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Discussion Starter #1
Hi...I am new here and I need help.

I have a 2006 ExigeS cup with AP 4Pot brake calipers with AP rotors.

To explain my problem...

Lets consider the brake padel travel is divided from 1 to 5

1 is initial brake travel
5 is the fullest brake travel

When I brake..I press from. 1 to 3...nothing happens...spongy feeling

When I reach 4....massive braking effect

When I reach 5...stops without activation of the ABS

The brakes are very non linear and I cannot moderate my braking pressure for trail braking....etc

What can I do to resolve this?

Where to check?

What to check?

FYI..this is a track car and driven on slicks

Thanks
 

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I've always wondered how AP's were with modulation - anyone with the 4pot APs installed can comment on this? I have a set that will be installed but this has been on my mind...
 

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I've got a 2009 Cup 260 and they are nothing like you describe...in fact, they are very linear and easy to modulate. The ABS comes on very predictably also. Did this just start happening on your car?
 

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I'm going to take a stab at this and guess that you have a vacuum leak to your brake booster (Lotus calles is a Brake Servo)...it could be as simple as a vacuum hose fell/rotted off…or the diaphragm itself in the booster tore (the whole booster would need replacing). There is also a check valve in the vacuum hose to the brake booster (A120J0008K)...that could be stuck/bad too.
 

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Discussion Starter #5
Thanks for the tip...I will take a look.

Driven the car couple of times on the track...it was very frustrating...

Couldnt heel and toe ....checked the other threads and apparently 2005 exige is known to have this problem...

Also Over heating issues....both water and oil over heated just one lap of hard driving..

So many problems...

Will try to fix the brakes first and then tackle the rest one by one

Thanks
 

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If it is over heating also, that just point to a lean mixture...also caused by a vacuum leak! You could fix both problems at once!
 

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Discussion Starter #7
"also caused by a vacuum leak! You could fix both problems at once!"

Sorry I don't understand...can u explain a bit more???
 

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Vacuum (drawn from your engine's intake system) is used to power your brake servo...if there is a leak anyplace in that system it will draw extra air into your engine. The vacuum air is drawn after the throttle body and the Mass Flow Sensor is in front of the throttle body so the ECU will not compensate for that extra air the engine is drawing in...causing a lean condition. Fix the vacuum leak and you will cure both symptoms.
 

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Vacuum (drawn from your engine's intake system) is used to power your brake servo...if there is a leak anyplace in that system it will draw extra air into your engine. The vacuum air is drawn after the throttle body and the Mass Flow Sensor is in front of the throttle body so the ECU will not compensate for that extra air the engine is drawing in...causing a lean condition. Fix the vacuum leak and you will cure both symptoms.
Although I will never have that problem - it probably makes sense to put a vacuum gauge on see what is going on at the booster/servo.

But on the track the TB will be open and the manifold pressure low, so a leak would not do much of anything, and in a S/C engine the leak would have to be between the TB and the S/C for full throttle and at least after the TB for partial throttle.
On the road; then the leak is much worse as it is more vacuum and the TB is closed.

A retarded ignition would also help to make some heat.
 

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Discussion Starter #11
forgive me for asking silly question.

If there is a leak in the system...the pedal feeling is spongy and long travel and no moderation??
 

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forgive me for asking silly question.

If there is a leak in the system...the pedal feeling is spongy and long travel and no moderation??
You are correct for the hydraulic system, but the discussion here is about the pneumatic portion of the braking system.
 

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Discussion Starter #13
Oh....ICIC

I get it..

Because there is a possibe leak in the pneumatic system...between the throttle body and the super charger...

So there are more air into the engine and therefore the engine runs lean and gets too hot..

at the same time...if there is a vaccum leak at the brake servo...the brake feeling is spongy and long travel..

Again...I am new to this...pls excuse my poor knowledge
 

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No...the brake servo helps braking. If you don't have it (by having a vacuum leak), you won't be able to push the pedal down...because you don't have any help from the servo. So it will be a very hard pedal with very little travel.
 
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