Soft brake pedal – could it be the Brake Booster?

[Maxan]

Hey guys!

So I have a Peugeot 205, CJ 1.4 1990.

Been struggling with a soft and bad working brake pedal (a wet sponge). I’ve changed shoes (they’re touching the drums as should) wheel cylinders and master cylinder and there’s no air when bleeding the brakes. Front brakes looks quite fine as well. I’m thinking it could be some air leaks at the brake booster. (The car is also hesitating a bit on acceleration).

Would it be an idea to go after the booster? And if so, what seals/gaskets/parts would I change? Check valve?

And most importantly, where would I find some kits? And would a vacuum hose/ check valve be some universal stuff or is ir hard to find?

Many questions hehe …

Would very much appreciate some tips. Thanks for now!

[mickthemaverick]

Have you done any work on the front calipers? If you are sure you have bled the system properly and they are still spongy then it is likely to be a leak somewhere allowing air in. I'd clean and lubricate the caliper pins and make sure the pistons are all free. then try again.

[RichardW]

Unlikely to be the booster - easy to check - with the engine off, pump the brake pedal a few times and the vacuum in the booster will be exhausted, and the pedal should go hard. If it doesn't then you have a hydraulic problem somewhere. On an older car a hose swelling up under pressure, or a failing master cylinder seal are likely causes.

[PaulC5]

I would have thought a faulty brake servo (booster) would result in the brake pedal needing a lot of effort. A check is to turn the engine off, then push the pedal a few times to remove the servo vacuum (you should hear air going in to it), the pedal should then be hard, then start the engine with a foot still on the pedal and it should then sink down a bit more.

Other possible causes of a spongy pedal apart from air in the system can include wear ridges on the brake drums and discs which can be filed off, rear drums being worn, rear brake shoes and adjusters not being set correctly, failing brake hoses which expand under pressure, a failing bulk head were the pedal pushes against so it flexes, any leaks, seized cylinders/pistons, seized sliders so calipers can not easily move.

[Gibbo2286]

If you rest your foot on the pedal and it slowly sinks to the floor it's likely to need the ABS bleeding. See my post here: viewtopic.php?t=84711&hilit=ABS+Bleed

[Sloppysod]

Try this, wedge a length of wood between the underside of the steering wheel and the brake pedal so the pedal is fully depressed. Then leave it over night.

Not sure of the reason why, but more times than not may cure your problem.

[Oldpug]

It’s nothing to do with the brake servo (booster). If that fails you will get a rock hard brake pedal and have to press it very hard to stop.
Spongy brakes are normally caused by air in the system.
Are you sure the master cylinder you fitted is exactly the same as the original, particularly where it fits to the servo and the servo push rod.
If so bleed m/cyl first before all four corners. Slacken a pipe nearest the servo and slowly depress the pedal, tighten the pipe and release the pedal. Do this a number of times to all four pipes. Then bleed all four corners.