

[stevieturbo]

_Mja_ said:

Hi,
I saw this technique whilst watching a YouTube video but can't figure out why brake fluid wouldn't squirt everywhere -

If you use a brake press tool to put pressure on the brake pedal and disconnect a brake connection you'll not loose any fluid or let air enter the system.

This sounds great but I just get how it works. Id have expected fluid to squirt everywhere.

Could someone explain it to me?

Cheers
Matt

It will eject some fluid.

And presumably what you're trying to describe and understand is holding your finger over the end of a straw with fluid in it...it does not leak out.

[Yogioes]

My understanding ....
It's a fluid so does not compress.
When you press the pedal down and hold it in that position and then open the system at one corner you will release the fluid pressure.
However it is not like a compressed air situation where the air will expand as it is released.

The benefit of doing this is that the master cylinder piston has moved past the fluid inlet port. If it is held there then no more fluid can enter the pipes to drain away.

I wish I had known this when I replaced some pipes on an old Corolla. I think I had drained the ABS unit as the brake pedal never felt as good as it did before I worked on it.

I'm curious to see how you sort this one.
I assume you wish to disconnect the joint to do the welding repair behind it.
Just a word of caution, it looks like the hard pipe has already been replaced, perhaps with copper?
While copper is easy to work with I find that it doesn't cope too well with too much bending.

Edited by Yogioes on Monday 22 March 20:58

[steveo3002]

you would want a female blank for that ..or pop a bleed nipple cap on it

i wouldnt over think it ...you will drop some fluid and have to bleed it anyway whatever you do

[_Mja_]

Cheers. Im defo overthinking. Will just disconnect it a crack on.

[_Mja_]

Well it only bloody worked! Litreally 2 drops lost when i disconneted the flexi.