I have a 1990 c4 automatic when i put it in gear in makes a pretty heavy clunk...Maybe U joints, but i went under the car and checked and everything was tight so i have no idea

 

You should also take a look at your transmission mount.

 

Both my camaro and corvette do this, if you mean the loud clunk is like a jerk when putting it into gear. I thought this was just normal for older chevrolets or at least the 700r4s?

 

mine does/did this too.

my tranny leaks a bit, and when i fill it up with fluid it is less noticable..but still there.

I don't know what its from. i've learned to ignore it. once it blows up, i'll replace it.

 

if you wait till the idle goes back down to 600 rpm after the computer goes through it's self check, it will be less noticeable.
If you stick it in drive or reverse when it's about 900-1000 rpm, remember, at 900 RPM, that's 45 mph, with TPI, that's a lot of torque.
I think they fixed that problem in 1988 with a valve body bleed-off orifice.

 

My 91 do the same and it s pretty normal .
Vette 700R4 are viril.
Drove a 89 same. Drove a 93 same.

Some are louder than others but nothing s gonna brake.

 

Nice to here that. My 87 does the same.

 

the vehicle has high miles (over 100K) the Ujoints are probably worn. I'd replace them as preventive maintenance before they fall out on the highway

 

Ya i dont want anything to happen when im going like 130mph that would be bad...lol
Why is every one saying that it is normal???

 

because we have already been through the panic factor, and we know what to expect.
at 100K, I changed u joints (all 6) bead blasted the parking brake shoe backing plate, resanding the parking brakes, sanded the rear brake pads, had the rear discs turned, changed front brakes, new front rotors, new master cylinder, new brake booster, bled the brake system, changed the tie rods, steering rack, had it aligned, replaced the plastic window tracks, had the seats and steering wheel redyed, new wipers, new heads, new radiator, new radiator and heater hoses, new mufflers, installed polyeurethane shock absorber biscuits, new air conditioning compressor, new fuel hoses, replaced the injectors, fuel filter, I figure I could get another 100,000 miles out of it if I did it right.
It's still going strong, it has 144,000 now.

 

but a LOUD clunk is NOT normal; some noise, yes.

 

how hard is it to change the u-joints?

mine does this too. it doesn't do it in reverse though, whats up with that?

 

Dam you could have bought another vette for the money you spent on parts bro!! But ya you should get another 100 thousand out of that easily.....

 

Not bad but deffinetly get a tool from harbor freight, makes it so much easier.

 

Im tellin ya i went under the car and i checked the U joints and they were all tight no play in the shafts so that clung might be trans related maybe any idea's???

 

a possibility, really need a tranny shop to check that out, one other possibility is worn ring and pinion gears...

 

I was never really a big fan of the 700r4 i think there crap for example mine slips from time to time that might have something to do with that clung?

 

josephf31 had the right idea. gears loose or the output shaft on the trany may be worn, it takes a lot to break it but the teeth can wear and get loose on the yolk to the drive shaft or also check from the drive shaft to the rear end. if you do the drive shaft u-joints, do one at a time and take the rear off first and then try to spin it when still hooked to trany and feel for play then do the same to the rear. just have one side still hooked up each time so you dont fight the rear and the trany at the same time.

 

I've had mine checked at AAA Transmission and they said there wasn't anything wrong.. My 84 has 79,xxx miles now and its done it since I rolled 65,000... Trans and car runs fine I learned to ignore it

 

I think im just gona deal with it since everyone else seems to be having similar issues..If anything im gona have the trans rebuilt in a bit when i get some money saved up.thanks