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Master Cyl - Disk Conversion- Stock P-Valve - Perfect Brakes Solved?

Discussion in 'The Garage' started by BorregoK5, Oct 3, 2003.

  1. BorregoK5

    BorregoK5 1/2 ton status

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    I've had hydraboost, 1/2 ton master cylinder, stock p-valve on 1 ton gear with a caddy disk conversion running with perfect distribution on my truck from day one - but others have been experiencing all kinds of rear lockup problems. Today I was replacing my master cylinder and decided to update the stock 1/2 ton non-hydraboost unit to a 1 ton hydraboost master cylinder. I cut the brake line fittings off and replace them with new ones while I was at it since the previous ownder had chewed them up, probably when splicing in the trailer brake line. While gravity bleeding the brakes, I noticed the smaller front chamber of the MC was draining for the front brakes - this struck me as odd since I always thought the larger rear chamber should be attached to the front (70/30 braking and all). The front brake tubing is much smaller than the rear brake tubing into the MC so switching it seemed a little rediculous - time to open the book. The book shows the larger tubing on the smaller chamber and thats when it hits me. The guy who previously owned the truck had switched the two around when slicing in the trailer brake sensor and I've been running the front brakes off the smaller reservoir. Having taken apart a MC before to rebuild it, I don't recall the smaller chamber having any less plunger feeding it than the larger chamber - so theoreticly fluid capacity should not be the difference, but perhaps one engages before the other which is how my brakes have always locked equally with no other changes. Any thoughts?
     
  2. tch777

    tch777 1/2 ton status

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    The size of the resivour doesn't affect the pressure or volume at the brakes. The reason for the larger resivour is that as disk brakes wear they take up more fluid to take up the distance that has worn away. And they designed the resiovors bigger so that people who don't check their fluids often didn't lose brakes and kill themselves. So the piston travel and the portioning valve control the flow and pressure of the fluid.

    Tim
     
  3. BorregoK5

    BorregoK5 1/2 ton status

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    Yes, my 70/30 was in reference to the brakes usage, resulting wear rate and fluid usage. I decided to make things right and plumb the smaller front brake line into the larger back reservoir and larger rear brake line into the smaller front reservoir, bleed the system and see what I get. The rear now locks just before the front which leads me to believe the master cylinders rear brake piston seal passes the reservoir hole first. Another note, the larger diameter 1 ton hydraboost master cylinder, while firm and as effective as the half ton cylinder, it does take more pressure to engage the brakes than before. The stock half ton master cylinder was more responsive.
     
  4. 84_Chevy_K10

    84_Chevy_K10 Banned

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    That would make sense. Even if your drum brakes are perfectly adjusted, there is still going to be SOME slack between the shoe and drum that needs to be taken up before the brakes can be applied.

    Since you have 4 wheel discs, you notice it because the rears come on before the fronts without delay.

    Lol your issue is simple. Can you figure out a way to keep my rear antilocks and my grabbing crappy drum brakes on my DD to keep them from fighting each other when I hit the brakes in the rain without me having to do any work? /forums/images/graemlins/smile.gif I was a dumbass when I put the Lock-Right in, got some oil on the drum I think and apparently the brakes grab now and I'm too lazy to change the shoes. /forums/images/graemlins/rotfl.gif Crappy Ford.....
     

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