SPEN555

I did a track day on Sunday morning at Croft and found the brakes to be performing poorly.

The car is an MY03 with Brembo's. I have recently upgraded to braided lines and performance friction discs and pads.

Prior to this I had a problem with what felt like warped discs as the steering wheel would vibrate when braking from 80mph+. These were checked and found to be 5 thou and 8 thou out for each disc which I was advised was not enough to cause the vibration as they were within tolerance. I drove these on the road as suggested for 400+ miles and the vibration improved to the point where it was not an issue.

When I did my track day though after a couple of laps I would press the brake pedal and it felt 'spongy' and the brakes did not apply properly. At no time did I get the vibration to suggest the problem above had returned. Upon coming off the brakes and re-applying they would work.

On the same track standard discs with pagid pads worked superbly (too good resulting in replacing the discs. ) I never once got the spongy feeling.

My thinking is the discs are warped but not a problem to be that noticeable and on track this is creating heat which is then boiling my brake fluid resulting in the spongy pedal feel. As on the way home the brakes worked straight away and pedal feel was firm.

Any suggestions?

D1CCY

I got overheating probs on my AP 6 pots (Pagid Blue) at Elvington 2 weeks ago. No spongy pedal or probs like that but smearing on the brake discs leading to a bit of vibration when back on the road until the discs cleaned up a bit on normal braking.

I think there is a fundamental cooling issue with not enough air getting behind the front wheels. As mine is an STi next time I go on track I'm removing the fog light covers and have cut a 3" square hole in the plastic wheel arch so air can blow straight in. You could try this. I don't know anything about performance friction products but your probs sound like a different manifestation of overheating.

PS Alyn suggested better rear pads to stop the front doing all the work so I'm putting PBs in there as well. Are you running Subaru 2 pots at rear and what pads?

SPEN555

IIRC, rears are 2 pot Brembo's with Pagid pads.

Thing is I have done track days before with the standard discs and not had this problem.

GC8Lee

Your discs will not be warpped at all as the juddering has gone away (more than likely the pad and disc have bedded in correctly now).

From what you have described its your fluid for sure...

What fluid are you using?

I recomend the Castrol SRF, its industry standard throughout the racing world, and cured the spongy pedal i got on my old GC8.

Is your brake system bled properly as well, any air in there would also cause this.

SPEN555

I am using Motil 5.1 brake fluid.

What I don't understand is if there is air in the brake lines it would also be a problem on the road?

GC8Lee

Yes,only if you use them hard enough on the road, you would experience the same once they are upto operating temperature.

SPEN555

Cheers for replies guys, I am starting to be convinced it is a fluid issue.

clivew

I had pretty much the same symptoms as you describe on my sti7 on track days. Thinking it was warped discs, I had the discs skimmed, which immediately helped, but after another couple more track days the problem returned. Anyway, to cut a long story short, the problem was eventually diagnosed as a nsf wheel bearing on the way out. I had this replaced and have done 6 or 8 trackdays since. I guess the nsf is going to get the most stress, as all the circuits I use run clockwise, so I'm expecting the bearing to start going again soon!!

JohnS

iTrader: (1)

I was also going to add that it may well be a wheel bearing that has gone, or is on the way out. As you go around corners, the play in the bearing allows a small movement of the disc, which pushes the pads back into the calipers. When you first press the pedal, you are just really pushing the pads back against the disc surface, and it will feel as though you have no brakes. Lifting off, and pressing the brakes again the pedal should be firm and you'll get good braking response.

The wheel bearing issue was one of the reasons that Subaru changed the PCD on the later cars, so they could fit a bigger/stronger bearing to the wheels.

John

GC8Lee

What you guys are describing is called pad "knock off".

Its not that, as his juddering has disapeared and he still has the spongy pedal at temperature.

I'm 100% certain if he re-bleeds the system (could still be an air lock in there), and to be on the safe side put some Castrol SRF, all his problems will go away, and the braking will be a solid warp free environment.

SPEN555

The symtoms you describe there is exactly what happened. But I would have thought if a bearing had gone then I would also know about it on the road?

I think I well get the bearings looked at and had the brakes bled. I will have to do another trackday though to test

SPEN555

Correct. The juddering has gone. As posted above I will get the brakes bled. What is Castrol SRF? Is it a race fluid which cannot be mixed with other brake fluids? Oh and where do you get it from?

JohnS

iTrader: (1)

You should also be able to detect it on the road, but it won't be nearly so obvious, as you won't be cornering at quite the same speeds. Also on track, the grease in the bearings will be at a much higher temperature (near melting point if not above), so movement will be easier than it would on the road.

A good test is to reverse a short distance on full lock (enought to go throguh 90 degrees like reversing out of a driveway). Apply the brakes when you straighten up, and then apply them again shortly afterwards in a straight line. if you have more pedal movement the first time, then it suggests that there is a bit of free play in the bearings.

Another more fun test is to go for a long hard drive on twisty roads, enough to get the brakes and bearings up to a decent temperature. try braking in a straight line, and see if you get the same symptoms (ie better pedal feel on 2nd press).

I found that the bearings wouldn't make a noise when first starting to go (hence difficult to diagnose the problem), but over time they did start to make a noise. I got used to making a quick tap on the brakes to push the pads back into place, and then pressing the pedal for real, as I was then guaranteed decent and repeatable braking performance.

You could also get it if the discs were out of true, but perhaps only when hot (ie on track).

If getting a front bearing replaced, then I believe you need to bleed the brakes also, so could do both at the same time to save time and effort.

John

SPEN555

Good advice John I will give that a try. Either way I think I will book my car in to have the bearings done and the brake fluid.