Gav's World

My Renault 5 GT Turbo : Brakes

Well, when I first got the car (21st of July 1996), it had standard brakes all round. In fact, the whole car was completely standard. Having had an MG Metro previously, I thought these brakes were superb.

During that year, I went to knockhill for their "Hot Hatch" track day where punters can take their cars on the track and give them a blast. Much fun!!!

The brakes held up pretty well for the first 6 laps or so and then started to fade. During the rest between session they glazed up and the first few corners of the next session were taken slightly slower to de-glaze the pads. After a couple of sessions on the track I noticed the brakes starting to vibrate. The discs were quite old, and by the end of the day were "rather" warped.

So, my philosophy with car parts is, "When they're broke, replace them with better." With that in mind I ordered a set of front Black Diamond cross-drilled and grooved discs with a set of Maxtorq Kevlar sports pads, also switching to DOT 5.1 fluid. Driving on normal roads, I couldn't believe the increase in braking performance from this combination. However, the next time at Knockhill, (after a month with the brakes) I was massively disappointed. After 3 laps of the circuit the brakes were completely useless and if I'd stayed out for another lap, I would have gone off the track. I read about possible fading during the bedding in period, so let them cool down and went out again. Exactly the same happened. Again I cooled them down and went out again and guess what: same again. I then had a closer look at the pads and discovered that I had totally destroyed a new set of pads in 9 laps - there was only 4mm left on them. They may be okay on flat discs (I don't know, but I doubt it), but I recommend everyone not to use these pads with grooved discs if going on the track.

Next purchase (a lot sooner than expected) was a set of Mintex 1144 pads. These were better than the Maxtorq on the road, but when I went on the track, well ... this was what I was expecting the last time. The brakes were amazing: very grippy with no fade at all. Even a couple of fellow club members who'd done some track driving in their own cars were amazed with the brakes - they were riding shotgun.

I then got a set of 15 inch alloys, keeping the same brakes. Again, the brakes were excellent (although not as good as with the 13inch wheels as they had to work a lot harder). On one session, I was getting faster and faster, braking later and later (as I was gaining confidence in my new wheels / tyres). All of a sudden at the hairpin, I lost the brakes. I pressed slightly harder on the pedal and all wheels locked up. I was at a point in the approach that if I'd tried to take the corner I would have run wide and into the tyre wall, so I slid the car into the gravel trap - that's what it's there for. The brakes were okay when I got back to the pits, so I went out again, just a bit slower this time. The only thing I could think of was that I got an air bubble in the fluid: the brakes were a bit spongy after that.

After a month or so with the big wheels, I was fed up of the big gap in-between the brake disc and the wheel, so I bought a 285mm cross-drilled and grooved upgrade kit. With that, I got a set of Ferrodo DS2000 pads. Now this is the dogs dangly bits in fun!!! (with a road car anyway). I had to laugh at some boy in a Cavalier SRi: I overtook him on the straight, and in the mirror I could see the look in his eyes as he was determined to get past me. I broke into the first corner (quite late, because I could). He must have waited until I slowed down before he did, thinking, "If he can do it, I can!" Not sure what he was thinking when he totally lost it on the corner and bounced down the grass ;-)

The DS2000 wore out eventually, and I fitted some EBC "Green Stuff." When I got them I noticed the word "Kevlar" and phoned up where I got them from to verify what he'd sold me. I have been assured that they are a completely different compound than the Maxtorq pads and he has "track day'd" them himself, so ... watch this space, I'll hopefully be there on Sunday 14th November 1999 to test them.

Well, the 14th has been and gone and I was on the track. The brakes were indeed as good as I'd been told. I had 3 sessions on the track, so roughly 30 laps with no brake fade at all. The only slight disappointment was with the new tyres: the A520s. They were very good around the corners but when it came to braking they felt and sounded like they were wanting to lock up, so I didn't have enough confidence in them to really stand on the brakes. The P5000s were actually better at slowing down (but only when they were hot - the only way to do that is by running them on the track). The pads themselves have worn down by about 5mm which is quite reasonable for that sort of abuse.

An update to this saga: I have since discovered that the heat generated in the brakes during the extreme braking at this last event has cracked both discs. An explanation given to me was that it was due (apart from the heat obviously) to the cross-drilled holes which cause weak points in the disc. After removing them, I can certainly go along with that as both discs are cracked through an outer hole - where there is least metal. Here is a picture of the discs as they are now. They have been off the car, lying around outside for over a week, hence the rust on the faces, but the cracks are clearly visible. Cracks are through both sides, from the outside of the disc into the centre:

Click on image for a larger view.

So, next set of discs will be very similar, but with no cross-drilled holes this time and I'll try the EBC Green Stuff again as those were very good pads. As a temporary measure, I have put my old Black Diamonds on the car until the new ones arrive.

Well, the new brakes have arrived, so here is a comparison between the cracked 285mm (slightly cleaned up), the 238mm Black Diamonds and the new 285mm discs, just to show the difference in size:

You may notice that there are holes drilled in the discs - bit of a cock up with the order, but if these ones crack, they will be taken care of. There are a few differences between the old and new 285s: The grooves are wider, deeper and longer (plus an extra one) and there is 3mm extra offset inwards, i.e. the calipers sit 3mm further inside the body of the car, so I shouldn't take as much off the lead weights as before! Also, the holes are spaced out for standard size pads whereas with the old set, the inner most holes were not used.

Here is an interesting picture: the front nearside brake disc and caliper as viewed from under the car (bumper removed to allow this). You can see the extension brackets to allow the standard caliper to be used with the over-sized discs.

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