Old Sprinter brake failure

Headintheclouds

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My 2006 Sprinter suffered brake failure whilst in France with brake pedal hitting the floor. Taken in to main dealer who diagnosed dud master cylinder and replaced with new.

It was ok for journey back but the next driver reported that pedal had excessive travel as he arrived in the yard. I went to check and the brake pedal went straight to the floor. Brakes were bled and lots of air came out of rear right. Since bleed nipple flats had been rounded off by French dealer we assumed it had not been fully tightened and had admitted air. System bled fully and seemed ok.

All well for another couple of hundred miles and I suffered pedal to the floor yet again. Once again, lots of air in rear right. No messing this time. New callipers all round as now 13 years old.

Another 150 miles or so and it's happened yet again. I'm now replacing both pipes and the load valve which are the only things on that corner that haven't been replaced.

Anyone else come across anything similar?
 

toolman1954

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Hi,
I have a really old Sprinter, yours is still a spring chicken compared to mine.
Anyway, if you are still getting air into the system, you need to trace its point of entry.
Do you have a pressure bleeding kit, such as a Gunsons et al? an invaluable tool for finding leaks. I note that the French garage replaced "Le maître cylindre", did they bleed this out? Of course you will not know what they did.
With the pressure bleeder attached, just slowly release the union nut on the master cylinder a smidgen until fluid flows out, see if any air comes out. Then go down the line, ABS unit, fronts, limiter valve and the rears. There is a proper sequence, for this , which I cannot remember, look it up on the net. Keep your eye on the fluid, you don't want to run out.
I have in the past left the pressure bleeder connected up overnight on a vehicle, just to try to encourage any resilient air bubbles to shift from where they are hiding.
Leaving the pressure bleeder on, will also put presure on the Master Cylinder seals, so put your hand down where the brake pedal joins onto the MC to see if there is any leakage or anything leaking out of the Master Cylinder or the Servo. Do not rule out a faulty master cylinder. Similarly, you can jam the brake pedal on with a piece of wood and leave it like that overnight. Advanced testing involves clamping off each flexible hose, which if you have not already renewed is a good candidate for having tiny holes in the rubber and they are not expensive.
I hope you get it sorted .

Steve.
The only other comment I would make is to ensure you have plenty of meat on your brake pads
 
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Headintheclouds

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Thanks, Steve.

On all occasions the system has bled out fine and worked as well as the dodgy Sprinter brakes ever do. The ingress of air has been alarmingly sudden in every case and after each near miss it has been the right rear that has bled out a load of air. Were the master cylinder the culprit I would have thought I would get plenty of bubble free fluid out of the rear before air was seen.

My guess is that it will turn out to be the load sensing valve or its pipework. If there is nothing obvious when the old unit is removed I have been thinking about purging all fluid and pumping the system up with an Easy Bleed and looking for a small air leak. However, since the vehicle would go happily for a few hundred miles and suddenly gulp air, even that might not reveal anything. Perhaps the air only came in when the load sensing valve was at a particular point in its travel.

Please point out any faults in my logic. I have been really lucky to avoid very serious consequences and absolutely cannot risk any chance that it happens again.
The vehicle now has new master cylinder, callipers, flexible hoses, rigid pipes on the rear right and about to have a new load sensing valve. I think that covers everything perishable doesn't it?
 

Bellow

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Air will find its way where fluid wont (re leak checking).
 
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Headintheclouds

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It looks as though the problem was due to the ABS pump seals letting in air. I had forgotten about this thread so details in a new one.
 

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