peter_964rs Posted June 7, 2004 Share Posted June 7, 2004 Other Academicians: please don't scoff at this blatant attempt to quote "excuse no.32" from the "driver's excuses handbook". Anyway... Context: Academy Roadsport 1.6, high-speed braking at Goodwood this Saturday ready for turning at Woodcote. Definitely braking in a straight line. Have done so before at the same point with similar effort two weeks previously at a track day and no worries at all; we're now sprinting and the lap time counts points for the championship. Same pads/discs used at Spa & the 'ring a week before the track day.. Car suddenly and unexpectedly slews sideways with a wheel locked (I think the left rear but can't remember for sure). I spin to a halt on the track, slot first gear and race for the line to grab twelfth place. Next and final timed lap I brake earlier and softer just in case, car suddenly slews sideways again but I can catch it this time, turn around Woodcote and, as I brake for the Chicane, again in a straight line but again the rear snaps sideways too fast to catch and I pirouette through the tyre barriers and onto the grass. Good news: I didn't damage anything. Bad news: I threw away two fabulous laps, the second in particular was an absolute blinder. Had I even matched my speed practicing - when I fluffed three corners and came into the pits annoyed with my performance - I would have finished fourth. I am also morose and depressed at the effort spent and wasted on preparation and practice; bah, humbug, etc. On mental review, I am convinced I braked in a straight line and no more (or much less) than I would have at any of the three previous track days (Spa/'ring/Goodwood) on those pads/discs. So why would the car suddenly snap out like that - is there anything I should look for? I had a brief look at the left rear calliper in the paddock but could see nothing arwy, a bit of scoring on the disc but plenty of pad material left. Should have spent Sunday disassembling both callipers and trying to spot any anomalies, but was too angry to go near the car! Pads are Pagid RS14 on the rear and RS15 on the front. So - what should I investigate? I have another sprint at Lydden in a fortnight. Deperate to avoid any unexpected car issues as I need the points. Link to comment Share on other sites More sharing options...
julians Posted June 7, 2004 Share Posted June 7, 2004 Check the pad material on both sides, I had a similar effect when one side was down to the metal. Link to comment Share on other sites More sharing options...
charlie_pank Posted June 7, 2004 Share Posted June 7, 2004 2 thoughts: 1. Having done my first wet trackday a couple of weeks ago, I found that the only time I spun was when I downshifted and didn't bring the engine speed up enough before releasing the clutch, could it be possible that you're revving very high at the point you start braking, and the lift-off is inducing oversteer? 2. Corner weights, I found on the same wet trackday that when I had a passenger in the car my front right wheel would lock up under long before all the others, but was absolutely fine when in the car by myself, might you be suffering from something similar? Do you know if one/both of the rears is/are locking up? Link to comment Share on other sites More sharing options...
peter_964rs Posted June 7, 2004 Author Share Posted June 7, 2004 1. I was heeling & toeing so should not have had a problem with engine speed & clutch engagement causing lockup 2. Car is fully corner weighted and ballasted although I did take 3kg of lead out of the passenger side on the day as I was overweight on the scales... but 3kg is insignificant (?) Link to comment Share on other sites More sharing options...
Pete Posted June 7, 2004 Share Posted June 7, 2004 Peter I was at Goodwood on Saturday and saw your problems from the viewing gallery on top of the pits. It was a little disconcerting to see you come into view going backwards at the end of Lavant! Glad that no damage was done. Hope you fix the problem quickly. regards Pete Link to comment Share on other sites More sharing options...
Paul Ranson Posted June 7, 2004 Share Posted June 7, 2004 Unless there's a correlation with gear shifts I would suspect something in the suspension. Or the front brakes aren't working. Paul Link to comment Share on other sites More sharing options...
JAG Posted June 7, 2004 Share Posted June 7, 2004 This sounds like premature rear wheel lock due to braking inbalance. One side is locking early due to the minor variation in the brakes/tyres/surface/disc etc... Look into the front/rear brake balance and either reduce the rear output or increase the front output. This can be most easily done by changing pads. Justin A closed mouth gathers no foot. Link to comment Share on other sites More sharing options...
Sheds Moderator Posted June 7, 2004 Share Posted June 7, 2004 I heard about a broken DD tube that caused snap oversteer in this way. I'd also check the rest of the susp to make sure nothing's broken or fallen off. Other than that chck discs and pads , something has obviously changed rapidly to cause this. Flat flooring/weight distribution type issues don't just appear, unlike broken suspension and worn out brakes. Link to comment Share on other sites More sharing options...
peter_964rs Posted June 7, 2004 Author Share Posted June 7, 2004 I am thinking about changing pads back to the stock ones shipped with the car - no discernable manufacturer and very soft and unresponsive, but what the hell; I'm sure I can underbrake and get round the corners somehow!!! There is no other way (that I am aware of) to adjust brake bias and adjustable bias mechanisms are illegal in the Academy anyway. Pete - if you were watching can you recall what happened - which wheel locked up and if it looked like I was braking in a straight line? Link to comment Share on other sites More sharing options...
CharlesElliott Posted June 7, 2004 Share Posted June 7, 2004 Pete, You may or may not value Nick Potter's opinion, but when I was discussing rear pads with him, he was saying that it's better to keep the standard pads and let them wear down. At least then you're not in danger of locking the rears, and they contribute very little to stopping power anyway! Charles --- My Caterham Academy 2004 Diary Link to comment Share on other sites More sharing options...
peter_964rs Posted June 7, 2004 Author Share Posted June 7, 2004 Actually I had Pagids in for Stowe and had so much trouble with lockup in the wet that I switched back to stock Mintex front/Unbranded rear for Aintree. Although we didn't brake much, if at all, at Aintree, so it made little difference. But switched back to Pagids for Spa, the 'ring and Goodwood and thought they were brilliant - assumed I'd become used to them, maybe they'd bedded in or something - and persevered for the sprint. In my practice run I had no trouble with locking up either. This was a very sudden and unexpected effect on the timed runs Link to comment Share on other sites More sharing options...
Chelspeed Posted June 7, 2004 Share Posted June 7, 2004 > There is no other way (that I am aware of) to adjust brake bias If you can afford to trash a set of pads in the interest of research you could massively widen the central groove in the rear pads. If it's 2mm wide now 10 minutes with the angle grinder (and a face mask!) would leave you with a 15mm wide "groove" which would mean approx 50% reduction in rear pad area which should mean a corresponding reduction in rear braking effort. Link to comment Share on other sites More sharing options...
kandyman Posted June 7, 2004 Share Posted June 7, 2004 Your rears shouldn't be locking before the fronts, so you'll be searching for the fault in the the front brakes. The front is underbraking, so the unloaded rear locks first. Do you have adjustable brake bias? Is it out of balance? Are your front pads worn? Discs clean? Anything else wrong with the front brakes? -Marin Link to comment Share on other sites More sharing options...
Chelspeed Posted June 7, 2004 Share Posted June 7, 2004 Academy cars are renowned for locking the rears first. It's a consequence of a mix of components, 1960's Herald front calipers, 1990's Sierra rears (could you get a worse mismatch?) and a fiesta master cylinder designed for diagonal split brakes and used with a front/rear split. This combinations works tolerably well on normal road cars but most people who use the brakes properly fit a limiter to the rear brakes. But it doesn't seem to work at all well on Academy cars, don't know why, the extra specially rubbish tyres chosen to control costs perhaps. There are all sorts of bodges, eg special pads, just to get the backs to work badly enough to pass SVA on the front to rear split. Why the Academy regs don't just allow a £30 brake limiter is a mystery. Link to comment Share on other sites More sharing options...
Pete Posted June 7, 2004 Share Posted June 7, 2004 Peter When you came into view at Woodcote you had already had your 'moment' but in the chicane I thought that you braked in a straight line. You only spun when the car got on the grass (understandable). Hope this helps pete Link to comment Share on other sites More sharing options...
_Tim_ Posted June 7, 2004 Share Posted June 7, 2004 If it's 2mm wide now 10 minutes with the angle grinder (and a face mask!) would leave you with a 15mm wide "groove" which would mean approx 50% reduction in rear pad area which should mean a corresponding reduction in rear braking effort. I suspect that is illegal in respect of Academy regs. Anyway I have the exact same pad setup as Pete and suffered no such problems at Goodwood (placed 2nd), so I don't think it's an issue with the pad choice, more likely some other factor. I still think you should have put that 3kg of lead back in and gone out for the last non-competative run to see if it made any difference. - Tim - 2004 Caterham Academy competitor build diary here Link to comment Share on other sites More sharing options...
charlie_pank Posted June 7, 2004 Share Posted June 7, 2004 the "rotational problem" that I had at a very wet knockhill, during a downshift was also whilst I was heel and toeing. My point is that I wasn't revving enough, even though I was executing the right technique. Just applying the right technique doesn't preclude you from having the problem I suggested. Charlie'n'Kermit The plan is: There is no plan S5EVN Link to comment Share on other sites More sharing options...
Chelspeed Posted June 7, 2004 Share Posted June 7, 2004 > I suspect that is illegal in respect of Academy regs. I'm shocked that you would accuse me of cheating.... "5.11.1 Brake Modifications Specifically Permitted (i) Brake friction materials are free" I reckon that allows you to remove 50% of the friction material on the rear pad. If they don't want you to do that then they need to say so. It's also a safety mod. Link to comment Share on other sites More sharing options...
_Tim_ Posted June 8, 2004 Share Posted June 8, 2004 True, it does say that. However we were all explicity told that if the regs don't specifically say you CAN do something, then you can't. Not the other way around. Worth asking Andy Billet about I reckon. - Tim - 2004 Caterham Academy competitor build diary here Link to comment Share on other sites More sharing options...
Peter Carmichael Posted June 8, 2004 Share Posted June 8, 2004 Check the pads on all corners of the car. Pad wear can be uneven, leaving the pads making only partial contact with the disc. This may be happening at the front, causing the rear braking effort to build up quicker. Take the pads off the caliper and place them face to face against each other and see that the contact is flat and continuous. If the pads can be rocked or if there is a visible gap, junk them. Another possibility is fuel leaking from the overflow in the vicinity of a rear tyre. I had this at Brooklands one time with Pagids where I lost all rear braking effort in the course of the day. Sahf London; every 1st Wednesday from 19:30 at The Duck just around the corner from Clapham Junction station Link to comment Share on other sites More sharing options...
CharlesElliott Posted June 8, 2004 Share Posted June 8, 2004 Another factor (and I don't know how new your pads are Pete or how long Pagid's last) is that I've been told that on the rear calipers, after a certain amount of wear one side can get 'stuck', meaning that there is only braking surface. The effect of this is to wear down one pad whilst the other looks fine, causing you to think that there is plenty of wear left when there isn't. Charles --- My Caterham Academy 2004 Diary Link to comment Share on other sites More sharing options...
peter_964rs Posted June 8, 2004 Author Share Posted June 8, 2004 Now, that's a very useful thought and correlates with some concern I had over noise from the rear in the days before the sprint - in the sunny weather I went out for a few countryside blats without a helmet on and could hear the rear pads rubbing against the discs. So I backed the handbrake right off in case it was too tight and causing the rubbing - wasn't sure if the noise was normal or not. Although it seemed to make little difference on the road. Link to comment Share on other sites More sharing options...
CharlesElliott Posted June 8, 2004 Share Posted June 8, 2004 Sounds like it could be interesting to take the rear wheel off and have a good look and the friction material (or lack of it!) left on both pads.... Charles --- My Caterham Academy 2004 Diary Link to comment Share on other sites More sharing options...
peter_964rs Posted June 8, 2004 Author Share Posted June 8, 2004 I will probably have calmed down enough to have a pop this evening ☹️ Link to comment Share on other sites More sharing options...
gordong Posted June 8, 2004 Share Posted June 8, 2004 Could it be the fronts overheating and going off, shifting bias unexpectedly to the rear? However, my experience of this happening is that the rear fishtails rather than slewing, and you have a chance to back off the brakes and catch it (assuming you have the correct instincts and fast enough reactions). Could be oil/grease/fluid leaking onto one front brake? If there was a problem with the rears, I would expect you to plough straight on. Spinning implies a problem with the fronts, either seriously unbalancing the force on the front or putting more bias on the rear and causing them to lock. G Link to comment Share on other sites More sharing options...
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