c4p ag agressive braking

[renel]

Hi, I have 2 c4picasso's year 2007, one is a Grand diesel egs and one is a gasoline manual. I expect the braking system to react similarly. The diesel brakes very good and is easy to modulate but the gasoline is quite agressive meaning it is difficult to modulate, and a sudden braking action almost blocks the car. It can be modulated as long as you are aware and are prepared but it is quite different than the diesel car. Is it possible that the vacuum modulation valve in the brake booster is defective? Has that been experienced on these cars? If so can it be repaired/cleaned or a new booster?

[GiveMeABreak]

I'd be more inclined to check whether the system has been properly bled when it last had it's brake fluid changed (which should be every 2 years). ESP systems require primary and secondary bleeding (with the diagnostic tool for secondary bleeding). Failure to properly bleed the circuit can lead to operational / performance issues with the system.

[PaulC5]

If the brakes have not been serviced (taken apart and cleaned) in the last 1 or 2 years then that would be something to do to help them work smoothly. You can also check if they have the correct brake pads.

[renel]

Thank you for suggestions, pads are fine and new, car bought used 18months ago, never bled?? will try that, have Diagbox/Lexia

[ozvtr]

pads are fine and new, car bought used 18months ago

Brake pad material makes a big difference!
If you do not like the performance of the brakes, change the front pads.
There are lots of things that will make the brake system perform poorly. But only the brake pad material makes the brakes perform too well!
Yes, "snatchy" brakes are annoying!

[renel]

Thank you for input, this is also worth trying, and easy, I remember now that one of the front bleed screws are actually broken (rust) which makes it not so easy to bleed.
Any good idea to get the bleed screw out? Can be drilled out but I do not want drill shavings near the brake system;-) maybe lots of heavy grease on the drill;-) and the thread tap!

[GiveMeABreak]

That is likely where your issue is then. If was not previously bled properly (indicated by the inability to loosen the bleed nipple), then you will likely have air in the system. I'm not sure about drilling out the brake caliper drain screw to be honest, as that may damage the thread if not careful. Either that or have the caliper replaced that will come with a new one in any case, then bleed the system correctly.

[ozvtr]

I remember now that one of the front bleed screws are actually broken (rust) which makes it not so easy to bleed.
Any good idea to get the bleed screw out?

Nope! Sounds like the calipers need to come out and be serviced. If we are talking rust, I'd want to make sure the piston bores are not damaged from rust (moisture) in the brake system. You wont be able to get the bleeder nipples out without drilling if they are snapped off. If they are also rusted an EZ-out probably wouldn't work either.

FYI. Air in the brake system gives the brake peddle a "spongy" feeling and reduces braking force. "Snatchy" brakes are from the brake pad material. If the brake peddle normally feels "fine" but sinks to the floor under constant and hard braking, that's brake fade and could be brake pads or poor (contaminated) brake fluid. A really hard brake peddle is a problem with the vacuum system, booster or non return valve. If the car pulls to one side under braking, that's probably a rusted piston or rusted/stuck slide pins.

[renel]

It brakes just fine and brakes straight, problem is it is too fine, "Snatchy" as you describe it, it is not spungy, I just mensioned the bleed screw to tell that an actual bleeding would be a little difficult. I mensioned the vacuum valve modulation, because it feels like it is just Catching like an anchor if you are not observant to "thread lightly", as mensioned my other car in comparison is more human when braking, it can brake hard but is easier to modulate. But I guess that the vacuumvalve is not a sparepart?
René

[ozvtr]

But I guess that the vacuumvalve is not a sparepart?

Not all cars have them. They are usually in the vacuum line from the inlet manifold to the brake booster. However newer cars tend to have a separate vacuum pump on the engine.
To check the vacuum system; put your foot on the brake peddle and push down firmly. It should feel very "hard", like there is a brick under the brake peddle. Then start the engine. The peddle should drop about a centimeter or so and become "softer" under foot.

If I could be so bold, the brake fluid is hydrocsopic. That is is absorbs moisture from the atmosphere. That moisture condenses, forms water and settles in the low spots of the brake system. The "low spots" are the piston bores of the brake calipers. The calipers are high in iron and rust very easily. To stop this, the brake system should be flushed every year. Because it's mostly sealed, the system can tolerate not being flushed for a long time...but not forever!

[renel]

ozvtr
Thank you for your input.
"renel wrote: ↑01 Nov 2024, 20:07
But I guess that the vacuumvalve is not a sparepart?", I was not correct on this, inthe text in mension more correctly "the vacuum valve modulation" which must be inside the vacuum booster and therefore probably not a spsrepart item. I am thinking/working on it, the car is driving a lot, so I need to ground it to get further on with it;-)