engine/trans shake when burning out

[tcodi]

I built a 1950 chevy pickup hot rod with a bb402 and 5 speed trans and ford 9" rear. I've always had horrible problems if I tried to spin the tires on dry pavement with what I thought was axle hop. I have a tri 4 link with coil overs, and I recently did a lot of work to the rear and added a panhard bar and rear sway bar. So after all that I went out thinking I solved the problem and still had major problems.
I asked a buddy of mine to come out with me one day with his camcorder and film my car doing a burn out so I could watch the axle in slow motion to try and figure out what is wrong, and I learned that the axle isn't moving at all, but from inside the car it shakes horribly. The whole cab starts shaking so violently that I can barely even hold onto the stick, and I immediately get off the gas so as not to break something.
I guess the issue is the engine/trans shaking when doing a burnout, but it is mounted properly and I've checked all my welds and mount points and nothing is bent or cracked.
Does anyone have any idea what I can do, or what the actual problem is here????

[Dave Severson]

How's about a picture of your setup so we could have a visual to go by? or put up a link to the video your friend took.... The obvious things would be a cracked flywheel, bad clutch disc or pressure plate....

[Bug]

Have you checked your transmission mount and tail shaft to be sure nothing is broken?
Did you check the motor mounts? (both sides)?
Have you checked all of the body mounts to be sure they are tight?
Have you checked the frame 100% for cracks?
Do you have a pilot bearing/bushing in the crank? If there is one, is it any good?

What starts shaking first? I.E. Does the shifter start shaking first and then the body?

Does it drive fine even when you are running the same rpm that you are at when the shaking happens when you are doing a burn out?

Just a few thoughts off of the top of my head.

[tcodi]

I'll see if I can link the video when I get home, I don't have it here, but unfortunately you can't see anything. My friend was actually confused at first because he thought nothing happened, and from outside it looks fine, all this time I just assumed it was wheel hop because from my perspective I just felt shaking.

yes I have checked all of those things and they are all good.
I have a needle bearing pilot in there and it was new just 6000 miles ago.
The weird part is that it runs perfectly smooth at any rpm, just as long as I'm not spinning the tires. It starts shaking immediately as soon as I have the clutch out if I'm on it hard enough to break the tires loose, I can get on it as hard as I want with no problems as long as I don't break those tires loose.
The trans is what starts to shake back and forth, and since it's a truck I have a big long stick coming all the way up from the floor and it starts bouncing back and forth sideways so violently I always get right off it.

I do have a 3600, so it is a full bed, and my driveshaft is over 70" long. Are there any rules of thumb for max driveshaft length? I know I've been looking at our full size trucks here at work, and both of them have intermediate bearing supports and two piece shafts instead of one long shaft.
My driveshaft angle is very mild, so it's not like I have crazy U joint angles or something, the truck is very low so it's just a few degrees on each end.

[sunsetdart]

May want to check and see if any of the balance weights fell off the driveshaft. With a shaft alomst 6ft in length, you may have alot of whipping at RPM and if any balance weight has fallen off, that will lead to big time vibrations.

[rspears]

Seems to me that if you have no vibration at any rpm/speed with moderate throttle you've ruled out component balance from the list - it would be shaking somewhere in the rpm/speed range if it were a balance problem. What are your rear tires? Are you trying to crank some massive pro-stock meats? I like Hoss's idea about a wet burnout - what does it do on wet pavement? How stout is your driveshaft? Did you have it built for the HP & torque, or are you using an OEM or cut down OEM? I'm leaning towards a clutch/pressure plate/flywheel problem, or maybe the driveshaft wrapping up and going harmonic under maximum torque. Personally I don't like needle bearing pilots, but that's just me. Bronze provides known support, is rugged enough to withstand stabbing the tranny with minor mis-alignment of the clutch disc, and will wear before the input shaft regardless.

[tcodi]

I switched the poly link mounts to heim joints because I thought I was getting flexing back and forth in those maybe, so now they are solid as a rock.
I had the driveshaft made custom, and there is no vibration even at 65 mph, which is the fastest I've ever turned it, so as spears said I def don't think there could be a balance issue.
I would hope the shaft is not wrapping, but I guess I can't be positive about that. The only thing is, I would think there would be less torque on the shaft after the tires cut loose than if I kept them planted, and there are no problems at all at full throttle in 1st gear as long as they don't slip.
I did try a burnout here at work, concrete plant, which is like wet conditions because there is a coating of dust on the pavement surface that makes them really slippery, and had the same results.
I wish I could mount a camera under the car to watch the trans when this happens.

[ojh]

You got rubber mounts on your 4 link?

[HOSS429]

try it on wet pavement as well .. john force type burnout ..

[Bug]

Also check your pinion angle. If it is too light and going past parallel with the trans, it could be bouncing around.

[34_40]

If the bed is not in place, it should be easy to see if the rear axle / suspension is flexing or binding.. yes/no?

[pro70z28]

If the bed is not in place, it should be easy to see if the rear axle / suspension is flexing or binding.. yes/no?

I think the bed is installed now, he has old pics. of the bed off.

[34_40]

I think the bed is installed now, he has old pics. of the bed off.

AH.. Got it, thanks.. This is a strange one, can't wait for a solution!

[ojh]

You changed from rubber mounted bushings to heims in a day?
Ok, so now what is it doing?
I'm with Bug, pinion angle. It sounds like you have positive pinion angle where the pinion is pointed upwards in relation to the driveshaft. When under power the driveshaft wants to run straight and true so it pulls the pinion downward and that effect tries to lift the tires off the ground.

[Bug]

Check this out about pinion angle and vibration.
Does pinion angle =vibration - Team Camaro Tech