Intermittent Brake Problem

J

JimmiVW

Member
 Manchester or Todmorden!
Hi Guys - hope you can offer some advice / experience...

I have an intermittent brake issue which under further testing seems to relate to full lock on the steering (I know, but hear me out!).
In a low speed situation with full lock (e.g. reversing into a parking space / parallel park) I experience the 'intermittent' brake problem.
- I am aware of 'differences' in pedal feel due to brake assist, but this is totally different
- after the aforementioned full lock situation the brake pedal will sometimes go fully to the floor (i.e. no brake at all)
- 'stabbing' the pedal will provide some resistance, and releasing / re-applying returns to normal feel

After initial diagnosis we swapped in a new master cylinder and changed brake fluids (this was done at a known indie). While the overall pedal feel is better, the 'full lock' issue remains. I am due to revisit the garage on Friday to diagnose further, but wondered if anyone has any similar experience / advice / pointers?
I have done a detailed search of this forum and the wider web, but to no avail...

It's a 2006 M Coupe, 33,000 miles... No warranty to fall back on so I'm on my own and trying to avoid a 'diagnosis' at a Dealership!

Looking forward to your feedback, James
 
Pants, that sounds awful & can't think of anything that would cause this - I assume there's no loss of brake fluid from the reservoir whatsoever
 
weird one... if this only a full lock problem, could a line be getting pinched under these circumstances??
 
Pinched lines or something catching was my initial thought too - will be checking that out on Friday.
Other thought is that for some reason the piston in the calliper is retracting under full lock, and then the pedal has to do a full 'throw' to get back where it needs to be... the full lock issue would at least suggest it's relating to the front brakes!

The car is relatively low, but not excessive so obviously anything catching under full lock situation seems to be the best initial option.
- the master cylinder was swapped in the hope that the seals were shot, and fluid was passing, but that seems to be out of the window now!

No loss of fluid anywhere in the system either, callipers, lines or reservoir.
 
I had a similar thing happen on my future son in laws old saxo, when he put it in reverse and turned the lock it made a binding type noise but once straight stopped it turned out to be the edge of the pad touching the lip of the disc due to a bit of wear on both we changed the pads and the noise stopped, this may not be your problem but might be worth a look :thumbsup:
 
It sounds like it is loosing hydraulic pressure when on full lock.

I would start by looking for the obvious things like electrical connections being stretched as these can brake a circuit and cause the servo pressure to drop, may even be related to the abs system as this allows the valves to open and the fluid to circulate relieving pressure.....peddle pumps under foot when driving, but it might be dropping to the floor when idling?

Other than that I am stumped.
 
JimmiVW said:
...Other thought is that for some reason the piston in the calliper is retracting under full lock, and then the pedal has to do a full 'throw' to get back where it needs to be... the full lock issue would at least suggest it's relating to the front brakes...
Click to expand...

I had exactly this when I fitted an H&R front ARB with KW Clubsport coilovers. With OEM drop links, the ARB fouled the calliper on full lock pushing the piston back. A pump or two on the pedal restored pressure to the system. Have you uprated the front ARB or significantly dropped the ride height or adjusted the front camber? If so, it's likely the calliper is fouling something. Mine was fine with the OEM front ARB and the Clubsports but I needed to fit adjustable drop links to allow the use of the H&R ARB and Clubsports together.
Try jacking up one front corner and go from lock to lock with the wheel off, you should see what is fouling the calliper.
 
BMWZ4MC said:
JimmiVW said:
...Other thought is that for some reason the piston in the calliper is retracting under full lock, and then the pedal has to do a full 'throw' to get back where it needs to be... the full lock issue would at least suggest it's relating to the front brakes...
Click to expand...

I had exactly this when I fitted an H&R front ARB with KW Clubsport coilovers. With OEM drop links, the ARB fouled the calliper on full lock pushing the piston back. A pump or two on the pedal restored pressure to the system. Have you uprated the front ARB or significantly dropped the ride height or adjusted the front camber? If so, it's likely the calliper is fouling something. Mine was fine with the OEM front ARB and the Clubsports but I needed to fit adjustable drop links to allow the use of the H&R ARB and Clubsports together.
Try jacking up one front corner and go from lock to lock with the wheel off, you should see what is fouling the calliper.
Click to expand...

their you go OP....
 
BMWZ4MC - excellent, exactly the kind of experience I was after and certainly sounds like it could be the culprit.
- I'm running uprated ARBs but thankfully with adjustable drop links so hopefully I can re-adjust to give sufficient clearances
- will make sure I update you all after getting it on the jacks on Friday... fingers crossed we'll have a fix by then!
 
Bit of an update... basically sounds like a very similar problem to that BMWZ4MC experienced...
- on full lock my ARB is making contact with the calliper (very slight, but enough to push it back)
- not great, but at least I know it's not mechanical

I've raised a flag with Roy at CA (who supplied everything) and he's chasing things up with the manufacturer...
... we'll see what they come back with - as far as I'm concerned it's a design issue...
... but if the worst comes to the worst I can easily shorten the ARB to stop it making contact!

Thanks again for all your input - I'd potentially still be bleeding the braking system without your experience! :thumbsup:
 
Hi guys... Finally got this sorted so thought I'd give an update.
- managed to adjust the drop links to get a bit more clearance, but still not enough to fully clear the calliper on full lock
- end result I had to take around 10mm off the end of the ARB to get 'full' clearance

Pleased to say no issues now! Thanks again for your help, experience and advise.
 
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