andreiu

Hello.Since I have this care I have a strange problem with the brakes.After airing the brakes,after 3-4 days my brakes become soft.I have no problems with the cilinders.Any ideea?Thx.

KenONeill

Do you mean "bleeding the brakes"? (bleeding or pumping air bubbles out of the hydraulic lines)

If so, and presuming you're doing the circuit in the correct order (I think right-hand rear, left-hand rear, right-hand front and last left-hand front for a left-hand drive car with 4 bleed points: Rear, RHF, LHF for an LHD car with 3, and reverse lefts and rights if it's an RHD car) then I'd say you must have an air leak somewhere, or else aren't topping up the reservoir often enough during the bleeding process. Is there any sign of brake fliud on the underbody or in the engine bay?

shytot

When you bleed (air?) the brakes does air come out? You hear a sort of spitting / spluttering noise. Or is it just fluid that comes out, more of a hissing noise?
The pedal could be going soft for several reasons besides air in the system. One or more of the flexible rubber hoses could be perished or damaged and it is expanding under the line pressure. Or the master cylinder seal may be worn, allowing fluid to flow past the seal.
Sorry not to be much help but it's difficult to fault find things like this without seeing the car in person!

Simon H

TeflonTom

my guess is that you've got a brake fluid leak somewhere, possibly one of the bleed nipples is not tightened up

andreiu

Hi.What is it for the valve wich is between the servo and the vacuum of the engine??Thx.Mine seems to be broken.

KenONeill

This sounds like it might be the "vacumn servo unit check valve". It's a one-way valve which should, if working correctly, allow airflow from the servo end of the valve to the inlet manifold end.

I'd expect a failure here to give you a very heavy brake pedal (because you'd have reduced or no vacumn assistance to apply pressure to the brake fluid, and hence the brakes), but not the spongy one you were complaining about earlier.

andreiu

Hi.How can affect the car if this valve is broken??Thx.

KenONeill

I don't know this, cos I've never heard of one failing, but as I said earlier, I'd expect to get a heavy brake pedal (meaning it takes a lot of force to stop the car) if one failed. I'd also expect the pedal to feel harder under your foot.

If you can borrow a car with known working servo brakes from someone else, then, with the engine off, pump the brake pedal several times until it starts feeling very hard to push it down. Now start the engine with your foot on the brake pedal, and you should feel the pedal (and your foot if you keep constant pedal pressure) descend. Take your foot off the pedal and let the engine idle for a minute or two. Try the pedal again and it should feel much as before. Switch the engine off and pump the pedal again.

You should have a good idea now as to how the brakes feel with the vacumn check valve (or the servo itself) broken.

TeflonTom

if the non return valve is broken you wont have any servo assistance

if the hoses are split it can lead to over fast idling problems

andreiu

Ok.I have repaired the non return valve.It seems that the brake it is not hard as before .And I hear a "fiss" sound know .Still if I hti the brake pedal 3 or 4 times the engine seems to "die".Any ideeas??

KenONeill

Well, the pedal feeling softer is normal, because the engine vacumn is now doing some of the work of applying pressure to the brake system, instead of you doing it all with your foot. If the "fiss" sound only happens when you brake, that may be normal too (I'm a reasonable mechanic, but I've never owned or driven a Favorit or Estelle (guess from the 135Le engine/trim designation so I don't know either way).

If the engine's dieing when you're idling and pressing the brake pedal repeatedly, it may just be that you've got the idle speed set too low, idle mixture too weak or need a new air filter element, because the brake servo works by using engine manifold vacumn (the air moving through the intake system is at a lower pressure than the atmosphere as a whole, because it's moving. This can be verified and explained in great detail by looking up works on "fluid dynamics", which I'll leave to you because my knowledge of Eastern European langauges is non-existant, and you may not want to try and understand an English scientific text).
In this case, start by looking at the air filter element to see if it is very dirty (it will probably look black, at least in part, if it is), and change it before touching the idle settings. This is because, if the filter is dirty, and get's changed after you've chainged the idle settings, you'll have to try and change them back again!

andreiu

Hi.I think I have solved the problem.I have looked again at the rear wheels brakes and I have changed all the garnitures and now the brakes works better.I stiil have the problem with the engine dying at idle when I press the brake pedal repeatedelly.I will try to change the air filter and then if it is no change ,adjust idle speed and/or the mixture.