Hey!

I have Skoda Felicia estate 1.9D '97, no ABS. The problem is this typical brake pedal sinking problem, which is also typical for some other Vw-Audi -Group vehicles. Brake pedal is quite normal in the beginning, but then it starts to sink and goes down, almost in down to the floor. There's no air in the system or leaks. This is typical also for Vw Polo, allthough the effect is not that strong as in Felicia.

Let's compare the brakes for example to Ford Sierra '89 1.6:

Master diam. 22.2 mm/front cylinder caliber 54 mm/239 mm disc diam/Rear cyl. diam. 22.22 mm.

And Felicia:

Master diam. 23.81 mm/front cylinder caliber 54 mm/236 mm disc diam/Rear cyl. diam. 20.6 or 22.22 mm.

So probably there's nothing wrong in measuring components.

Once I have once heard from one mechanic that the Vw vacuum booster is too powerful and is the cause for this effect.

If you have experiences on this area, please tell me about your upgrades or ideas how to get rid of this effect.

if the pedal sinks it's likely there is a hydraulic problem rather than mechanical.. i've seen the master cylinder seals get inverted before by pushing the brake caliper piston back in too fast. this would give the same effects you describe

Resurreting this post because i have the same issue. No longer ago, brake pedal start to sink, so today i payed a visit to local shop , he performed a change of brake oil with the machine but i said i wasn't able to perform bleeding from the rear left cylinder saying to try driving and see how it goes. He said that could be the cylinder bleeding valve(that he remove completely) not working may cause air bubble to be still trapped and resulting in bad braking or the pump has "gone".

Any advice where to have a look myself or solution?

Still bad braking.... i was testinkg brake system according to the manual below and after some pumping , the pedal start to sink when depressed firmly ....so tomorrow i will have to check the non return valve

The brake pedal sinks if the system is either losing pressure from an external or an internal leak. Check for external leaks by looking at each wheel for brake fluid seeping outside or inside. Look also for cracks in brake lines and brake hoses. Internal leaks usually refer to a leaking brake master cylinder that it is leaking inside itself. The solution for the latter possibility is to buy a brake master cylinder repair kit (seals) if you're broke or buy a quality new brake master cylinder if you're rich and value your life.

 

PS The test shown in your illustration is for the servo brake mechanism.

Felicias do have quite a lot of travel on the brake pedal

Change the rear left drum cylinder. 

Then bleed again. If brake pedal is still going deep in its travel and feels like there is no end you should remove the 2 bolts holding the master cylinder and look if it's wet on the rear

If it is remove it from the car use compressed air to pop out the piston. 

Go to your local plumbing shop and buy all the seals required. (remove the old and have them as samples don't forget to mention that they are intended to be used with oil not water). 

Then rebuild the whole thing, bench bleed it put it on the car and do a proper 4 wheel bleed. 

Everything should be back to normal and you would have spent less that 10 euros for the whole rebuild. 

Edited 23 October, 20196 yr by Thefeliciahacker

6 hours ago, RicardoM said:

The brake pedal sinks if the system is either losing pressure from an external or an internal leak. Check for external leaks by looking at each wheel for brake fluid seeping outside or inside. Look also for cracks in brake lines and brake hoses. Internal leaks usually refer to a leaking brake master cylinder that it is leaking inside itself. The solution for the latter possibility is to buy a brake master cylinder repair kit (seals) if you're broke or buy a quality new brake master cylinder if you're rich and value your life.

 

PS The test shown in your illustration is for the servo brake mechanism.

Thanks for the reply

I was testing as per manual and the brake fail so i thank to start from there....wrong?

2 minutes ago, Thefeliciahacker said:

Felicias do have quite a lot of travel on the brake pedal

Change the rear left drum cylinder. 

Then bleed again. If brake pedal is still going deep in its travel and feels like there is no end you should remove the 2 bolts holding the master cylinder and look if it's wet on the rear

If it is remove it from the car use compressed air to pop out the piston. 

Go to your local plumbing shop and buy all the seals required. (remove the old and have them as samples). 

Then rebuild the whole thing, bench bleed it put it on the car and do a proper 4 wheel bleed. 

Everything should be back to normal and you would have spent less that 10 euros for the whole rebuild. 

Many thanks !

What could be the cause of that fail? Brake pads and rotors are at their end of life but not finished? Nor the back .

Lack of brake fluid?

9 minutes ago, Zimo said:

Many thanks !

What could be the cause of that fail? Brake pads and rotors are at their end of life but not finished? Nor the back .

Lack of brake fluid?

If the pedal goes deep down and then firmly stops everything is OK and it is most likely some air or squishy components 

If the pedal never stops it is an internal leak of the master cylinder

Driving to work brake "brake" at beginnig than goes down but if i do a lot of pression with foot it brakes. And i can i hear a hiss/whistle coming from the servo zone

4 hours ago, Zimo said:

Driving to work brake "brake" at beginnig than goes down but if i do a lot of pression with foot it brakes. And i can i hear a hiss/whistle coming from the servo zone

Yes a hiss is normal if you press fast you have to investigate further

 

24 minutes ago, Thefeliciahacker said:

Yes a hiss is normal if you press fast you have to investigate further

 

Yes i know it is normal but it is not the same hiss as a normal...seems that something deflate...

1 hour ago, Zimo said:

Yes i know it is normal but it is not the same hiss as a normal...seems that something deflate...

As I said remove the master cylinder and check the back side if its wet. 

So, rear left drum cylinder changed (and bleeding done as the shop said) but breaks still dont operate properly. No always the same behavior sometimes breaks quite good at first than slowly pedal goes down and i have to apply a lot more strenght to brake(like no servo); sometimes it goes down (like no servo) . And seems that is rev related : if i rev much seems that breaks better.....

Still to have the no return valve checked....

 

More if i have to do a strong braking seems that pull on the left side.....

Edited 28 October, 20196 yr by Zimo

Very dangerous to keep driving like that. Your description points to brake servo on the last leg (corroded, dirt, bad diaphragm). Pulling to one side means you have to do a thorough inspection of the front calipers. The piston gets corroded, the sliding pins get stuck, etc. As a thumbs rule for a humid environment, look first for corrosion, dirt, and only then look for mechanical/electrical failures.

Checking all the front brake callipers is on the way, but what about the pressure regulator?

4 hours ago, Zimo said:

what about the pressure regulator?

Its role is to regulate the pressure for the rear brakes depending on load. At worst it is probably stuck from corrosion but I don't think it has any role in pulling to one side.

22 hours ago, RicardoM said:

Very dangerous to keep driving like that. Your description points to brake servo on the last leg (corroded, dirt, bad diaphragm). Pulling to one side means you have to do a thorough inspection of the front calipers. The piston gets corroded, the sliding pins get stuck, etc. As a thumbs rule for a humid environment, look first for corrosion, dirt, and only then look for mechanical/electrical failures.

I have to still check for the non return valve but the pickup now is closed in my garage to check brake, hard top and so on....

I have take a look to the net (by 7zap.com) and seems that may not exist a spare parts for the servo.... bit scary....

I doubt the non-return valve is bad but check it anyway.

Food for thought.

 

18 hours ago, RicardoM said:

Food for thought.

 

Many thanks it has a lot of infos....so changed the front  brake pads because of were quite at the end and have the "retaining" springs broken. The front left piston caliper was pretty hard to made go back , so a have to use a "press". Still have to check the non return valve and have a test run....this period is crazy busy and the felly seats in garage....

Out of pure frustration reading your posts, I am going to join in on this thread!

 

Why are you jumping all over the place regarding these brakes? You have two people giving you the right answers, you do not follow them but jump to something else that has no bearing on the matter! Why?

 

You originally came in with 'pedal slowly sinking all the way' and you had the right answer - an internal leak on the master cylinder. Have you done as instructed by unbolting the master cylinder to see if it is wet behind? Do this as priority and not worry about non return valves at this stage. I fear you have a bucket of problems with your brakes and not enough knowledge to put them right on your own. Therefore you MUST follow instructions from those that do! Check the back of the master cylinder and report back!

5 hours ago, Zimo said:

Many thanks it has a lot of infos....so changed the front  brake pads because of were quite at the end and have the "retaining" springs broken. The front left piston caliper was pretty hard to made go back , so a have to use a "press". Still have to check the non return valve and have a test run....this period is crazy busy and the felly seats in garage....

You said it was pulling to the left and now you say that the left caliper was stiff. 

So yeah one problem sorted. 

Try to free it or repair it. 

Secondly all the non return valves or vaccum regulator and what have you should make braking easier. 

Even if you totally disconnect the vaccum the brakes should just feel really stiff and be hard to depress. 

I bet vaccum is just another problem but not your major one. 

Felicias brakes are quite simple in regards to their proportioning. 

They just have pressure regulators for the rear brakes at one side of the master cylinder and that is it preety much. 

It may be confusing but you have to track the problem don't methodically and not jump from issue to issue. 

@Haladams thanks for ur message sometimes us usfull some rimg bell but my concern about the non return valve come from the skoda workshop manual and the changing of the brake pads was to be done because also Ricardo told me to check the callpiers and so i decided to put new ones.

@Thefeliciahacker as always thanks for the suggestions. I in the process of bed restoring, actually hard top better installation so after finish that i will try to check the valve and master cylinder but this one i think would assorb much time(and as u know i dont have much now). I still have to watch whole video that Ricardo posted above but if u can suggest a process to disasseble the master cylinder from the servo i will be vary gratefull.😃😃😉

Two very visible nuts hold the master cylinder to the servo - undo them most of the way, prise off the cylinder 10mm,  and put a QTip in the back. If you do not have any leaks at the wheels and your pedal is going down all the way, then the QTip will be probably be wet.  Which means you probably have fluid in the servo. Before you do anything else, the cylinder needs attention, the servo needs cleaning along with the vacuum line BEFORE you move to the next item...