Talk Morgan Forums Morgan Sports Cars Morgan Aero 8, 2012< Plus 8, SuperSports, Coupe & Aeromax ABS Unit problems on 2013 Aero Plus 8

As an adjunct to my earlier (embarrassing) question about retro-fitting ABS to a car that already has it...

I've now found that the rear left brake calliper isn't receiving any brake pressure and if I disconnect the brake line at the ABS unit, it isn't pressurised.

So I'm guessing at a stuck valve within the ABS control unit.

I've tried driving the car and braking hard to get the ABS unit to kick-in - which it does, but this doesn't free the valve.

I've also tried to cycle the ABS unit electronically using a fault reader set to BMW X5 (which reads the ECU) but it tells me that the ABS unit can't be cycled electronically.

Any ideas (other than hit it with a hammer) ?

I'm no expert on ABS, but on conventional systems, the first suspect when there's no fluid pressure on a corner, is the flexible hose. They can delaminate internally and block up.

Suggest farming it out to an ABS specialist for service/repair unless any obvious issue can be found as per Dave's post above.

One such specialist here.

Thanks Dave - have tried back flushing the line and it works well so don't think its a hose but appreciate the advice.

If you want to have a go yourself, perhaps not hitting the ABS module with a hammer , have a look at these BMW specific AI suggestions:

1. Perform a Software-Driven ABS/DSC Bleed.

Trapped air pockets can occasionally lock up the internal valves on BMW DSC systems, especially if the reservoir was allowed to run completely dry during a past service. Standard pressure or vacuum bleeding cannot clear this. Connect a BMW-specific diagnostic tool (such as ISTA/D, INPA, or a high-end bi-directional scan tool like a Foxwell). Navigate to the DSC/ABS service functions and initiate the Brake System Bleeding Procedure. This routine commands the internal ABS pump motor to run and rapidly pulses the solenoid valves, forcing air pockets out into the lines so they can be bled at the wheel.

2. Clear a Stuck Mechanical Solenoid Valve.

If software cycling does not restore fluid flow, an internal valve inside the ABS block is physically stuck closed due to old, contaminated, or moisture-laden brake fluid.

The Tap Method: While an assistant applies steady, firm pressure to the brake pedal, gently tap the metal block of the ABS module with the plastic handle of a screwdriver. The vibration combined with hydraulic pressure can sometimes pop a stuck valve free.

If software actuation and tapping fail to restore output pressure to that single port, the internal mechanical valves of the ABS block are permanently damaged, and the ABS hydraulic assembly must be replaced or sent out for a rebuild.