just wondering cause my camaro had a th350 in it and no vibrations. the driveshaft had two even crosses. when i shifted to a th400 i had to use a u-joint with an uneven cross in the front. now i have a recurring vibration at about the same rpm. worst at 30 mph in drive. is a driveline with one uneven cross unbalance-able? i can feel it about every second go thru the car regardless of rpm speed, but only under load.

Sounds more like something in the Turbo 400...?

You need to make sure joint is installed correctly.Check for alignment and freedom to rotate in all directions,shaft must be removed to ck . If length of shaft was altered,proper phasing is a must. Fixed part of either end joint must be parellel to each other. Sounds like a phasing problem or a bound up bearing. Hope this helps. Jerry

Don't think that you can blame the uneven size of the "U" joints...............many makes use them without trouble.

More likely a driveshaft balance problem, or like stated, the "U" joint may not be installed squarely. The tranny suggestion is also something to look at.

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okay then. i didnt want to pay $75 to balance something right off the bat, so i did two things that helped almost eliminate it:
first i rotated the driveline 180' and that reduced it some. the thing is in phase, i think, cause it hasn't been altered. i replaced all the ujoints and made sure they flop around like they're spozed to.

then i, per advice, unbolted my torque converter and rotated it 120'. the vibration, that was noticeable to anyone, is now only noticeable to me, cause i'm looking for it. i dont think anyone will notice without my bringing it up. before i did this, the most noticeable vibrations took place at 30 mph in drive and that's about it. now it occurs at about 45mph in drive and at about 20mph in second. i did it on my first rotatation. there is one more position of the t-c on the flex plate i havent tried yet, but i dont think it could get better. it would have to totally eliminate it to do that. it was a royal p.i.t.a. let me tell you but it's good to have it in a more sellable condition so i wont have to listen to anybody pissandmoan about it.

Sounds like a phasing issue or bearing binding as mentioned above, was the shaft shortened? Are you sure one of those pesky needle bearings didn't fall to the bottom of the cup when you pressed it together?

If it is doing it at different speeds in different gears, I would suspect that it is coming erom the engine. Is the vibration coming at a certain RPM of the engine?

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i'm pretty sure this driveshaft came with the th400 it's whole life, like from a big block car, i took the whole thing out of a donor 73 camaro, it hasnt been shortened. no binding and no loose needles, everything was good when i put it together. it could be an engine thing, cause a mech. that looked at it thought it might be missing, which i seriously doubt, and another thought it looked like it was vibrating at idle. i'm sure it's not the xe262 cam cause it's really mild, but not stock. i balanced all the rods on a triple beam, but not the pistons, which are sealed power. i balanced the big end of the rods, the small end, and the whole rod. they all weigh within 3 grams of each other. i didnt buy a new harmonic balancer tho, i'm wondering ...
but whatever it is, like i said, i drove it last night and it's really not going to be noticeable to anyone whose not looking for it. or driving it at a steady 30 mph in drive.

it is a rpm issue i think, from what i said about it doing it at different speeds in different gears. @ the same rpm, but i dont have a tach in the car so i dont know what rpm.