Sticking Brakes When Hot - Ideas? | Page 2 | 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. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    Yes, that's what I was getting at in my last post. If you don't remove them it will keep pressure in both circuits that would take time to bleed away.
     
  2. toopy

    toopy
    Z Club Member

    Never heard of them!

    But even so that only affects the rear circuit which doesn't appear to be an issue, there shouldn't be one in the front circuit?
     
  3. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    The silvermine ad describes having one in each circuit, presumably for when installed in cars with drums front and back.
    It's not a Z specific MC.

    I believe the point is that drum brakes have retraction springs, actively removing the shoes from the hubs unlike disc brake setups. So you need to retain some pressure in the line or you get long pedal travel.
     
    slaphead, Woody928 and Albrecht like this.
  4. Albrecht

    Albrecht Well-Known Forum User

    This. CP valve with drum brakes = Good. CP valve with disc brakes = Bad.

    So with discs on the front and drums on the rear, you need a M/C CP valve in the rear circuit, but not in the front circuit.
     
    Woody928 likes this.
  5. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    Very interesting so these MCs are sold in the 'states where old cars may still have drums? Simple check, try to push the pads back (hot or cold). Toopy could this be your problem solved too?

    Always read the instructions :blush:

    This could cause major overheating surely?

    Just make sure you know which cct is F and which cct is R. They are different depending on year as far as I know. It can be confusing because (if you don't read the markings) R can be at the front!
     
  6. uk66fastback

    uk66fastback
    Z Club Member

    So, the big question - were they removed? Sounds like they might not have been ... we're all ears, Mark!
     
  7. Woody928

    Woody928
    Z Club Member
    Staff Member Moderator

    I think you may have just hit the nail on the head Jon!

    I can confirm that neither were removed, I left it with my dad and didn't check the website for any info having left it on the shelf for several years (complete oversight on my part :oops:). It's still installed so stands to reason must be the culprit, I must confess I've never actually heard of these before. I pressume the residual pressure in the brake line would be just enough to cause some sticking/rolling resistance once driven?

    While I've thought the car is cooling then its more likely that the pressure is alleviating hence giving me the impression of a temperature issue? Certainly once the car has been left for a while sitting then the issue goes away.

    I'll have to disconnect the front line tonight, remove it, and rebleed to see what happens.
     
  8. Woody928

    Woody928
    Z Club Member
    Staff Member Moderator

    Complete cock up on my part :leaving:

    Looks like you're correct based on the pic in the link, I'll have to double check mine however the front one is the rear brakes and rear one the fornt brakes. Perfectly logical!

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

    toopy
    Z Club Member

    I bought my MC from Rockauto, it's a Centric one and i definitely didn't read anything about constant pressure valves in the instructions, that's something i would remember as Ive never heard of them before this thread!
     
  10. Albrecht

    Albrecht Well-Known Forum User

    There's a fluid return port in the M/C which allows the disc pads to 'relax' to a just-touching position. If the pushrod is too long it can stop the piston in the M/C from returning to a point where it uncovers the port, and that stops the fluid from returning.

    We might get caught up in the terminology (sorry) but I think the root cause of the problem here is M/C and/or pushrod.
     
  11. IbanezDan51

    IbanezDan51
    Z Club Member

    Definitely sounds like the pushrod is adjusted too long - I did this once - got stuck trying to make it off an A road on a slip road with seized on scorching hot brakes, fortunately had tools with me to relieve the pressure and adjust the pushrod.
     
  12. Woody928

    Woody928
    Z Club Member
    Staff Member Moderator

    Thanks for the insight Alan, really helpful. I've certainly learnt something new!

    Well I need to give a huge thank you to everyone on here, in particular JB :thumbs: Turns out it was the constant pressure valve that had been left fitted to the front of the MC.

    We stripped the MC last night and finally got it all bled up today and the problem has completely disappeared EXTRA:D

    As usual it wasn't without confusion or error, turns out we needed to ignore the F and R labels on the MC as they don't correspond to the front and rear brakes, in fact it was the opposite! Once we worked that out and swapped everything around correctly to match the Haynes Manual everything was golden.

    Car is now ready to do nearly 3000 miles over Europe come Saturday :party:
     
    IbanezDan51, atomman, Mark N and 3 others like this.
  13. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    Glad you're sorted. Bounty shared with MarkN. There was a bounty wasn't there?
     
    Mark N likes this.
  14. uk66fastback

    uk66fastback
    Z Club Member

    Lovely job! Can't go over to Europe with hot brakes!
     
  15. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    Glad it's fixed. Perhaps we have all learned something.

    So Mark you may have replaced the original master cylinder with a version that's the opposite way around without realising it. Not sure how that affects the operation but I THINK front fluid should 'build' slightly after rears (to move drum cylinders) and that's configured in the MC.

    Anyway I hope it all works fine and you have a trouble-free holiday.
     
    Last edited: Sep 12, 2019 at 9:13 AM
    slaphead, Woody928 and Paul_S like this.
  16. Woody928

    Woody928
    Z Club Member
    Staff Member Moderator

    I owe you both beer when I next see you ;)

    Well the MC is marked as F at the rear and Rand the front, however it is sold as a 240Z 15/16 MC. According the the Haynes Manual the front reservoir should feed the front brakes and rear one the rear brakes which makes sense when looking at the location of the pipes and proportioning valve below, it is however the reverse of the markings on the MC. I couldn't say what difference it would make as I don't know, however its set up per the Haynes manual and works... :conf2:

    Thanks chaps, certainly looking forward to the trip :)
     
    atomman likes this.
  17. atomman

    atomman
    Z Club Member

    Glad it's all sorted ready for you trip :)
     
    Woody928 likes this.
  18. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    I've done a bit of searching and so far I have only found that the front brake circuit should have the larger reservoir so that when the pads wear there is sufficient fluid to keep safe. However there are a few people who have done what you have.
     
  19. Woody928

    Woody928
    Z Club Member
    Staff Member Moderator

    I'm glad we agree on that as we've swapped the resevoirs around now so that the larger resevoir feeds the front brakes and is at the front of the MC. It looks like it was previously fitted incorrectly however looking at photos online most MC's have the smaller resevoir at the front and bigger at the back like ours was orginally which is confusing.

    Also interestingly looking at the resevoirs fitted and comparing it to the 240z and 260z MC setups in the haynes manual we seem to have 260z style reservoirs. Who knows what got done by who is the cars past life...
     

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