more vibration?

[phreaknature]

so i got my cat converter replaced a week ago cause i wasn't passing smog, plus when the mechanic showed me the old part i saw how badly clogged it was. still didn't pass smog, but i payed an extra $20 to get a certificate so throughout the week i've been noticing a strong vibration coming from roughly the rear leftside of my car, mostly on the first acceleration after a start up for that day (ex: car's been in the garage overnight, then when i turn it on and pop it into first, the vibration occurs for the first 5 maybe 10 seconds of accelerating at a normal pace). the vibration ALSO occurs when my speed begins to drop and NEEDs to be downshifted, or when i'm at roughly around 75mph. i don't know why it doesn't vibrate at 80, but 75 seems to be the rough patch, ideas anyone?

also, maybe i'm just dreaming things, but since the cat was changed, that means i've REGAINED the hp i lost when i had a clogged one right? maybe the fact i've regained that lost hp also set off the vibrations? can't tell u the cat brand, it was just an oem part for my car that the shop had. i didn't get into the specifics of it.

[JdrifterCA]

wuz kinda of viberation? ... i think all cars viberates when shift too early.. and rpm goes low. be more specific.

[maj Andres]

240's vibrate, get used to it

[Philipio]

Exhaust hangars?

[S13Joe]

Exhaust hangars?

x2, or a ****ty cat, what kind of exhaust setup are you running?

[phreaknature]

stock exhaust and the vibration is not the normal vibration. its specifically on the left side, near the rear and alot more stronger than your normal 240 stock vibration... hahah stock vibration.... yeah anyways idea?

[Tsukiko]

make sure everything was mounted correctly and nothing looks out of place. the shop may have... neglected something.