24/05/2025
I went out to this car last night for front pads and disks and two new front brake callipers and issue wasnt rectified, diagnosed as the abs valve block (they have shuttle valves in the aluminium ports inside the block that corrode over time and get stuck - steel shuttle valve that runs in an aluminium cylinder, NSF brake line port was blocked by the shuttle).
ABS pump on an Astra - valve block had a sticking pin for NSF calliper, pulling to the right upon breaking, fitted new callipers, no brake fluid in nsf brake flexi line, traced back to ABS valve block. Bleed lines at the valve block first - starting with feed, return, then Nsr, osr, Nsr and then osf. Then bleed all 4 callipers in the same sequence.
Break down of the cause of this failure;
• poor servicing, brake fluid is hydrophilic (hygroscopic), meaning it absorbs moisture (moisture is always present in the air, by not flushing brake fluid readily, you will accumulate moisture in your hydraulic braking circuit, causing corrosion and damages internally…
• the abs (anti-lock-braking) module was impacted in this instance, the valve block has steel shuttles (like small bullets/pins) that travel in aluminium channels, solenoids in the module control these shuttles, causing them to open and close ports to affiliated brake circuits very quickly (depending on wheel speed sensor feed back to the abs module)
• now, in this instance, internal corrosion caused one of the shuttles/pins to become stuck in its channel blocking the port to the nsf brake line
