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Thread: Big Brake kit expert thoughts needed

  1. #1
    Join Date
    Feb 2004
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    4,894

    Default

    You are on the right track about needing bigger master cylinder to compensate for brake travel on larger pistons calipers or otherwise the pedal does go to the ground.

    I don't know the equation of the fluid dynamic but cracking open a brake handbook should yield the info. I will check my Bosch handbook later tonite to see if they mentioned anything about this.

    The smallish piston on multiple pistons caliper means more contact area on pads and thus more force on the greater area of the brake pad and thus better pad perfomance and better braking. As your website said, the balance of the front and rear braking performance is very important.

  2. #2
    Join Date
    Dec 2003
    Location
    Canada, ON
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    Default Big Brake kit expert thoughts needed

    As some people know I am working on a BBK for the E28/E24.

    I am working on a 635csi but brakes are interchangeable across the board.
    I changed my master cylinder to the 750il which should be close to the E34 one.

    I installed front wilwood calipers with 1.38" pistons (4) and rear 540i caliper with 40mm (1.57" x1)

    Now, the idea is to keep the stock master cylinder and keep the stock pedal height or something similar.

    My guess is to achieve it, I need to keep the overal piston surface the same.
    Meaning stock setup overal piston surface = 4 pot caliper piston surface.
    That should give me the same pedal height.

    Am I going through it the right way? I intalled some 1.75" piston calipers (4 pot) are the front and the pedal seems too low.

    The idea is to have front and rear 4 piston calipers on the stock master cylinder.

    Thanks.
    '85 Euro 635csi Race Turbo, megasquirt, Group A
    '92 525i Touring 5 speed, 3.46 diff, UUC 8.5lb flywheel, soon to be turbo.
    '02 Subaru WRX Wagon with STI springs, bigger sway bars

  3. #3
    Join Date
    Dec 2003
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    Here are some information from the UUC kit:
    Brake kit options for: E28/E34 5-series/M5 (1982-1988)
    E24 6-series/M6/M635CSi (1982-1990)
    E32 735i/iL (1987-1991)
    E31 8-series (front only)

    Stage 2 is a front-only kit using a 4-piston Superlite front caliper with 348mm front 2-piece slotted rotors. Optional black or red caliper color. Maintains correct bias with original rear brakes.

    Stage 3 is a 4-wheel kit using a 6-piston Superlite front caliper with 348mm slotted rotors and a 4-piston Dynalite rear caliper with 328mm slotted rotor. Optional black or red caliper color.

    It would seem that 6 pot front and 4 pot rear works... But do they keep the stock master cylinder???

    I just need to figure out the pistons diameter for a 4 pot front and 4 pot rear setup.
    '85 Euro 635csi Race Turbo, megasquirt, Group A
    '92 525i Touring 5 speed, 3.46 diff, UUC 8.5lb flywheel, soon to be turbo.
    '02 Subaru WRX Wagon with STI springs, bigger sway bars

  4. #4
    Join Date
    Dec 2007
    Location
    Northern(occupied) VA
    Posts
    409

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    Quote Originally Posted by Bruno
    But do they keep the stock master cylinder???
    It says they do use the stock master in the explination on the UUC web site
    Conforti chip, K&N filter, Racing-dyn sways, EBC pad/rotor, SS brakelines, UUC DSSR, custom sound+alpine receiver, 17" PS2s, H&R/bilsports.
    "Speed is the product of doing everything right"

  5. #5
    Join Date
    Dec 2003
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    Canada, ON
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    Quote Originally Posted by healtoeit
    It says they do use the stock master in the explination on the UUC web site
    Sooo, to keep a pedal travel that is similar, the caliper piston area has to stay the same...

    Meaning the volume of brake fluid displaced has to stay the same so:
    Area 4 pot caliper piston x 4 = Area single piston caliper x 1

    Right? so comparing with 750i calipers front: 60mm piston= 2.36" Area= 4.37 sqin.
    So my 4 caliper piston diam shoul be similar to: 2xSQRT(4.37/(4*PI))= 1.18"

    Hummm, seems pretty tiny. And I know that the 1.38" works great for the front.

    EXCEPT... if the flotting caliper displace twice as much fluid??? in that case the result would be: 1.67"...???...
    '85 Euro 635csi Race Turbo, megasquirt, Group A
    '92 525i Touring 5 speed, 3.46 diff, UUC 8.5lb flywheel, soon to be turbo.
    '02 Subaru WRX Wagon with STI springs, bigger sway bars

  6. #6
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    Dec 2003
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    98

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    i'm still trying to figure out what you just said but i'm definately interested. I've been thinking about TCD's kit because of price and pad availability and options but this seems interesting.

  7. #7
    Join Date
    Dec 2003
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    Canada, ON
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    Quote Originally Posted by Lee in Ottawa
    i'm still trying to figure out what you just said but i'm definately interested. I've been thinking about TCD's kit because of price and pad availability and options but this seems interesting.
    Track / race Corvette brake pads aren't cheap... and this setup seems to go through a lot of front pads.

    I bought a set of corvette calipers and sold them once I realised how much flex these had. Then I decided to get a cheaper setup (in the $500.00 range) with tons of pads available from $15 to $100.

    But they do look cool on the car.
    '85 Euro 635csi Race Turbo, megasquirt, Group A
    '92 525i Touring 5 speed, 3.46 diff, UUC 8.5lb flywheel, soon to be turbo.
    '02 Subaru WRX Wagon with STI springs, bigger sway bars

  8. #8
    Join Date
    Dec 2003
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    98

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    whats the cheaper setup your using? what pads fit the willwood's

  9. #9
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    Quote Originally Posted by Lee in Ottawa
    whats the cheaper setup your using? what pads fit the willwood's
    Wilwood superlite calipers and pads that go along with them. I am using my car on the track so I am not worried about pad noise but performance.
    '85 Euro 635csi Race Turbo, megasquirt, Group A
    '92 525i Touring 5 speed, 3.46 diff, UUC 8.5lb flywheel, soon to be turbo.
    '02 Subaru WRX Wagon with STI springs, bigger sway bars

  10. #10
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    Dec 2003
    Location
    Canada, ON
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    I think that the single piston floating caliper displace twice as much fluid as a fixed caliper:

    My calculations should be:
    Area 4 pot caliper piston x 4 = Area single piston caliper x 2
    '85 Euro 635csi Race Turbo, megasquirt, Group A
    '92 525i Touring 5 speed, 3.46 diff, UUC 8.5lb flywheel, soon to be turbo.
    '02 Subaru WRX Wagon with STI springs, bigger sway bars

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