Chevy Pickup Brake Help
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    Nitro Addict 54POP's Avatar
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    Chevy Pickup Brake Help

    Not sure if you good people can help but I have a 49 pickup with a fatman front and a Jag xj6 rear, the front setup is 2.75" single piston GM3 calipers with - 1 & 11/16" jag rears - I have twin wilwood 7/8" m/cyls on a balance bar plus twin mgb remote servos (servo ratio on these are only 1.65:1 ) - pedal is quite soft but reasonable line pressure, however the pedal moves a long way before full pressure acheived, giving generally uninspiring brakes, I tried one 3/4" and one 7/8" m/cyl but found it is too small for this combo, I may try a 1" on the front circuit but may have to swap one servo for a larger one (1.9:1 ratio) to improve line pressure, if anyone has something similar that works please let me know, I'm at the end of a 3 year rebuild and spending too much time and money on trial and error when I should be driving the thing. If you dont help I'll have to use the wifes PT
    Do you have a different setup that works for you ?
    Cheers - Andy
    I read the news today - Oh Boy!

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    Re: Chevy Pickup Brake Help

    Andy , are the servos angled up towards the outlet pipe as they need about 25 degrees as without that you can get air bubbles that simple won't come out and cause long pedal travel ?


    If they are fine then my ramblings are that the GM calipers are going to need a lot of fluid (as Yank stuff is much bigger bore than Brit, most Brit / Euro is around 54-60mm ) plus some additional line pressure from somewhere, due to loss of line pressure with bigger bore .

    As you say I'd go with a higher level of boost servo on that circuit. You need at least a 1 inch cylinder for the front, to bring the pedal up , and I'd go with the 7/8 on the Jag rear ( 48mm bore from memory again )

    You need to calculate the fluid required to move the front brakes , from memory it's calculated based around a 1/16th movement but one side of one caliper only ie don't double the volume required.

    A correctly sized m/c, on a full 4 wheel system, moves between 10-15mm for full travel. So I'd guess you'd halve that for 2 m/cs , not sure , I normally go by 'feel' as you have so far.
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    Nitro Addict 54POP's Avatar
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    Re: Chevy Pickup Brake Help

    Thanks Kev, your inputs always appreciated, yes the servos are angled upwards something I didnt know about until I read the fitting instructions - every days a school day eh!
    I'll try a 1" mc when I've saved some more pennies.
    Still be nice to know of any other setups that work.
    Cheers - Andy
    Last edited by 54POP; 17-05-2010 at 06:53.
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    Re: Chevy Pickup Brake Help

    The trouble is one persons 'works' is someones elses '****e' . I've seen recommendations of set ups for cars that I wouldn't use if they were stationary !!

    The hot set up on EVRYTHING used to be Mk 1 Fiesta servo because it was small and didn't show on the side rails . The fact that it always needed double pumping to get a realistic pedal feel / travel ( not enough volume ) was always overlooked

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