buell

Okay the cars an 87 iroc-z with a 350 and for the most part its stock except for a few mods the previous owner did, but they were mostly things like putting a torgue bar in the engine bay. (are 3.27's a decent gear for our cars (auto?).

Anyway the car has been making a knocking sound when its in neutral or park for the past 4 months or so. As soon as i put it into a gear the sounds goes away completely and immediately. Me and my father just crawled underneath the car last night and after starting up the car my father thought the sound was coming from the flexplate. So I took off the inspection cover and rotated the flexplate at least 4 times by hand and tightened all the bolts on the flexplate. This did not get rid of the sound though. Alot of people who first hear it (the sound is loud enough to hear when your standing 15ft away sometimes) think it sounds like a knock. I've had people say it sounds like a rod knock, i've had others say it was an exhaust knock, and still some who say it was something in the drive train. My father said its not a rod knock though for the following reasons:
rod knocks are a hollow sound and this sounds more like something rolling around in a drum. And also a rod knock wouldnt just go away when you put the trans into gear.
So besides a rod knock what else could it be? It sounds like the sound is coming from either insides the transmission pan cover or the torgue converter.

Ohh and i'm not sure if this was coincidence or not but this might help to figure out the problem. About 2 weeks before this sound started i was pullng up to my garage door, which was still down and i was only 4 foot away, and was prolly doing about >2 miles an hour and accidently put the car in park. I was tired and had thought i had already stopped the car but i realized very quickly it was moving and slammed on the brakes. I didn't shear anything off in the trans did i?

Anyway any help would be great because im stumped here.

Air_Adam

Does the sound change or go away when it warms up? Does rpm affect it? Sounds like possibly a cracked flexplate, but sounds like you checked that already. Is it a knock, or more like a rattle?

buell

No i've driven the car for an hr before and when i go to put it into park or neutral its starts again. So temp def doesn't change anything. Nah i saw the flexplate with my eyes and there was no cracks... least not visual. I also didnt see any cracked bolts on the flexplate either. My father said its more like rattle. He also said he thinks its coming from inside the torque converter. Any ideas. And thanks for the help so far. if anyone has anymore ?s just ask

Hazzard

Not a 3rd gen but I bought a car a long time ago (chevy elcamino) dirt cheep because the guy said the engine was going. It had the same problem as you have, knocks in park and neutral but went away in drive and reverse. Anyway it drove me crazy for about 2 months because it ran great, didnt burn oil, had lots of power and got good gas milage. My problem was there was only 1 bolt holding the tranny to the engine, in park the two would hit together making the rapping noise. When it was in drive the torque between the engine and tranny would make the guide pins tight with the tranny and the knock would stop. It cost me about a dollar to fix, check the flex plate between the bolts if this is the problem, mine developed 2 hairline cracks.
Hope this helps

chevymec

iTrader: (5)

I would pull the trans and look at the flexplate real good. It does sound like its cracked.

buell

ill go and check over all the bolts by the flexplate and tranny again. It sounds like everyone is leaning towards the flexplate crack idea though right? And hazzard you said a dollar to fix? what did you have to do?

Thanks for the responses so far guys!

Hazzard

I just had to replace the 4 bolts, probably about $3.00 now. I didnt notice the cracks in the flexplate for a few months tho, that cost a few bucks and 6 hours on my back to fix.

buell

ight well you just replaced all the bolts holding the flexplate to the troque converter. Umm i only have three of them holding the flexplate to the torque converter though......

BASSETT IROC 85

iTrader: (2)

GM have three bolts ?

Hazzard

I had to replace the bolts that held the tranny to the engine, all but 1 had fallen out. Also my flexplate was cracked between the bolts where it attached to the crankshaft not where the torque converter bolts on.

buell

I'll have to check that spot specifically. Thank you again, if anyone has anymore ideas let me know

BASSETT IROC 85

iTrader: (2)

Yes the flex plate will crack around the crank.

84z28350

^^^

like bassett said, they most commonly crack around the bolts that hold the flexplate to the crank. i highly doubt you will be able to check it without pulling the trans/tq conv back. Good time to install a high stall tq converter