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Brake pedal constantly going soft
In the M6 the brake pedal has gone soft & I am stumped as to why this is happening.
1. The first time it did it was just after I bought it, the pedal was soft & it failed the NCT for excessive brake pedal travel. A brake bleed was completed & it was fine for about two weeks.
2. Then it went soft again, about two weeks after the brake bleed was completed, again with pedal getting soft & the pedal travel is ridiculous. It was diagnosed as a defective master cylinder. The master cylinder was replaced and everything was good....for about two weeks.
3. So after two weeks with a new master cylinder it then was left in for another brake bleed & without any driving (it was in the dealer's compound) the pedal again went soft after a brake bleed.
4. This time the issue was diagnosed as a defective Servo. So the servo was replaced.
Here were are again about 2 weeks after that & the fucking pedal is soft again! :mad:
Anybody got any ideas as to why this in happening? The dealer doesn't seem to be doing a great job so far at identifying root cause but maybe it is just one of those hard to trace issues. The car is under warranty, while it is good that I am not being hit in the pocket for the work I would really rather just have the car fixed & be able to drive it. It's spent nearly 25% of my ownership in the dealers, brakes are not rocket science stuff either so the whole thing is getting frustrating.
Any help appreciated.
After each "fix" the pedal feels great for a week or so, and there's no leaks. It is wrecking my head at the minute.
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RE: Brake pedal constantly going soft
Is the fluid level changing at all? I presume you've checked it but I said I'd put it out there anyway. It sounds like it's getting air into the system somehow although the fact that it's not been driven half puts that theory out the window.
Definitely a strange one. I'd also go about checking all the brake hose and calipers for leaks, could omit be possible that a brake hose was caught off the ground somewhere? You could isolate the calipers by putting a vise grips on each brake line and leave the car for a while to see if the softness returns.
Is there any leaks around the abs pump?
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RE: Brake pedal constantly going soft
I'd agree. Sounds like air in the system or seals gone. Had a similar issue with an audi. Was going to the floor until all 4 corners were bled.
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RE: Brake pedal constantly going soft
Quote:
Originally Posted by Smokey Bear
Is the fluid level changing at all? I presume you've checked it but I said I'd put it out there anyway. It sounds like it's getting air into the system somehow although the fact that it's not been driven half puts that theory out the window.
Definitely a strange one. I'd also go about checking all the brake hose and calipers for leaks, could omit be possible that a brake hose was caught off the ground somewhere? You could isolate the calipers by putting a vise grips on each brake line and leave the car for a while to see if the softness returns.
Is there any leaks around the abs pump?
If it would be leaking !!! U would lost all brake fluid in minutes ! It wouldn't be ok for days weeks or hours .
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RE: Brake pedal constantly going soft
Yeah, there are no leaks. That was checked many times. Here's a few things that I was thinking of but they are kind of "grasping at straws" type ideas.
- Would a hairline crack in the master cylinder fluid reservoir cap allow air in over time (2 weeks) & cause the pedal to go soft?
- Am I potentially braking too hard boiling the fluid? Would this cause the fluid to go off? I'm not that hard on the brakes, at least I think so anyway.
- The pedal stays good for about a week or two,so am I correct in saying that the flexible brake lines & pads/discs should not be to blame?
:rolleyes: :@ Very frustrated.
Thanks for the replies so far.
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RE: Brake pedal constantly going soft
Unlikely you'd be boiling the fluid. Unless youre really trying on the back roads?!:hehe!:
Does the pedal go hard if you give it a few pumps or stay soft? If it goes hard after one or two pumps it could be something simple like a pad binding? Ie a pad getting slightly stuck on the carrier and needs an extra push to get to the disc.
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RE: Brake pedal constantly going soft
Quote:
Originally Posted by Hobbs
Unlikely you'd be boiling the fluid. Unless youre really trying on the back roads?!:hehe!:
Does the pedal go hard if you give it a few pumps or stay soft? If it goes hard after one or two pumps it could be something simple like a pad binding? Ie a pad getting slightly stuck on the carrier and needs an extra push to get to the disc.
Thanks I just thought I'd check, as you know there's a fair bit of muscle under the bonnet and I thought that maybe I was putting it under a it more pressure than normal. Go faster, stop faster scenario.
Why would the pads only start to bind after a week or so & then instantly recover after a brake bleed? To answer your question yes the pressure does get better with pumping,but is that always the case, e.g. even if there was air in the system?
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Brake pedal constantly going soft
I know you know this Mark but I'm sure they done the active brake bleed procedure?
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RE: Brake pedal constantly going soft
Quote:
Originally Posted by HealyC
I know you know this Mark but I'm sure they done the active brake bleed procedure?
Christ, I hope they have done it! Otherwise a lot of money has been thrown away on master cylinders & servos!
I am tempted to do a sneaky bleed of the system myself, but would be afraid it would void my warranty. At the same time its a joke that it has to go in for a 4th time to troubleshoot, particularly when it was in for a 3 week stint the last time.
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Brake pedal constantly going soft
Quote:
Originally Posted by rebel.ranter
Quote:
Originally Posted by HealyC
I know you know this Mark but I'm sure they done the active brake bleed procedure?
Christ, I hope they have done it! Otherwise a lot of money has been thrown away on master cylinders & servos!
I am tempted to do a sneaky bleed of the system myself, but would be afraid it would void my warranty. At the same time its a joke that it has to go in for a 4th time to troubleshoot, particularly when it was in for a 3 week stint the last time.
Had a similar issue before with an X5 and it turned out to be pads. The rear pads weren't sitting in the brake caliper carrier correctly so the piston was travelling too much to squeeze the pads. Fitted them correctly and it was perfect.
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Brake pedal constantly going soft
Quote:
Originally Posted by rebel.ranter
Quote:
Originally Posted by HealyC
I know you know this Mark but I'm sure they done the active brake bleed procedure?
Christ, I hope they have done it! Otherwise a lot of money has been thrown away on master cylinders & servos!
I am tempted to do a sneaky bleed of the system myself, but would be afraid it would void my warranty. At the same time its a joke that it has to go in for a 4th time to troubleshoot, particularly when it was in for a 3 week stint the last time.
I wouldn't want to give any recommendation that might be seen as breaking a warranty but if I was an engineer who routinely worked on all parts of cars from ICE to the oily bits I'd bleed the system and check the pads myself at this stage [emoji6]
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RE: Brake pedal constantly going soft
Could be a bad caliper. My mate had a golf the other day with this problem and also failed nct for excessive travel. Clamped off each caliper hose separately and left the car over night. Checked it the next day and on the third day found a rear caliper was causing the problem. Fit a recon unit and the car has been fine for weeks so far and passed nct also.
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RE: Brake pedal constantly going soft
If its not a calliper or pads and no fluid loss, that only leaves the master cylinder,servo (which I know you've changed) or abs pump. Unless their still not bled out properly? (doubtful,I know).
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RE: Brake pedal constantly going soft
The master cylinder & servo have been swapped out for new items. This is wrecking my head. I am dreading dropping it in again for more bullshit work.
Would a loose or perished vacuum hose cause a pedal to sink?
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RE: Brake pedal constantly going soft
?????????????????????
I know the bulletin doesnt apply to your exact car but its worth a try.
Does your car have a brake booster?
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RE: Brake pedal constantly going soft
Hey John, I'm not sure you attached the right document but the car does have a vacuum pump Part number 6769029-01.
http://i175.photobucket.com/albums/w...psxm4gkxv0.jpg
http://i175.photobucket.com/albums/w...pss6w1gocv.jpg
http://i175.photobucket.com/albums/w...psvtka3hom.jpg
I just checked last night & the fluid in the reservoir seems OK colour wise (can be hard to tell), and the level definitely has not dropped.
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RE: Brake pedal constantly going soft
Ok, a new development. Driving along the South Ring Dual Carriageway I noticed that the car was slowing itself, I thought I was losing power. Pulled over, rear wheels hot as hell, centre of discs white with heat, smell of brake pad burn, also brakes locked solid.
Starting to make sense now, I think, but why would both rears bind/lock up? Weird. At least now there's something to target.
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Brake pedal constantly going soft
Ok, this might be completely unrelated.
Does this car have any kind of brake bias controller?
I know this is chalk and cheese, but I had an old MK2 golf gti do exactly the same thing.
There's a valve on the rear swing arm that actuated a valve depending on the attitude of the car.
So unless you actuated the brake bias controller when you were bleeding the brakes, you created an air pocket when you were trying to bleed them.
At least the issue is developing.
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RE: Brake pedal constantly going soft
I think the ABS (DSC) unit does this job of biasing the brakes.
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RE: Brake pedal constantly going soft
Quote:
Originally Posted by Dave
Ok, this might be completely unrelated.
Does this car have any kind of brake bias controller?
I know this is chalk and cheese, but I had an old MK2 golf gti do exactly the same thing.
There's a valve on the rear swing arm that actuated a valve depending on the attitude of the car.
So unless you actuated the brake bias controller when you were bleeding the brakes, you created an air pocket when you were trying to bleed them.
At least the issue is developing.
It's called brake load valve ,for old as my life cars with non independent suspension
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Brake pedal constantly going soft
Quote:
Originally Posted by Valdelisbmw
Quote:
Originally Posted by Dave
Ok, this might be completely unrelated.
Does this car have any kind of brake bias controller?
I know this is chalk and cheese, but I had an old MK2 golf gti do exactly the same thing.
There's a valve on the rear swing arm that actuated a valve depending on the attitude of the car.
So unless you actuated the brake bias controller when you were bleeding the brakes, you created an air pocket when you were trying to bleed them.
At least the issue is developing.
It's called brake load valve ,for old as my life cars with non independent suspension
I know what the valve is and while it is in no way physically related to the system that exists on the M6 it must surely be possible for the modern equivalent of that system to go wrong and incorrectly bias brake pressure to the rear.
In just throwing out an idea. Might be pointless.
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RE: Brake pedal constantly going soft
Quote:
Originally Posted by Dave
Quote:
Originally Posted by Valdelisbmw
Quote:
Originally Posted by Dave
Ok, this might be completely unrelated.
Does this car have any kind of brake bias controller?
I know this is chalk and cheese, but I had an old MK2 golf gti do exactly the same thing.
There's a valve on the rear swing arm that actuated a valve depending on the attitude of the car.
So unless you actuated the brake bias controller when you were bleeding the brakes, you created an air pocket when you were trying to bleed them.
At least the issue is developing.
It's called brake load valve ,for old as my life cars with non independent suspension
I know what the valve is and while it is in no way physically related to the system that exists on the M6 it must surely be possible for the modern equivalent of that system to go wrong and incorrectly bias brake pressure to the rear.
In just throwing out an idea. Might be pointless.
ABS ASC DSC now does the lot
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Brake pedal constantly going soft
Hi Mark,
Does the pedal go to the floor with the car turned off?
Was a pressure bleeder used to bleed the brakes? Or were they bled manually?
Was the ABS unit bleed procedure done?
Has the car recently had new pads etc fitted?
www.instagram.com/super4bmw
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RE: Brake pedal constantly going soft
No new pads fitted recently.
As mentioned all work is being done by BMW under their warranty so the brake bleed procedure is to use their machine which is both a pressure bleeder & hooks up to ISTA for ABS unit bleeding.
With the car off the pedal does not travel to the floor, also when driving the pedal doesn't travel as much as it does when stationary or driving at very low (eg car park manoeuvring speeds), the travel is much more pronounced.
I am wondering if the rear brakes binding is a new separate issue to clamping the rear flexible hoses (using proper hose tool), done to rule out dodgy callipers? The hoses look fine but maybe damaged internally?
Looks like I'll be saying goodbye to it for another few weeks as it goes in for diagnosis, maybe even for good. Getting fed up with it.
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RE: Brake pedal constantly going soft
Don't give up on it yet Mark. When this is all done, you'll have a pretty well sorted M6 that you'll be able to enjoy finally! It's also possible that the new vaccum pump/ master cylinder is faulty too so wouldn't rule that out either!
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RE: Brake pedal constantly going soft
I'd agree with the above Mark, try to keep the faith. I'd be looking for some good will from BMW though, they should be offering a free service or something as compensation for all the hassle you've had so far.
Even if you add up the time it's spent in the garage, it cost's €150 a month to keep your car taxed, so you've wasted at least that through not having the use of the car for weeks on end!
Hopefully it all gets sorted for you, once and for all!
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RE: Brake pedal constantly going soft
Well, car has been dropped off again this morning to the dealers, God knows when I'll get it back this time.
It seemed to manifest itself every two weeks but it could also have been once I have done around 500kms of driving.
You can imagine the one word I'm thinking of:
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RE: Brake pedal constantly going soft
New DSC module fitted yesterday. But has to stay for another week to get a new fuel tank! :eek
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RE: Brake pedal constantly going soft
Do they give you a courtesy car mark? Ask for something of a similar calibre- like an extended m4 test drive :)
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RE: Brake pedal constantly going soft
^ what he said!!! And call me when you get it :p
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RE: Brake pedal constantly going soft
It will be some car to buy when you get sick of it , most of it will be brand new!
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Brake pedal constantly going soft
Quote:
Originally Posted by rebel.ranter
New DSC module fitted yesterday. But has to stay for another week to get a new fuel tank! :eek
Holy moly! I'd hate to buy one out of warranty. What's wrong with the fuel tank?
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RE: Brake pedal constantly going soft
Was offered a 1 Series for two days, but of an insult really given all the trouble I've had. Here's what has been replaced under warranty so far:
- Heating mixer valve
- 1 ignition coil
- Brake master cylinder
- Left fuel tank sender
- Brake Servo unit
- Head up display
- DSC Unit
- Fuel tank
- Carbon canister
-Labour on all of the above
Pain in the arse, and by my reckoning the list tots up to €15k. I've only done 3.5k kms in it so far!
The fuel tank is in the region of €1,200 for the part alone, I did a price check on it on CarParts-Pros and it came in at €900, add 25% to account for rip off Ireland (this is being conservative by the way). I would imagine the labour would be intensive enough too.
There is a problem with a vacuum build up in the tank, the vent system was blocked & it caused the tank to suck in, come off the support brackets & deform. I reckon it has been going on for a while, perhaps that's why the fuel tank sender broke too. Frightening to think what might have happened here, could the tank have spilt under constant deforming, cracked and split fuel all over the exhaust. Doesn't bear thinking about
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RE: Brake pedal constantly going soft
You'd never know , you might fall in love with the 1 series! !!
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RE: Brake pedal constantly going soft
Jesus mark that's some bill.If the rear brakes are binding and getting hot it would boil the brake fluid which would cause the soft brake pedal.hope you get to the bottom of it.Is the fuel tank a problem with all the m6 and m5.
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RE: Brake pedal constantly going soft
I've researched and the fuel tank issue popped up twice on forums.
I am looking forward to the brakes issue being over.
Got offered a Dacia Duster for the weekend, would rather walk! I thought it was a bit insulting offering that bucket of shit to me. Maybe I'm being too fussy....
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RE: Brake pedal constantly going soft
Your not being to fussy, their customer service is just not good...This kind of stuff would also drive me mad.
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RE: Brake pedal constantly going soft
Quote:
Originally Posted by rebel.ranter
I've researched and the fuel tank issue popped up twice on forums.
I am looking forward to the brakes issue being over.
Got offered a Dacia Duster for the weekend, would rather walk! I thought it was a bit insulting offering that bucket of s*** to me. Maybe I'm being too fussy....
Fussy me hole ! That's something insult after coming out of an m6 :surprised:
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RE: Brake pedal constantly going soft
Quote:
Originally Posted by camnhoj
Quote:
Originally Posted by rebel.ranter
I've researched and the fuel tank issue popped up twice on forums.
I am looking forward to the brakes issue being over.
Got offered a Dacia Duster for the weekend, would rather walk! I thought it was a bit insulting offering that bucket of s*** to me. Maybe I'm being too fussy....
Fussy me hole ! That's something insult after coming out of an m6 :surprised:
Tbh if I showed up on foot, I'd think being offered a Dacia Duster is an insult.
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RE: Brake pedal constantly going soft