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[chrisgixer]

Following another thread.

There's a story that says, don't push the brake caliper piston back in without opening the bleed nipple, or this will cause the seals in the master cylinder to "flip" or get damaged when the fluid is forced back up to the master cylinder, instead of out if the bleed nipple.

I believe this to be a myth. Certainly on the omega.


I'm not talking about the rights and wrongs of how to bleed brakes. Opening the bleed nipple when pushing the pistons back all makes perfect sense, to clear the old fluid that cops the most heat around the pistons in the caliper.


But I've never had a problem pushing the pistons in so the fluid is forced back to the reservoir. Not any of my bikes, and not on any of my cars. 3 of which have been omegas that I would say that I owned as day to day cars. I've had two others that where not daily drivers.

Question is, have you?
Have you ever seen or witnessed flipped or damaged seals in a master cylinder? And if so was it on an omega.

I say, MYTH.

[Temetsy]

Did that whit a Primera, an 626, Omega, Carlton, and tons of friends cars i've done any repairing that needed to remove caliper/s and none have complained nor have i broken my own car that way. Guess you just need to have a seal old enough to do the trick

[Seth]

Only had the seals invert on our old Astra 1.7TD van.

For a day or two after, there'd seemingly be more pedal travel than usual.
Gradually, the pedal travel improved to 'normal' I put the condition down to weak seals

Never experienced this problem on any of the three Omegas that we've owned!

[05omegav6]

Might be that vehicles without abs are more susceptible to it, therefore older vehicles suffer from it whereas newer don't 

[Ever Ready]

Never seen it myself and I have pushed back a few caliper pistons.

[4x4]

Never had that problem either.....

[Weds]

I've never opened the bleed nipple when changing pads on any of the numerous cars I've owned.. And so far never had a problem with inverting the seals..

[plym ian]

All I read in this thread was inverted and nipples

God I love school boy humour

But seriously no I have never had inverted seal on any of my cars that I've done brakes on

[chrisgixer]

Ah. Inverted is differant to flipping. Maybe its a description thing.

It's not actually possible to flip a seal surely? I have not seen every design of master cylinder, obviously, but the ones I have seen have an o ring set into a piston, or fit into a grove in a bore the piston sits in.

To me, flipping implies turned over like tossing a coin. That's not possible.

But a profiled o ring or seal could turn inside out....?

[Magwheels]

Done the brakes on many cars and motorcycles over the years and never had any seals flip and never released the line pressure by undoing a bleed nipple. In all honesty I can't see how it could happen to a master cylinder seal as there is not pressure in the system once the return hole is uncovered (else the brakes would stay on) so the fluid just returns to the master cylinder. It would make more sense to say that it should not be done on a modern car with ABS in order to stop any dirt in the system affecting the ABS actuator and associated delicate components.

Lets face it the seals in the system are designed to create pressure in the system to make the thing work and as the pressure is on the same side of the seal as designed them why should it "flip"? The pressure is just being created from a different end.

[Webby the Bear]

I personally always break the bleeder loose first and drain old fluid out when pushing piston back  as I was told it could damage the seals of the mc.

Have I ever see it however? Nope 

[Marks DTM Calib]

Exhibit A is a master cylinder seal which is typical of modern setups:



Note the return on the seal which can be flipped (inverted) if fluid is forced backwards.

Seen it once on an Omega, quite a bit on smaller cars of various makes.

[Magwheels]

Not doubting you but how can that happen if the return port on the master cylinder is open and the seal is sitting in a closely fitting bore?

The thing that gets me is that when you jump on the brakes as hard as you can the system is under the same (if not more) pressure from the same direction and yet there is no problem.

When I heard the stories about the seals turning I always suspected the "technician" had flipped the seals in the ABS unit by forcing back the caliper pistons to quickly with a tool attached to an air tool. I would have thought that if it is possible to flip the seal on a braking system it would be caused by pushing the fluid back through the system faster than the release port hole could cope with, pushing a piston back slowly should make no difference to the normal operation except to maybe put dirt back up the line should there be any.

I like these conversations....

[tigers_gonads]

Never come across this myself but I do tend to crack a bleed nipple off if possible or at the very least, remove the cap off the fluid reservoir 

[Marks DTM Calib]

I suspect it's the sheer volume of fluid you are suddenly forcing back up the pipe and trying to push through a tiny feed drilling.

The additional bonus of cracking the bleed nipple of curse is you get the crappy old fluid out of the calliper (which you don't get out with a fluid flush)