I have been recently driving my 89 Birebird 305 5.0 L T.B.I. a lot with my t-tops off and I have started to notice a recurring knock with regular tempo echoing off the walls whenever I drive through ally ways or on ramps. At first I thought this to be an issue with U-joints as previous experience has taught me. However, after I replaced them the sound returned after a few couple mile drives. There isn't any play in the driveshaft. It is almost a clanking sound as if metal on metal. It is faint enough that I can't hear it on the open road but it does seem to be getting worse. It doesn't happen when in park or when in drive and not moving. Speed doesn't seem to effect it much, I notice it more low speeds, but I don't know if that is just becuase of the nature of the area I'm driving through (allys, on-ramps). It is extremely hard to identify becuase I have to be moving to hear it and then I only hear it echoing off the walls from what sounds like the rear end of vehicle. I need to get this fixed as I am worried about some part critically failing. If anyone has wisdom to share on this subject please help me before my Firebird takes a dump. Thank you!

 

Bad shock maybe? Exhaust hitting?

 

Scotch the front wheels and put the rear on jack stands and start the car and put it in gear when you let off of the pedal if the sound is in the rear you can pinpoint where it is . If you hear nothing put it in park , shut it off and lower it back to the ground and shake and bonce the rear of the car and see if you hear anything if you do it is in the suspension or the exhaust or the brake cables . Happy traceing .

 

lol i no this sounds funyn but i had the same prob.. i was like wtf is that knocking sound. so i checked the spare tire in the little capartment in the back it was the tire banging against the wall lol!

 

check your flex plate check your shocks

 

Nope not shocks. Tried bouncing the rear end and no sound. Exhaust is solidly mounted and driveshaft has no play.

 

Did this as you as described and nothing. Not a sound. Got a good view of everything turning as it should though. tried to wiggle everything i could get my hands on under there and nothing wanted to move. I did however notice a very very slight up and down play in driveshaft yoke.

Thank you for your advice. After inspecting the bottom thoroughly I put it back on the ground and bounced rear around. No sounds.

 

I bought it off a guy who aparently thought a spare tire wasn't important as the Firebird had none in the compartment. At this point I have removed all pieces in the rear hatch compartment and the back seats as well (hoping to hear it better).

 

Checked both and nothing. I took it out for some highway miles and noticed that sounds returns most in low gears at low speeds and becomes more noticable when driving over speed bumbs or uneven allys (anytime the Firebird jostled around a bit). I think I may have been mistaken as to where the sound originates from. The echo made it hard to locate and I was reading a lot in the forums about rear ends going bad. This time out I actually semi felt the knocking almost right under my feet! So I have almost completely detailed the underside of the looking for evidence.

 

Alright I'm thinking transmission mount now could that make the sound?

 

I had the bottom of the spare tire mounting bracket break loose. Epoxied back in place and all was well.