Yet another brake issue

[hovgaard]

I have dodgy brakes. "Yeah - don't we all" I hear you saying. But I think mine are dodgier than that. I have an S4 with the dreaded ABS and pre-pressurised fluid system. The whole brake setup just seems way too complex to me, and I don't fully understand how it works. And who needs ABS anyway?

What happens is this: When I press the brake pedal, nothing much happens for about half a second. During this time, a small hissing sound is heard from the front of the car. After the half second, the brakes are working normally including the ABS and all. After some use, the brake fluid becomes white with microscopic air bubbles, but they go away after a day or so. Other than that, it's working normally, the dashboard light doesn't come on when it shouldn't, the pump comes on for a little while after a few stops, and there are no spills.

So now I wonder - is this a master cylinder issue or is it an accumulator issue? Anybody have the skill or experience to tell me what is going on here?

I could try the 'brakes only ever made cars slower' mindset. But now see as I think brakes are important, I would be much appreciative of an answer.

[Guest esprit geoff]

I'm no expert - but could be that the system needs bleeding.

Geoff.

[hovgaard]

Tried that a few times - it helps, but only a bit and only for a short period.

[fflyingdog]

I have dodgy brakes. "Yeah - don't we all" I hear you saying. But I think mine are dodgier than that. I have an S4 with the dreaded ABS and pre-pressurised fluid system. The whole brake setup just seems way too complex to me, and I don't fully understand how it works. And who needs ABS anyway?

What happens is this: When I press the brake pedal, nothing much happens for about half a second. During this time, a small hissing sound is heard from the front of the car. After the half second, the brakes are working normally including the ABS and all. After some use, the brake fluid becomes white with microscopic air bubbles, but they go away after a day or so. Other than that, it's working normally, the dashboard light doesn't come on when it shouldn't, the pump comes on for a little while after a few stops, and there are no spills.

So now I wonder - is this a master cylinder issue or is it an accumulator issue? Anybody have the skill or experience to tell me what is going on here?

I could try the 'brakes only ever made cars slower' mindset. But now see as I think brakes are important, I would be much appreciative of an answer.

<{POST_SNAPBACK}>

Hi Jens

I have an S4s with the abs system and have lots and lots of snags with it most times mine has been troubleshot down to a bad pressure switch ,the new modded one is grey and the old one black,located on the abs pump/accumulator assembly.

As to your 'hiss' I have never ever heard mine 'hiss' even when braking like a man posessed,are you sure you dont have a leak?maybe your seals are going bad in your master cylinder?(although i cant see it). Dont what ever you do change the accumulator without first changing the pressure switch(

[hovgaard]

Come to think about it, I rather like the idea that it is merely a matter of bleeding the system (I like cheap solutions). Until now, I have tried to do this the traditional way out at the wheels, with no convincing results. So I was just wondering, with this brake system being such a weird mothertrucker, is there a special procedure in place for bleeding the device itself? It does have a couple of intriguing nipples on it (no joke implied). If there is, then that would also be news to this towns self-appointed Lotus mechanic (whom I trust).

[s4simon]

Just reading through the S4 Brake manual, the whole bleeding process is almost 3 pages long.

If you want I can scan tomorrow and email over the relevant bits.

Choice is:

The bleeding process (small attachment size - 100k)

ABS Service Notes (Large attachment size - maybe 10 meg), which is not the whole manual, only the first half as the last half is fault finding.

PM me if you require any of the above.

[joakim_adolfson]

Come to think about it, I rather like the idea that it is merely a matter of bleeding the system (I like cheap solutions). Until now, I have tried to do this the traditional way out at the wheels, with no convincing results. So I was just wondering, with this brake system being such a weird mothertrucker, is there a special procedure in place for bleeding the device itself? It does have a couple of intriguing nipples on it (no joke implied). If there is, then that would also be news to this towns self-appointed Lotus mechanic (whom I trust).

<{POST_SNAPBACK}>

Hi,

had the same problem with my 92 highwing earlier this spring. I changed the accumulator to no effect. I then bleed the brakes properly ( http://lotusespritworld.co.uk/EMaintenance...ingBrakes.html) and the brakes are now as good as they are ever to get, in other words I spent 200 euros on a accumulator I didn't need.

GoodLuck!

[hovgaard]

Why didn't I spot that web page before??? Simon has just been kind enough to provide much the same thing by email...

[hovgaard]

Thanks for you helping efforts so far.

I have attempted to bleed the brakes by the book, but there isn't much difference.

Some observations:

* The pump comes on after 1 or 2 stops.

* With pressure in the accumulator, there is always a half-second hissing noise before the servo effect is felt on the brakes stopping power. Pedal feels good though, and ABS works.

* With the car switched off, there is pressure in the accumulator for plenty of stops, until you can feel the pedal feel changes when the accumulator is empty, and the hiss stops.

* With the accumulator empty, there is no sound, no delay, no servo-effect, and a nice firm pedal.

* Pulling a few fuses to disable ABS makes no difference to the matter of noise and delay, but it felt nice not to have ABS, I think I can brake harder without it. The dash light came on (fixed light).

Am I the only one with noisy brakes? How to proceed from here? Will changing out the pressure switch have any bearing on these symptoms? Did I simply screw the bleeding up?

[fflyingdog]

Thanks for you helping efforts so far.

I have attempted to bleed the brakes by the book, but there isn't much difference.

Some observations:

* The pump comes on after 1 or 2 stops.

* With pressure in the accumulator, there is always a half-second hissing noise before the servo effect is felt on the brakes stopping power. Pedal feels good though, and ABS works.

* With the car switched off, there is pressure in the accumulator for plenty of stops, until you can feel the pedal feel changes when the accumulator is empty, and the hiss stops.

* With the accumulator empty, there is no sound, no delay, no servo-effect, and a nice firm pedal.

* Pulling a few fuses to disable ABS makes no difference to the matter of noise and delay, but it felt nice not to have ABS, I think I can brake harder without it. The dash light came on (fixed light).

Am I the only one with noisy brakes? How to proceed from here? Will changing out the pressure switch have any bearing on these symptoms? Did I simply screw the bleeding up?

<{POST_SNAPBACK}>

Change your pressure switch

[hovgaard]

Okay.

[hovgaard]

Dont what ever you do change the accumulator without first changing the pressure switch(