89formula350b2l

iTrader: (11)

Well I ghetto fabbed up a way to make the Accel TB for earlier tpi cars to work on my 89 firebird. I took her out for a spin on the highway and floored it going onto the interstate. At about 5000 RPMS, the tach kinda floated and the engine hiccuped, so i shifted not wanting to jack up my engine. Well when I shifted (it was pretty snappy with the Raptor rebuild kit hehehe), i heard a loud thump come from the rear of the car. I took it easy until i got home and now I am here posting it about it.

1. Why is my car doing that funny floating at 5000 rpms?
2. Why is my car making that thump sound?

spina74

iTrader: (5)

my rear use to make a thump when it went 2 chirp a gear but wasnt able to spin the wheels

89formula350b2l

iTrader: (11)

well that accounts for the thump sound

1989GTATransAm

iTrader: (3)

Might also be the rear motor mount has a problem. Another posibility is you ran over something while shifting.

Mikz86TA

iTrader: (4)

Do you still have a rubber tranny mount??? If so, check it out. I replaced mine 3x's after I bought the 86 in 95. One was on the stock tranny..no shift kit. The 2nd and 3rd was with shift kit. And it didnt take long. I got a EnergySusp Poly mount (they have an internal interlock) and its been in there through 4 trannys and 2 motors since 1997. Hands down the best and longest lasting investment I ever made. The thump occured during the shift and it was felt/heard in the mid floor pan area. Part # for that mount is 3.1108......most likely your issue. It can also casue shifting issues due to the tranny case floating under torque.

89formula350b2l

iTrader: (11)

well i am replacing the rear end with a 4th gen one soon....anybody for the floating dilema?

89formula350b2l

iTrader: (11)

isnt doing the floating thingie now....guess its ok..in fact the tires chirped tonight going from 2nd to 3rd