Sticking Brakes When Hot - Ideas? | The Z Club of Great Britain
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Sticking Brakes When Hot - Ideas?

Discussion in 'S30 (240Z,260Z,280Z) Suspension,Brakes and Steerin' started by Woody928, Sep 9, 2019.

  1. Woody928

    Woody928
    Z Club Member
    Staff Member Moderator

    Hi All,

    Looking for some input here, in short my brakes are starting to stick slightly when they get hot (regular road driving).

    After a longer journey the car is harder to push on the flat however once its cooled down its glides along with very little effort. Both front wheels are suffering the same.

    Giving you all of the facts:

    Newly rebuild R32 Calipers by BigRed (within the last coupld of thousand miles)
    New Vented disks (within the last coupld of thousand miles)
    New Porterfield R4S pads (within the last coupld of thousand miles)
    Braided brakes lines, seen some miles but seem perfectly serviceable
    New 15/16 Brake MC (recently fitted and new adjustable rod made)
    DOT 4 Brake fluid

    What I've worked out to date is that the rears are completely unaffected after a longer journey.

    Now this only seems to have been an issues since we've changed to the new bigger MC however when the car is hot we've disconnected the MC and nothing changes in terms of rolling resistance so I've ruled out any issue there.

    By deduction in my head there either has to be an issue with the calipers or pads, I'm inclined to say its not the calipers as before the MC change I had no issues like this and they were so recently rebuilt.

    In my head I'm wondering whether the Porterfield pads are expanding under the heat and taking up the slack space therefore making the calipers stick? Am I misisng something?

    Any input greatfully accepted.
     
    Last edited: Sep 9, 2019
  2. atomman

    atomman
    Z Club Member

    Strange it's happened after the new MC was fitted,

    Is there enough free play on the rod to the master cylinder ?

    Flexi collapsed maybe not letting fluid back when it gets hot and expands?

    Try opening a bleed valve when it happens,

    I'm still running the standard MC on my car with the R32's and haven't had that problem , a job for winter was upgrading like you have ,
     
    Last edited: Sep 9, 2019
  3. atomman

    atomman
    Z Club Member

    I also run dot 5.1 in mine coz of the higher temp range
     
  4. uk66fastback

    uk66fastback
    Z Club Member

    Do you have some other pads you can drop in there and then test? Pads ain't as cheap as chips as I remember they were many years ago though ... so you might be spending £££ to achieve not a lot if this isn't the problem (unless you have some others on the shelf - but if you've upgraded then maybe unlikely). I would have mentioned drilled discs to try and keep the heat down but you have them already ...
     
  5. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    I think as Gary says, something isn't allowing fluid return. pads aren't actively removed from the disc surface: you remove pressure from the pedal and the disc pushes back on the pad and it passively finds the right clearance. This would work the same for expanded pads I think.
     
  6. Woody928

    Woody928
    Z Club Member
    Staff Member Moderator

    Very strange, I'm very confused! The rod is adjusted fine I believe, when cool the car rolls fine and the wheels spin no problem. It's only when everything has got up to temperature.

    If it was a flexi would it be effecting both sides though? Surely only one side would be sticking not both? (correct me if I'm wrong). Seems a logical suggestion to be fluid but I don't know how else to test?

    I supose I could always refit the old MC and see what happens maybe?

    I've got some stock Nissan pads that could be dropped in however I'm not convinced its the pads as they've done a couple of thousand miles already. Certainly not cheap to just buy spare sets though!
     
  7. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    1. The problem affects both sides, the mc affects both sides
    2. The problem started when you fitted the new mc

    I'd put the stock mc back on
     
  8. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    In a process of elimination I would run the car and get the brakes hot, take a wheel off and then try to push the pads back with a flat blade like a wide chisel or scraper.

    Obviously you will need to work at speed with tools ready.

    Could the pad-backing i.e. the metal be expanding and become a tight fit in the calipers? It may not be a fluid problem but purely a metal expansion.
     
    Last edited: Sep 9, 2019
  9. Woody928

    Woody928
    Z Club Member
    Staff Member Moderator

    It doesnt effect the rears at all though and they're linked to the MC so surely that rules it out? :conf2: It may also have always done it and I didn't notice....

    I could give it a go, I think I'm going to swap to the standard R32 brake pads tomorrow evening and run it to see what happens.

    I wouldn't have thought it would expand that much, the pistons are still clearly outside of the caliper body so must still have room to move I'd think.

    This really has got me stumped!
     
  10. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    The mc has separate pistons for front and rear circuits.
     
  11. hallie

    hallie Active Forum User

    Are you sure that it is the brakes and not the bearing getting tight?
     
  12. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    Which 15/16 MC is it? There's some rubbish aftermarket stuff about. Not that I know which is which
     
  13. Woody928

    Woody928
    Z Club Member
    Staff Member Moderator

    It's not diagonal circuit?

    Front right wheel bearing was recently changed but the problem occurs on both sides surely ruling out bearings?

    This one, bought several years ago before they got to that silly price though! Nothing is ever plug and play or quality these days it seems...

    https://www.silverminemotors.com/featured/15-16-upgraded-master-cylinder-for-240z-260z-280z
     
  14. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    No, not diagonal - split is front/rear.
     
    Woody928 likes this.
  15. Robbie J

    Robbie J
    Z Club Member

    not sure it if much help but I have similar issues on my stock 280z, it looks like its the MC that's the issue on mine

    both rear and one front wheel gets hot
     
  16. toopy

    toopy
    Z Club Member

    As a start, seeing as you have a new adjustable push rod, i would adjust that by 0.5mm at a time and see if it helps.

    Also, as you well know, the fronts do a lot more braking so would heat up much quicker than the rears, plus if the adjustment is a little out on the back they will re-treat from the drum, more than the pads from the disc will. :D
     
  17. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    Looks decent. Did you remove the drum brake doodahs? Is it possible to reassemble it wrong? E. G. Get something swapped over between the rear and front pistons?

    If you didn't remove them, it'll leave pressure in the line...
     
  18. toopy

    toopy
    Z Club Member

    Just thought, you could also check the rod that connects to the brake pedal hasn't shifted some how.
     
  19. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    Mark I was suggesting that the pads were expanding sideways to clamp themselves in the caliper housing. It was just a thought seeing as you'd changed pads.
     
  20. Mark N

    Mark N
    Z Club Member

    Reading the Silvermine description, it mentions having to remove the constant pressure valves from the MC if it is to be used on disc brakes.
     
    slaphead and Woody928 like this.

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