I have a front wheel with the brakes stuck on almost permanently. Obviously there is pressure in the brake line to this wheel only which does not go away when the brake pedal is not engaged. I have pulled the whole left hand front brake system apart and there are no mechanical problems. I have bled the entire system with new brake fluid. I pulled the pistons out of the calipers and all looks good. The brakes are actually made by Brembo and rebadged by Alfa. I suspect that there is some sort of fluid return valve in the ABS unit which is sticking and results in pressure not bleeding back into the system for that wheel. Apparently the ABS unit is non-servicable and they cost around $3,000 AUS which is a lot of money if I am not 100% sure that this is the cause of the problem. The ABS unit is a Bosch 5.1. Can anyone help? Thanks Paul

Paul Garratt, April 2007

Hi,
I was in this web site the other day (BBA-Reman.com) and you may find this helpful.

Other factors can cause ABS problems. Be sure to check these before purchasing a new system
1. Incorrect Jump Starting. If one incorrectly reverses the connections (even momentarily), a relay or the main controller may get burnt out.
2. Different tyre or wheel sizes will confuse the controller and may give a speed comparison alarm
3. ABS Wheel sensors do fail. Check resistances to specifications.
4. ABS Sensor Lead Faults
5. Sender rotor is cracked or warped
6. Wheel bearing wear that can cause gap between sensor and rotor to vary

How ABS Works
The three parts of any ABS system, whether combined or separate, are very similar to the human body. The brain or the controller monitors external sensors for wheel lock. The modulator acts as the muscles of the system, controlling the braking force on each wheel by venting pressure using solenoids. If the pressure eventually becomes too low under ABS conditions the heart of the system, the pump, starts to drain the vented fluid from expansion chambers in the modulator back in to the system to maintain correct pressure. All the driver experiences is a slight vibration of the pedal, as this cycle happens many times a second.

Cheers now

Ken Chapman, April 2007

Paul,

My only experiences with stuck front brakes were GM products, but perhaps this will help.

The flexible brake line going to each caliper over time tends to develop defects inside which act like a one-way valve..like the ones in your veins, preventing the pressure from being released and allowing only braking and bleeding direction of fluids. With the GM vehicles, the brake would lock temporarily, then slowly release until you hit the brake pedal again. Then the process would repeat.

I don't know if this will help, but a brake line is going to cost a lot less than the $3K.

Geno M., April 2007