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Weird brake issue has me stumped
27-03-2019, 12:10 AM
Post: #1
Weird brake issue has me stumped
Hi guys
Hopefully someone can help me, my nephew bought him a E46 M43, had a bearing knock, that was all sorted and the car drove fine, then suddenly after +-200km he had no brakes, I removed the brake master and found scoring in the cylinder, replaced the unit, bleed brakes, pedal is nice and firm, test drive, all is well (now this is where it starts getting weird) when he leaves the car parked (+- 2hrs) after the bleeding and test drive, there's no brakes. I need to add the pads all round are in good nick, there's about 65% lining all round.

I've replaced the master twice thinking it was the fault, until I decided to test the master on a bench, it holds it's pressure without issue, obviously there's air getting into the system but for the life of me I can't trace it, there's no leak to indicate my problem, whenever the brakes dissappear I have to bleed it again which is obvious but then I have to add 250-350ml of brake fluid (dot 4) to top it up, brake booster is bone dry inside, then I discovered a leak today, the fluid after being test driven and parked leaks out by the cap of the reservoir, like air is being sucked into the system from one of the lines and pushes the fluid out by the reservoir through the cap (picture a caliper piston being pushed open and the fluid going to the reservoir)

I've checked the abs unit and that is good, no leaks, also did a diagnosis with inpa, find no fault on the brakes, so imo it's a mechanical issue and I'm missing something, been battling with this for over a week now, my last resort was to block off the cap today, to prevent the brake fluid from flowing out, my thinking is, if it can't suck air into the system, hopefully the leak will show itself at a wheel or pipe but that I'll have to check tomorrow.

Today I've bled the brakes again and the pedal was good, blocked the cap off, there's still air entering the system as he last reported (after a 3hr rest) there's about 60% pedal which is more than the now 'usual' (usually there'd be no brakes after standing that long) which I tested, has anyone experienced what I'm going through and fixed it, for the love of brakes please respond if you have lol.

Also what I've discovered, it doesn't matter in what sequence (even if I do it wrong by bleeding the front wheels first) I bleed it, the rear brakes always takes way longer to get fluid into the lines and out the nipple compared to the front, the front brakes you pump 6-7 times and fluid starts coming out, rear ones (any caliper) takes at least 20-35 pumps to start seeing fluid, I know rear will take longer as the lines are longer but that also tells me the rear lines runs completely dry, I'm just hoping for some sort of sign at the wheels but they're bone dry when the brakes dissappear.

Thanks in advance for any responses gents.

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27-03-2019, 07:44 AM
Post: #2
RE: Weird brake issue has me stumped
I do not know the I4 however I would look at the vacuum line and the one way valve which should be on it..

Other than that I am as stumped as you are.

The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end, there it is. ~ Winston Churchill


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francoishensen11
27-03-2019, 07:58 AM
Post: #3
RE: Weird brake issue has me stumped
have you gone through all the lines - non have been crimped or bashed under the car.

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francoishensen11
27-03-2019, 08:11 AM
Post: #4
RE: Weird brake issue has me stumped
Have you tried to pressure bleed?

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27-03-2019, 08:44 AM (This post was last modified: 27-03-2019 09:00 AM by francoishensen11.)
Post: #5
RE: Weird brake issue has me stumped
(27-03-2019 07:44 AM)Peter@AEW Wrote:  I do not know the I4 however I would look at the vacuum line and the one way valve which should be on it..

Other than that I am as stumped as you are.
Hmmm, I haven't checked the one way valve, the air line is good as I checked the pipe for any cracks and leaks (car is idling perfectly that's why i didn't look at it) thank you Peter, I'll have a look at the valve.

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(27-03-2019 07:58 AM)MikeR Wrote:  have you gone through all the lines - non have been crimped or bashed under the car.
Yip, gone through each line, from master to abs and from abs to every wheel, there's no physical damage to any line, I used a scope to check the rear lines where it runs above the tank and they're completely undamaged, the rubber pipes at the wheels are also good, on my way to the car now, hopefully there's a sign of the leak after blocking the cap off.

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(27-03-2019 08:11 AM)ZaynM Wrote:  Have you tried to pressure bleed?
Haven't pressure bled as I don't have a unit with me, I'd go pick one up if I thought it would help but I doubt it will purely on the fact that when I'm done bleeding, the brakes are there 100% there's about +-2cm travel on the pedal then it starts to brake after bleeding, I believe there's air getting sucked into the brake line, that air pushes all the fluid out the lines and leaves the car without brakes, my issue is it's not showing me where, if I can't get this sorted, I just might replace all calipers, brake lines and the air line with the one way valve, heck I might even replace the master again too, booster and all, this is the 1st time I've ever come across an issue like this in over 20 years working on cars lol.

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27-03-2019, 09:44 AM
Post: #6
RE: Weird brake issue has me stumped
this happened to our e90 . turned out to be the air vacuum line , a rat bit a small hole in it
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27-03-2019, 11:49 AM
Post: #7
RE: Weird brake issue has me stumped
(27-03-2019 09:44 AM)zubz.parker10 Wrote:  this happened to our e90 . turned out to be the air vacuum line , a rat bit a small hole in it
Just came from the car now, vacuum line intact, no holes, Peter I've checked the one way valve, the valve is working 100% with air only moving from the booster into the intake, when I tried to reverse the valve (air moving the opposite direction from the arrow) no air returns, it's a dead block which confirms the valve is working as it should, was no brakes again and had to bled again, this time I overfilled the reservoir to leave as little possible place for air to be pushed up, it seems blocking it off has prevented the overflow from the cap but it still dry all around, starting to wonder if it's crap brake fluid I'm using to date I've used 2.5L on the system which disappeared, where to I have no clue.

Cut out the floor and stop flinstone style?

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27-03-2019, 01:59 PM
Post: #8
RE: Weird brake issue has me stumped
Best way to confirm/Ruleout Air/Vac Leaks, SMOKE TEST

I setup something with a Rubber glove, Hooka pipe Tube and a Vape, on my 325i Motor Rofl

Worked like a Charm
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27-03-2019, 06:08 PM
Post: #9
RE: Weird brake issue has me stumped
Wait a minute

The system leaks fluid but the fluid cannot be traced

You mentioned that you looked in the brake booster.

Take the master cylinder off and check for leaks from the shaft and seal

I suspect it is pooling in the bottom of the brake booster.

The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end, there it is. ~ Winston Churchill


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27-03-2019, 06:21 PM
Post: #10
RE: Weird brake issue has me stumped
(27-03-2019 06:08 PM)Peter@AEW Wrote:  Wait a minute

The system leaks fluid but the fluid cannot be traced

You mentioned that you looked in the brake booster.

Take the master cylinder off and check for leaks from the shaft and seal

I suspect it is pooling in the bottom of the brake booster.
Will check maybe tomorrow, after the last bleed (6hrs ago) there's still brakes, I did change to "engine dot 4 +" fluid, maybe, just maybe it was the brake fluid, I also need to mention the cap is still blocked off and fluid is topped off past the max point, if the brakes fail again, removing the master again and checking the booster will be the next step, also, between 2 replacement masters, I did check inside the booster with the master off and it was completely dry inside, I'll report back tomorrow with an update regarding the brakes, thank you everyone for the help thus far, I really appreciate it.

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28-03-2019, 01:11 PM
Post: #11
Weird brake issue has me stumped
Ok gents, update time....
So this morning there was 40% pedal, the brakes sank away overnight, popped the bonnet and removed the blocked off cap, I saw I lost about +-40ml brake fluid, filling it to the brim and blocking the cap off helped me trace the leak, my reasoning was, if I filled it to the brim and restricted the air coming in, the pressure on the system was bound to show me where air was being sucked in (fluid was bound to flow the opposite direction) so then I inspected the wheels and found 3 of the nipples was wet and fluid was present (I completely dry the nipples after each bleed for inspection afterwards, to make sure there's no leaks present)

Why it didn't show me the leak sooner was because the cap wasn't blocked off and the fluid overflowed past the cap as air was being sucked in slowly through the nipples, currently bled the brakes and blocked off the nipples, took her for a test drive (note the nipples will be replaced, I'm just doing a final test on them, although I'm now 99.9% certain that's the problem on the brakes) I'll report back again tomorrow on the condition of the pedal and no, the car won't be driven with the nipples blocked off, well, just test driven and parked.

Once again, thanks for all the advice, hopefully this helps someone else in the future...


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28-03-2019, 08:15 PM
Post: #12
RE: Weird brake issue has me stumped
BravoBravoThumbs

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29-03-2019, 09:28 AM
Post: #13
RE: Weird brake issue has me stumped
The fact that you said it takes a lot of time to get the fluid out at the back tells me there is air locked in the system somewhere.

Why it would only manifest after driving, and leaving the car is quite simple.
As it heats up, the air expands, so it pushes the fluid back into the pipes, back into the master cylinder reservoir. The reservoir then overflows, and that is where the fluid disappears to.

Before selling out on an expensive pressure bleeder, try and push all the calipers' pistons in as far as possible (as you would when changing pads) without opening any of the bleed nipples. Then pump them back out. Repeat this process 2 or 3 times

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francoishensen11
29-03-2019, 10:45 AM
Post: #14
RE: Weird brake issue has me stumped
(29-03-2019 09:28 AM)Fordkoppie Wrote:  The fact that you said it takes a lot of time to get the fluid out at the back tells me there is air locked in the system somewhere.

Why it would only manifest after driving, and leaving the car is quite simple.
As it heats up, the air expands, so it pushes the fluid back into the pipes, back into the master cylinder reservoir. The reservoir then overflows, and that is where the fluid disappears to.

Before selling out on an expensive pressure bleeder, try and push all the calipers' pistons in as far as possible (as you would when changing pads) without opening any of the bleed nipples. Then pump them back out. Repeat this process 2 or 3 times
Thanks, I'll keep this mind, when I tested the brakes now, I see I've lost +-5% of travel (pedal feels slightly spongy) checked the nipples and found one still leaked, I do now 100% believe the nipples are at fault, changed them and bled now, will report back later or tomorrow.

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29-03-2019, 11:11 AM
Post: #15
RE: Weird brake issue has me stumped
What an ordeal, glad you got to the bottom of this.

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francoishensen11
03-04-2019, 04:56 PM
Post: #16
Weird brake issue has me stumped
Hi guys
Small update:
Brakes still holding strong after nipple replacement, can confirm now it was the nipples and it's now fixed

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