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Discussion Starter #1
Astra 1.7 TD Isuzu engine.

Failed MOT on balance of front brakes, rear drivers side wheel not braking very well, plus a couple of other things that I've already done.

So, brake imbalance means one disc is more worn than the other.

Partco, get replacement discs and pads and rear wheel brake cylinder.

I've done brakes millions of times before, but now I'm stumped.

I've put the discs and the pads on the front, and now the system acts as if its got air in the lines, because pedal goes to the floor and needs to be pumped to get proper brake force. This lasts ten seconds before it needs to be pumped again.

All I did was force back the pistons on the calipers and this seems to have thrown the system into a sh!tfit!

I've bled the both fronts, and there is absolutely no bloody difference in the brake force. Unless its pumped, the brake force is crap.

Ok, so I leave that and put on the rear brake cylinder because that had a leak, now I know what your thinking, "thats why it wasn't braking properly". Alas no!

The brakes on the front worked fine before I changed the discs and pads, so the rear cylinder isn't an issue.

I've bled the brakes and bled them. The pistons only moved 5cms. Could it really cause an airlock so far up the brake pipes?
 
C

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I'd just get a litre of fluid and run each corner until clear, all new fluid.
Remember on cavs should use pressure bleeder, and do nearest to reservoir first.
 

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Discussion Starter #4
Only for about five seconds, then it goes 'soft' again.

I've just bled three wheels and its still the same. I have the fourth to do, and I really can't see this fixing the problem.

If I don't get this sorted, I'm eventually gonna get stung for another £44 retest!
 

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CavWeb's Oldguy
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If you are not losing fluid, about the only thing left is the master cylinder seal, had one with similar symptoms. Replacement about £15 from a scrappie and an hour to fit plus more bleeding bleeding.
 
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Yeah if you didn't take the lid off the reservoir you could have knackered a seal.
 

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Discussion Starter #7
But it was fine this morning. With the old pads and discs on, it was absolutely fine. As soon as I chuck on the discs and pads, its buggered. There is no air leak sounds coming from the master cylinder, the vacuum pump is working fine, there is no leaks from the piping from the pump to the cylinder.

This is absolute bloody arse!
 

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Discussion Starter #9
Hmmm. I don't remember taking the lid off the reservoir!!!!

Jesus, schoolboy errors!?!

Which seal is most likely to have gone? Does a MK2 Astra GTE one fit?
 

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Discussion Starter #10
CallyT said:
You qould have squeezed the pistons back in to get the new pads in.

I did squeeze them in, had to to get the pads in. But I don't remember taking the top off the reservoir.
 

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CavWeb's Oldguy
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Galahad said:
But it was fine this morning. With the old pads and discs on, it was absolutely fine. As soon as I chuck on the discs and pads, its buggered. There is no air leak sounds coming from the master cylinder, the vacuum pump is working fine, there is no leaks from the piping from the pump to the cylinder.

This is absolute bloody arse!
There are no sounds that come from the cylinder or vacumn if it is leaking, just loss of pressure as you describe.

Just by pushing back the piston you run the rick of 'flipping' the seal in the master cylinder. Especially if you don't remove the lid of the resevoir.
 

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CavWeb's Oldguy
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Galahad said:
Hmmm. I don't remember taking the lid off the reservoir!!!!

Jesus, schoolboy errors!?!

Which seal is most likely to have gone? Does a MK2 Astra GTE one fit?
With without ABS is the main difference. See if they look the same.
 
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Galahad said:
I did squeeze them in, had to to get the pads in. But I don't remember taking the top off the reservoir.
I never did on any of my cavs - just put a rag under it for the fluid that came out.
Looking back, all my cavs brakes were dissapointing, and needed a pump before hard braking. Reckon I buggered all of them :lmao:
Just didn't know :shame: :bust:
 

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Discussion Starter #14
Right, I'm unsure which seal I should be replacing. Any ideas please?

I'm assuming its inside the Master Cylinder, or am I just better off replacing the whole unit?

I assume Cavalier Isuzu TD Cylinders are the same?

Just to recap so I don't go buying something I don't need. The seal is gone on the CYLINDER or the SERVO?
 

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Registered
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Sounds like you've flipped the seal on the master cylinder. Never push the pistons back into the calipers without releasing the bleed nipple as the fluid you've forced back up the line has turned the master cylinder seal inside out. If you ever do this again then put a bleed pipe with the end in a jamjar of brake fluid to avoid the system sucking in air through the bleed pipe. I use aquarium pipe as it's the right size and it's clear so you can see air bubbles easily.

You could try removing the piston on the master cylinder and refitting the seal the correct way round or just fit a second hand MC that you know is good.
 
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