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saltshaker 05-05-2010 06:46 AM

Metric brake problems
My pedal is very hard and the wheels wont lock up....the car doesnt stop well!front brakes are GM Metrics and rears are Ford Explorier with a 84 Corvette MC and a p. valve for disc to disc and then a inline p. valve for the rears. I think the MC is 1-1/8th"bore....could go power but engine has 14"s of vacum

rdc767 05-05-2010 11:15 PM

Same brakes you have but I'm running 76 vett M.C. Manual no power. Works great. Might be your leverage on you pedal. Not enough.

Sam Bozzette 05-10-2010 07:03 AM

If I remember correctly the instruction manual calls for a 1" master cylinder, if I am correct you dont have enough mechanical advantage in the pedal to use the larger MC with the size of the brake calipers you are using. Now Im no engineer, but the best way I can explain this, is that brake systems use a smaller bore MC with a longer stroke to move fluid to a large bore short stroke caliper the small bore has less surface pushing on the fluid and the calipers have a greater surface so even though the PSI at both end is the same the calipers actually apply more overall pressure. PSI is just that, pounds per square inch, the more square inches the greater the force. So by using an MC with a larger bore you lost some advantage over the calipers.

All of that being said I used a 1" bore manual Corvette MC and although the car stopped well I wasnt satisfied with the stiffness of the pedal. So I removed the pedal and repositionad the MC push rod pivot point 3/4" closer to the top pedal pivot point increasing the advantage. now the pedal feels like it should and the car stops great.


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