master cylinder help on 1995 Chevrolet 1500 Pickup

i replaced the master and slave cylinder about 2 weeks ago iv been trying to bleed it right for along time i cant get it to work right i can get it to work if i pump it for about 1 minute be for i drive it then it will work for about 15 minutes why dose the pedal go soft after that long?, i took it to a shop and they told me i had the wrong master cylinder so i went to 3 other auto stores to try and find the right one but all of the stores gave me the same one is it bad if the master cylinder isnt straight?

by in Redding, CA on April 24, 2010
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1 answer
ANSWER by , April 24, 2010
Maybe the m. cylinder you bought is defective and if so you could return it and purchase one from another store.