Soft brake pedal

[Gaspen]

Hello

 

I hope I can find some help here. The car is a Skoda Octavia 2.0 petrol, APK engine, basic ABS Mk60 (no ESP, no brake 

 

The symptom :

 

1) Engine switched off : the brake pedal is pretty soft. It can not pumped to hard, always remains soft.

2) Engine started : pedal will be light/easy, almost go to the floor, there is still no definitie "bite" point

3) Engine switched off agaian : after 2-3 press on pedal it became hard as a good brake, but with further depresses we get to point 1)

 

I've made a short test on the street and the car has a good brake effect even with this condition. The ABS unit worked and activated in at heavy braking.

 

Before these symptom these  parts were replaced :

 

- new rear calipers, new rear pads and discs

- new front pads

 

During the repair the ABS unit was replaced from a working vehicle as the original was tested but became faulty. With the "new" ABS unit nothing changed.

 

I noticed a crack on the vacuum pipe, it was replaced.

 

I've closed  the outlets of the master cylinder with plugs : the pedal became hard as it should be. After that I closed the outlets of the ABS unit : the pedal still hard. The fault is after the MC/ABS

 

The calipers moving freely, no sticking, so the pistons. There is no leaking at the pipes or connections. The system was bleeded hundred times with pressure bleeding, no more air bubbles coming out.

 

Then I pinched the two front brake hose and the pedal became harder, but I can not find any fault on the front brakes.

 

I know that the brake circuits work diagonal, so I will pinch the LF/RR and RF/LR hoses. 

 

What else should I check ?

 

 

 

 

 

 

 

[J.R.]

That the front calipers are not reversed side to side.

[Gaspen]

28 minutes ago, J.R. said:

That the front calipers are not reversed side to side.

 

No. The front calipers are not reversed. Bleeding nipple is on the top

[J.R.]

The pedal will become harder when you clamp off any caliper but unless it becomes solid ie no trace of sponginess I would not assume the problem lies there, calipers are easy to bleed and air usually gets trapped along horizontal sections of brake pipes, bends etc, the ABS block or the master cylinder being the highest point.

 

Regarding the latter the MK1 Octavia actually has one possibly two (it was a long time ago) bleed nipples on the master cylinder, they are quite hidden and bleeding them cured my spongy pedal problem, I cant recall why I was working on it, perhaps I had changed the fluid.

 

My symptoms were just like yours, I had never before seen a bleed nipple on a master cylinder.

[Gaspen]

7 hours ago, J.R. said:

The pedal will become harder when you clamp off any caliper but unless it becomes solid ie no trace of sponginess I would not assume the problem lies there, calipers are easy to bleed and air usually gets trapped along horizontal sections of brake pipes, bends etc, the ABS block or the master cylinder being the highest point.

 

Regarding the latter the MK1 Octavia actually has one possibly two (it was a long time ago) bleed nipples on the master cylinder, they are quite hidden and bleeding them cured my spongy pedal problem, I cant recall why I was working on it, perhaps I had changed the fluid.

 

My symptoms were just like yours, I had never before seen a bleed nipple on a master cylinder.

 

I wrote about the bleeding nipples on the front calipers : both positioned upwards, they are not reversed.

 

There is no bleeding nipple on the master cylinder but I pre-bled it ont the bench before install to the car.

[J.R.]

I know you wrote to confirm it, I gave you a thumbs up and made no further mention of calipers being reversed.

 

I am only trying to help, thats what the forum is for.

Edited 15 July, 2023 by J.R.

[Dean]

On 15/07/2023 at 05:56, Gaspen said:

 

I wrote about the bleeding nipples on the front calipers : both positioned upwards, they are not reversed.

 

There is no bleeding nipple on the master cylinder but I pre-bled it ont the bench before install to the car.

Did you bleed BOTH nipples on the reservoir? A lot of people forget to bleed them which results in this, including myself.