I just upgraded my brakes to 87-93 spindles and calipers that i had laying around...When i slam on the brakes the pedal stops halfway down and feels like a rock... what could that be? It slow me down but not as much as it used to. Could it be the master cylinder isnt strong enough? If so where could i get a direct bolt in that is more powerful?

 

Sounds like you need to bleed the brakes a bit more. I'm venturing a guess that if you pump the pedal it will stop better.

 

my guess is master cylinder, air in the system usually lead me to a spongey brake pedal. ive hadan instance where the master cylinder was too big, and same affect, but my jeep at the time stopped on a dime. for 2 minutes, until it locked the brakes up and i to ride 2 miles back to the shop at 3-4,000 rpms going 10 mph in first.