Brake Failure?
Discussion
Help, has anyone experienced similar brake failure problems?
This evening I accelerated quite harshly towards a junction in 1st gear from < 5mph to approx 25mph then went straight to the brakes to stop for a 'T' junction. Nothing happened
I recall pressing VERY hard on the pedal prior to wrenching on the handbrake and spinning sideways
into the main road that I was about to join. Fortunately I had worked late and the road was empty and I ended up facing straight down the road and set off as if nothing had happened to those around me 
but requiring a new pair of underpants and new seat.
The brakes were cold and later I drove back in my wifes car and found the road surface to be very grippy - dry and no sign of oil/grease/diesel
I have owned the car (Monaro VXR) since new with no similar issues.
Can anyone suggest what went wrong?
This evening I accelerated quite harshly towards a junction in 1st gear from < 5mph to approx 25mph then went straight to the brakes to stop for a 'T' junction. Nothing happened
I recall pressing VERY hard on the pedal prior to wrenching on the handbrake and spinning sideways
into the main road that I was about to join. Fortunately I had worked late and the road was empty and I ended up facing straight down the road and set off as if nothing had happened to those around me but requiring a new pair of underpants and new seat.The brakes were cold and later I drove back in my wifes car and found the road surface to be very grippy - dry and no sign of oil/grease/diesel
I have owned the car (Monaro VXR) since new with no similar issues.
Can anyone suggest what went wrong?
Ive had this when its wet as the pads move away from the disks due to water and you have to double pump the pedel a little. Even the APs have suffered very occasionally but not at the speeds you were talking about. You sure it was not locking up and are the brakes working ok now..? Try the same situation but on an industrial estate to see if you can repeat the problem...
Failing that get the brakes bleed through properly and check the pads etc.
Failing that get the brakes bleed through properly and check the pads etc.
After going back to check the road surface I am pretty sure that I did not lock up the brakes I would have stopped easily.
I braked fairly late and straight from the accelerator but I would judge that I was driving no where near the limit of the road conditions.
Applying the hand brake must have slowed me as it slid me sideways into the main road (typical 'B' road width - not very wide!!!)
I tested the brakes successfully many times within the next 100yds and then on the 4 mile trip home.
It felt to me like the ABS completely over reacted preventing the brakes from being applied at all
I realise this may seem a bit far fetched - is it?
thanks
Jon
I braked fairly late and straight from the accelerator but I would judge that I was driving no where near the limit of the road conditions.
Applying the hand brake must have slowed me as it slid me sideways into the main road (typical 'B' road width - not very wide!!!)
I tested the brakes successfully many times within the next 100yds and then on the 4 mile trip home.
It felt to me like the ABS completely over reacted preventing the brakes from being applied at all
I realise this may seem a bit far fetched - is it?
thanks
Jon
ABS could have cut in if you stamped on them and it can seem like an age for them to come back on TBH. I know as this happens at the Ring alot on 2 corners if you dont know to stop braking as you crest a rise and then re-apply the brake, riding the brake over the rises causes the ABS to cut in and the time it takes for it to re-apply the brakes is long enough for you to hit the armco! Take it out and do exactly the same - accelerate hard and stamp on the brake remembering that you are expecting and immediate decelaration rather than any delay at all.
imho, maybe totally wrong, but...
If you'd hit the "stop" it would feel hard, and yes I had a similar incident at slightly more speed when i tried to do an emergency stop behind a range rover. Brake pedal went down, hit the stop and that was that, just had to wait for the car to slow - which seemed to take forever.
Do you remember how long you were braking for before you used the hand brake?
reason i ask, cold, wet discs would need a few rotations to disperse the water on the surface before gripping properly, and the brake assist(??) (feels like pedal coming up, the harder you press, the harder the pedal pushes back up) takes a few seconds to work iirc.
Oh and is your hand brake ok?
We've all been worried recently about applying our handbrakes whilst still moving, It would be nice to know if it has broken anything.
If you'd hit the "stop" it would feel hard, and yes I had a similar incident at slightly more speed when i tried to do an emergency stop behind a range rover. Brake pedal went down, hit the stop and that was that, just had to wait for the car to slow - which seemed to take forever.
Do you remember how long you were braking for before you used the hand brake?
reason i ask, cold, wet discs would need a few rotations to disperse the water on the surface before gripping properly, and the brake assist(??) (feels like pedal coming up, the harder you press, the harder the pedal pushes back up) takes a few seconds to work iirc.
Oh and is your hand brake ok?
We've all been worried recently about applying our handbrakes whilst still moving, It would be nice to know if it has broken anything.
S600VXR said:
ABS could have cut in if you stamped on them and it can seem like an age for them to come back on TBH. I know as this happens at the Ring alot on 2 corners if you dont know to stop braking as you crest a rise and then re-apply the brake, riding the brake over the rises causes the ABS to cut in and the time it takes for it to re-apply the brakes is long enough for you to hit the armco! Take it out and do exactly the same - accelerate hard and stamp on the brake remembering that you are expecting and immediate decelaration rather than any delay at all.
Yes! I get this all the time on my local road, there is a large man hole/drain cover on the road just before the T Junction, so I am always braking when I hit it, I ALWAYS have to lift and reapply in order to stop properly as the ABS does take a long time to sort itself out.
Very different sensation than hitting the stop though (see my previous post)
Going out for a brake test, back shortly.
If you dont hear from me later , you may find an accident damaged Monaro in classifieds next week!
The handbrake seems okay, I did notice the other thread as i was searching for a similar instance and i am now reluctant to do the same test.
My natural reaction in the past to brake fade/failure has been to pump the brakes and not pull the handbrake i am unsure as to whether i pumped the brake this evening but I would have used the handbrake as a last resort after realising I was in serious trouble (blind exit onto a usually busy main road)
If you dont hear from me later , you may find an accident damaged Monaro in classifieds next week!
The handbrake seems okay, I did notice the other thread as i was searching for a similar instance and i am now reluctant to do the same test.
My natural reaction in the past to brake fade/failure has been to pump the brakes and not pull the handbrake i am unsure as to whether i pumped the brake this evening but I would have used the handbrake as a last resort after realising I was in serious trouble (blind exit onto a usually busy main road)
Maybe an issue with the servo? If you accelerated at high load there would be no manifold vacuum to "charge" the servo. So going straight to braking the pedal would be hard and unresponsive. Normally though the servo stores the vacuum from at any point previously you were at low load and not braking.
Just tried several stops going from 0 to 30 to 0 without pause.
The abs kicked in and stopped me very quickly - half the distance that I believe I allowed for during the incident.
Shouldn't confess this but as i have been so confused about what happened I even tried to put my right foot on the clutch to see if i had somehow missed the brake but I found that my left foot was already there I am sure that that would have been the case earlier and I should have noticed
The suggestion of a servo fault does seem very plausable from my limited knowledge and I would say that it does seem to fit all the symptoms.
I will give it a quick look over
The abs kicked in and stopped me very quickly - half the distance that I believe I allowed for during the incident.
Shouldn't confess this but as i have been so confused about what happened I even tried to put my right foot on the clutch to see if i had somehow missed the brake but I found that my left foot was already there I am sure that that would have been the case earlier and I should have noticed
The suggestion of a servo fault does seem very plausable from my limited knowledge and I would say that it does seem to fit all the symptoms.
I will give it a quick look over
granada203028 said:
Maybe an issue with the servo? If you accelerated at high load there would be no manifold vacuum to "charge" the servo. So going straight to braking the pedal would be hard and unresponsive. Normally though the servo stores the vacuum from at any point previously you were at low load and not braking.
But the instant you let off the accelerator to brake, there would be ample vacuum to allow braking.I have no recollection of ABS juddar and with a lack of braking even with high applied pedal pressure it does seem to tick all the symptom boxes.
But, I would agree that after maximum throttle and 4000rpm you would expect a significant vacuum.
Note - The rpm may have been higher as even though I was travelling at about 25mph the engine/drive train may have been trying to go faster (if you get my drift)
Do you feel that somehow there could have been too much brake pressure or the mismatch between road speed and engine speed - confused the ABS system?
But, I would agree that after maximum throttle and 4000rpm you would expect a significant vacuum.
Note - The rpm may have been higher as even though I was travelling at about 25mph the engine/drive train may have been trying to go faster (if you get my drift)
Do you feel that somehow there could have been too much brake pressure or the mismatch between road speed and engine speed - confused the ABS system?
Yes I have had the same problem, for me I was in a full throttle overtaking manoeuver in third gear overtaking two cars at once. The rear end was in the squat position as the first car in front of me jumped out into the right lane. I stood on the brakes and nothing, I had to take to the grass verge on the wrong side of the road!!!!
Like you this has never happened again, I have asked the question on here about AP brakes, and the people that responded said that they have no problems with the ABS system with the increased stopping power.
Interestingly though reading you post, you were at a wide throttle opening, then dropped the throttle and straight on to the brakes. My conclusion is weight transference through inertia effectively doubling the cars wheight and showing up the problem that these cars on standard discs are under braked.
Like you this has never happened again, I have asked the question on here about AP brakes, and the people that responded said that they have no problems with the ABS system with the increased stopping power.
Interestingly though reading you post, you were at a wide throttle opening, then dropped the throttle and straight on to the brakes. My conclusion is weight transference through inertia effectively doubling the cars wheight and showing up the problem that these cars on standard discs are under braked.
Edited by slackalice on Wednesday 11th March 08:12
I think you've just had a combination of a lot of engine inertia and harsh ABS application. A V8 spinning 4 or 5k RPM has a lot of forward drive to the wheels when you snap the throttle shut suddenly and jump on the brake hard with the clutch still out.
www.dervman.com/abs.htm
When you do an emergency stop in a car, it is important to dump the clutch as soon as you hit the brakes, rather than delaying it (as you were probably taught in a non-ABS car that you took your driving test in). If you keep the clutch in, the ABS system has to cope with both the forward momentum of the car and the engine at the same time.
ABS Helps You Stop?
In simplistic terms the braking effort on the wheel when ABS is working varies from a locked wheel (or a nearly locked wheel) to no brakes being applied at all. Even if the system goes from one extreme to the other many times a second, the average braking effort will be less than “full on.” Therefore, do not assume that ABS always shortens stopping distances.
www.dervman.com/abs.htm
From www.dervman.com/abs.htm said:
When you do an emergency stop in a car, it is important to dump the clutch as soon as you hit the brakes, rather than delaying it (as you were probably taught in a non-ABS car that you took your driving test in). If you keep the clutch in, the ABS system has to cope with both the forward momentum of the car and the engine at the same time.
ABS Helps You Stop?
In simplistic terms the braking effort on the wheel when ABS is working varies from a locked wheel (or a nearly locked wheel) to no brakes being applied at all. Even if the system goes from one extreme to the other many times a second, the average braking effort will be less than “full on.” Therefore, do not assume that ABS always shortens stopping distances.
Edited by robkarloff on Wednesday 11th March 09:42
Thanks again for all your responses.
I understand Stevieturbos point that engine speed has nothing directly to do with the ABS but throttle opening and engine rpm will affect the the vacuum in the Servo and hence master cylinder pressure.
I would expect that there is some sort of regulation in the servo to moderate the assistance though I am not familier enough to know.
From all the suggestions can I summarise the different possible causes
1) Mechanical failure
The servo failure fits all the faults though it seems odd that i have gone from no fault to serious failure and back to no fault within three applications of the brake pedal.
2) Control system (electrical) failure
The focus would be the response from the ABS system. If this somehow got confused then it could potentially give me the hard brake pedal with no stopping power.
Could it be possible that if I applied the brakes whilst I was exiting a wheel spin then would the system have decided that the front wheels were going too slow (when compared to the rears that were going too fast) and therefore taken pressure from the front axle giving me very little decelaration as the front tends to apply nearly all of the braking effort on a good dry road surface?
I would expect the ABS system to always decide that the slower wheels are locking up - am I correct as agian i am no expert on this?
3) Human error
Can't rule this out but I would argue that I am no numpty having driven the car for 18mths with no accidents or spins as yet. I do feel that after last night I can feel one coming imminently and I am very worried about my safety (and others) until I understand what went wrong. If all else fails i will have to accept that somehow I completely misjudged the cars and my performance though currently I cannot accept that i got it so wrong especially after going back to the road surface and testing the brakes later that evening.
Please feel free to suggest / comment on the above and if once the discussion ends it infers that I must swallow my pride and accept blame then so be it!!!!
I understand Stevieturbos point that engine speed has nothing directly to do with the ABS but throttle opening and engine rpm will affect the the vacuum in the Servo and hence master cylinder pressure.
I would expect that there is some sort of regulation in the servo to moderate the assistance though I am not familier enough to know.
From all the suggestions can I summarise the different possible causes
1) Mechanical failure
The servo failure fits all the faults though it seems odd that i have gone from no fault to serious failure and back to no fault within three applications of the brake pedal.
2) Control system (electrical) failure
The focus would be the response from the ABS system. If this somehow got confused then it could potentially give me the hard brake pedal with no stopping power.
Could it be possible that if I applied the brakes whilst I was exiting a wheel spin then would the system have decided that the front wheels were going too slow (when compared to the rears that were going too fast) and therefore taken pressure from the front axle giving me very little decelaration as the front tends to apply nearly all of the braking effort on a good dry road surface?
I would expect the ABS system to always decide that the slower wheels are locking up - am I correct as agian i am no expert on this?
3) Human error
Can't rule this out but I would argue that I am no numpty having driven the car for 18mths with no accidents or spins as yet. I do feel that after last night I can feel one coming imminently and I am very worried about my safety (and others) until I understand what went wrong. If all else fails i will have to accept that somehow I completely misjudged the cars and my performance though currently I cannot accept that i got it so wrong especially after going back to the road surface and testing the brakes later that evening.
Please feel free to suggest / comment on the above and if once the discussion ends it infers that I must swallow my pride and accept blame then so be it!!!!
There's a non return valve on your booster, so it wont leak vacuum back out under normal circumstances. You would have to have absolutely no vacuum generated by your engine plus some active use of the brakes to empty it. It'll still stop, but it'll scare you (And no this isn't a re-type of something I found on Google, it's my experience from having no vacuum on a supercharged car). Still stops, just have to push harder. A broken/sticking non return would give a hard pedal, but stop too. I had a T5 that the vacuum lines collapsed on, and that would have no vacuum after being WOT for a while, and was scary as hell but stopped.
LawrenceF said:
I had a T5 that the vacuum lines collapsed on, and that would have no vacuum after being WOT for a while, and was scary as hell but stopped.
The servo is simply on/off ususally.
The common thing on 850/V70 Volvos is the ABS controller develops a fault as it gets a bit old. Easily cured by removing the PCB from the unit and re-soldering the joints on the back (mine had this last year, fixed it myself and good as gold since). But it can cause the ABS to kick in even under light braking for no good reason, which usually means you end up flying towards a corner pressing hard on the brake pedal and not slowing down fast enough. The only solution is to lift off an re-apply the brake, usually after one or two attempts it behaves normally and you get the anchors properly on! I remember first experiencing this in my friends 850 T5 years ago, he was convinced it was a duff wheel sensor, but in the Volvos it's nearly always the ATE controller unit. Scary tho!
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