Brake Pedal goes to floor...

[TREMAiNE]

Our track car lost half its brakes during its last outing.
They worked, but barely. Possibly one of the circuits has gone?

Anyway... we replaced the master cylinder and have bled the brakes but the pedal is still going to the floor.

Any suggestions about what is wrong or what we can do to fix this issue?

Car is a ZC31S Suzuki Swift Sport.

Thanks.

[Super Sonic]

Fluid leak, air or broken linkage.

[TREMAiNE]

No visible leaks or broken lines, everything was replaced 2-3 track days ago with decent quality braided lines.

Calipers have just been refurbished over winter, too.

[E-bmw]

Basically, it sounds like you need to get the brakes looked at from end to end by somebody competent to do so.

Brakes don't really just "stop working" in use.

All calipers need checking out, the discs & pads need to be checked, and the system needs to be bled properly from end to end.

The situation you describe could be a number of related issues & systematically diagnosing them is your only answer.

[stevieturbo]

TREMAiNE said:

Our track car lost half its brakes during its last outing.
They worked, but barely. Possibly one of the circuits has gone?

Anyway... we replaced the master cylinder and have bled the brakes but the pedal is still going to the floor.

Any suggestions about what is wrong or what we can do to fix this issue?

Car is a ZC31S Suzuki Swift Sport.

Thanks.

This would then suggest they are not bled properly.

And before, you seemed to imply only one circuit had a problem ?

How did you bleed them, and do you have any brake operation at any corner ?

[Pica-Pica]

I would start with a visual check. Then see how they perform on a normal road, and then on a brake roller machine (i.e. MOT). Then you will have a record for the brake efficiency at each corner. It’s quite possible that the brake fluid is old/inadequate, and the fluid has boiled any water in it and created the sponginess.

[b0rk]

To throw a random idea at the problem, as the callipers where rebuilt recently you have checked that all the boots and seals are still present? and that the channels are clear.

Did you rebuild the callipers or where these done professionally? Did you check that no foreign particles had enter the callipers during or post rebuild. Something thing as simple as the rebuilder not plugging the entry or bleed ports and a particle becoming dislodged during use.

[Kerniki]

I have the same thing on one of ours (not track car) where it works fine when cold but when things get warm (not hot) the pedal disappears and only one wheel just about stops the car.

I’m thinking increase in temperature means one of the rubber seals is becoming weak… no fluid leaking anywhere.

[TREMAiNE]

Thanks all... Every possible avenue we've looked at looks like all is ok. We'll have to try bleeding again, as air still being in the system is surely the only logical issue. Hopefully we can get sorted before next weekend when our next TD is! :HEHE:

E-bmw said:

Basically, it sounds like you need to get the brakes looked at from end to end by somebody competent to do so.

Brakes don't really just "stop working" in use.

All calipers need checking out, the discs & pads need to be checked, and the system needs to be bled properly from end to end.

The situation you describe could be a number of related issues & systematically diagnosing them is your only answer.

With all due respect, this is an incredibly patronising comment.
We've had this track car for years, my friend who I do this with has refurbished the brakes on multiple occasions, we've bled the system on multiple occasions over the years.

We are aware that there are a number of issues that could cause the problem, and we have been trying different solutions as to what it might be, hence the reason for this post - asking for some advice of what else we could look at to see if we can sort ourselves.

Your comment is of absolutely no value, relevance or help to the question asked.

stevieturbo said:

This would then suggest they are not bled properly.

And before, you seemed to imply only one circuit had a problem ?

How did you bleed them, and do you have any brake operation at any corner ?

We've bled the system multiple times before over the years and never had a problem.
My friend does think that there is still air in the system - maybe unlucky as we've not had this problem before.

It's a track car, so not road legal to properly test. Pedal goes straight to floor with minimal resistance.
Not sure if any braking is applied or if there is nothing at all (I wasn't there today when he tried again).

Pica-Pica said:

It’s quite possible that the brake fluid is old/inadequate, and the fluid has boiled any water in it and created the sponginess.

It's brand new race spec brake fluid, so we know that's not the problem.

b0rk said:

To throw a random idea at the problem, as the callipers where rebuilt recently you have checked that all the boots and seals are still present? and that the channels are clear.

Did you rebuild the callipers or where these done professionally? Did you check that no foreign particles had enter the callipers during or post rebuild. Something thing as simple as the rebuilder not plugging the entry or bleed ports and a particle becoming dislodged during use.

Good suggestion - checked and everything present, everything plugged. Everything appears to be as it seems, all worn seals etc were all replaced.

[Evanivitch]

I think it's worth saying the answer is not an Italian tune up in this instance.

[GAjon]

Calipers upside down.

On the wrong side.

Edited by GAjon on Monday 1st April 17:45

[TREMAiNE]

GAjon said:

Calipers upside down.

On the wrong side.

Edited by GAjon on Monday 1st April 17:45

Do you think maybe we should not have bought callipers made of marshmallow?
Maybe that'd explain the sponginess.

[Hammer67]

Clamp all 4 hoses.

If that restores the pedal, release one at a time until it goes soft to isolate which corner is causing the problem.

[Quinten]

Some advice I got for my Westfield and turned out to be working for me, is to pump the pedal a few times hard and then jam it with a plank of wood and leave overnight.

[GAjon]

TREMAiNE said:

GAjon said:

Calipers upside down.

On the wrong side.

Edited by GAjon on Monday 1st April 17:45

Do you think maybe we should not have bought callipers made of marshmallow?
Maybe that'd explain the sponginess.

You didn’t say they were AB (Aunt Bessie’s) calipers!

As regards to fitted wrong way around, you wouldn’t be the first and certainly not the last.

[GreenV8S]

Did you boil them? If they're about to boil, they will usually do it after you come off the brakes. Common symptoms are that the brakes are OK on one corner and the pedal goes to the floor on the next, often accompanied with brake fluid blown out the reservoir.

[stevieturbo]

TREMAiNE said:

It's a track car, so not road legal to properly test. Pedal goes straight to floor with minimal resistance.
Not sure if any braking is applied or if there is nothing at all (I wasn't there today when he tried again).

I didn't ask you to drive it.

I asked you if there is any braking effort at all on any corner.

[stevieturbo]

Hammer67 said:

Clamp all 4 hoses.

If that restores the pedal, release one at a time until it goes soft to isolate which corner is causing the problem.

Can be a useful tool, if rubber hoses. I wouldn't go clamping teflon hoses.

[TwinKam]

I think you may have air trapped in the ABS unit. We try our damnedest not to allow this to happen as it can be a bh to get out, but sometimes eg replacing the master cyl it is inevitable.
You can bleed it 'electronically' via the OBD if you have a compatible scan tool, but you could try to manually bleed it at each of the four line-out unions on thd ABS unit, before bleeding the four corners again.

[RemarkLima]

I've read that ATE make a blue brake fluid, so when bleeding it's clear when you've got fresh fluid. Could be worth a shot to make sure each corner is flowing correctly?