Brake pedal still soft!

Discussion in 'E46 M3 (2001-2006)' started by schooner32, Feb 10, 2013.

  1. 9 Mar 2018 at 7:00 PM #41
    E46CoupeM3

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    Basic assumptions
    If you have engine off and pump pedal say 3-5 times to fill servo is pedal hard (hard not pumped up)
    If you then push brake is pedal hard?
    Keeping foot in brake start car does pedal go down under your foot by itself ?
     
  2. 9 Mar 2018 at 7:35 PM #42
    Jonnym3

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    Thanks buddy really appreciate that
     
  3. 9 Mar 2018 at 7:38 PM #43
    Jonnym3

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    Yer basically it goes hard but not tried the start bit yet ? Where’s this leading pal ? I’ll have to go out tomorrow and test this
     
  4. 9 Mar 2018 at 9:31 PM #44
    svvg

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    I can pump the pedal with engine off and pedal goes rock hard. Engine on it sinks and feels like it has too much travel. I think maybe servo has a leak?
     
  5. 9 Mar 2018 at 10:22 PM #45
    E46CoupeM3

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    with the servo full (of air) and no assistance if the pedal is hard it is bled properly
    Don't start it after the pumping
    Leave half an hour ( for example )
    Go back
    If pedal is now soft and pumps up you have air in or duff seals
    If you stand on the pedal and very very slowly goes down and no external leaks don't dip the servo through the vac hole to check for brake fluid to show leaking seals
    If the pedal is just as hard as before it should Ben properly bled
    If when you are standing on the pedal and start the car the pedal goes down further the servo is working as intended
    If your feet get all the way to the floor and you have bigger calipers you've exceeded master cylinder capacity


    Something like that most of it assumes properly bled
     
  6. 10 Mar 2018 at 8:56 AM #46
    svvg

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    Thanks mate - you’ve usually got the asnwer:thumbsup:

    Would you mind clarifying a few points though?

    1) If I pump the pedal and the pedal goes hard, leave it half an hour without starting and try again, only to find it is soft when I start - you suggest it’s “air in or duff seals”. What seals do you mean? Servo to brake assist pipe? Master cylinder (which was changed so I am told - but doesn’t look like it!).

    2) “if pedal very very slowly goes down” (there are no leaks of fluid) - you then mention “don’t dip the servo through the vac hole to check for brake fluid to show leaking seals”. Not quite sure what you mean here - would you mind clarifying?

    I have standard calipers - all this started when I had a seized caliper, rebuilt it and swapped to braided hoses and PF pads at the same time. This was several years ago and the car stops hard and abs will kick in - so don’t think it’s air... I initially suspected I’d pushed through the seals on the master cylinder, as initially did the two man bleed method - pushing to the floor - which now I’ll never do again amd have a proper pressure bleeder - but I (apparently) had the master cylinder changed.... although am not convinced it was done... or perhaps wasn’t bench bled properly. If I pump the pedal it doesn’t hiss like a properly knackered servo, but does sort of scrunch a bit...

    Grateful for your help as usual!
     
    Last edited: Mar 10, 2018
  7. 10 Mar 2018 at 12:53 PM #47
    E46CoupeM3

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    Re1
    If the peddle pumps up hard then Goes soft when left usually means you squashed air in system or seals. The servo is full of air so doing nothing after a few pumps with engine off so you are feeling the real pedal feel not the assisted pedal feel

    Re2
    When master cylinder seals go it leaks out the back of the master into the servo so you either have to unbolt it and look OR have a way to detect brake fluid in it (if sufficient leaked) but should never use a piece of clear pipe as a dipstick then put your thumb on the end and pull It back out


    Much easier to turn master seals with a pressure bleeder than a 2 man bleed. The system is designed for an adrenaline fuelled scared person to stomp on
     
    Last edited: Mar 10, 2018
  8. 10 Mar 2018 at 6:53 PM #48
    svvg

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    Thanks mate. I don’t think I’ve lost any brake fluid - but where exactly do I poke the pipe into the servo to check? Remove master cylinder?
     
  9. 11 Mar 2018 at 2:04 PM #49
    E46CoupeM3

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    nope it's an "or"
    Either you take cylinder off or dip it through vacuum pipe location
     
  10. 11 Mar 2018 at 2:58 PM #50
    svvg

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    Ah - that makes sense! Much appreciated.
     
  11. 13 Mar 2018 at 7:51 PM #51
    Jonnym3

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    Well lads Iv ordered a new MC well second hand one, so I ripped out the old one and took it apart to see if there’s anything obvious that could of gone, and from what I can see there’s nothing no leaks out the end etc. I don’t see how it could be over stretch as it’s just one big spring with 2 o rings that meetS another sprung loaded part at the base of the MC, and even if these o rings did pass a little the unit as a hole would still be pressurised.
     
  12. 13 Mar 2018 at 7:55 PM #52
    Jonnym3

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    Nothing too it


    [​IMG]

    [​IMG]
     
  13. 13 Mar 2018 at 8:07 PM #53
    E46CoupeM3

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  14. 13 Mar 2018 at 8:18 PM #54
    Jonnym3

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    Yer that’s the vid I followed bud, done it a million times and made no difference.

    Proper had a gut load of it now, out of doing the hole rear end resto I didn’t for a second think the brakes were going to be a issue :mad:
     
  15. 13 Mar 2018 at 8:39 PM #55
    E46CoupeM3

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    I didn't have those options and only access a job screen where you add and remove jobs and just used the prime pump one. I'll have to go have a look where it actually is.
     
  16. 13 Mar 2018 at 9:20 PM #56
    Jonnym3

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    Thanks mate, need all the help I can get now haha
     
  17. 14 Mar 2018 at 11:12 AM #57
    TouringRob

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    As something else to check (if not mentioned). I struggled very badly on a car a few years back with a very similar issue - the problem turned out to be a small amount of grit/dirt on the threaded section of one of the brake lines. I could bleed system, an hour later pedal would be soft. Once brake line union/joint was cleaned and greased the problem was solved.

    I also now use grease on bleed nipple threads, so when you slacken off to bleed pressure air cannot be drawn back in.


    About to buy either one of these which I think look great in terms of one man fast bleeding kits.

    https://www.ebay.co.uk/i/172325092345?chn=ps&adgroupid=51190283679&rlsatarget=pla-413085737683&abcId=1133936&adtype=pla&merchantid=113358636&poi=&googleloc=9045942&device=c&campaignid=1057753379&crdt=0

    https://www.machinemart.co.uk/p/gunson-77021-eezibleed-pro-brake-bleeder/?da=1&TC=GS-040817021&gclid=Cj0KCQjwkKPVBRDtARIsAA2CG6Hfpt6vASNwgEIuoK8QEMMFWYVskFrK653xezcWNdLh3vOgjWDsmO0aAn1OEALw_wcB

    I've seen good reviews on the VS820 but not read much about the vacuum type gunson if anyone has any advice!
     
  18. 14 Mar 2018 at 1:12 PM #58
    JamesNL

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    I have the Sealey one. Its great but as I mentioned earlier, personally I still can't get the pedal to feel right. I'll keep trying.
     
  19. 14 Mar 2018 at 2:56 PM #59
    M3Chas

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    A well known Porsche specialist said that on some 4 pot setups this is normal. In my case I had a Porsche 944 Turbo with the Big Black brake upgrade. That is the brake from a 928 GTS/965 (964 Turbo). The pedal was decent but not as solid as I would have liked.

    I took his word for it as he sold me the car and I had used him many times before with superb diagnosis; he was someone who didn't guess what was wrong; it was uncanny! He was also the only 944/968 specialist to have a front engined Porsche complete the Britcar 24 hour challenge. The fact that he's been a mate of mine who's got me out of trouble was another one.

    I then sold my 944 to a 'tuning' bloke who read the internet alot. He rang up the specialist too; he has a great reputation in the 944 circles. He told him the same thing as me. He changed all sorts! Brake lines, and possibly even a master cylinder! It was no different. It's fair to say the specialist was getting sick of the phonecalls to him in search of what he saw as being fine.

    On my RS Turbo I had a similar thing going from Wilwoods to Cosworth sliding calipers; the braking power massively improved however despite a slightly softer pedal. I put down to the following:

    1) Effective Piston Area was much bigger than the Wilwoods ; it was around 1.5 times the size
    2) The above gave me a longer pedal but probably also a slightly softer one too
    3) Going from a solid caliper to a sliding arrangement probably also brought about some of this.

    I bled that using the air pressurisation too.

    I did track days etc. with it and the brakes were always dependable; With Super DOT 4 fluid and Pagid Blue pads it was scarily good to stop that car. it was something I never had with the Wilwoods despite having a firmer pedal. I needed a prayer for it come to a stop previously!
     
  20. 14 Mar 2018 at 3:48 PM #60
    TouringRob

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    Do you still have your RST?

    Mine had cosworth calipers with a long pedal - in the end I found out that the master cylinder had been swapped for an XR3i which had a smaller piston, the RST unit had been out of production for years hence most people had an XR3 MC without even knowing it.

    I switched the servo to one out of a MK2 (or 3, can't remember) Mondeo and used a quite rare but available non ABS master from an RS2000 MK5 (I think, also a long time ago!!) which solved the soft pedal completely. Also removed the crappy old ABS system and re plumbed it as a front rear split (rather than diagonal) so that I could use a wilwood adjustable bias valve. Brakes were great after all of that!

    Also remembered another trick a mate uses on his 4 pots on a race car - sometimes when he bleeds he removes caliper from hub and places a spacer in the caliper - he can then move the caliper around to get any trapped air out - seems that on some multi piston calipers the bleed nipple isn't sensibly located...

    Of course non of that really helps the OP!
     

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