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Dan posted this somewhere else on the board:

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.

Just thought I would share

Dan
 

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Dan posted this somewhere else on the board:

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
......deleted......
ally 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.

Just thought I would share

Dan

Dan,

I think you have got it. This thing happens to me mostly when I tap the brakes to steady the car on entry (or just fear :eek:) I find that it hapens when I have a bit of steering input, probably enough to de-weight one of the rears. I have found that straightening out the wheel makes the brakes seem to come back to normal.

Malcolm
 

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I forgot to say this in my post, but I think that Dan was quoting (or paraphrasing) the "official explanation" from Lotus. This was not his own theory as much as he was sharing what he had heard (or been told) by Lotus.
 

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I forgot to say this in my post, but I think that Dan was quoting (or paraphrasing) the "official explanation" from Lotus. This was not his own theory as much as he was sharing what he had heard (or been told) by Lotus.
Im not sure I buy that explanation though.
 

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I have no stake in the argument, I'm just posting what Dan had shared. Me, I run without ABS and don't worry about it. Sure, I'd prefer to keep the ABS on, but I cannot stand the "hard brake pedal" syndrome -- or whatever you want to call it -- which I get any time after being at wide-open throttle that I stand on the brakes really, really hard where the pavement is -- in any way -- uneven.
 

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I will throw this out there for people to think about. I recently switched from Pagid RS4-2 pads to Carbotec XP10 Front XP8 Rear and have either greatly reduced or totally stopped my problems with Ice mode. I can't recall the last time Ive had it happen. Maybe my driving style changed, maybe its because its a more aggressive race pad and doesnt require as much pedal pressure for the same amount of braking force. Who knows, but Im much happier with my brakes now.
 

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I forgot to say this in my post, but I think that Dan was quoting (or paraphrasing) the "official explanation" from Lotus. This was not his own theory as much as he was sharing what he had heard (or been told) by Lotus.
Correct ... the explanation was supplied by Nick Adams of Lotus.
 

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From what I have heard firsthand...success in fixing this comes with 1-altering braking style, being smoother and braking earlier...or 2-disconnecting the ABS fuse
 

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In my view, "altering style" effectively translates into "brake less hard and give up time in the braking zone". Disconnecting the ABS plug definitely eliminates the problem -- at the cost, of course, of not having ABS. My logs suggest that I lose a fraction or two running without ABS, but I also enjoy the challenge of being entirely responsible for what the brakes are doing. Just a thought...
 

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Malc, I don't pay much attention to Autox classing rules, but (instead of pulling the fuse) can you disconnect the ABS wheel sensor and still remain legal? I don't pull the fuse because I lose the spedometer, so I just disconnect the ABS plug going into one of the front wheels.
 

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Has Allan's information been posted? I don't believe I saw it within the thread. I'm curious if this is to be the final solution.
 

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Has Allan's information been posted? I don't believe I saw it within the thread. I'm curious if this is to be the final solution.
link?
 

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Has Allan's information been posted? I don't believe I saw it within the thread. I'm curious if this is to be the final solution.
I thought this was *not the solution (using a additional vacuum container). Verified by several people that track down here in SoCal...I might be wrong but again the last I heard was getting rid of ABS or altering driving style.
 

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After several years of experimentation, I believe there is a combination of problems. After I nearly ran into the crowd in San Diego last year because of this problem(and I had a vacuum tank), I found that my check valve on the engine was bad. This was releasing the vacuum from the vacuum tank. Replacing the check valve made the problem much better. I installed vacuum guages and used the ChaseCam to look at other icemode events. (Which were much fewer and farther between) We noticed that too much front rebound would contribute also. The front wheel starts hanging up in the air over a bump or esp in a corner. Grab the brakes hard and get the hard pedal. So we've backed down the front rebound to reduce this tendency. I do think for autocross & track the vacuum canister is good because there can be times where you brake hard for a split second and are back on the gas(esp w/ left foot braking) where the engine doesn't have much time to generate vacuum. Then you get your 3 stops and that's it. Frequent bleeding also seems to help, but its not a sure correlation.
 

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Has Allan's information been posted? I don't believe I saw it within the thread. I'm curious if this is to be the final solution.
Allen here... I thought I should chime in since my name is mentioned. We have spent A LOT of time on track trying to figure this out. Bottom line, the long technical explanation from Nick Adams is correct. It is the ABS unit butting in. It's very annoying and very scary. We have found that there are some things that make it worse. 1.TOO much rebound. 2. TOO much spring. 3. bumpy brakng zones.
We have also found a few things that help. 1. renew your check valves, they do wear out, like everything else. 2. vacuum reservoir, especially if you are of the firm belief that if your foot is not on the gas or on the brake you are going slow.

We have concluded that the Lotus ABS is another part on the car that is a "road car" part and not a "race car" part.

So, you can either slow down you braking input, as implied by Nick Adams (which will probably make you pay more attention and help you become a better braker and less reliant on the ABS), or you can disable the ABS. Or your third option is to get a"race car" ABS system, eg. Bosch Motorsport.
BTW pulling the maxi-fuse is the WRONG way to do it. All you need to do is disconnect the right(passenger)front wheel speed sensor. Please be careful!! It is a very different car without ABS!!!
 

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Why is pulling the fuse "the wrong way to do it"?
Pulling fuse also disables your speedo and gives you a check engine light.
Doing it the way Allen states works correctly, just have your ABS light on all the time. Will also have to disable your TC or it will kick in all the time.

Ice mode has been a major problem with folks racing in LCS. Fine to suggest light braking, but with the red mist of racing, everyone will push the braking zone and even good drivers get into trouble with ice mode. Had one near miss due to ice mode and one incident of light contact probably due to ice mode.

We ran an exercise with ABS on and ABS off in LCS Big Willow event, but most folks ignored, as they'd rather just turn laps. Fine until it bites you. Now that this is being recognized as a problem, will run this exercise again - probably at Spring Mountain event.
 
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