Braking problem with 488

So...back on track,


there seems to be a recurring history of complaints with 458,488 and others.

I don't think anybody is making this stuff up and I guess if you haven't experienced it you just don't understand the problem.
And it is a problem or it would not be brought up by so many.

I don't think its tire treatment or anything remotely related to that.
It happened to too many and all very similar situations.

Again,,, never had anything like this with any other car I have owned.
I searched long and hard for what I wanted and now it never gets driven as I don't know when it will reoccur.

 

Or no brakes......

 

The other day I was messing around with my pickup and I turned the motor off and was going down a hill testing something related to vibrations etc. I hit the brakes a few times and everything was fine and then the 3rd time I guess I had depleted the vacuum in the booster... wholly cow, I had to stand on the pedal to get the truck to even begin to stop. At the time I was running a track pad on the pickup, but still. I wonder if Badbruno's issue might be related to lack of vacuum (or however Ferrari powers their booster system)?

Ray

 

The issue described here does not look like the most commonly reported though - analysis of sudden and unexpected behaviour (leading to a crash in some cases) is not easy but there is a pattern seeming to relate to a brake booster failure, which is not really speed dependent.

 

when I experienced this problem I was doing between 60 and 70 mph and had what would normally be enough distance to slow to make a
turn.

 

That is very normal for a Pista. Those ceramic rotors need to be hot to work properly. My Scud was the same.

 

Never experienced any issues with brakes on the 488 or Pista hot or cold. Those pads all use the same old T4300 compound and the discs are regular Brembo CCM. They work the same on a Pista as they do on an 812 or Lusso, or a Corvette. Heck, even with Pagid RSL 1 race pads cold bite is very good, and so is RSC 2.

These pads and discs don't glaze due to excessive heat. That would mean taking them above 800 C. That will not happen, ever.
These brakes glaze for one reason, and one reason only, and that is too soft driving. It is not a big deal with T4300 road pads, but race pads need a few hard stops every so often to keep them clean.

If the stock brakes get really hot during tracking, they do fade a bit. But this fade goes away as soon as the temp drop in the system. This is primarily due to the fact that Ferrari uses a pretty normal road style fluid. The T4300 pads also gas out a bit when really hot, so that can add to the fade too.

But these brakes should not feel as described just because they are not hot, that is not normal.

Sent from my SM-G930F using FerrariChat.com mobile app

 

Sounds like a lack of vacuum at the brake booster. With most cars than run a booster, if the vacuum isn't supplied to the booster to assist with braking, then stepping on the brakes is like pushing your foot into a brick wall and then the car barely slows down. You have to really stand on the brake pedal to stop the car when the booster fails; it can be pretty shocking the first time it happens, because you are so used to just pushing fairly lightly on the brakes when they have vacuum assist.

Keep in mind, you are using your foot to stop a several ton vehicle traveling 80 or 100 MPH - with maybe only 40 or 50 lbs of force. That's quite a trick if you really stop and think about it. If you really study how that's done, it's very interesting. There is a rather large leverage multiplication factor at work, with the pivot point of the brake pedal itself and then hydraulics accounting for most of the stopping force. However, the brake booster can often double the line pressure, so it's very important in the force multiplication equation.

I recently re-engineered the entire brake system on my pickup truck, while converting over to 4 wheel disc brakes (basically my 1990 Toyota has F40 brakes on it). And yes, it stops! I don't have the exact calculations for brake line PSI for my pickup truck project, but when I redid the brake system on the pickup, I wanna say the target clamping pressure on the front rotors was around 4000 lbs per side with a brake line pressure of 800 or 1500 PSI or something. I don't remember all the exact math, but the basic idea is that the brake booster usually is doubling the pressure in the brake lines, if not more. Therefore, if it's not in the loop, you're operating at 50% braking - or worse.

Okay, so here is the rub.. on a N/A (normally aspirated) car, the vacuum supplied to the brake booster comes from the vacuum naturally present inside the intake manifold. However, here's the problem with a turbo charged car: you have forced induction, so the manifold actually has positive pressure. This can cause issues for the brake booster if a check valve fails. If I had to take a few wild guesses, I'd say perhaps there is a check valve which is allowing positive pressure (i.e. boost) into the brake booster which is defeating its reserve of vacuum or something. Either that or there is a hose which has popped off the turbo to intake manifold, which is not only screwing up the vacuum that the booster needs, but also allowing boost from the turbo's compressor wheel to escape instead of go into the engine.

The other possible thing could be some malfunction in the waste gate system. In turbo motors I've built in the past, usually the waste gate operation is fairly analog, in that it's simply operated off springs and boost pressures. However, with Ferrari, I'd guess it's probably operated by the ECU and/or some sort of vacuum operated solenoid or something. Perhaps there is a vacuum line off, which is going to the waste gate (or a pressure hose) which is allowing it to remain totally open instead of being closed (sort of like how the exhaust valves on the 458 exhaust system function). If that were the case (and the waste gate was stuck open), it might be allowing all the exhaust gasses to bypass the turbine.

My guess is either a hose coupling has come off (or split) and/or the waste gate is wide open and killing the turbine speeds (and thus the compressor speeds). Either that or maybe the blow off valve is stuck wide open or the ECU controlling the entire system is faulty.

Has anyone tried the cigar trick yet? Or stuck a vacuum gauge on to see what the idle vacuum is showing?

Has anyone reset the ECU's by disconnecting the battery?

Ray

 

The turbo engine only sees positive manifold pressure during open throttle input in boost. At idle there's a bypass so that the engine is under vacuum. This is also very normal with supercharged setups. Not sure what the vacuum is but, probably between 17-20 hg. Most normal boosters need about 15-17 hg to work properly. In some cases the turbo is so inefficient at idle that there's no need for a bypass valve, and thus there's natural vacuum in the plenum.

Sounds to me like there can be a few things going on.

1: Defective brake booster.
2: Vacuum leak.
3: Defective intake bypass valve.

All of these conditions will cause a low vacuum situation at idle for the brake booster.

 

I think it has to be something actively drawing away vacuum, not intermittent. Typically the brake booster has some level of reserve capacity to it (usually 2 to 3 brake presses), so to have absolutely no braking assistance points to something killing the vacuum on a continual basis; otherwise, I think you'd see peaks and valleys of when the brakes seem to work and then seem to become overly difficult to press.

Also, throwing a code usually means it's something which isn't resolving on its own.

Ray

 

True. Here's what I would try. Find a safe place and run the car up to speed, then put it in neutral and see if it stops.

My thought is that the blow off valve might be defunct. This means that on the overrun when you let go of the gas, you don't get vacuum. The engine breaking keeps the turbos spooled and thus without vacuum in the intake. That air is normally bled off so that the brakes work. If that air is not bled off, the the intake will probably see 1 atmosphere of pressure. It could of course be a software glitch that fails to regulate the valves, and therefore it's related to speed and rpm directly.

Of course the car is in the shop now, but it would be interesting to see how it would stop at high speed in neutral. That puts the engine at idle and gives it the best chance for the same stopping power it has at lower speed.

But hey, it might also be ESC/ABS related. I just think it's valve related with the error on the induction system.

 

The intermittent brake failure is well known to 458 owners. Ferrari is denying that it's happening and it id difficult to diagnose by dealers since it's not a constant issue with the car, it only happens once in a while. There are no codes stored in the ECU either since there are no sensors, it's a purely mechanical operation. Thankfully the braking system is fairly simple and replacing the check valve in the back of the engine and/or the brake servo/booster solves the problem.

On a turbo-charged car hopefully the computer sees a vacuum leak and can point you in the right direction.

 

You lost me here? If it's vacuum related, the brake booster should charge even at idle (where vacuum is typically strongest and when there is no positive boost from the turbos).

Am I not understanding something with regard to the need to get up to speed in neutral in order to test something else?

Ray

 

He says that the car has the issue at higher speeds. When you are at speed and you let off the throttle to apply brake, the drivetrain stays in gear thus the revs are up and there's potential for less vacuum as the turbos are spooled during the engine breaking. If the valves cannot bleed off the air coming from the turbos which they normally should in this situation, there will be positive pressure in the intake instead of vacuum.

If you put it in neutral before applying the brakes, you should have maximum vacuum as the engine is now at idle speed rather than revved up for engine breaking.

It was just a way to see if it was related to engine and turbo speed.

I'm explaining it to the best of my abilities, but sometimes this is where the language barrier kicks in.

 

"P0299 OBD-II Trouble Code: Turbo / Supercharger Underboost Condition"

This is why I think it's related to a valve control issue. If the valves are not working right, like it could create too little vacuum for brakes, it could also result in a boost leak at the same time. If a valve is stuck, it could be the case where it does not let enough air out when vacuum is needed, but enough to cause a boost leak when pressure is high.

I'm just guessing here, but that's what I think.

 

That makes sense. But at the same time, you don't see this type of brake issue with other turbocharged cars. The check valves are made by Valeo. The brake booster is a Bosch unit. Fundamentally there is nothing different between a Ferrari, a Porsche, or any other European manufacturer that uses the same parts bin for their cars. And yet, 458s and 488s have intermittent brake failures where there is no vacuum assist when you hit the brakes...

 

Oh okay, I see what you are getting at. Sounds like some testing is definitely in order to help diagnose the issue.

Ray