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348 - brake/bleeding issues

Discussion in '348/355' started by 968cs_red, Mar 29, 2005.

  1. 968cs_red

    968cs_red Rookie

    Aug 27, 2004
    24
    UK
    Full Name:
    Matt H
    Hi there,

    I have a 348 and I've been having a few problems with the brakes. A couple of weeks back I fitted new front discs (grooved) and new stainless braided brake lines all round, new Mintex pads up front too. I then bled the brakes, replacing the fluid with ATE super blue stuff. After the new pads and discs bedded in there was a definite improvement in the braking from before... more bite and a firmer pedal. But the pedal then, over a period of a few drives and 100 miles or so started too feel slightly softer than before.. it felt like a small amount of air in the system.

    I re-bled all four calipers again (x2 bleed nipples) starting from the one furthest from the master cylinder and working my way to the nearest. I did this, as before, using a pressure bleeder (the type you connect to a spare tyre set to 20 psi max.). All seemed to go well and no air bubbles seemed to be present. I ran another ~500-750 ml through. I used around 1 litre the first time.

    Again, after doing this the pedal felt nice and firm and as I would expect with the goodridge lines and new fluid... however after a couple of hundred miles over a week... the pedal now feels noticeably softer again! :(

    The only thing I noticed during my work which concerned me was when I disconnected the pressure bleeding line from the reservoir after finishing the bleeding, a lot of brake fluid from the reservoir on the car seemed to get sucked back into the bleeder reservoir quite quickly and looked like it was quite airated ? Can't remember if this happens usually when I have used this bit of kit on other cars.

    One other thing was after bleeding, with the brake fluid reservoir cap on etc, I tried the brake pedal... nice and firm... but pressing the pedal didn't seem to apply enough force to the rears (I had car on axle stands)... I turned the ignition on and repeat the pedal press... this time the rears calipers were being activated properly. I guess this has something to do with the servo but I'm not properly clued up on this system yet.. ? Should I bleed with the ignition on?

    Would really appreciate any thoughts or suggestions or possible causes of the pedal going a bit soft.

    My next plan at the moment is to bleed again without the pressure bleeder using the traditional pedal pressing method.

    cheers, :)
    Matt
     
  2. 968cs_red

    968cs_red Rookie

    Aug 27, 2004
    24
    UK
    Full Name:
    Matt H
    I heard yesterday from someone that the system on the 355 is 'self bleeding' and all is needed is to have the ignition turned on and the system is pressurised - then all that is needed is to bleed from the calipers as normal with no brake pedal pumping etc required ... he thought it may be the same on the 348 - can anyone comment on this???

    thanks,
    Matt.
     
  3. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
    25,491
    Austin TX
    Full Name:
    Brian Crall

    Your source of info is wrong.
     
  4. Ken

    Ken F1 World Champ

    Oct 19, 2001
    16,078
    Arlington Heights IL
    Full Name:
    Kenneth
    Are you losing any fluid at all? If so, I'd suspect a booster; yours works on vacuum from the engine I assume? Brake fluid may be bypassing a seal and getting burned in the engine. If you're not losing any fluid I'd suspect the master cylinder has a seal that's not sealing. Just 2 guesses on my part...

    Ken
     
  5. 968cs_red

    968cs_red Rookie

    Aug 27, 2004
    24
    UK
    Full Name:
    Matt H
    Thanks for the replies, chaps.

    Pretty sure I'm not losing any fluid - well not from anywhere that I have checked so far. I've inspected all the joins at the new brake lines, at the caliper and the joins to the hard lines. Also checked all the caliper bleed screws and all are dry with no sign of leakage.
    Don't appear to be losing any fluid, the level in the reservoir has not gone down.

    My theory is its something to do with the brake fluid rushing back into the pressure bleeder reservoir when I disconnect from the spare tyre.... also the fact that I didn't realise its best to have the ignition on when bleeding won't have helped.

    I'll try again with ignition on, without using the pressure bleeder and see how it goes!

    cheers :)
    Matt.
     
  6. sf348s

    sf348s Karting

    Oct 8, 2003
    168
    Lazio, Italy & UK
    Full Name:
    Steve Holden
    Did it work Matt ??
    I'm thinking of doing my brakes soon and i don't want to be in the same position! Also where did you order your parts?
     
  7. 968cs_red

    968cs_red Rookie

    Aug 27, 2004
    24
    UK
    Full Name:
    Matt H
    Hi,

    Haven't tried yet, going to try perhaps this weekend, but more likely next weekend. Will let you know.
    I get the ATE super blue from powermarques.. http://www.powermarques.co.uk really friendly chap and very helpful. Mainly a porsche specialist (I have a 968 Club Sport).

    cheers,
    Matt.
     
  8. 512Professore

    512Professore Karting

    Feb 3, 2004
    145
    USA, GA.
    Full Name:
    Brian Strasburg
    Since you had mentioned that you had replaced the brake lines with new stainles steel versions, the entire hydrualic system had probably drained itself, including the clutch line. In your post, you had NOT mentioned that you bled the clutch, and since the clutch shares the same reservoir with the brakes, most likely air got into the clutch line, and when you drive the car, the air from clutch has probably worked itself back into the entire system.

    I would suggest bleeding the clutch after you have re-bled the brakes. Also, I am sure you know that the pressure must be released from the tank before disconnecting from the reservoir.

    Hope this helps you out.
     

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