Posted by Joe Lorenzino on Saturday, February 15, 2003 at 1:52PM :
In Reply to: Finished Brakes today 4 in Pedal OK? posted by Willy-N on Thursday, February 13, 2003 at 11:05PM :
Just a few more thoughts on the brake pedal travel issue:
- master cylinder diameter- since this is simply a hydraulic system that depends on a certain volume of fluid movement for proper effect, a master cylinder change from 11/4" down to 1" will result in a nearly 50% increase in pedal travel to move the brake shoes the same amount. It will however result in a Similar Increase in Applied Presure once the shoes contact the drums, but just takes a lot more movement to get them there.
-residual presure check valves - these should be in the outlets of the MC to hold a small amount of line presure on a drum brake system. Modern disc brake systems do not use them, and some of the aftermarket MC suppliers may not have installed them in their product. Without these, you are starting from zero line presure instead of the 5 - 7# that helps overcome the return springs. On an old system with the check valves, it is pooible to bleed the brakes by yourself (but slowly)as there is always a certain amount of line presure present.
- change of geometry - moving the MC up or down relative to the operating rod mounting point on the pedal changes the part of the arc that the rod operates on. this may not be noticable at the top of the pedal travel, but could result in a lessening of pushrod travel as the pedal moves. Like the smaller MC, this again gives more pedal travel, but a Higher Applied Presure due to a change in the leverage/mechanical advantage of the system.
My guess is not that there is one problem somuch as a few smaller ones all working in the same direction. my 1 1/4 cents (2cents CANADIAN) Joe L
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