JHOW66 & 70BLOWNGMC: the pedal does sink some when the engine starts. I compared it with my wife's IROC and my pedal felt almost but not quite as hers felt before and after cranking the engine (my booster came off an 86 IROC)
PUTTER: so what you are saying if my booster isn't working the oak tree will stop me or the water will soften the stop?
SNEAKYSNAKE: The engine doesn'tidle rough and you can't hear any hissing.
The booster is off an 86 IROC Z28 and the master cylinder is off a 79 cadillac. It's possible the master cyl. could be stiff but not likely.
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If it don't fit, force it,...If it still don't fit , modify it 'till it does fit !!!