Spongey brakes

[DuncS3]

Since the recent Castle Coombe trackday my Porkers seem to be more spongy than they were, or have ever been after a track day.

Boiled the brake fluid?

Dunc

[DavidT]

Brake fluid is the most likely mate, time for a change or upgrade even ?

[Prawn]

Stick some Castrol SRF in it, that will solve all your boiling problems, bit pricey though.
Needs to be changed every 9/12 months as well.

[Scotty]

Dunc - is it still no better. I've had this a bit in the past and within a day the spongyness has gone away.

Did you have a lot of brake fade?

[DuncS3]

no brake fade - cars has been in dealers for two days so I'll check tomorrow.

I have 5.1 in there but it could be due a change...

Dunc

[JohnW]

Sounds like fluid to me.
I cooked the fluid on my porker at a track day ( having too much fun )
and this is exactly the feeling I got afterwards.
I had to bleed the system twice to get rid of it for some reason.

Also, don't forget to bleed both sides of the caliper (inboard side first I think).

Cheers,
John.

[DavidT]

My brakes were the same until the fluid was changed last week.

I also noticed the stopping force was reduced a little, no matter how hard I pressed. It stands on its nose again now

[DaveP]

My brakes were the same until the fluid was changed last week.

I also noticed the stopping force was reduced a little, no matter how hard I pressed. It stands on its nose again now

Will never forget your brakes at LeMans matey!...Awesome stoppers.

[DuncS3]

I think I'll get the fluid changed then....just where to get it done..

[JohnW]

Do it yourself !!

Get down to halfords and buy an eazi-bleed kit and a bleed nipple spanner. Or, if you prefer you can borrow my eazi-bleed and spanner.

With that, a bottle of fluid, and an old milk bottle or jam jar to collect the old fluid it takes less than 5 minutes a corner once you have the wheel off.

Go on, get your hands dirty

[sitas3]

I changed mine once on my old S4 using the eazi-bleed kit and some ATE Super Blue fluid and I nearly blew the top off the fluid reservoir. Think i was using too much tyre pressure through the device

[JohnW]

Err, yes, I imagine you were !!

It does say on it not to use more than about 20psi, so not a good idea to connect it straight to your tyre with 36ish psi in it. I've done the same too before now, but realised the reservoir wasn't meant to be that shape...

[Scotty]

The above confirms my original thoughts from many moons ago but a couple of years ago I was told that if you boil the fluid then you don't have to replace it. The theory is that it's a closed system and hence the gas doesn't escape. Over a day or two the gas gets reabsorbed into the fluid and you're back to normal.

Of course this doesn't get around the problem of fluid ageing but I did find the above worked a couple of times on my old TT.

[JohnW]

Boiling the fluid apparently changes its properties, and means it will absorb moisture more readily. It also means as you say gas is created.

Fill a piece of clear plastic tube with some fluid, leave a bubble in the middle and block the ends. Leave it for a week/month/whatever, and I bet it will not get absorbed, even if under pressure. At best it will migrate to the top, which on a car is hopefully the reservoir, but on a lot of calipers is just the top of the caliper next to the bleed nipple...

Fluid will absorb moisture but not oxygen/hydrogen on its own.

Well, that's my understanding anyway. If in doubt do a web search as there is loads of information (as well as speculation) to do with how fluids react over time/temperature.

[Scotty]

I agree with what you're saying but if it's a closed system where would the moisture come from?

p.s. This is my attempt at searching the web!!