Brake bleeding not working - Page 3

SD1too · 24th October 2016, 12:41

Quote:

Originally Posted by eric27

... when you disconnect the battery before you start bleeding the brake systeem the internal valves are then open and there is no power to the abs module to close the valves.

Hello Eric,

Why do you think that the valves close when a power supply is applied to the module? Think about how the anti-lock braking system works. The hydraulic pressure to a wheel is only cut by closing a valve when a locked wheel is detected via the sensor.

I don't see the need to disconnect the battery prior to bleeding. Why do you do that Eric?

Simon

klarzy · 24th October 2016, 16:06

does not the valve chatter to temporarily release the pressure in the line back to the reservoir??

eric27 · 24th October 2016, 16:08

Quote:

Originally Posted by SD1too

Hello Eric,

Why do you think that the valves close when a power supply is applied to the module? Think about how the anti-lock braking system works. The hydraulic pressure to a wheel is only cut by closing a valve when a locked wheel is detected via the sensor.

I don't see the need to disconnect the battery prior to bleeding. Why do you do that Eric?

Simon

Yes I know what you mean but why are there some cars where the internal valves are closed when you will bleed the brake system after a brake hose or pipes change?
If you have a working well brake system the internal valves are open and when you then disconnect the battery the ABS system cannot closed the valves. (power off)
Renew the brake hose or pipes than bleed the system all the internal valves must be open. Then connect the battery.

Thats how I think about it or I am wrong?

Eric.

David Lawrence · 24th October 2016, 16:22

If the valves default to closed then surely if you suffered engine failure your brakes would fail? Doesnt the T4 procedure merely assist the process by operating the pump rather than simply opening valves? So it helps the process when used but is not essential.

SD1too · 24th October 2016, 18:35

Quote:

Originally Posted by eric27

... why are there some cars where the internal valves are closed when you will bleed the brake system after a brake hose or pipes change?

Are there? Who says so, and what is their evidence?

Quote:

... when you then disconnect the battery ...
Thats how I think about it or I am wrong?

I still would like to know why you disconnect the battery Eric.

It's not specified in RAVE and T4 isn't mentioned either.

Simon

chris75 · 24th October 2016, 18:59

Quote:

Originally Posted by Chuckles

I have two manuals and one does mention they are a sealed unit; how stupid is that?

This only refers to the rubber diaphragm (or "condom" ) under the cap in the master cylinder , which prevents moisture getting into the fluid . It is instantly removable , as you will know from topping up the cylinder

24th October 2016, 16:06	#22
klarzy This is my second home none but not gone Join Date: Mar 2013 Location: March, Cambs Posts: 16,437 Thanks: 894 Thanked 4,247 Times in 3,025 Posts	does not the valve chatter to temporarily release the pressure in the line back to the reservoir?? __________________ [SIGPIC][/SIGPIC]….All praise Bananaswan….

24th October 2016, 16:22	#24
David Lawrence This is my second home Rover 75 CDT-2001 Join Date: Jan 2009 Location: Wrexham, North Wales Posts: 3,606 Thanks: 195 Thanked 606 Times in 501 Posts	If the valves default to closed then surely if you suffered engine failure your brakes would fail? Doesnt the T4 procedure merely assist the process by operating the pump rather than simply opening valves? So it helps the process when used but is not essential.