Brakes Issue (Advice needed)

[Pwskii]

Hello fellas,

 

I am writing to you as I've run out of ideas of what is wrong with my 2004 Skoda Octavia mk1 1.9TDi PD (ASZ). Issue as title say is with brakes.

 

I took it upon myself to replacement pistons in my front calipers. I have decided that for the safety of brake pipes it will be safer to remove it and do it of the car. I disconnected pipes and blank them with nipped bolt and nut on connections.

 

I've changed pistons, no issues encountered it went as smoothly as I expected it. 

 

My problem occured after I bleed brakes. So, issue is that when I am driving and begin to brake, initially all happens as expected and the car slows as expected, then after about 3-4 seconds you can hear hissing and brake pedal begins to lift and automatically I am loosing control of braking as they are no longer as effective as the were before pedal lifted, now I either have to slam them hard or let foot of the brake for a second and repeat the process. 

 

Now, prior to that brakes were working fine apart from binding.

 

Anyone willing to share some experience when it comes to brakes, servos and before I fried my brain for the day i was reading about "Brake Booster pressure sensor"

 

Any help would be greatly appreciated.

 

Pat.

[petrolbloke]

Did you replace the seals in the calipers or just the pistons? Have you checked for fluid leaks from the calipers, bleed screws and connections?

 

Please don't keep driving it - it sounds quite dangerous at the moment!

[Pwskii]

3 minutes ago, petrolbloke said:

Did you replace the seals in the calipers or just the pistons? Have you checked for fluid leaks from the calipers, bleed screws and connections?

 

Please don't keep driving it - it sounds quite dangerous at the moment!

Hi, I've drove it on a industrial estate to test drive it, trying to establish what is happening.

 

So I've replaced everything. Also brake cleaned everything dry after to observe for leaks. Nothing, fluid level is perfect.

[J.R.]

Did you put the left and right calipers back on the correct sides?

[Pwskii]

12 minutes ago, J.R. said:

Did you put the left and right calipers back on the correct sides?

Yes.

[J.R.]

I didn't think having upside down calipers & not being able to bleed them properly could have caused your problem but reversing them is very common so just wanted to eliminate that.

 

It sounds like the servo is losing vacuum, check all the hose connections.

[KenONeill]

1 hour ago, Pwskii said:

My problem occured after I bleed brakes.

Yes. Which technique did you use to bleed them?

[Pwskii]

8 minutes ago, KenONeill said:

Yes. Which technique did you use to bleed them?

I flushed them first to get fluid in front calipers and then I pressure bleed from furthest point to nearest point. So RL RR FL FR.

 

I did classic pedal pumping technique. 

[KenONeill]

10 hours ago, Pwskii said:

I did classic pedal pumping technique. 

Right order (I think), but pedal pumping rather than vacuum bleeding risks getting air into the ABS block, with possibly the results you document. I think you may need to do a VCDS bleed of the ABS.

[Pwskii]

12 hours ago, J.R. said:

I didn't think having upside down calipers & not being able to bleed them properly could have caused your problem but reversing them is very common so just wanted to eliminate that.

 

It sounds like the servo is losing vacuum, check all the hose connections.

I will have a good look around today.

 

1 hour ago, KenONeill said:

Right order (I think), but pedal pumping rather than vacuum bleeding risks getting air into the ABS block, with possibly the results you document. I think you may need to do a VCDS bleed of the ABS.

I will try to get in hold of VCDS and bleed ABS.

[Dean]

With pedal pumping, you risk rupturing the seal on the master cylinder, it's advised to use VCDS (as mentioned above). Also, there are two bleed nipples on the master cylinder, make sure you bleed both or you'll pedal will sink to the floor. It took me 2 days to finally work that out myself!
 

Quote

When bleeding using the pumping the pedal method, the piston will move further down due to less pressure past where a ridge would have been worn in. The seal catches on the ridge and flips.

I posted a video in another topic -

 

[J.R.]

It does not sound like there is air in the system from the description.

 

It sounds like there is a firm pedal, the servo initially works, the brakes retard the vehicle & then for reasons as yet unknown the vacuum fails at which point the full force of the massive servo control loading spring opposes the drivers foot on the brake pedal.

 

Its definitely worth bleeding both the master cylinder nipples which may bring a firmer pedal once the servo issue is resolved but bleeding the ABS block risks making things even worse for no possible (in my opinion) gain.

[Pwskii]

1 hour ago, J.R. said:

It does not sound like there is air in the system from the description.

 

It sounds like there is a firm pedal, the servo initially works, the brakes retard the vehicle & then for reasons as yet unknown the vacuum fails at which point the full force of the massive servo control loading spring opposes the drivers foot on the brake pedal.

 

Its definitely worth bleeding both the master cylinder nipples which may bring a firmer pedal once the servo issue is resolved but bleeding the ABS block risks making things even worse for no possible (in my opinion) gain.

Thanks for a reply JR. I bled both nipples and then straight after all round. But issue remains the same.

 

I am intrigued what is causing pedal to lift and go stiff with air hissing sound. Hence I am considering ABS bleed as this is unit that is designed to aid brakes. I could be wrong I am trying to connect the dots. 

[J.R.]

There is no question in my mind that the hissing noise you can hear is air leaking into the brake servo vacuum chamber, that is 100% why you are feeling what you are feeling through the brake pedal.

 

Other than checking all of the vacuum hoses for splits and leaks, and the one way valve to the servo I cannot guess where the leak is occuring but if the one way valve is working correctly then any vacuum leak of all the myriad emissions devices should not bleed air into the servo so that valve would be at the top of my list together with any servo connections downstream of it.

 

Its probably simply a perforated diaphragm.

Edited 11 July, 2021 by J.R.

[Pwskii]

Thanks guys for all the responses. My plan of action will be to first of all inspect all the vacuum hoses and pay particular attention to one way valve. I might consider replacing it.

 

My next step will be to look into servo itself. I think the only option is to replace it  "Goaal!!". As it is a sealed unit.  Unless any of you guys know how to test it.

 

I will keep you posted of progress and eventually a solution.

 

P.s. Guys it's coming home

[Pwskii]

I had a good look around all the vaccum pipes and checked one way valve. They all look good which leaves me with faulty diaphgram.

 

I have found Bosh brake servo on euro car parts (Part Number: 131440477) using Reg Plate search. I burned myself once using it and was wondering whether anyone purchased one or can verify whether this one would fit 1.9tdi ASZ.