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[chrisgixer]

. I was driving and when I pressed the brake nothing happened, pedal straight to the floor. Second, panicked, press had them working fine. I got home and went to find the cause only to find one of the front pads had gone. Pad material had separated and vacated the car.
 

I had the very same thing happen on the wife's Golf, luckily it was me driving and I was going slow....foot to the floor and lights flashing on the dash, I grabbed the handbrake and pumped the pedal and suddenly all was normal. Drove a bit further (as I was on dual carriageway) and on next application heard the sound of metal on metal. Drove home cautiously and when I looked at the pad ALL the friction material had gone from one side.

Looking on the internet it seems it is not that uncommon an occurrence nowadays!!

Nice!!!

Hmmm. That would seem to add up. Bit like the first press of the pedal after they've been worked on, after a pad change or whatever, as the pistons are pushed back to get the pads out and new ones in. First thing you do on an auto is press the brake pedal to turn the key and engage gear etc. So your guaranteed to do the safety check of pressing the brakes after a brake service etc.
 Not the case on a manual as the first thing you habitually do is press the clutch, most likely.

On bikes there's a couple of instances that spring to mind from this. One is a tank slapper. Usually on track, if the rider slides the rear and has a moment, as the rear snaps back into line its said it can shake the handle bars so violently the forks can flex or twist in a torsion motion. That puts pressure on the brake pads as discs move off centre in the caliper, which pushes the pads back in the caliper.
 If the rider stays on, he then arrives at the next corner and runs on, because theres no brakes. He pumps the lever and gets brakes on the second press., as the pistons are pushed out to the disc again. But too late to make the corner.

The other instance is a recall on the Yamaha R1. First model. Due to an issue with the pad material not binding correctly to the metal backing.

So for the op, check your pads. Although surely there would be an audible grinding of pad metal on disc?

[chrisgixer]

What turns the seals over is pushing the caliper pistons back without opening the bleed valve first.....

Hi Alan.
Can you explain where these seals are and how they get turned over? I can't think where that could happen in the master cylinder?
I appreciate its better to push the old fluid through by releasing the bleed nipple, when pushing the pads back, but by nature, a brake system has to allow its hydraulics to move both ways at some point.

[al brown]

. I was driving and when I pressed the brake nothing happened, pedal straight to the floor. Second, panicked, press had them working fine. I got home and went to find the cause only to find one of the front pads had gone. Pad material had separated and vacated the car.
 

I had the very same thing happen on the wife's Golf, luckily it was me driving and I was going slow....foot to the floor and lights flashing on the dash, I grabbed the handbrake and pumped the pedal and suddenly all was normal. Drove a bit further (as I was on dual carriageway) and on next application heard the sound of metal on metal. Drove home cautiously and when I looked at the pad ALL the friction material had gone from one side.

Looking on the internet it seems it is not that uncommon an occurrence nowadays!!

Nice!!!

Hmmm. That would seem to add up. Bit like the first press of the pedal after they've been worked on, after a pad change or whatever, as the pistons are pushed back to get the pads out and new ones in. First thing you do on an auto is press the brake pedal to turn the key and engage gear etc. So your guaranteed to do the safety check of pressing the brakes after a brake service etc.
 Not the case on a manual as the first thing you habitually do is press the clutch, most likely.

On bikes there's a couple of instances that spring to mind from this. One is a tank slapper. Usually on track, if the rider slides the rear and has a moment, as the rear snaps back into line its said it can shake the handle bars so violently the forks can flex or twist in a torsion motion. That puts pressure on the brake pads as discs move off centre in the caliper, which pushes the pads back in the caliper.
 If the rider stays on, he then arrives at the next corner and runs on, because theres no brakes. He pumps the lever and gets brakes on the second press., as the pistons are pushed out to the disc again. But too late to make the corner.

The other instance is a recall on the Yamaha R1. First model. Due to an issue with the pad material not binding correctly to the metal backing.

Although surely there would be an audible grinding of pad metal on disc?
[/quote]

Didn't on mine, there was some material left on the back plate, not much, but enough to stop metal on metal contact. As it was only one pad I couldn't say I really noticed much difference in breaking, although I did drive it gently home after that and didn't really use the brakes until I found our what had happened. The pedal going straight to the floor at 60mph had me not trusting them much.

[alank46]

You have missed the point of my comment which was the falsehood that changing the rear brake hoses at the same time as the fronts would somehow be detrimental to the master cylinder.  Absolute tosh.

I agree that pushing fluid back through the master cyl is highly unlikely to flip the seals, but it is very slightly more plausible than changing brake hoses causing it.

The main reason for not pushing fluid back through the system is to reduce the possibliity of contaminated fluid being intoduced to the ABS block, but I'm sure you knew that.

What turns the seals over is pushing the caliper pistons back without opening the bleed valve first.....

Hi Alan.
Can you explain where these seals are and how they get turned over? I can't think where that could happen in the master cylinder?
I appreciate its better to push the old fluid through by releasing the bleed nipple, when pushing the pads back, but by nature, a brake system has to allow its hydraulics to move both ways at some point.

[dejbear]

Did you disconnect the pipes and not bleed them properly? could you have possibly flipped the master cylinder seals when pushing the pistons back in, often heard of it but took it as an urban myth as i've never come across it actually happening

Not urban myth but only delco master cylinders usually only on early mk3 Astra's.

[chrisgixer]

You have missed the point of my comment which was the falsehood that changing the rear brake hoses at the same time as the fronts would somehow be detrimental to the master cylinder.  Absolute tosh.

I agree that pushing fluid back through the master cyl is highly unlikely to flip the seals, but it is very slightly more plausible than changing brake hoses causing it.

The main reason for not pushing fluid back through the system is to reduce the possibliity of contaminated fluid being intoduced to the ABS block, but I'm sure you knew that.

What turns the seals over is pushing the caliper pistons back without opening the bleed valve first.....

Hi Alan.
Can you explain where these seals are and how they get turned over? I can't think where that could happen in the master cylinder?
I appreciate its better to push the old fluid through by releasing the bleed nipple, when pushing the pads back, but by nature, a brake system has to allow its hydraulics to move both ways at some point.

Fully understood. But, seeing as other members have now come up with a viable reason for the fault, I'd like to go slightly off topic and persue what I personally believe to be another oof myth re flipping seals. It might be applicable to other models, I wouldn't know. But has anyone seen a shred of evidence the flipping seals applies to the omega?

[Marks DTM Calib]

I have seen the seals flip on pretty much all types of master cylinder.

If  you look at the seal shape and consider the fluid being forced the wrong way, then you can understand how it can happen.

The old mallet job can fix this in most cases.