We have done 4 trackdays in our track impreza so far this year with no issue...

However last wednesday after a reasonably hard 15-20min session, the brakes were starting to fade a little towards the end (nothing unusual there), but they have not returned to there previously sharp feeling, even after cooling down & overnight.

I'm thinking we could have dislodged some trapped air... so I will be bleeding them shortly, or could there be a problem with the servo/master cylinder?

We have no leaks and the fluid hasn't dropped at all, you just have to stand on them to get any kind of stopping!!

Any ideas...?

Forgot to add, brake setup as follows...

Front
Compbrake 4pot ProRace 1 Calipers
330mm x 32mm two piece slotted rotors
Hawk Race Pads

Rear
Subaru 2 Pot Calipers
290mm x 18mm vented grooved & drilled rotors
Hawk Race Pads

ATE Dot 4 Racing Blue Brake Fluid

 

sounds like you have over-heated the fluid, if you flush it thro with new they should return to normal

alyn

 

Always bleed after each track day to refresh the fluid in the caliper - will return to normal as Alyn says.

 

Thanks for the replys...

I have ordered some Motul RBF 660 (higer dry boiling temp than ATE stuff), so will purge the system, replace and re-bleed.

Will let you know how we get on.

Cheers!

 

Right then,

Have replaced the fluid today, and fully bled the system... and they're still no better!!

It feels like the servo isn't assisting in any way, as you have to stand on the pedal to get any reasonable braking force, the 'bite' has totally gone...?

Could we have buggered the servo in any way...?

 

Did you get every last drop out of the system? With that stuff you are supposed to put a whole bottle through first, and then a fresh bottle after. I put uprated Ap fluid in, and it didnt work for me as there must have been some residual fluid in it, so have gone back to DOT 4 to get brakes back, and will put DOT 5 in next weekend.

You did bleed both sides of the rotors too didnt you?

 

We have run 1 litre through the system, and to be honest could have done with some more as there were still traces of blue (old ATE fluid) coming through...

Would that be enough to make this much difference...?

It does feel like there is air in the system, but how can this happen during a track day... considering it hasn't happened in the last 3 track days, and they were as hard if not harder on the brakes...?

I'm bloody stumped!!

 

Thats the same as I had, and thats how the brakes felt.

So you did bleed both sides of the caliper? On 4 pots there should be 2 bleed nipples on there, but think your issue is the old fluid mixing with the super fluid stuff.

Try some normal DOT4 and see how you go would be my advice.

 

Hi Grant,

We did bleed through both sides of the front calipers, and single nipple on the rears...

Have ordered some more Motul 660 so will run that through and see how we get on.

All of the fluid we use is DOT 4, there's much confusion over DOT 5.1 being better but it isn't... for track work, it's the dry & wet boiling points that are more important than the conforming standards.

Will let you know how we get on.

 

I mainly do hill climbs, so ultimate temp isnt really an issue- on the track it is, and may as well stump for the extra £10 or so for the 5.1, but know what you mean re boiling points.

Only issue is that if the existing fluid is contaminated, you are going to need to flush some through, and all of that out, and then put the expensive stuff in.

If the fluid turns out not to be the issue, then thats an expensive way to find out- maybe cheaper to try the cheap stuff, until you find what it is?

I presume its not just your tyres that have gone off? I heat cycled mine badly, and they were truly awful at braking, turning everything

 

That's a very good point about running some cheaper stuff through first... didn't think of that!!

Don't think the tyres are the issue, as we have put our road set on and it's no different.

Fingers crossed it just needs some more fluid put through it, will know at the weekend.

Cheers.

 

regardless of what fluid you put in, the pedal should recover, if it doesn't and your happy you have bled it correctly my money would be on a wheel bearing or caliper issue................

alyn

 

Whats the pedal feel like , hard or spongey ? does it get better with a couple of pumps ? it could be a servo leaking as you have metioned that , that would give you a hard pedal that you have to press hard to work , or it could be the pads have glazed over ,
If the pedal is spongey , I would say its a fluid issue , if the pedal is firm but just not stopping , a pad issue , or servo or even a caliper problem , or if you are just losing the pedal and you need to pump it to get it back then a bearing issue
Cheers Ian

 

It could also be ball joint / track rod end related if it is pad knock off as this caused that symptom on mine a while back.

 

You would only get pad knock off with a worn bearing , or flex in the hub under very hard cornering , a worn ball joint or track rod end cannot cause pad knock off. worn joints can cause shaking in the rack

The disc is running against the drive flange , which is running on the bearing , if the bearing is tight the disc will run true in the caliper , if there is flex in the bearing , then the disc can move side to side in the caliper which pushes the pistons back into the calipers , again if there if flex in the hub , it can do the same , this is the only way you will get pad knock off , no other worn joint would cause this
Cheers Ian

 

Thanks for the responses guys...

Pad knock off is a new one to me, so I will have to get my head around that before I begin to understand it properly!! However bearings/ball joints all feel/look fine with no undue noise coming from anywhere.

In terms of the feel, the pedal is consistent regardless of pumps and would describe it as more spongey than hard... it does have more travel that it used to and you really do have to stand on it before the braking force is there. To the point that sometimes you can feel the ABS kicking in.

Before, the brakes were at the top of the pedal and you had instant bite with very little force applied... now it feels like you're at the end of a trackday/hard session with really bad fade even though you're not...?

Have checked the servo and associated pipes, and they all seem fine... one way valve is working and the servo lets off pressure when you disconnect the hose, so it's holding pressure ok!!

Have still to run more fluid through it as it hasn't turned up yet... am hoping it is just a fluid/bleeding issue.

 

Right then...

It's now sorted, and was just a case of running more fluid through... as there were still traces of ATE Blue coming through, and some cloudy crap out of one of the front calipers!!

It's now perfectly clear out of all four, and so it bloody should be as we've gone through nearly 2 litres of fluid... that's £70 i'll never see again!!

The pedal has now returned to normal, with good initial bite and firm braking response. Will take your advise Dynamix and now bleed after each event...

Cheers guys!

 

So it was an issue with bleeding the high performance fluid through! Im still not convinced that running normal fluid with changes after events isnt the way forward

 

We've experienced too much brake fade with normal fluid (even freshly installed), so racing fluid is the only way to go I think.

No one said this racing lark was going to be cheap!! (The words of my brother)

 

Yeah im going through RBF600 like its going out of fashion too. Perhaps we should try and get a group buy together. Id happly buy a ton if it was heavily discounted.

 

glad you sorted the problem, think i need to do the same as my pedal is spongey and doesnt bite till near the bottom of pedal travel. is there a specific way to bleed the brakes? start furthest from the resevoir, ie, rear passenger side rear drivers side front passenger side front driver side, or is there a better way?

cheers

daz

 

get it done properly mate, if you have to ask....

wont cost much and will give a garage the responsibility.... might also be something else like a ruptured pipe expanding, or a dodgy wheel bearing (yes this can induce the effect of not having brakes - in extreme cases).

worth looking into to be on the safe side

 

sorry to hi-jack but i have fitted brand new 4 pots/reconditioned ones from Biggred,new stainless steel pistons new seals etc so as new, with the standard sliding calipers at the rear,the pistons on the 4 pots are all out equally but i have half of the pedal travel doing nothing then i get bite

im using redstuff pads that have 2000 miles use on a 2nd hand set of discs,and have just fitted brand new grooved/dimpled discs and since its rained can see only a very small amount of contact of the pad to disc is being done,there is still rust on the disc after 20 miles of braking !!!!

could it be the dot 5.1 fluid or just air still, i bled half a litre thru and cant see any air bubbles coming out

any ideas ?