Sieze

I have recently upgraded my breaks to Group N Pagid cut discs and fast road Pagid pads. They also bled the breaks and put fresh dot 4 fluid in (they didn’t use 5 as apparently the system has to be purged). The car is due to go to the Nurburgring in a few weeks which is obviously up and down some serious hills. Anyway to my disappointment after about eight minutes of hard driving I got some bad fade and then sponginess especially after going down a hill at 115mph and then breaking. At first I was pissed about the pads but in all fairness they had been fairly consistent with only a bit of fade till the hydraulics overheated. My questions are thus; should I take some competition pads for the ring rather than using a compromise road/race pad? Obviously I need a higher dot fluid but surely that will take the discs to the limit of warping/cracking or should group N discs be up to it? I have an STI type RA which does have some break cooling ducting but are there hoses/brackets available to direct airflow more efficiently to the calliper/disc? Are there people who have designed their own ducting systems? I feel the pads/discs should be up to it if only they can cool a bit more between breaking zones. In addition I do realise that a big break upgrade will cure all my problems, but it is not an option at the moment!

IWatkins

Seize,

Have a word with Mike at ScoobyMania as they have a kit showing on the site for brake cooling.

Pete Croney

Seize

Whilst the Pagid set up is a great improvement for fast road use, it is not suitable for hardened track use. No brake parts that use the standard size disc and pads will ever be completely fade free. They are just too small.

Braking down hill, from 115mph, after 7 or 8 miles of serious fast road driving puts you well into the sort of demands found from track driving. The conditions you describe are no different to being on your fifth lap of a circuit like Donnington, which is well beyond what the standard brakes can normally cope with.

Your set up uses the 2 pot calipers and the smallest of Subaru's front disc arrangements. Not ideal for a car with RA power and gearing!!

The problem is definitely heat loss and your use is exceeding even the improved ability of these parts/fluids.

Silkolene ProRace fluid is rated as DOT4, but its boiling points (wet and dry) are slightly higher than AP's DOT 5.1 fluid. It is used extensively in rallying and racing, and by several of the corporate track day companies for their track fleet.

If your use demands better cooling, fitting some ducting will help, but avoid fitting very aggresive pads. You are already generating more heat than the system can cope with and generating much more heat will lead to disc and wheel bearing failure.

The best ways to increase cooling to the standard size discs are to remove the back plates, as these shield the back of the disc from a decent airflow or, if this isn't enough, cut holes in the back plates and duct air to the holes so it gets forced out through the centre of the disc.

The only way to guarantee fade free braking is to go for a big brake kit. These have a larger gap between the disc's friction plates, normally with vanes that actually pump air through, and have a massive overall surface area.

I hope this helps.

Steve vRS

Pete,

Is it possible to buy the big disks you talk of and by using adaptor brakcets, use the standard calipers (MY01 4 pots).

Steve

Pete Croney

We don't do this, but a company called Hi Spec in Dartford do it.

Sorry, don't know their number.

Sieze

Thx Pete,

I had a look at the back plate today and wasn't quite sure what purpose it serves? It definitely has to go, and I am determined to improve the ducting. The scoobymania ducting looks like it cools one side of the disc, wouldn't this predispose to warping? I intend to confirm whether all the brake fluid was replaced or if they were just bled a little. I find it hard to believe that approx 2 seconds of fade was followed by the hydraulics overheating (in one braking zone). If the fluid had sucked up lots of moisture over the years that might explain the lack of warning. I agree using race pads is not the answer because the hydraulics are the limiting factor. It is seriously scary when the peddle goes spongy. Fade I can handle but no brakes at all is suicide. I must admit I am starting to realise that standard size discs are just not up to the job of repeated hard braking.

Aero

Will removing the back plate have an effect on the temperaure of the bearings etc in the wheel? It'll be great having more cooling, but surely not at the expense of boiling the grease out of the hub. Will that be a problem?

WRT the Scoobymania product, I can't say enough good things about the service I've had, and I don't mean to be rude, but 70 quid!

Stef

The Ring also doesn't tend to be too hard on the brakes, as there are lengthy stretches between each hard braking zone.
I am running the Scoobymania ducting kit but as of yet haven't had the chance to try it out properly, as I had faulty discs at the last track day.

Stef.