Spongy brake pedal

[Dave W 0]

I have replaced brake master cylinder, brake pipes front to rear. Have bled numerous times. Have a nice stiff pedal until I start car. How much travel should be on pedal. I have a brake but its a couple off inches before anything happens. Is this normal. Non abs model. Going for its mot on Monday. don't want to be wasting my money.

[Sean_Jaymo 0]

Sounds like a vacuum leak to me.

[Brunty 10]

A vacuum leak should result in a very stiff pedal that you need to exert a lot of pressure on to have any effect. (Try switching your engine off while moving and pump the brake a few times. In a safe environment, obviously!)

 

It's possibly normal, Dave. Does the car stop well? If you can lock the wheels up doing an emergency style stop then it should be fine.

[Dave W 0]

There is a brake, just a lot of pedal travel before anything happens. Cant remember my last corrado having this much travel. Will find out on Monday at mot.

[vw rule 19]

Hello there,

 

on my old MK2 Scirocco that I used to have years ago,

that always had a spongy brake pedal.

I even had I drive in a mate's Scirocco,

to see how it compared to mine and it was exactly the same,

with a spongy brake pedal.

 

But on the MK2 and MK3 Golfs with standard none ABS brakes,

the brake pedal is that bit more firmer,

compared to the MK2 Scirocco.

 

On my Corrado it has got ABS brakes,

the brake pedal is nice and firm.

But on the early none ABS Corrado's the brake pedal,

should feel fairly firm similar to that on the Golfs.

 

I would check you've got the correct master cylinder fitted,

just incase it is the wrong one fitted,

I'm not saying it is but just best to be sure.

Your brake master cylinder inner chamber / seal size,

is about 22mm to 22.2mm for none ABS I think,

so if a master cylinder is fitted with a slightly,

different sized inner chamber / seal,

this can sometimes make the brake pedal feel different.

 

Plus in the past I bought a new master cylinder,

fitted it to the car and the brake pedal kept on feeling spongy, even when I had bled the brakes several times,

so in the end I checked everything that I had removed,

everything looked ok no leaks anywhere.

I thought then the only other thing is a faulty new part,

so I took it back and tried another new replacement,

and it fixed the problem for me.

 

So check everything you've removed / replaced,

get someone to assist you by holding pressure on the brake pedal,

and have a look at all the bleed nipples / brake pipes,

that you've unscrewed or had removed completely for any leaks.

 

Hope this helps.

 

Si

[Dave W 0]

Hi Si, master cylinder is correct one, compared it to old one before fitting. All brake unions and bleed nipples are ok. Don't know what car was like before as I got it as a non runner due to 8 years storage. Really good solid pedal until you start car. Maybe im being over critical. Will see what mot man s got to say. Cheers, David.

[vw rule 19]

Hello mate,

 

fair play if you've checked everything.

 

If the brake pedal is really firm with the engine switched off,

then that's a good sign the system possibly is ok.

 

When the engine is switched off, pump the brake pedal 3 to 4 times,

and on the 4th pump hold the pressure down on the brake pedal,

and once you've switched the engine back on,

the brake pedal should push down slightly as the vacuum assistance,

produced from the suction of the engines cylinders pulls the diaphragm,

inside the brake servo which in turn pulls the brake pedal down slightly,

this makes it a lot easier and saver to brake when driving at speed.

 

That is a test I think they do when a garage carriers out an MOT,

or when they service your car,

they check to make sure the vacuum assistance and servo are working correctly,

and check there's enough pressure with in the brake master cylinder / braking system.

 

The brake pedal should never really go down past half way,

it can come close to it or be between a 1/4 and 1/2 way down,

but must never go past half way.

If it does then you could well have a leak or pressure problem within the braking system.

 

If the brake pedal is pushed past half way down or fully down,

it often damages the seals with in the master cylinder,

so if you are or do bleed your brakes by pumping and holding pressure,

down on the brake pedal only push down half way.

 

The brake pedal should push down around a 1/4 of the way from the top,

or towards half way max, at this point the brakes should be fully applied.

If not then you may well have a problem somewhere.

 

Like I say on my old MK2 Scirocco the brake pedal on that was spongy as standard,

and went down close to half way.

 

On the MK2/3 Golfs as far as I remember the brake pedal on them,

with standard none ABS brakes,

the pedal went down roughly a 1/4 or just over.

 

On my Corrado with ABS brakes the brake pedal goes down,

roughly a 1/4 of the way but some times it can be a little more,

but really depends on how hard you're driving and if the ABS pump is kicking in or not.

Most of the time it goes down 1/4 of the way.

 

But on a none ABS braking vehicles you normally feel more of a consistent feeling pedal,

if you know what I mean.

 

On your Corrado it should be very similar to the Golfs.

 

If in doubt then get it checked at a garage as your brakes are very important to you and other road users.

 

 

Hope this helps.

 

Si

[Brunty 10]

The Scirocco and mk1 Golfs have the problem of the servo being on the wrong side, so there's a pull rod assembly. It's this that needs checking over the years as it's fully adjustable. My mk2 Sciroccos have rock solid pedals.

 

The other thing that came to mind though is that have you checked the rear calipers? They're on sliders too, so are prone to seizing. This can lead to a strangely spongy pedal as you're bending them rather than applying equal pressure with the pads. The results could be visible via the pads, eventually they will go wedge shaped.

[Dave W 0]

All must be ok as just passed its mot. Thanks all.

[Diamond Hell 0]

Is vw rule actually posting in Haikus?

[Sean_Jaymo 0]

A vacuum leak or bad check valve can cause these issues... A lack of vacuum can cause a hard OR soft pedal.

[vw rule 19]

Is vw rule actually posting in Haikus?

 

:lol: Oh yeah could be.

 

It's just easier to read when a large text is broken up in to paragraphs :)

 

 

Si

[Brunty 10]

A vacuum leak or bad check valve can cause these issues... A lack of vacuum can cause a hard OR soft pedal.

 

Can you explain how a vacuum leak causes a soft pedal?