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Old 03-12-2009, 07:32 AM
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First, don't fret about line size. All brake lines do is transfer fluid and their diameter has zero bearing on brake function. Can be 1/8" or 1/2" brakes will function the same. Critical dimensions are the master cylinder/slave cylinder ratio and booster pressure output. The dual 7" is good for ~1200psig @ 18" vac and 1" bore which apparently isn't enough for your application. According to the list below, you probably need to go to a 7/8" or even 3/4" master cylinder or to step up to a 9" or larger booster which may need to come from a Pick-A-Part car? As your system stands, you don't need the resid valve if your pedal stroke is not excessive and you don't need a proportioning valve which is only needed if the system is unbalanced, especially if the rear brakes lock up before the front. That is a dangerous situation causing your car to endo faster than Hussein can sign a $trillion spending bill or Slick Willie could undress a White House aide. Your's doesn't sound imbalanced - it is uniformly bad!!

Here is some info I posted in another thread;

"The 7" street rod booster requires 18" of vacuum to operate properly. With this vacuum level the booster will produce a maximum pressure output of 950 psi with a 1" bore master cylinder. This pressure level will work great for four wheel drum systems and disc/drum vehicles which are relatively light. This booster is not recommended for heavy disc brake cars like 55 Chevy's or for any four wheel disc brake system."

"The 7" dual diaphragm street rod booster requires 18" of vacuum to operate properly. With this vacuum level the booster will produce a maximum pressure output of about 1200 psi with a 1" bore master cylinder. This pressure level will work great for four wheel disc systems and disc/drum vehicles which are heavier."

"The 8" booster requires 18" of vacuum to operate properly. With this vacuum level the booster will produce a maximum pressure output of 1200 psi with a 1" bore master cylinder. This pressure level will work great for four wheel disc systems and disc/drum vehicles which are heavier. This booster is recommended for heavy disc brake cars like 55 Chevy's or for any four wheel disc brake system."

"The 9" dual diaphragm ultra booster requires 18" of vacuum to operate properly. With this vacuum level the booster will produce a maximum pressure output of 1400 psi with a 1" bore master cylinder. This pressure level will work great for four wheel disc systems on heavier cars and trucks."
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