Help Please Mysterious brake problem after pad replacement

[Mark365]

This is an absolute mystery to me and I would appreciate it if someone with an understanding of brake systems could give me a few tips.

I had the front brake pads replaced on my A4 B8 2010 sedan and ever since the replacement the brake pedal felt a lot softer. I can press the brake pedal until it hits the floor. Initially, I thought this is due to the pads adjusting to the brake disc, since I kept the old discs because they are perfectly intact.

However, after over 1200, miles the brake pedal behavior is the same. With the engine running, I'm able to press the brake pedal to the floor. However, when the engine is off, this is not possible. Also, if the engine is on or off but the electronic handbrake is on, the pedal cannot be pressed to the floor but there is some strong resistance just before the pedal would hit the floor.

I've been in touch with the shop that did the replacement and they said the brake fluid is old and must be replaced. Fluid replaced, but the problem remains. The shop says everything looks ok.

What could the cause for this behavior be? What mistakes could the shop have made that causes these symptoms?

 

[OliNix]

Personally I would vote on the shop having left the calliper hanging by the brake line when doing the disks. In turn damaging the line and its structure.

What you are feeling as a soft pedal is the line expanding like a balloon when you press the pedal.

1) Jack the car up, remove the wheels (you can do one at a time if you don’t have jack stands).
2) Turn the car on but leave in P or N.
3) Take parking brake off.
3) Set up a camera to look at the calliper and brake line.
4) Get in car and press HARD on brake pedal.
5) Do this for each calliper.
6) Review videos to see which line is ballooning.

When the fluid was changed was VAGCOM used and the ABS also bled? This could also be a reason for a spongey pedal.

 

[Mark365]

Thanks for the tip, I'll see if I can try that this weekend. What do you mean by using VAGCOM? Should the car be told that the pads were changed? I'll ask about the ABS.

 

[Simon]

check that the brake fluid reservoir cap is fitted

 

[OliNix]

Thanks for the tip, I'll see if I can try that this weekend. What do you mean by using VAGCOM? Should the car be told that the pads were changed? I'll ask about the ABS.

When you change the brake fluid you do a standard bleed to each caliper. You then have to activate the ABS pump using VAGCOM and bleed the fluid out to the drivers side front caliper I think. This flushes the old fluid and air from the ABS. If you don’t do this the ABS can be left full of old fluid or air and then contaminate your nice new air free fluid you have just put in.

Other than this it could also be corrosion on your caliper pistons, letting air into the system. You are seeing this now as the pistons have been pushed back in and the seals could now be operating on a corroded area. On a 2010 car this could be possible, depending on what kind of climate you live in.

 

[RAF_S7]

Sounds like classic air in the system...

 

[jasonj1965]

as previous reply you have air in your system you have to bleed it out . get someone to help you pump the brake pedal while releasing nipple with a clear hose on it when you feel pressure and there is no bubbles in the tube just fluid you should be ok


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[Retroman]

Does the point at which the brake pedal gets hard, rise if you pump the pedal? If so it is likely to be air in the system unless you notice some fluid loss. It must have happened during the pad fitting - sometimes a mechanic will slacken a bleed screw in order to push back a caliper piston and it's not unknown for bleed screws to get damaged during a brake fluid change process. Once the brake pedal is used, any air gets dispersed around the system as can be more difficult to bleed and may take two circular bleeding sessions around the 4 wheels to extract it. Not rocket science and a garage (shop) shouldn't really let the car back out to a customer like this.

 

[Mark365]

I had a look on both sides if the brake lines bulge while pressing down the pedal and I couldn't see anything. I also braked hard a few times from around 100 mph to 60 mph. The screws holding the wheel in place were actually hot to touch! I tried to brake as hard as I can a few times on gravel and on tarmac. The ABS kicks in well before the pedal "hits the floor."

After all this, there is no change in behavior. But I did notice that the pedal doesn't actually hit the floor. If I press it all the way, I can still fit a shoe underneath it.

I'll try to see what exactly happens if I pump the pedal repeatedly.

The very slight grooves shouldn't be causing this, right? You can barely feel them and the pad should already be adjusted to them. https://imgur.com/FKWVXkF

 

[Simon]

A soft pedal is usually air in the system or bad fluid, it could be a vacuum leak perhaps and you are not getting enough assistance?

 

[OliNix]

This is definitely air in the system then.

Take it back to the shop and complain! It will need to be bled again, if you want it to be rock hard.

If you did it yourself check all the bleed ports are tight and none are leaking (this can be tricky).

If it’s getting better and your not that bothered by it, just leave it.

 

[audiwaterpump]

This is an absolute mystery to me and I would appreciate it if someone with an understanding of brake systems could give me a few tips.

I had the front brake pads replaced on my A4 B8 2010 sedan and ever since the replacement the brake pedal felt a lot softer. I can press the brake pedal until it hits the floor. Initially, I thought this is due to the pads adjusting to the brake disc, since I kept the old discs because they are perfectly intact.

However, after over 1200, miles the brake pedal behavior is the same. With the engine running, I'm able to press the brake pedal to the floor. However, when the engine is off, this is not possible. Also, if the engine is on or off but the electronic handbrake is on, the pedal cannot be pressed to the floor but there is some strong resistance just before the pedal would hit the floor.

I've been in touch with the shop that did the replacement and they said the brake fluid is old and must be replaced. Fluid replaced, but the problem remains. The shop says everything looks ok.

What could the cause for this behavior be? What mistakes could the shop have made that causes these symptoms?

What's amazing is that the garage returned the car to you in that state. Its dangerous.
Seems like air in the system.
But the person who did the work doesn't seem competent, and may of damaged one or more parts; maybe master cylinder seals have been damaged.
Have they done any work for you before?

 

[Mark365]

I checked the pedal today.

With the engine on: the pedal does become harder and the point of resistance moves up as the pedal is pumped. If I stay on the pedal, it slowly sinks back to its "normal" position close to the floor.

With the engine off: the pedal gets hard when pumped and stays hard. The free travel decreases with each pump. At the end, the pedal cannot be pumped at all. Without turning on the engine it's impossible to press it down.

Doesn't this suggest there is no air?

 

[audiwaterpump]

I checked the pedal today.

With the engine on: the pedal does become harder and the point of resistance moves up as the pedal is pumped. If I stay on the pedal, it slowly sinks back to its "normal" position close to the floor.

With the engine off: the pedal gets hard when pumped and stays hard. The free travel decreases with each pump. At the end, the pedal cannot be pumped at all. Without turning on the engine it's impossible to press it down.

Doesn't this suggest there is no air?

Seems like air to me.
First, and cheapest step will be to bleed the front brakes.
Have you ever done that before?

 

[Mark365]

If it was air, wouldn't the pedal stay soft when the engine is off? The shop already changed the brake fluid and they're sure there's no air, but I think I'll call them and ask if they also bled the ABS pump with VCDS.

 

[Retroman]

Definitely sounds like air in the system. The situation you describe above Mark365 (engine on and off) merely shows the affect of the servo assistance. It sounds as if the brakes just need another good flush/bleed which will also ensure nice clean, good fluid in the system. Should be an easy, everyday job to a professional garage.

 

[audiwaterpump]

If it was air, wouldn't the pedal stay soft when the engine is off? The shop already changed the brake fluid and they're sure there's no air, but I think I'll call them and ask if they also bled the ABS pump with VCDS.

I think the garage is giving you the run around.
I wouldn't rely too much on what they say.
Would also be a good idea to bleed it yourself, or get someone other than that garage to do it.

"The shop already changed the brake fluid !" - Other than taking their word for it, how do you know the brake fluid has been changed? Usually what they do is just change the fluid in the brake reservoir (the bit you can see ), and that's if you're lucky.

 

[OliNix]

+1 to audiwaterpump’s comments.

It’s easy to at least check a brake bleed. You will need a friend and a pot. Ideally some small diameter hose that fits over the bleed nipple.

One of you goes to a brake caliper (rear passenger side is the longest line and most likely to have old fluid in) we will call this person 1

The other sits in the drivers seat with the engine off. We will call this person 2.

1) Take cap off of brake fluid reservoir
2) Person 1 undoes the bleed screw 1/2 turn.
3) Person 2 presses on the brake pedal till it reaches the floor and holds it there
4) Person 1 does up the bleed screw
5) Person 2 releases the brake pedal.
6) If no fluid comes out, repeat steps 2-5 but undo the bleed screw 1/2 a turn more each time until it does.

If the fluid that comes out is a nasty black/grey colour then the shop hasn’t done the brake bleed. Keep it, it’s evidence for your argument!

This is the process to follow to do a full brake bleed manually without a pressure bleeder. If you are going to do the full bleed yourself always make sure that the brake fluid reservoir is full, never let it go empty or you will have to start again!

Bleed the brakes in the below order (the amount of fluid needed to fully replace the fluid in each line is in brackets):
i) Passenger Rear (0.3L)
ii) Driver Rear (0.3L)
iii) Passenger Front (0.2L)
iv) Driver Front (0.2L)

Keep repeating steps 2-5 on each caliper until you have expelled at least the amount in each line. Personally, I would keep going till the fluid that comes out is the same colour as your putting it in the reservoir.

If your callipers have 2 bleed screws, first do the inner and then the outer.

According to Audi and their ELSA-WIN service instructions:
– Check pedal pressure and free travel: No more than 1/3 of total pedal travel.
– If free travel of brake pedal is greater than specified, or if brake function is impaired: Check brake system for leaks and renew brake fluid again.

I would say the second statement is true for you and it needs bleeding again.

Either good luck with the shop or good luck bleeding again!

 

[Mark365]

First of all, thanks for all the tips. Today I was at the inspection and the mechanic there was helpful and said my front brake discs are at their very minimum width and should be replaced. I'm a little irritated the shop earlier didn't suggest replacing them and only replaced the pads. I will have the discs replaced with ATE discs. Also, the inspector said the brakes were fine, even though the pedal travel is a little more than usual, the brakes work exactly as they should.

 

[audiwaterpump]

Is that the same garage?
Were the brakes like that before they did the work?
What were the disc measurements, compared to what they should be?

I had some work done on my car, and they said the disks and pads needed replacing.
Went to a different garage and they said they were all ok.

 

[Mark365]

No, it was a different one. If I recall correctly, the disc measured 28 mm and that is the minimum. I ordered new discs and will have them installed next week.