Excessive pedal travel | The Z Club of Great Britain
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Excessive pedal travel

Discussion in 'S30 (240Z,260Z,280Z) Suspension,Brakes and Steerin' started by Peato40, Dec 28, 2018.

  1. Peato40

    Peato40
    Z Club Member

    So I've just finished upgrading my front brakes by utilizing the 4-Runner 4 pot calipers and it certainly has more stopping ability but it hasn't cured a problem I have been encountering, which is excessive pedal travel. During the upgrade, I also removed the master cylinder and bled it independently as I've seen a few threads suggesting this is the best method.

    Sitting in the car without engine running, everything seems as it should but then when I start driving the car the pedal travel needed is greater and therefore not giving me the braking confidence I would like. The car will stop pretty well but the pedal is almost to the floor. I've bled the brakes several times but no no avail, could it be something wrong with my brake booster I wonder?
     
  2. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    I believe that's a natural consequence of switching to 4 pot calipers: you're moving more fluid so the pedal moves more.
    I believe people switch to a bigger master cylinder to compensate.
    Stock is 7/8" I think and maybe options are 15/16 and 1". I'm sure some one will explain....
     
  3. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    I don't think things are that extreme Jon. The pedal shouldn't go almost to the floor.
     
  4. atomman

    atomman
    Z Club Member

    Have you checked the rod that pushes the master cylinder ?

    its adjustable and needs to be a couple of mm from contact on the master cylinder ,

    Are the rear drum brakes adjusted properly ?

    I've got those calipers and a new standard master cylinder and the pedal should be nowhere near the floor !
     
  5. Albrecht

    Albrecht Well-Known Forum User

    I think it's the vacuum booster that's the problem, especially if - have I understood correctly? - this was a problem that was already present before the switch to 4-pot calipers?

    As a reference, I've deleted the booster completely on my 432-R replica project car (432-Rs didn't have boosters, and ran a different pedal ratio to compensate) and I'm running Nissan Sports Option MK63-20S 4-pot calipers and vented rotors on the front with stock drums on the rear. Master cylinder is early 7/8" type. Pedal is high and hard. The 4-pots on their own are not enough reason for a long and soft pedal...

    [​IMG]
     
    Woody928, SacCyclone, franky and 3 others like this.
  6. Peato40

    Peato40
    Z Club Member

    Hi all and thanks for your advice.
    The problem was existing before I switched to four pot caliper and had assumed that the master cylinder wasn't bled properly.

    I sat in the car today and stabbed the brake pedal and immediatly felt hydraulic pressure, which then seems to somewhat slowly collapse, meaning that the brake pedal continues to travel in order to maintain the pressure and then eventually reach full hydraulic lock. The consequence is that when needing to gently brake the pedal travels more than is comfortable before it starts to bite.

    Although it's a new unit, I wonder if there might be something wrong with the master cylinder. I noticed whilst bench bleeding the master cylinder that the front circuit become active first and then the rears further along the stroke. I found this curious as it could mean with new brakes, low travel and therefore less oil displacement that the rear circuit might not even become active. Then I wondered if the master cylinder might even have some sort of fine bypass gallery in the front circuit which will ensure enough travel to make the rear circuit active, which would then likely behave exactly as I'm finding mine.
     
  7. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    If there was such a connection between the two circuits, I don't think it would result in a delayed reaction like that; there's be continuous uncompressible fluid throughout both so the pressure would act equally in both circuits at once.
    If the pedal sinks after it first goes hard, I think there must either be air in the hydraulic system or a problem with the servo as Alan suggested.
     
  8. toopy

    toopy
    Z Club Member

    I have a similar problem, new 7/8 master cylinder, Toyota 4 pots and vented discs, I've bled, re-bled and bled again and still the pedal goes almost to the floor before the pads bite!
    The car can be driven up and down the road.... carefully! and there is enough bite to stop quite sharply, but it's obviously dangerous as is.
    I don't understand why its not working, with the engine off it feels firm while bleeding, engine on and it sinks almost to the floor before anything happens!
    Prior to this the brakes were fine, i replaced the calipers and pads, but the master cylinder failed when i refilled with fluid. Replaced it, but still no joy.
    Surely if the booster wasn't working properly the pedal would be harder to push not softer?
     
  9. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    That's what I originally thought too.
    But the pedal rod on the drivers side isn't directly connected to the rod in the master cylinder and so leaks in the wrong place in the servo could I think have the effect you guys are seeing.

    It's all new to me

     
  10. Turn & Burn

    Turn & Burn
    Z Club Member

    It sounds like a leaking servo/booster to me. They do give a feel solid without the engine running, but lack power.
    Can you try and pull a vacuum on the pipe that connects in your inlet manifold and see if this holds. Any loss of pressure would point to your servo leaking/failing.
     
  11. Peato40

    Peato40
    Z Club Member

    Yes, looks like you guys are right. I used one of those brake bleeding vacuum pumps to see if the servo will maintain a vacuum. Seems that the leak is such that I couldn't even create a vacuum, so looks like I need a replacement servo ☹
     
  12. toopy

    toopy
    Z Club Member

    So, where to get one and what spec? I believe there are 8" and 10" versions, plus maybe variations!

    RockAuto would be the obvious choice i guess, but buying the wrong thing could get expensive, if they're available even!
     
  13. chris frizzell

    chris frizzell tango ratsun

    dont you need to put a 1" master cylinder on i have the same brakes but have left it stock and iam going to see how it goes . the kits from silvermine all have the upgaded master cylinder included .all to do with the extra fluid it pushes round .have a look on there web page chris
     
  14. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    I only ever post from experience.

    7/8" is fine.

    How much fluid are we talking about here - the pads should be very close to the discs or you are going to get a long pedal anyway?

    My track car and my blue car are/were 7/8".

    I was out in the blue car yesterday and the pedal does not go to the floor.
     

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    MaximG likes this.
  15. Peato40

    Peato40
    Z Club Member

    Rockauto can offer service exchange but then that is likely to become expensive shipping in both directions.

    I was wondering if servo from a 350z complete with master cylinder might fit? I guess there should be enough oil displacement and boost available from a set up like that but then I wonder if the stud pattern is suitable, as I wouldn't want to modify my bulkhead too much.
     
  16. toopy

    toopy
    Z Club Member

    Ive driven a car with the same brake upgrade and a 7/8 master cylinder, and it made virtually no difference to the feel, for me anyway.

    If you didn't know, you probably wouldn't realise!
     
    AliK likes this.
  17. Albrecht

    Albrecht Well-Known Forum User

    But the fluid doesn't get 'pushed around', does it? Ideally there's no movement in the fluid, and it's just hydraulic pressure doing the work in the fluid.

    As has been pointed out, moving from two pot front calipers to four pot front calipers is not enough reason on its own for a long and soft pedal. Yes you can mess around with regard to pressure/effort by changing master cylinders, but the symptoms being described here are almost certainly related to a vacuum booster problem.
     
    MaximG and toopy like this.
  18. Col-b

    Col-b
    Z Club Member

    Hi there did anyone solve this problem ? I have purchased the stage 4 front kit from Silver Mine Motors too and the brake pedal does seem to go nearly to the floor ? I have only done a few miles since installation so will see if the bed in any better. I have sent Silver Mine an email about it but no reply yet.
    On another note has anyone used there electric power steering kit ?
     
  19. Col-b

    Col-b
    Z Club Member

  20. Col-b

    Col-b
    Z Club Member

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