Brake failure

Solberg

Solberg

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Evening lads,

So when I had the S3 out for some winter drifting something happen that never have occurred while Ive had the car, not even hard asphalt driving.

3-4 times on one evening the brakes failed, what happens is when say I come to a stop sideways on the redline and slam the brakes the pedal just gets hard as stone, its impossible to push it in, which makes me unable to brake/stop. SUPER SCARY.

Any ideas why this happens? My brother said it was "normal" on some cars that when you try to brake hard during a drift and on high RPM the brakes can do this sometimes, and he meant this happened several times on his cupra r..... This cant be serious?


20161105_163540.jpg
 
<tuffty/> said:
No vacuum in the servo....

<tuffty/>
Click to expand...
So not normal then? Not even when slamming brakes while on redline ish? I mean could not be some "defence mechanisme" from the cars brain or some stupid shait?

How do I forward this? Brakes are fine else, brakes good as always, just that this have happened a handfull times over 2 nights of sliding...


And when I say the brake pedal was hard, it was not just hard to push in...it was impossible to push even 1 cm in, like it was stuck if you feel me.
 
I sometimes get this if I am reversing into my parking space at home as I use the brakes a bit then keep the revs going so no real vacuum is generated at that point...

I would imagine this is why TFSI's use a vacuum pump like derv's so there is constant vacuum...

Try pumping the brake pedal with the engine off... the pedal should go harder and get to a point its difficult to push down... if this feels the same thing as you are experiencing then its vacuum related...

Not sure if its a fault as such though as you are doing something they didn't really design the car to do... I assume everything returned to normal once driving normally?

Vacuum is only generated off boost so idle and cruise... if you are keeping the car mostly on boost and dabbing the brakes every now and then the vacuum reserve will get used fairly quickly...

In motorsport its not unusual for cars to have a vacuum pump fitted for this very reason...

<tuffty/>
 
So this might be some of the idea with the vacuum chamber for the n249 which I have deleted, eh?

Vacuum pump sounds smart. It brakes fine elsewere, only get the trouble when braking off high rpm.
Dont wanna end up like this fella lol
 
Solberg said:
So this might be some of the idea with the vacuum chamber for the n249 which I have deleted, eh?

Vacuum pump sounds smart. It brakes fine elsewere, only get the trouble when braking off high rpm.
Dont wanna end up like this fella lol
Click to expand...


Nothing to do with the N249 or the vacuum store... thats purely for the DV

<tuffty/>
 
hard pedal and no braking effort can also be glazed pads... ******..
long pedal is usually boiling brake fluid..

if you loose vacuum, which you should have a lot of on overrun braking?!?! you should be looking for a split pipe from inlet manifold to servo. (usually the hard plastic joiner near the servo, prone to splitting, or the joiner itself I've seen pop apart..)
 
badger5 said:
hard pedal and no braking effort can also be glazed pads... ******..
long pedal is usually boiling brake fluid..

if you loose vacuum, which you should have a lot of on overrun braking?!?! you should be looking for a split pipe from inlet manifold to servo. (usually the hard plastic joiner near the servo, prone to splitting, or the joiner itself I've seen pop apart..)
Click to expand...


I'm starting to think this is a limitation of design , patently stupid idea to feed the servo from a system that spends most of its time under positive pressure at high speed , my xr4x4i was 10 yeas older and had a fully pumped breaking system , as do the new models

work round on this , could be to fit the alternator from the DIESEL version ..... Vac pump is part of that ... so 100% vac while engine is running , thats if the thing fits

G, )
 
Depends how many presses you are doing while Flat out. A full servo will last about 3 and while @WOT you are generating no vacuum either. I am also surprised the car lets you left foot brake as they are programmed to drop the throttle while the brakes are engaged
 
AGB-S3 said:
..work round on this , could be to fit the alternator from the DIESEL version ..... Vac pump is part of that ... so 100% vac while engine is running , thats if the thing fits
Click to expand...

Vac pump on PD engines is on the end of the head driven off the cam... alternator is the alternator

<tuffty/>
 
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<tuffty/> said:
Vac pump on PD engines is on the end of the head driven off the cam... alternator is the alternator

<tuffty/>
Click to expand...
so much for that bright idea then .. some have vac pumps , would of been simple fix ,
 
AGB-S3 said:
I'm starting to think this is a limitation of design , patently stupid idea to feed the servo from a system that spends most of its time under positive pressure at high speed , my xr4x4i was 10 yeas older and had a fully pumped breaking system , as do the new models

work round on this , could be to fit the alternator from the DIESEL version ..... Vac pump is part of that ... so 100% vac while engine is running , thats if the thing fits

G, )
Click to expand...

On ebay now ... is this the only vac source on the A4 V6 ??

AUDI A4 B6 3.0 V6 QUATTRO , Electric Brake Vacuum pump 8E0927317
 
Sounds like a god damn sewing machine then, can´t have it like that can we? :confounded::confounded:
 
Better than the sound of braking glass when you hit something :) but I guess , there is a Vac switch , so once the servo is under vac it would stop running , as its not the primary ....... lots of comments round big over lap cams etc so its not a unheard of situation .. just another of these ' never notice things ' like the emission's ..... where on earth would it fit though ..
G,
 
AGB-S3 said:
I'm starting to think this is a limitation of design , patently stupid idea to feed the servo from a system that spends most of its time under positive pressure at high speed , my xr4x4i was 10 yeas older and had a fully pumped breaking system , as do the new models

work round on this , could be to fit the alternator from the DIESEL version ..... Vac pump is part of that ... so 100% vac while engine is running , thats if the thing fits

G, )
Click to expand...

aside from being pointless as braking issues simply do not happen on a functioning system
>2001 cars have a suction jet pump which is there to provide vacuum also..
 
I doubt there are any leaks, he was just at WOT and applying the brakes multiple times.

Its not really a fault, as in normal use you never brake while at WOT, and the instant you shut the throttle the vacuum is restored.

Try it on a straight road. Apply full throttle and hit the brakes a couple times. You'll get 2 or 3 goes and then a solid pedal.
 
Not a problem for daily use, and I imagine how it works.

But for spirited trackdays I hence this could be a troublemaker at some point. One fail at the wrong time could end with a kabam really. Havent crashed yet but Ive been damn close, and then I mean a few centimeters from going straight into car infront on a stop because the brakes did not respond not on pumping like a maniac and neither trying to push pedal trough the floor, it takes a few seconds before vacuum is restored and driving spirited you dont have a few seconds to wait for the brakes to work when you need them.

The second time this happen I was drifting countersteer-countersteer on a loong straight high speed, and when the road was at its end and I was coming at high speed....no brakes, and on snow. That there is super scary. How does the fellas with silvias, skylines, supras etc do it when drifting on track? Do they all have a extra vacuum pump fitted for the brake booster?
 
Proper track driving is never an issue, as your not applying brakes while accellerating. The servo has a check valve, and stores a quantity of vacuum ready for use, and the engine replenishes this while braking, which is typically performed with the throttle shut...

I dont drift, so i dont actually know what your doing with the pedals, but if your braking while the throttle is open, then clearly your going to expend that small reservoir of vacuum and end up with no assistance.

You need to go analyse whats actually going on in a calm manner, rather than while sideways at stupid speed. If for instance the check valve on the servo is bust, then the vacuum will vanish as soon as you open the throttle. The vacuum should be restored instantly if you close the throttle, especially if the engines at high RPM. You certainly wont be waiting a few seconds... Just look a the boost guage and you'll see how quickly it drops back to -20...

The ABS can also do silly things on low traction surfaces. ABS works by turning the brakes off, and then waiting for the wheels to start rotating again. If your on a low grip surface, that can take a while, and so you end up with nothing.

If it really is simply a case of expending the vacuum reservoir, then an electric pump will do the job just fine. You could even put it on a switch so it only runs while your drifting around.
 
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if its track use and essentially left foot braking he's doing (not normal or what the car was designed to do) then adding a vacuum store may mitigate his use. Presumes there's no actual fault or vacuum leak he's unaware of, which I personally doubt.
 
badger5 said:
aside from being pointless as braking issues simply do not happen on a functioning system
>2001 cars have a suction jet pump which is there to provide vacuum also..
Click to expand...

>2001 cars have a suction jet pump

Where is that located , any pic diagrams etc ??
 
aragorn said:
I doubt there are any leaks, he was just at WOT and applying the brakes multiple times.

Its not really a fault, as in normal use you never brake while at WOT, and the instant you shut the throttle the vacuum is restored.

Try it on a straight road. Apply full throttle and hit the brakes a couple times. You'll get 2 or 3 goes and then a solid pedal.
Click to expand...

''instant you shut the throttle the vacuum is restored.'' That feels like eternity ! , but at least its not just me , who found something undesirable lurking in the breaking system design ...
 
Just to say it happend after going off the throttle, I was only breaking while coming off high rpm. And it tok several seconds before I had any brakes.
I was not breaking while on WOT, but just after. Couldve been mixed a few times i dont know, but when I feel like I am going to crash I keep my foot faaar off the throttle usually :tearsofjoy:

I have not had this problem on asphalt racing, like when you keep wot while breaking to keep boost, has only happened on snow. It could be a ABS problem as mentioned, Ive had the abs lamp come on when drifting on snow atleast 1 or 2 times. But it dont feel like a normal abs "stop" when you get the pedal vibration because then you can still use the brakes, most be a faulty abs if so.
 
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