Bleeding 90 C4 brakes and diff locks
09-11-2004, 02:57 AM
#1
Racer
Thread Starter
Bleeding 90 C4 brakes and diff locks
Advice needed,
Big service coming up - parts all ordered from Pelican - garage cleaned etc'.
I will have a Motiv brake pressure bleeder so I expect to be able to change fluid in the brakes - I have read the previous posts and Adrians book.
BUT... how can I bleed the two diff lock servo's at home without a hammer?
My thoughts are as follows...
Looking at the layout of the system I believe the following points are true:
1 - the ABS pump pressurises the system.
2 - the wheel speed sensors and the movement sensors (located inside in front of the gearstick) tell the computer when to open the solenoids to lock the two diffs.
3 - the hammer simply opens the two solenoids and then starts the ABS pump allowing the two servos to be bled.
4 - following bleeding the hammer closes the servos and opens some other fluid pathway to depressurise the system.
Given the above 1 - 4 (and I hope they are true) is it possible to "home bleed" the locks by the following procedure:
A - disconnect battery.
B - install Motiv brake bleeder to pressurise the whole fluid system through the reservoir.
C - disconnect the wires to the solenoids.
D - use 12volts through a jumper wire to open the solenoids.
E - open the servo bleed nipples and bleed the system.
Have I missed something?
Thanks for the thoughts of those who are more familiar with the sysyen than I am.
Regards,
Michael Gibney
Big service coming up - parts all ordered from Pelican - garage cleaned etc'.
I will have a Motiv brake pressure bleeder so I expect to be able to change fluid in the brakes - I have read the previous posts and Adrians book.
BUT... how can I bleed the two diff lock servo's at home without a hammer?
My thoughts are as follows...
Looking at the layout of the system I believe the following points are true:
1 - the ABS pump pressurises the system.
2 - the wheel speed sensors and the movement sensors (located inside in front of the gearstick) tell the computer when to open the solenoids to lock the two diffs.
3 - the hammer simply opens the two solenoids and then starts the ABS pump allowing the two servos to be bled.
4 - following bleeding the hammer closes the servos and opens some other fluid pathway to depressurise the system.
Given the above 1 - 4 (and I hope they are true) is it possible to "home bleed" the locks by the following procedure:
A - disconnect battery.
B - install Motiv brake bleeder to pressurise the whole fluid system through the reservoir.
C - disconnect the wires to the solenoids.
D - use 12volts through a jumper wire to open the solenoids.
E - open the servo bleed nipples and bleed the system.
Have I missed something?
Thanks for the thoughts of those who are more familiar with the sysyen than I am.
Regards,
Michael Gibney
09-11-2004, 05:19 AM
#2
RL Community Team
Rennlist Member
Rennlist Member
About your mentioned points:
#1 - it's a hydraulic pump separate of the ABS circuit that pressurizes the system.
#2 - the computer tells the solenoids to function based on the sensor input in certain conditions
#3- the hydraulic pump is activated when the pressure drops to a certain level - no Hammer control of the pump is available - it's not controlled by any means other than the pressure; the Hammer tells the PDAS computer/controller to first pressurize the lock circuit, then pulse the solenoid to bleed the locks
The Motiv bleeder will not come close to providing the pressure used by the PDAS system. It's un-necessary to use the Motiv bleeder since the pressure applied will not be "felt" by the PDAS system - to pressurize it, just turn on the ignition to activate the hydraulic pump.
There is a post somewhere about doing a lock bleed without a Hammer. You could probably do it in a much safer manner than you suggest by simply turning on the ignition, loosening the bleeder screw, turning on the PDAS switch to activate the locks - this will express fluid if the bleeder is open. Now, if this introduces more air into the system... don't know - would not do it on my own car. Plus, I don't know how much pressure is applied when this occurs - you might be in for a big surprise. The Hammer may pulse the solenoids with a much lower pressure which keeps this a SAFE procedure.
My advice - get/borrow/rent/purchase/steal a hammer. Less risk, and it's satisfying knowing you did it correctly.
If you decide to do it without a Hammer, I am curious how much pressure the lines are under when you turn that bleeder screw! Wear eye goggles!
#1 - it's a hydraulic pump separate of the ABS circuit that pressurizes the system.
#2 - the computer tells the solenoids to function based on the sensor input in certain conditions
#3- the hydraulic pump is activated when the pressure drops to a certain level - no Hammer control of the pump is available - it's not controlled by any means other than the pressure; the Hammer tells the PDAS computer/controller to first pressurize the lock circuit, then pulse the solenoid to bleed the locks
The Motiv bleeder will not come close to providing the pressure used by the PDAS system. It's un-necessary to use the Motiv bleeder since the pressure applied will not be "felt" by the PDAS system - to pressurize it, just turn on the ignition to activate the hydraulic pump.
There is a post somewhere about doing a lock bleed without a Hammer. You could probably do it in a much safer manner than you suggest by simply turning on the ignition, loosening the bleeder screw, turning on the PDAS switch to activate the locks - this will express fluid if the bleeder is open. Now, if this introduces more air into the system... don't know - would not do it on my own car. Plus, I don't know how much pressure is applied when this occurs - you might be in for a big surprise. The Hammer may pulse the solenoids with a much lower pressure which keeps this a SAFE procedure.
My advice - get/borrow/rent/purchase/steal a hammer. Less risk, and it's satisfying knowing you did it correctly.
If you decide to do it without a Hammer, I am curious how much pressure the lines are under when you turn that bleeder screw! Wear eye goggles!
