Consequences of opening bleed valve to push piston back in?
Discussion
I opened the bleed valve to allow me to wind the calliper piston back in after changing the pads, a small amount of fluid leaked out, maybe 5-15ml at a guess, difficult to say but looked small.
So will i likely get a pocket of air inside the calliper near the piston or just some air bubbles and do these air bubbles ever work their way back up to the reservoir?
I didn't bleed the brakes as i don't have the bleeder bottle and so far the brakes feel good no problems. Will i be ok just leaving it?
So will i likely get a pocket of air inside the calliper near the piston or just some air bubbles and do these air bubbles ever work their way back up to the reservoir?
I didn't bleed the brakes as i don't have the bleeder bottle and so far the brakes feel good no problems. Will i be ok just leaving it?
It shouldn't have been necessary. The fluid would normally be displaced back into the reservoir. As long as you haven't made the mistake of topping up the reservoir as the pads/shoes wore down, there will be space for it there.
You could easily have let air into the system. If so, it'll be there until it's bled out.
Did you clean, check for wear and regrease the brakes while they were apart? That's part of a normal brake service.
Do you know the age of the brake fluid? It doesn't last forever and will need replacing at some point.
You could easily have let air into the system. If so, it'll be there until it's bled out.
Did you clean, check for wear and regrease the brakes while they were apart? That's part of a normal brake service.
Do you know the age of the brake fluid? It doesn't last forever and will need replacing at some point.
Whats your resevoir level like now? If its low then top it up before you do anything more, if it's high then extract some of it with a turkey baster
It's likely you'll have let air in, you'll need to bleed them now either with an ezi-bleed (or similar) or using an assistant to operate the pedal
At least you know the bleed screw isn't so rusted or rounded it can't open
It's likely you'll have let air in, you'll need to bleed them now either with an ezi-bleed (or similar) or using an assistant to operate the pedal
At least you know the bleed screw isn't so rusted or rounded it can't open
It is always possible that you may have let air in.
It is also possible that you were lucky & didn't.
You shouldn't have needed to do that as the fluid will just go back to the reservoir when the piston is returned.
As you say the brakes feel good you may well have dodged a bit of a bullet, what is the reservoir level like now?
It is also possible that you were lucky & didn't.
You shouldn't have needed to do that as the fluid will just go back to the reservoir when the piston is returned.
As you say the brakes feel good you may well have dodged a bit of a bullet, what is the reservoir level like now?
I used to own a Vauxhall Astra, and the Haynes manual actually advocated using a clamp in the brake flexi and using the nipple to bleed some fluid out whilst pushing the piston back in. I seem to recall it was something about seals in the master.
So it's a valid approach, with at least some pretty ordinary cars.
So it's a valid approach, with at least some pretty ordinary cars.
donkmeister said:
I used to own a Vauxhall Astra, and the Haynes manual actually advocated using a clamp in the brake flexi and using the nipple to bleed some fluid out whilst pushing the piston back in. I seem to recall it was something about seals in the master.
That doesn't make sense as the master cylinder piston is fully retracted leaving a route through to the reservoir therefore bypassing the master cylinder seals.martygturner said:
Unless you pushed the brake peddle down then released it when the nipple was open you will be fine...think of it like this when bleeding brakes you push the peddle down and hold, you did the same thing with the piston.
If fluid came out and the system was not under pressure at the time then there was an opportunity for air to go in.donkmeister said:
I used to own a Vauxhall Astra, and the Haynes manual actually advocated using a clamp in the brake flexi and using the nipple to bleed some fluid out whilst pushing the piston back in. I seem to recall it was something about seals in the master.
So it's a valid approach, with at least some pretty ordinary cars.
Doesn't seem valid to meSo it's a valid approach, with at least some pretty ordinary cars.
Maybe in 1980s....
Modern cars you surely just push pistons back, opening bleed nipple just introduces air.... and any fluid will be pushed back to fluid reservoir at point of retracting the pistons?
Will now need a full bleed
Nothing to do with the master cylinder seals, but it in my experience it is good idea to dump excess fluid out from the bleed nipple when you do a pad change, instead of pushing it back up the brake system, because these days we all have ABS pumps that don’t like displaced dirt that resides in the calliper. You only ever want to be pushing clean fluid ‘down’ through the braking system and not dirty fluid back up.
You may need to bleed the system afterwards, but you can but many easy bleed kits for the price of a refurbished ABS module!
You may need to bleed the system afterwards, but you can but many easy bleed kits for the price of a refurbished ABS module!
CarCrazyDad said:
donkmeister said:
I used to own a Vauxhall Astra, and the Haynes manual actually advocated using a clamp in the brake flexi and using the nipple to bleed some fluid out whilst pushing the piston back in. I seem to recall it was something about seals in the master.
So it's a valid approach, with at least some pretty ordinary cars.
Doesn't seem valid to meSo it's a valid approach, with at least some pretty ordinary cars.
Maybe in 1980s....
Modern cars you surely just push pistons back, opening bleed nipple just introduces air.... and any fluid will be pushed back to fluid reservoir at point of retracting the pistons?
Will now need a full bleed
All great in theory.....I just hope I do a good (safe) job on my dads car!
CarCrazyDad said:
donkmeister said:
I used to own a Vauxhall Astra, and the Haynes manual actually advocated using a clamp in the brake flexi and using the nipple to bleed some fluid out whilst pushing the piston back in. I seem to recall it was something about seals in the master.
So it's a valid approach, with at least some pretty ordinary cars.
Doesn't seem valid to meSo it's a valid approach, with at least some pretty ordinary cars.
Maybe in 1980s....
Modern cars you surely just push pistons back, opening bleed nipple just introduces air.... and any fluid will be pushed back to fluid reservoir at point of retracting the pistons?
Will now need a full bleed
liner33 said:
Plenty of mechanics do release the bleed nipple when pushing the piston back , its unlikely to introduce air into the system
I used to open the bleed nipple at every pad change, made it easier to move the piston.Afterwards I always gave the brakes a quick bleed. Never had a problem with all my years in the trade.
Old Merc said:
???? I said I always bled the brakes afterwards.
The OP said he didn't and asked whether that was a problem. Others have said it's fine and your reply also suggested that you thought it was an acceptable practice. I'm emphasizing that IMO it's only acceptable if the brakes are bled afterwards.GreenV8S said:
Old Merc said:
???? I said I always bled the brakes afterwards.
The OP said he didn't and asked whether that was a problem. Others have said it's fine and your reply also suggested that you thought it was an acceptable practice. I'm emphasizing that IMO it's only acceptable if the brakes are bled afterwards.Sure, if you open the nipple and just leave it open, without a hoseclamp on the flexi, then over hours/days/weeks it will syphon out, but surely that's going to drain the reservoir before it lets air into the calliper.
Don't misunderstand me, I know it's no great undertaking, but I've done both approaches (clamp and crack / just push it back) and never had evidence of air in the system (or knackered master cylinder seals) after either approach. I'm not convinced that exchanging a few teaspoons of fluid will do much for the cleanliness of the system (regardless of what my Haynes manual claims) but I suppose the real benefit to the clamp and crack is that you're exercising the nipples every time you change the pads, so less likely to end up with nipples corroded into the calliper from lack of use (had that... and it sheared off)
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