When does the wheel lock? As soon as you start braking, when you have nearly stopped?
Does it do it every time?
Have you removes the pads and checked that the caliper does slide easily and over all its movement? Are the pads free to move in the caliper?
The flexible brake hose may be internally damaged and stopping the fluid pressure dropping off.
The master cylinder may have a fault on the relevant circuit.
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When does the wheel lock? As soon as you start braking, when you have nearly stopped?
Q>> It seems to do it mainly when you have nearly stopped. It only happens on N/S front. I checked the tyre pressures this morning. All are OK at 2.2 bar.
Does it do it every time?
Q>> No only some of the time and only when braking quite hard.
Have you removes the pads and checked that the caliper does slide easily and over all its movement? Are the pads free to move in the caliper?
Q>> No I have not done this yet. I guess this is a job for the weekend!
The flexible brake hose may be internally damaged and stopping the fluid pressure dropping off. The master cylinder may have a fault on the relevant circuit.
Q>> I guess I will come to this if new pads and a clean do not resolve the problem.
Thanks for your input. I will let you know what I find.
Q.
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There's also the possibility that the rear bush on the suspension wishbone is worn, so check this. I had exactly the same symptom on a secondhand Peugeot 306. This would repeatedly lock up the n/s wheel on heavy braking.
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Swap your front wheels,side for side and see if the lock-up changes sides.
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Having had the same problem on an old Fiesta I would suggest a faulty brake hose is 60% likely...
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OK here is an update.
Replaced front pads and brakes seem much better. The old pads still had around 4mm left so worn but not too bad. I also rotated the tyres so the best are now on the front and the cheap China make is now on the rear.
However, when testing the brakes I had the same symptoms as before. This only happened once in around 100 brake applications. The pedal would go down a long way and the brakes did not work very well. N/S wheel locked up and the car slowed gradually. If I pump the brakes they work as normal. There are no leaks and I have not been loosing fluid.
Two thoughts spring to mind.
1. Problem with the split circuit on the Master Cylinder which has an intermittent fault on one circuit?
2. There may be a problem with the pressure limiting valve on one of the rear cylinders?
This is a 3 door AX and has special pressure limiting wheel cylinders on the rear wheels. There does not seem to be a problem with these cylinders but you never know? The servo seems to be OK as well.
Anybody got any good pointers? Am I on the right track to resolve the problem?
All inputs gratefully received!
Q.
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I did not notice any problem with the brake hoses. Looked at them under pressure; there was no apparent bulges.
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If the pedal is travelling further than usual then yes I would suspect the master cylinder. Get a new one.
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Internal brake hose collapse has NO external symptons...
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Worth checking the automatic adjusters in the rear drum brakes.
Suppose the auto adjuster in the N/S rear brake has failed. This means that the shoes are too far away from the drum. When you brake, this gap has to be taken up. It makes the N/S rear brake, and O/S front brake less effective. (Because they are linked hydraulically).
Result is excessive brake pedal travel, and N/S front wheel locks up under heavy braking or in the wet.
This is more or less what happened to my wife's Citroen ZX, which shares many of the braking components with the AX.
If not this, chances are sticking front caliper, or flexible hoses which are failing internally.
My wife found out about the braking problems, when it went for the MOT, and it got three fail items for the brakes, all marked *** DANGEROUS ***.
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I did think about this as a potential cause of the problem. Why would it only happen occasionally if the adjuster had failed? Surely it would be like this all the time?
There are no sticking calipers, (changed the pads this morning and everything was OK).
I guess I will take off the rear drums next week and see what trouble lies inside!!
If there is no fault there i think it will be a master cylinder fault, (I am thinking that this is the problem already but hoping for an easier, (and less expensive) fix).
Thanks for your thoughts.
Q.
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