Brake help please! Soft pedal only when car is running

[Amjad]

I'm guessing this is my MC that's failed/failing? Did half of my 4 hour track session at JF2 with a little air in the system, would this have caused the MC to fail?

Pulled in, bled system and it was way better.

Did the second half of my session fine, but found that leaving Donington my pedal was pretty soft! Got a mate to jump in when I was bleeding so I'm not sure if he was pressing pedal a bit too hard at the time?

Gonna check pads aren't just low but I would think that low pads, after giving more pedal travel than usual would still give a firm pedal towards the end of the travel? The pedal just stays soft at the moment

Any help is much appreciated!

Amjad

[turbo Grant]

Just give it a good pressure bleed. Release the bleed nipples when someone is inside pushing the pedal down. Then lock it back up before they relise the pedal. Works a treat that way.

[WallaceGlanza]

Getting rid of the ABS will sort it, brakes feel much better without!

[mikey4410]

Maybe the trackday has caused a few issues somehow.bleed thoroughly and that should make it better.

and yeah abs sucks balls

[morgey]

Theres a possibility the fluid behind the pistons has boiled creating air in the system again.

A quick bleed should sort it.

I was told that you should bleed your brakes after every track day becuase of this. Also it keeps fresh fluid in the system

[Keri-WMS]

My understanding is that once brake fluid has boiled it needs changing because it can retain gas bubbles, and it will also boil in future at a lower temperature (!!) and that it is also APPARENTLY more compressable even excluding the bubbles!

So a full flush is a good idea if you've ever boiled your brakes.

[DavidAshton]

My pedal has gone quite soft since my short 20 minute track session, not sure they would have survived a long session.

It strange though as they were perfectly fine on track and when I parked up, went to drive home and they were softer.

Hoping a bleed will bring them back in.

[morgey]

My thoughts would be You'll have air circulating when driving, as soon as you park up the cooling would stop and cause excess heat which might in turn cause the issue.

[Amjad]

Cool, thanks for the advice fellas! Sorry I haven't been on in a while, car has been the same but I've gotten used to it. Will have to try a fresh bleed and fluid replacement when I get a chance!

So much for Gulf "Racing" brake fluid lol

Oh and I don't have ABS

[MARC MOSS]

Flush it through and Go get some synthetic dot 5.1 from opie oils mate I bet any money as already said you have boiled the fluid behind the pistons, I have done it many times on track and this fluid will help although after a hard day on track it will still feel like the pedals shit. That and when you have bled the system pump the pedal up as hard as poss with the engine off and force it down over night when it's at it's hardest as it will force the remaining air from the fluid.. Trust me

[daniel_g]

Cant beat a good brake & clutch bleed sesh lol.

[Amjad]

Just a quick update, I bled the system at Xmas and it improved things, but still felt "off". Got a bottle of ATE Type 200 (thanks ID-Workz!) and flushed 900ml through the system after extracting as must as I could with a syringe from the MS. And it's pretty much back to normal! There's a slight bit of travel before the brakes engage but I guess that's pads running low?

Flush it through and Go get some synthetic dot 5.1 from opie oils mate I bet any money as already said you have boiled the fluid behind the pistons, I have done it many times on track and this fluid will help although after a hard day on track it will still feel like the pedals shit. That and when you have bled the system pump the pedal up as hard as poss with the engine off and force it down over night when it's at it's hardest as it will force the remaining air from the fluid.. Trust me

Marc can I just run through what you've said to make sure I've understood it correctly?

I've replaced all the fluid now so that's cool. To get the last bit of air out if there is any:

-Pump pedal until it's hard, leave it overnight

-In the morning, just bleed a little from each caliper in case there's air left?

[AdamB]

When you come off track did you put the handbrake on at all?

That will boil also the fluid so when you come off track just leave the car in gear rather than putting the handbrake on.

[Amjad]

I was aware that you shouldn't apply handbrake after pulling in so I'm pretty sure I didn't

[Calum122]

Yeah that's interesting I am getting this problem after fitting new brakes.

Seems to bleed fine, then once the engine is running the pedal goes all soft.

I did notice I was using Brembo DOT 4, then saw the mastercylinder cap specify DOT3 but that shouldn't matter right.

I have recently rebuilt the rear calipers and needed to put in a rear line. But I was sure to bleed these lines and test them before I started on the fronts.

Do I need to go around each caliper even though I am only replacing the fronts.

[AdamB]

I would recommend to bleed all 4 corners

You can just gravity bleed them also.

[dan106]

Did you have the handbrake on when you bled them?

I did when I changed front calipers and I have a soft pedal now, haven't managed to fix it yet mind

[Calum122]

Yes I did as a matter of fact Dan.

I guess I never thought about taking it off...

Can't see why this would make a difference though?

I'm using a vacuum pump to remove the fluid, rather than pumping the pedal.

But maybe I didn't.

I will bleed all the corners.

If I can sort this, then that would be really awesome.

Cheers lads

[dan106]

I'm not sure how it would make a difference but I'd definitely re bleed them with it off just to be sure, hoping this will fix mine aswell lol