need some help 350 to 455 swapped.

[LEWETHETIGER73]

So I swapped my 350 for a 455 and my brakes seem to of gotten worse. After driving it about 300 miles all of a sudden the got really worse. Could this be a vacuum isssue? Someone said that I might need to change my brake booster or something like that. My car is a 73 pontiac lemans. Thanks

[BR3W CITY]

Does sound a bit like a booster problem. Does it increase if you pump the brakes, or is the pedal soft all the way down?

[pjturkey]

So I swapped my 350 for a 455 and my brakes seem to of gotten worse. After driving it about 300 miles all of a sudden the got really worse. Could this be a vacuum isssue? Someone said that I might need to change my brake booster or something like that. My car is a 73 pontiac lemans. Thanks

I had to switch back to manual brakes because my cam was too big (which as the Above Poster stated would be a vacuum issue)

[Midnightfab]

Were the brakes working fine before the swap? If so you could have a vacuum line off or missing. There is also a one way valve in the vacuum line to the booster. Is that working?

[SSDude]

As long as you have more than 13" of vacuum at idle you should be fine on the vacuum. Obviously the more vacuum the better. Mine runs at a little over 13" and the pedals like a rock.
It really depends on what you mean by worse? Is the pedal soft? As you press the pedal does it slowly go to the floor? What's the general conition of components like pads rotors?
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