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Simon and I were at Brands GP today, about 23c ambient - very hot day and hard on the cars with 30min sessions. I am also very hard on my brakes generally. However, today and on other cooler track days, I have had instances where the brakes appear to temporarily stop working (I don't mean to be dramatic!). Difficult to describe. It's not fade. The pedal doesn't go mushy, it's actually the opposite. Its as though they've turned into full on single seater race brakes - the pedal has resistance but sort of loses travel, as though someone has jammed a pin into the pedal system, preventing you pushing the pedal to the floor. I'm not new to track days (I've averaged 12 a year for 5 years), so have some experience of brake issues in a variety of conditions (eg chocolate teapot BMW M series brakes), but am struggling with this one.

Today in particular, it happened approaching the left hander after Druids, but then was fine for the next left, and then also fine for the big brake at the end of Hawthorne. Simon and I thought this pointed to a heat issue - ie you've braked long and hard into Paddock, then again into Druids, then a slow section with little cooling downhill into the left (when I had the issue today). Then the long run along Hawthorne cools them a bit. Not sure about this as I can't see how you would get such extremes from one part of the track to next.

Any thoughts?

g

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Could well be an overheating issue epscially if you are hard on the brakes. Maybe you should try a more aggressive pad or a set iof grooved disks which disipate the heat much more efficiently.

You could always go for the Big Brake option. (Which I highly recommend)

P

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Could well be an overheating issue epscially if you are hard on the brakes. Maybe you should try a more aggressive pad or a set iof grooved disks which disipate the heat much more efficiently.

You could always go for the Big Brake option. (Which I highly recommend)

P

I agree Paul, I have an AP big brake kit on the CSL, and that works well.

The disks get to about 200c on the Lotus, whereas the APs on the CSL get to 550c (obviously a lot heavier). I would have thought that 200c would not have troubled the Lotus brakes, but clearly it does.

What do you think about the strange feel in the system though, ie pedal gets harder, rather than mushy?

g

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I agree Paul, I have an AP big brake kit on the CSL, and that works well.

The disks get to about 200c on the Lotus, whereas the APs on the CSL get to 550c (obviously a lot heavier). I would have thought that 200c would not have troubled the Lotus brakes, but clearly it does.

What do you think about the strange feel in the system though, ie pedal gets harder, rather than mushy?

g

Doesn't sound like your brakes are overheating if that is as hot as the brakes are getting which would result in the brake fluid boiling and causing mushiness.

Maybe there is a manufacturing defect in one of both of the brake pistons being slightly oversized that cause them to expand and stick in the bores when used in anger which would I'd imagine produce the sypmtons of a harder pedal and for the symptons to disappear when they cool down.

I think that you should get it checked out by the dealer.

P

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The pedal doesn't go mushy, it's actually the opposite. Its as though they've turned into full on single seater race brakes - the pedal has resistance but sort of loses travel, as though someone has jammed a pin into the pedal system, preventing you pushing the pedal to the floor.

Whilst not a racer like you guys, I have had this (or something very similar) happen a couple of times. For me it has always been on the approach to Quarry at Castle Combe and I had assumed it was the brakes cooling too much as I tootle down the straight, through Folly and Avon. I found if I take my foot off the pedal and re-apply, everything is fine (apart from the underwear).

Saving up for a sequential gearbox
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Recently whilst charging around an airfield, I had an instance when, on applying the brakes, they went into ABS mode and continued despite me backing off significantly on the pedal pressure. The result was I went sailing past the turn-in point going way too fast.

The collected wise heads on the day diagnosed this as "ice" mode of the ABS, when it determines that you have very little mechanical grip. They suggested this was probably triggered by me applying the brakes whilst airbourne/light due to a bump.

My thought at the time was that this was pure BS - the ABS doesn't need a special mode for ice and it doesn't measure grip, it measures wheel rotation. If the wheel stops rotating (regardless of speed, grip, surface etc) then the ABS gets triggered to momentarily release the pressure on that wheel. If the wheel locks again when full (demanded) pressure is re-apply, the cycle repeats.

I know (from personal experience) that ABS doesn't seem to work so well when going backwards but thought that was due to the software not coping so well with large negative wheel rotation speeds.

Do any you technical gurus have any thought about this? If if wasn't an "ice" mode then why couldn't I slow down (no change in track surface, tyre conditions, etc) - it was fine about a minute later when I did the same corner again.

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Topics merged ;)

88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

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Just an update to say that I did a track day at Castle Combe yesterday where I was concentrating on braking harder and later (had spare underwear with me) ;)

Didn't experience any problems with brakes at all - maybe I am still not trying hard enough (biggest stop is for Quarry - doing about 125mph over Avon Rise, down to about 60mph for turn in for Quarry)

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Just an update to say that I did a track day at Castle Combe yesterday where I was concentrating on braking harder and later (had spare underwear with me) ;)

Didn't experience any problems with brakes at all - maybe I am still not trying hard enough (biggest stop is for Quarry - doing about 125mph over Avon Rise, down to about 60mph for turn in for Quarry)

One of the biggest thing you will notice if you look at the telemetry readout of a professional racing driver compared with an average driver is that they brake hard but for a much shorter period. This produces less heat sink and allows more time for the brakes to cool theyby reducing brake fade.

However this does not mean that leaving the braking to the last moment and standing on the anchors necessarily the fastest way around a circuit. It's all about carrying the optimum maximum speed into a corner which will result in the fastest exit speed from a corner. Particularly important on the corner before a long straight. Going in too fast will just mean you understeer or oversteer and which scrubs off speed and too slow in will be just that.

When it's done properly especially on fast corners it car is in a perfectly balanced 4 wheel drift. Easy to say but damned difficult to do, especially when you are an old git like me and gonads start to shrink!! :)

P

Edited by pgn340r
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Doesn't sound like your brakes are overheating if that is as hot as the brakes are getting which would result in the brake fluid boiling and causing mushiness.

Maybe there is a manufacturing defect in one of both of the brake pistons being slightly oversized that cause them to expand and stick in the bores when used in anger which would I'd imagine produce the sypmtons of a harder pedal and for the symptons to disappear when they cool down.

I think that you should get it checked out by the dealer.

P

I've been on SELOC doing searches. Not that helpful and now my eyes hurt. Some people seem to have a piston problem, but that seems to have resulted in a pedal to the floor moment (which I've had when I boiled the CSL AP 6 pots! and would recognise). Root cause seems to be a master cylinder seal or shagged piston in those cases.

I don't know how to test for a dodgy piston (does anyone?). It might make sense though. If the piston doesn't extend properly, and my system is closed with no air, then this would cause the pedal to only get half way down + little retardation, which are the symptoms I have.

But how would that explain it happending on the approach to Graham Hill Bend almost every lap but not other corners? Only other bit of info. is that the approach to that corner is quite steep downhill (after Druids).

Sorry to bang on about this, but it's unerving not knowing why your brakes suddenly fail.

I might be off to see Scott...'group buy' on some APs???

Quick question - vent holes in front right disks are caked up. (Why didn't they use grooved disks? No cracks and no filled holes.)

What problems does that cause?

g

Edited by gavinp
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Quick question - vent holes in front right disks are caked up. (Why didn't they use grooved disks? No cracks and no filled holes.)

What problems does that cause?

g

Potentally will cause the discs to overhat and warp. Grooved discs are an option on the BIg Brake option ( didnt have any of the grooved discs when I ordered mine).

Have had nobraking issues at all with them.

P

I've been on SELOC doing searches. Not that helpful and now my eyes hurt. Some people seem to have a piston problem, but that seems to have resulted in a pedal to the floor moment (which I've had when I boiled the CSL AP 6 pots! and would recognise). Root cause seems to be a master cylinder seal or shagged piston in those cases.

I don't know how to test for a dodgy piston (does anyone?). It might make sense though. If the piston doesn't extend properly, and my system is closed with no air, then this would cause the pedal to only get half way down + little retardation, which are the symptoms I have.

But how would that explain it happending on the approach to Graham Hill Bend almost every lap but not other corners? Only other bit of info. is that the approach to that corner is quite steep downhill (after Druids).

Sorry to bang on about this, but it's unerving not knowing why your brakes suddenly fail.

I might be off to see Scott...'group buy' on some APs???

Quick question - vent holes in front right disks are caked up. (Why didn't they use grooved disks? No cracks and no filled holes.)

What problems does that cause?

g

Difficult one if the problem is intermitent. I can only suggest you have Scott check it out. If the problem is with the master cylinder or brake lines fitting the big brake kit won't cure it.

Try to get the problem resolved first as you could end up spending money you may not need to spend.

p

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Would it be helpful if I discussed this problem with Nick Adams in my weekly 'Chat with Nick'™ slot?

88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

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Well, looking through some video footage I have (you might have noticed I've been a bit prolific on the old iMovie over the last day or two), I seem to have some of the recurring Graham Hill braking issue. Taken from a bullet camera, pointing at the nearside tyre. Can't see a lock up (which supports the lack of response from the braking system, rather than over zealous stamping on the peddle), but absolutely can see me heading towards the back of a white GT3, and the resulting wobble as I gather it up!

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Personally, I can't recommend them highly enough. You'll be breaking 25 metres too early when you first get them. Whether they are worth the additional 2 grand is something you will have to decide for yourself. If you do get them go for the grooved disk option not the drilled.

P

Edited by pgn340r
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  • 1 month later...

Gavin,

I believe that your brake issue is a vacuum issue or more precisely a lack of sufficient vacuum to give you the normal degree of brake assist. The result is a very "hard" pedal with the car not wanting to slow down. If you release the brakes momentarily and then get back on the them, all will be back to normal.

I've experienced this on both my Cup240 and Cup255 cars (i.e., regular brakes and lotus big brake kit). It will typically happen only at a particular corner at a given track. The on-track scenario that sets this issue up is: full throttle for a period of time, followed by the need for hard braking for the corner in question. You will never encounter this issue during street driving. The big brake kit will not solve the issue...perhaps an additional vacuum accumulator canister.

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Jack, that's far from the case so I've chase this up with Nick...

The symptoms being described are a result of the Electronic Brake Distribution (EBD) system operating. This system is also referred to as Dynamic Rear Proportioning (DRP) and is, as the name implies an electronic system which, through the ABS control valve block restricts the line pressure to the rear brakes automatically to a pre-programmed algorithm. You can consider it as an electronically controlled proportioning valve which measures parameters like the rate of deceleration and rate of pedal application and uses this data to anticipate a rear wheel lock-up and then reduces the braking effort at the rear wheels as necessary. If the ABS system is left to do this, it can only react to a wheel as it starts to lock and therefore the car can already start to spin before the ABS can start to work. In extreme circumstances, if the driver brakes very suddenly the EBD system can lock off the pressure to the rear wheels completely; what pressure was at the rear brakes as the EBD system engaged remains there and the rear brakes are still working as a result, but further increases in pedal effort will not increase the braking at the rear of the car because the pressure to the rear brakes cannot increase. When this happens the brake pedal goes hard, as it is now pushing against the front callipers and a closed valve only, instead of against the front and rear callipers. The rear callipers are single piston and therefore quite flexible, so they are a major factor in making the brake pedal feel 'soft'. When the valve closes, the brake pedal pressure no longer flexes the rear callipers, hence the increase in pedal hardness. The front brakes are still working just as well as before the valve closed and will give more braking if the pedal effort is increased, while with the rear brakes working as hard as they can the braking is NOT affected. The problem is the driver feels like braking is reduced (even though it is not) because of the change in pedal feel. If the driver continues to push hard on the pedal, the car will continue to slow as fast as it possibly can in the circumstances. If he increases the pedal effort the front braking effort will increase and the rear effort will remain where it was. If he was to back off the pedal for a fraction of a second, the valve will reopen and the rear brakes will operate as normal again, with the pedal feel going back to normal.

In the case of releasing and re-engaging the pedal the car should not be able to slow any faster than it was with the system engaged unless either 1: the driver triggered the system in the first place by stamping on the pedal too fast or 2: the system triggered because a rear wheel was unloaded when the brakes were applied and would have locked up but is now fully loaded once again and able to sustain a greater braking torque. If the rate of deceleration does improve when the pedal is reapplied then it is telling the driver that he is over braking either in terms of the ultimate ability of the brakes (cause 1 above) or the track condition (cause 2 above) and needs to adjust his driving style to suit. If the system were not fitted or disabled and he continued to drive that way he would be in danger of spinning when applying the brakes.

The suggestion that the system is running out of vacuum is just plain wrong. The system carries an internal reservoir of vacuum sufficient for three full brake applications. As with every servo system ever fitted to a car there is a one way valve which prevents the vacuum being lost when the car is on boost. The only way this reserve can be depleted is if the driver is maintaining boost while applying full brakes, i.e.: left foot braking very badly. In this instance I would argue that depleting the vacuum is probably a good thing as it should provide him with a warning that he is doing something awful to the car and it may reduce the speed of impact when he finally hits something as the brakes fade to nothing!! In normal use the throttle is closed when the brakes are applied, there is therefore no boost and the vacuum is automatically replenished as it is used.

88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

Evora NA

For forum issues, please contact the Moderators. I will aim to respond to emails/PM's Mon-Fri 9-6 GMT. 

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