This is a job I have done on several cars before but looking at the Haynes manual they recommend that when the pistons are pushed back that the bleed nipple is released so the fluid does not flow back to the master cylinder and flip the seals.
My question is how easy is it to flip these seals and is this warning just belt and braces?
Appreciate your comments.
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Its just good practise to release the nipple, you pump some of the crud as when you push the cylinders back. Having said that, changing the lancer pads and disks this year, I didnt do it, just left off the master cylinder cap. Just pushed them back slowly and steadily.
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I do it like Z, have done so for some 40 years and never had a problem yet, steady and slowly does it.
If the fluid looks mucky in the master cylinder, could be a good time to change it, in which case a good opportunity to try the recommended method for yourself without the worry of letting air in as you'll be bleeding the system through.
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I have always undone the bleed screw since * see below - with a bleed tube plus one way valve attached.. and the hose to the caliper clamped with a brake hose clamp.
* I have found older master cylinders problematic and ruined a 10 year old Mark 3 Fiesta one by attempting to push back teh piston without cracking the bleed nipple. Mind you.. the car was a heap - which then passed MOT tests for 5 years with a new master cylinder..(£110 ish).
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It's not just about the risk of flipping the seals in the master cylinder. If the brake fluid is old, you can risk damaging the ABS pump by forcing dirty brake fluid through it in the wrong direction.
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>>If the brake fluid is old, you can risk damaging the ABS pump by forcing dirty brake fluid through it in the wrong direction
How?
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When using the brakes in the usual manner, only small amounts of fluid are pushed one way or the other. As the carp/sediment tends to settle at the lowest part of the system, when fitting new pads a considerable amount of brake fluid is pushed back through the sytem (including the carp/sediment) into the master cylinder reservior when pushing the pistons back in unless you release the bleed nipples and clamp off the pipes.
If that fluid is dirty or contaminated with moisture, then that's what can cause the damage to modern braking systems.
The ABS unit has various components which modulate the pressure applied to the calipers, it's these components which could get damaged, along with degenerating seals.
I'm sure someone like Numbercruncher can explain it better than I can, but that's how I understand it.
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but how would one force fluid through the ABS pump the wrong way? And is it the "wrong way" bit or the "dirty fluid" bit which is the issue?
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I don't claim to be an expert, but from what I understand it's the dirty fluid that can cause the damage to the braking system.
When bleeding a system, fluid is fed from the master cylinder to the calipers, through the ABS system. As the majority of the dirty fluid should be at the lower end of the system, bleeding it pushes it out through the bleed nipples. If you push the fluid the other way (i.e. when changing pads), then you push it back up though the ABS pump.
>> how would one force fluid through the ABS pump the wrong way?
As mentioned in my previous post.
"when fitting new pads a considerable amount of brake fluid is pushed back through the sytem (including the carp/sediment) into the master cylinder reservoir when pushing the pistons back in (to accommodate the new brake pads) unless you release the bleed nipples and clamp off the pipes."
Chances are, you'll get away with it, but there is always a risk you won't. I guess a lot of it is how dirty the brake fluid is, and when/if it has been changed.
Last edited by: VxFan on Tue 9 Oct 12 at 12:53
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If the vehicle's brake fluid change is not overdue, you would be very unlucky to damage an ABS system, even though the fluid is pushed backwards up the system during a pad change if you don't open the bleed nipple.
What I used to find more incredible was the idea of flipping the seals in the master cylinder - until I saw one happen (~1990). The mechanic a couple of ramps away from me had done a pad change, but couldn't get a firm pedal. I helped him find the fault, and eventually, we had replaced the brake pipes coming out of the master cylinder with bleed nipples, and when we found the brake pedal was still poor, that only left the master cylinder itself. I didn't give it a lot of thought at the time, but, that must have been a difficult conversation with the customer for the staff on the front desk.
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Master cylinder seals can be a problem if the calipers are pushed back too quickly, true, but I'm not convinced by this idea of crud getting into the ABS sensors.
How exactly is crud supposed to be getting into the brake pipes anyway?
I used to clamp the pipes and open the bleed nipples, but stopped doing this on the last couple of pad changes. Its saved my lots of messing about bleeding the brakes and no ill effects so far.
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>>I used to clamp the pipes
A better way is to open the bleed nipple, and prop the brake pedal part way down, thus covering up the ports to the reservoir.
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>> I'm not convinced by this idea of crud getting into the ABS sensors.
Not the sensors, the ABS pump.
>> How exactly is crud supposed to be getting into the brake pipes anyway?
Never heard of a car failing its MOT for having rusty brake pipes?
Brake fluid over time becomes hydroscopic (absorbs water). The inside of the brake pipes can rust as well as the outside.
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>>The inside of the brake pipes can rust as well as the outside.
I'd like to see an MOT that inspects the inside of the brake pipes. ;>)
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>> >> I'm not convinced by this idea of crud getting into the ABS sensors.
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>> Not the sensors, the ABS pump.
>>
>> >> How exactly is crud supposed to be getting into the brake pipes anyway?
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>> Never heard of a car failing its MOT for having rusty brake pipes?
>>
>> Brake fluid over time becomes hydroscopic (absorbs water). The inside of the brake pipes can
>> rust as well as the outside.
>>
Ok, but what difference is it going to make by *not* using the bleed nipples. Sure, you push some fluid backwards up the pipes, but it was still fluid that came down the pipes, which means that as the brakes wear, it naturally moves through the pipes anyway, only in the other direction. So the fluid moves back and forth, and perhaps, maybe some rust might appear inside the brake pipes, which might be a good argument for replacing the brake fluid regularly, but is pretty much neither here nor for when you're replacing brake pads... I think... ;)
Or am I missing something here?
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>> Or am I missing something here?
I explained it earlier in this thread.
"When using the brakes in the usual manner, only small amounts of fluid are pushed one way or the other. As the carp/sediment tends to settle at the lowest part of the system, when fitting new pads a considerable amount of brake fluid is pushed back through the sytem (including the carp/sediment) into the master cylinder reservoir when pushing the pistons back in (to accommodate the new brake pads) unless you release the bleed nipples and clamp off the pipes. "
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>> >> Or am I missing something here?
>>
>> I explained it earlier in this thread.
>> As the carp/sediment tends to settle at the lowest part
>> of the system,
Exactly. So anything pushed up would soon settle back at the bottom again! :)
I feel we are going round in circles here... lol.
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Hydroscopic?
What's that then?
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The clue is inside the brackets after the word.
Alternately, try googling it ;)
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>>Alternately, try googling it ;)
Oooo, too smart and quick for me.
Right then, lets do that....
Aaah, here we go......
hydro·scopic (-skpk) adj.
Item pertaining to an optical device used for viewing objects far below the surface of water. [hydroscope]
Mmm, nope, still confused.
Tell you what, help me out here, you look it up on Google and tell me what you find.
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oooohhhhhh, hyGroscopic.
I seee.
why didn't Dave say that.
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>> why didn't Dave say that.
Because I make the occasional spelling mistake, just like someone else I could mention on here
www.car4play.com/forum/post/index.htm?v=e&t=11575&m=257500
As well as few others too
tinyurl.com/8od9m72
Anyway, isn't the word hydro associated with water?
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I make loads.....
>The clue is inside the brackets after the word.
>
>Alternately, try googling it ;)
But may I suggest that you google it first next time, before you suggest it to others.
Also, that wasn't a spelling mistake, it was the wrong word.
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Well if we're gonna get nit picky,
I DID give you the correct answer. i.e. "The clue is inside the brackets after the word"
(absorbs water)
Hydroscopic / Hygroscopic. Who cares. As per the previous example I gave, loads of people spell it with a D instead of a G.
Still, if it makes you feel better by highlighting someone's misspelling of a word, then who am I to argue.
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Nissan Micra - 04 1.2 Replacing front pads and disks - Zero
