Brakes Still Spongy After Bleeding......

[Guest IanD]

This is the situation..............I did my first trackday at Donny recently & managed to boil the brakes & warp the discs. I think the majority of the damage was done when I saw the red flags just after I'd done the big stop after the dunlop bridge straight & just pulled in and parked it up. The brakes were nearly on fire but I just stupidly stood there & thought it was cool rather than driving it round for a bit in the car park to let them cool. Two sessions later & they were properly foobarred!

 

Got some new discs (they are the 307 hdi setup btw) but had difficulty getting uprated pads in time for this forthcoming trackday tomorrow........started ringing round too late I see now as I assumed people would have them in stock & been busy as hell at work. The car needed a new MOT so I got one of the apprentice technicians at work (I work in a merc garage) to fit them & replace fluid with DOT4+ (as I get it for free through work as it's already in the bleeding machine) & bleed the brakes. We didn't replace the pads (std) as I just wanted it to pass MOT initially & then I could fit some new std ones tomorrow before setting off (again due to time constraints at work).

 

The lad has bled the brakes system twice but they're still ridiculously spongy with no real power? What else could be causing this does anybody know? A technician suggested master cylinder but can you kill these through excessive heat? There don't appear to be any leaks anywhere?

 

Cheers,

Ian

 

 

 

Just spoke to the cars previous owner & he suggested bleeding them with the engine running but surely if it's done using a machine theres no need to do this? Would have thought you would only need it running when doing it manually by pumping the brakes? They don't need the mercs running to bleed theirs?

[pug309twin40s 1]

did you check the condition of the pads as they could have gone soft and knackered after getting them so hot!!

 

 

does the pedal go hard with engine of, then soft with engine running? or is it soft all the time.

 

 

try bleeding the brakes the normal way without using the bleeding machine.

[jonah 1]

It won't be the master cylinder - it's miles away from the discs so won't be affected by the heat (would have thought that's obvious!), and a faulty m/c won't cause spongy brakes anyway.

 

Engine running while bleeding the brakes will make no difference. All it will do is let the servo operate which would make the pedal easier the press if bleeding using the conventional method, but it'll have no effect on the hydraulics.

 

The pedal will always be firmer with the engine off (provided the servo is working), so that won't really tell you anything. Faulty servo also will not cause spongy brakes.

 

I would agree though that it may be the pads that are the problem - I've found that they flex under heavy braking and end up with a concave friction surface. This causes a gap between the disc and pad surface and therefore a soft brake pedal and reduced efficiency.

 

Only other thing I can think of is that the heat has damaged the flexi hoses and they are now swelling under pressure... never heard of that happening though.

[Guest IanD]

Thanks for the help lads, set of pads sorted it out

 

Didn't manage to get to the trackday though due to something else beyond my control