Brake Bleed?

Sha170

Registered User
Hi, I replaced my front pads today, whilst replacing the first side I forgot to take the cap of the reservoir as I was pushing the piston back some fluid leaked from reservoir. Only realised then and I took the cap of and the fluid was right at the top.

Changed the other side as normal and pumped the brakes many times however when I press the pedal the first time it is soft and goes all the way down but is fine after that until I stop and set off again then it is soft again.

Do the brakes need bleeding?
 

Rob2k68

Well-Known Member
VCDS Map User
It very much sounds like it yes - I'd probably just do the fronts to start with. When I last changed my pads nothing would budge without the reservoir cap being off.
 

cemerson

Registered User
I did my pads without taking the cap off just fine... Just used a couple of G clamps and block of wood to push the piston back in. There is an official tool you can get as well. As far as I remember, the workshop manual didn't have anything in it about removing the cap. Personally I think you'll be fine, but I'm not an expert. The brake pedal being soft on first push is normal - as long as you didn't slam the pedal down and did it slowly. This is just the pistons extending again to the right position for the new pads.
 

Sha170

Registered User
I did my pads without taking the cap off just fine... Just used a couple of G clamps and block of wood to push the piston back in. There is an official tool you can get as well. As far as I remember, the workshop manual didn't have anything in it about removing the cap. Personally I think you'll be fine, but I'm not an expert. The brake pedal being soft on first push is normal - as long as you didn't slam the pedal down and did it slowly. This is just the pistons extending again to the right position for the new pads.

That's exactly what I did, I used a g clamp and block of wood.
When I was pushing the driver side caliper back, fluid leaked from the resoviour down into the gap behind the hub.
The pedal is still soft when driving as I have to press extra to brake.
 

cemerson

Registered User
Oh, if it's still soft then yes, bleeding is probably needed. I didn't have any fluid leak when I did mine.
 

Rob2k68

Well-Known Member
VCDS Map User
IMG_3732.PNG
 

Sha170

Registered User
Tried bleeding the breaks today using a different kit from halfrods. A few air bubbles did come out from the first caliper, none from the second caliper.
Pedal feels a little bit better but still feels as if its not right.

The first time I press the brake after starting the car, or breaking after stopping the pedal goes all the way down and then becomes harder on the next few pumps as it should. Is it supposed to go all the way down on the first pump?
Comparing to my mates scirocco his doesn't go all the way down at all.
 

Retroman

Audi A3 2010 Sportback 2.0 TDI 170 (CBBB engine)
If air is in the system and you pump the brake pedal (with all bleed screws closed) it tends to disperse the air into smaller bubbles and thus make it harder to bleed. I would just repeat the process and put plenty of fluid through - it's cheap enough.

I've heard people make mention of the master cylinder seals "reversing" when pushing cylinders back to allow fluid back into the reservoir - as opposed to loosening the bleed screw to allow a small quantity to be pushed out. Personally, I have never experienced this and I have changed brake pads on many cars over the years and therefore, wonder if it is an "urban myth" given the high pressures and destruction testing applied to master cylinders. Furthermore many electronic handbrake pistons are pushed back electronically (using something like VCDS for example) with no problem.
 

SevenW

Registered User
Tried bleeding the breaks today using a different kit from halfrods. A few air bubbles did come out from the first caliper, none from the second caliper.
Pedal feels a little bit better but still feels as if its not right.

The first time I press the brake after starting the car, or breaking after stopping the pedal goes all the way down and then becomes harder on the next few pumps as it should. Is it supposed to go all the way down on the first pump?
Comparing to my mates scirocco his doesn't go all the way down at all.
Something is wrong if your first push of the pedal after starting the engine, goes all the way down to the carpet.
I would take the car to a garage and get it checked out ASAP! I am a keen DIYer and change pads discs. Normally after fiddling with the brakes the first time stepping after start up the pedal will hit the floor after a few pumps everything is back to normal, then after that it is set.
If it was a master cylinder seal breaks every pedal stop will reach the carpet, been there done that on an ancient Toyota Corolla, the master cylinder was actually flawed had some pits and lumps on the wall it caused one of the piston seals to break, the breaks would grab but the pedal would reach the carpet at every stop.

Bleed once more for a longer period, if no change take it to get checked out.
Nothing worse than not having confidence in stopping.
 

mr_pepps

Registered User
Hi all,
Just want to piggyback on this for a moment.

I changed rear discs and pads today on my 1999 A3 1.8T. Struggled to push the piston back so I attached a bleed kit and undid the bleed valve while I pushed the piston in.
Did this on both rears.
Then bled the whole system - front and rear. Took ages! 45 mins of peddle pumping to get all the bubbles out of the front left caliper!

Anyway. Finally got good pedal firmness - engine off ignition on.
When I started the engine I had no firmness to the pedal.
Drove (cautiously) around a carpark. No feel came back to the pedal.
I could stop the car, but only in the last half inch of pedal travel.

Checked for any leaks around the bleed valves and calipers. Couldn't see anything.

What have I done wrong??

Please help. All comments/suggestions appreciated.
 
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