Torque Cars

Do bigger discs need a bigger servo

Discussion in 'Brakes' started by obi_waynne, 3 August 2015.

  1. obi_waynne

    obi_waynne Administrator Staff Member Moderator

    Messages:
    41,214
    From:
    Deal, Kent UK
    Car:
    A3 1.4 TFSI 150 COD
    If you fit larger discs and calipers do you have to uprate the servo?

    How much leeway is there in a braking system if you make the brakes more powerful?
     
  2. claymore

    claymore The Torque Meister

    Messages:
    1,888
    From:
    Shrewsbury
    Car:
    T-10k,
    I would have said the opposite.
     
  3. obi_waynne

    obi_waynne Administrator Staff Member Moderator

    Messages:
    41,214
    From:
    Deal, Kent UK
    Car:
    A3 1.4 TFSI 150 COD
    A smaller servo? I don't get that, what am I missing here?
     
  4. claymore

    claymore The Torque Meister

    Messages:
    1,888
    From:
    Shrewsbury
    Car:
    T-10k,
    Bigger discs and calipers would mean you need less braking effort to achieve the same braking performance.
     
  5. TCJBOLDIE

    TCJBOLDIE Torque King

    Messages:
    4,783
    From:
    Brisbane
    Car:
    JB Starion
    I think Obi may be thinking that larger calipers will have larger/more pistons then it comes down to the overall volume of fluid required to push the pistons out.

    IF the multi piston calipers have say a 100 cc capacity and the sliding calipers only say 80 cc then the brake pedal will have to move closer to the floor before they start to slow you down so a larger master cylinder would be required.

    In my front brake upgrade the brake master was bored and stainless steel sleeved 1/16 oversize to compensate and the pedal height was at factory height.

    Hope that all makes sense;)
     
  6. claymore

    claymore The Torque Meister

    Messages:
    1,888
    From:
    Shrewsbury
    Car:
    T-10k,
    Obi was talking about the brake servo not the master cylinder though?
     
  7. TCJBOLDIE

    TCJBOLDIE Torque King

    Messages:
    4,783
    From:
    Brisbane
    Car:
    JB Starion
    .V( :oops: Was thinking Obi may have thought they were one and the same

    FWIW my servo not changed only the MC piston to allow for the 4 piston upgrade on my car
     
  8. obi_waynne

    obi_waynne Administrator Staff Member Moderator

    Messages:
    41,214
    From:
    Deal, Kent UK
    Car:
    A3 1.4 TFSI 150 COD
    It was the Servo I was thinking of. ;)
     
  9. HDi fun

    HDi fun TC ModFather

    Messages:
    15,384
    From:
    Buckinghamshire UK
    Car:
    Passat 2.0 TDi
    Chances are if you fit 4 piston calipers in place of singles you will need a larger bore master cylinder otherwise the pedal travel would be too great. This is due to the fact that brake fluid is not perfect, it is slightly compressible. A larger bore master would require a larger servo to retain the same pedal pressures. That said, many cars are over servoed so it may not be essential.

    VW/Audi had a habit of ridiculously over assisting brakes in the mid to late 1990s. I am thinking Audi A4 and Golf GTi that I drove back to back at that time. The merest touch on the pedal would stand the car on it's front bumper and nearly pop your eyeballs from their sockets. It's all fine when you apply them for the second time, very easy to compensate.

    So much so that getting back into the 2.0 midrange-ish Montego I had at the time made it feel like there were no brakes at all. (Not totally untrue either - they didn't stop especially well).

    I like the old Citroen way of doing things - pressurise the whole system - vacuum servo assistance strikes me as crude in comparison.

    Brake setup is a vague science or a precise art depending upon your stance. Most cars are fairly heavily front biased to reduce risk of sudden oversteer during braking. Pre-emptive brake force distribution is good - it's pretty much universal now I think.
     
    Last edited: 9 August 2015
    obi_waynne likes this.
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