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[Greenbay packer]

When changing brake pads is it necessary to open the bleed nipple on the wheel in question before pushing the caliper piston back into the caliper?  I have never done this on any vehicle and my Horrible Haynes manual doesn't mention doing this for my V6, but I have recently read advice on this forum that says a nipple should be opened to prevent back pressure inverting the seals in the master cylinder and possible problems with the ABS.  Is this really necessary, or is the risk minimal?

I've recently replaced my front brake pads without doing this (hopefully I've done no harm), but would be grateful for some opinions before doing the rears.

[dbug]

Ideally you should crack bleed nipple but if you don't risk is minimal if you are careful.

[Andy H]

I only do it to prevent the reservoir overflowing. Not really a problem on the Omega but it does help on my motorbike.

A beneficial side effect is that if you do it regularly you will be replacing the old fluid with new fluid.

[Kevin Wood]

The master cylinder seals can invert on an Omega if you don't open the bleed nipple.

The brake fluid that's in the slave cylinder will be manky anyway as it's in the hottest part of the system. Might as well let it out and drain it off rather than pushing it back up into the system, IMHO.

Kevin

[Greenbay packer]

If I do open a nipple will the system take in air and need to be bled, or will pushing in the caliper piston expel any air?

[Broomies Mate]

If I do open a nipple will the system take in air and need to be bled, or will pushing in the caliper piston expel any air?

By pushing the piston inwards with the nipple cracked open, the fluid will take the easiest route, which will be to the floor (I use an EzeBleed pipe into a jam jar).  As you finish pushing the piston back, nip up the nipple again, and job is a good 'un.

Just please dont forget to check and top up the reservoir when you are done.  As usual, pump up the brakes with the engine started, and check the level again, then take it for a test drive.

[harpersimon]

The master cylinder seals can invert on an Omega if you don't open the bleed nipple.

The brake fluid that's in the slave cylinder will be manky anyway as it's in the hottest part of the system. Might as well let it out and drain it off rather than pushing it back up into the system, IMHO.

Kevin

Ditto
...but you ought to bleed them anyway after opening part of the system (ie bleed nipple) - does no harm and replaces probably crap fluid.
The rears might want a wind back tool (not done the back of mine so don't know) sure someone will confirm or deny..

[Greenbay packer]

So long as a lot of air doesn't get into the system I should be able to bleed just the wheel I'm working on regardless of any left-right front-back sequence shouldn't I?   

[harpersimon]

yeah thats what I was getting at, replace the pads, then bleed each corner for good measure

[Agemo]

Never heard about the seals inverting, nice tip, will remember that.

[Hannah Judes Dad]

The master cylinder seals can invert on an Omega if you don't open the bleed nipple.

The brake fluid that's in the slave cylinder will be manky anyway as it's in the hottest part of the system. Might as well let it out and drain it off rather than pushing it back up into the system, IMHO.

Kevin

Ditto
...but you ought to bleed them anyway after opening part of the system (ie bleed nipple) - does no harm and replaces probably crap fluid.
The rears might want a wind back tool (not done the back of mine so don't know) sure someone will confirm or deny..

You don't need a wind back tool they just push back,if they are difficult to move you can use a G clamp just like on the front brakes

[erubus]

i've only ever used firm pressure on the piston without any problems, however the point about the manky fluid being replaced is a good one.