Still got brake issues

[AudiLeon]

Y Reg 2001 Audi A3 100bhp TDI

Put the new caliper on today, fully bled the system. Including the master cylinder.
With the engine off, its firm as you like, rock solid from the top.
With the engine on it's spongey. Also if you keep your foot on the brake, it goes to the floor and eventually the revs dip.

This leads me to think there is a vacuum leak. I've disconnected and sealed the branch off from the valve just after the vacuum pump. But it still does it, so this would suggest the leak is on the solid pipe to the servo, but i find that hard to beleive.

Anyone had this before?

Cheers in advance.

 

[Broken Byzan]

The A3 brakes are notoriously bad to bleed. Give another go, and another and another. It will eventualy come up.

How are you bleeding? Pumping,easibleed or vacuum bleeding?

 

[AudiLeon]

Pumping the brakes. I don't have a pressure bleed and idealy would like to avoid having to buy the kit.

What makes them so bad to bleed?

 

[<tuffty/>]

Pressure bleeder mate... you stand a chance of buggering the seals in the master cylinder if you pump them.

Gunsons EEZI Bleed... get one from Halfrauds or ebay, costs about £15 and will save your life... quite literally...

Also need to bleed the master cylinder once the brakes are done...

<tuffty/>

 

[AudiLeon]

I might have to buy one. Means mooooooore fluid to buy lol.
I did the master cylinder too.
I think I'll just have to get one

 

[<tuffty/>]

Its the best way to bleed them tbh... well worth the investment as you will need to change the fluid every 2 years anyway...

<tuffty/>

 

[beachbuggy]

You will definately benefit from using an pressure bleeder and for £15 will save you a whole lot of hassle and easy for one person to use.

I don't agree with the addage that if you let the fluid fully drain and put the peddle to the floor you're flip the seal and knacker the master cylinder. I've seen a seal in the rear cailper pop, all the fluid drained and the resevour and MC was completely emptied. The peddal still worked fine after it was refilled and bled. This is only my opinion and if anyone can show me a flipped seal then I will change my mind

Also depending on how much fluid came out, an ABS cycle could be needed but this is only in the advent in the fluid being drain from the MC and air getting into the ABS pump. Only way to do this is to use VAG-COM but like I say for a caliper change you almost certainly wouldn't have to do this.

As previously stated it's likely you still have air in the system. Use a pressure bleeder and your stand a good chance of getting all the air out, even a small bubble will cause a problem.

 

[Broken Byzan]

I don't agree with the addage that if you let the fluid fully drain and put the peddle to the floor you're flip the seal and knacker the master cylinder. I've seen this when a seal in the rear cailper popped all the fluid drained and the resiviour and MC was completely empty. The peddal still worked fine after it was refilled and bled.

That is not an addage, it's a fact, i have seen it happen and had to change the MC because of it. Just be aware is all i will say, it's unlikely, but possible. Mostly due to surface rust on the piston/cylinder from where the piston doesn't normally travel, it's just enough to flip or tear the seal

 

[AudiLeon]

I'm wondering if its already happened.
Might source a fresh MC

 

[<tuffty/>]

I'm wondering if its already happened.
Might source a fresh MC

Try the pressure bleeder first... new MC's are around £200 from Audi and around £100 from GSF... and you will still need to bleed it afterwards...

<tuffty/>

 

[AudiLeon]

I've woke up with this on the mind, i just can't help but wonder why the revs dip if you keep your foot hard on the peddle. As it lowers to the floor, the revs dip slightly.

 

[<tuffty/>]

Had a similar issue with a BT A3, checked the one way valves and all ok... the servo draws a vacuum from the inlet mani so it may be that the servo has a leak somewhere but couldn't find one in the A3... brakes worked fine though and nothing came up in VAGCOM.

I can't say I have noticed it myself as I don't dip the clutch when I brake (unless its an emergency stop) so maybe they all do it...

Priority of course is to get the pedal up, pressure bleeder, job done

Had a guy come in with a TT he had fitted 6 pot brembos... pump bleed them and got no where... pedal would sink straight to the floor... told him to pressure bleed them which he did and all was good... it works... simples

<tuffty/>

 

[AudiLeon]

Such a odd thing isn't it! lol
I think i'll get one then, like you say it'll only need doing again in 2 years, plus i can do the A4 sometime too.
Thank you all for your help, even if i am slow on the uptake

 

[<tuffty/>]

lol, no probs mate... first time I bled the brakes on my S3 I used the pump pedal method and they were crap... they work quite well now

<tuffty/>