There is a loud thump or Knock that comes from the rear of the car when the car is shifted hard from first to second. keep in mind that it is only 1-2, and only when shifted above about 4000 rpms. Can the gears be set in place wrong or something like that? or maybe just the posi differntal is shot?

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my cousin has a --- 86 IROC with a 350 crate motor,3.73s, flowmaster, T-tops, shift kit, Holly 650 carb., automatic, 94 Trans Am seats--- i just do the research for him.

some thing is loos i would check the u joints then the rearend

Another thing that it could be is if your springs are old,(mono or multi) the rearend could actually be hitting the bump stop underneath the driveline tunnel. Good luck

Worn leaf spring bushings could be the culprit too. So you need to check these out also. I would check everything externally before you go tearing into the rear end. I doubt that's where the problem is anyway. In a real severe case just like mine it'll do it just putting it in gear. I guess that's what you get for buying a car that wasn't running. But it's running now and getting ready to tear it down for the restoration..

Also check the rear trans mount; I believe several people have had those break and it causes the trans to thump on the bottom of the car.

Jody

UPDATE:
just to let everyone know, NevinKez (the guy that actually owns the car), blew out his rear end yesterday. his local garage told him that it was gonna set him back about $500 to have it rebuilt. Well, i guess that you should listen to your older and wiser cousin when he tells you "you should get that checked out" about 3 weeks before it happened. thanks to everyone who gave advice.

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my cousin has a --- 86 IROC with a 350 crate motor,3.73s, flowmaster, T-tops, shift kit, Holly 650 carb., automatic, 94 Trans Am seats--- i just do the research for him.

Tell him if he is going to drive it hard to investigate getting a stronger rear end for it.
The stocker is not going to last, no matter what you do.
David

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Check my web page for First Gen Camaro suspension info:
David's Motorsports page (http://ourworld.compuserve.com/homepages/David_Pozzi/)
First Gen Suspension Page (http://ourworld.compuserve.com/homepages/David_Pozzi/first_gen_suspension.htm)
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Chev 350 Can-Am Vintage Racer

David,
what can he do to make it stronger. Hes aiming at having about 500+ horses with a shot of NOS. can you give me some suggestions?
thanks

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my cousin has a --- 86 IROC with a 350 crate motor,3.73s, flowmaster, T-tops, shift kit, Holly 650 carb., automatic, 94 Trans Am seats--- i just do the research for him.

buy a good 12 bolt or ford 9" www.moserengineering.com (http://www.moserengineering.com)

don't get all huffy and offended, but i think you and your cousin should maybe learn a little more about how stuff works on cars before you go playing with 5oo horses. from the few posts i've seen from you, the simple stuff seems to baffle you. i aint saying i'm an expert, but i have been playing with cars for 15 years or so, and am now working with 400 horses- the most I've had so far. the car should be physically capable of not only holding up to 500 horses, but stopping you quickly and safely from the speeds you will quickly hit with that much power.

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1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16" IROC wheels

NovaD,
sorry to seem so dumb at these things, but cars a fairly new to us. you have been working with cars almost as long as we have been alive. And i am not the GM man, i am a Ford guy (dont hate me). I just do the research for my cousin since he is really new to the game (had the iroc only 2 months). and there was no NOS or 500hp when the rear went.

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my cousin has a --- 86 IROC with a 350 crate motor,3.73s, flowmaster, T-tops, shift kit, Holly 650 carb., automatic, 94 Trans Am seats--- i just do the research for him.

GM was making a bolt in assembly for the 3rd gen f body's , I believe it was a dana (can't remember what #) . Check Your local Chevy Dealer...I think the price dropped from original price... And like NovaD says...Make sure the car is SAFE......if You hear strange noises figure out what they are and fix them....don't drive it untill it breaks....that little popping noise in the front end might be a loose balljoint for example....good luck...