Thread: engine/trans shake when burning out

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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.

Originally Posted by pro70z28

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!

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

IMG_2822.jpgI didn't change to heim's in a day, I wish. Last month I lifted the bed off the frame and added a panhard bar, a sway bar, and changed from poly ends to heim's. It took me about 5 weeks or so. The sway bar addition was solely to help with the fact that my truck handled like a boat, but the panhard and the heim's were supposed to solve the shaking problem. I was focused on modifying axle components because I just assumed the shaking was coming from there.
Unfortunately after all that work I had the same problem.
I'm going to try to attach the 2 video's my buddy took from two different perspectives. They aren't the greatest and you can't see the whole vehicle in the framing, but it definitely got me thinking in a different direction. You can't see much of the cab in the video's, so you'll just have to take my word for it that from inside there was significant shaking.
-attached should be a pic of the suspension set up long ago before I even got it on the road, but it is still the same except now it has a panhard and heim's.
I can't see how to attach video's. They aren't showing up the way they do to attach pics. So for now here is just the pic, I'll keep looking on how to do video's.

Probably the easiest way to attach the video is to upload it to youtube then copy & paste the code in the message box here.

I know the videos are terrible, there is a tiny portion of time where the wheels are actually slipping, but the reason I so quickly got off the throttle is because of how much the trans starts shaking and how bad it seems inside the cab.
I wish I got a video from inside the cab too.

Also, my axle pinion at ride height is point slightly down in relation to the ds, I think about 3 degrees, and the trans shaft is pointed above the ds about the same degree, so as accurately as I can tell they are basically equal and opposite angles.

Looks like you've done a good job and alls' about where it should be, the suspension geometry and pinion angle. Not shown is the panhard bar and an antiroll bar? I don't much care for a panhard bar and it can cause some binding with that type of suspension - but it isn't affecting anything at launch. The antiroll bar, is it one of those kit types similiar to competition engeering? Did you adjust it to neutral on both links with a driver behind the wheel, fuel etc so that it is at starting line weight? By neutral, i mean can you rattle both links that drop down to the rear housing? They should be loose so that you can slide the attachment bolt in or out?
The one thing that i thought odd is that at low rpm, not much power at all there is smoke coming from the tire - try throwing some weight in the bed, a couple hundred pounds of sand in bags and see what happens.
I tubbed a pickup and tried to drive it out of my shop without the bed on it. It got stuck at the curb in front of my rollup door to keep rain water out of the shop - i had to back up and get a running start. There isn't much weight at all in the back of a pickup and maybe that that is what you're seeing the results of.

right, the sway and panhard are not shown in that pic only because that pic is from 5 years ago and I just put those on last month. I chose that pic anyway because it was the best picture to show the suspension.
The sway bar wasn't from a kit, I had to make it custom. I did not actually check it was completely neutral with me in the cab, 99% of the time I am single handed so that stuff is tough, or if I'm really in a pinch I ask my wife for help and listen to her complain the whole time. It was definitely neutral with nobody in the cab because I checked that.
but yes, in the video from the rear perspective you can see smoke come up right away with only a few revolutions of tire spin. I did re-locate the fuel tank behind the rear axle so there is at least a little more weight back there, but it is still light.
I do think the video does show that the axle is very stable, and from inside it feels like the trans is going to launch to the moon.

Sorry - read the post wrong....

If the truck is smooth at any speed or rpm while cruising, should pretty much rule out driveshaft, U-joint, and alignment issues on the rear.... Other considerations could be a bad shock or shocks that are wrong for the application. Do you recall what weight the springs are? I've seen many instances on cars-trucks that are light in the back where the springs were way too much for the little bit of weight. I can't tell from the pic what coilovers you have, but if they're the generic 'one shock valving fits all' your problem could be there. With something light in the back, takes different valving and light springs to make it work right. Just because you can't see the tires hopping, doesn't mean that the coilovers are doing their job correctly......

As OJ mentioned, you might try adding a few hundred pounds to the rear, and along with that drop your tire pressure down to about 20 psi and try it again. Could be your coilovers are doing the hopping!!!!

Originally Posted by Dave Severson

If the truck is smooth at any speed or rpm while cruising, should pretty much rule out driveshaft, U-joint, and alignment issues on the rear.... Other considerations could be a bad shock or shocks that are wrong for the application. Do you recall what weight the springs are? I've seen many instances on cars-trucks that are light in the back where the springs were way too much for the little bit of weight. I can't tell from the pic what coilovers you have, but if they're the generic 'one shock valving fits all' your problem could be there. With something light in the back, takes different valving and light springs to make it work right. Just because you can't see the tires hopping, doesn't mean that the coilovers are doing their job correctly......

As OJ mentioned, you might try adding a few hundred pounds to the rear, and along with that drop your tire pressure down to about 20 psi and try it again. Could be your coilovers are doing the hopping!!!!

Not taking credit for your post Dave,but darn if you and I was thinking the same thing.LOL-kind of scary isn't it??.

I want to x2 the thought of a marginal pinion angle where until you apply heavy torque to it,it's effect doesn't show up with normal driving.

Stick shift burnouts are hard on drive-line components.A clutch that is grabbing and releasing-chatter,would have a heavy vibration during a burnout and there again "could" operate normally.Question is do you have a line lock on it??.

From the pictures I saw,it seems the four link doesn't have adjustment holes for you to set the instant centers.Any chance given the light wt rear end and a instant center set to bite too hard??.If you raise(and I really don't want you to break parts in doing so)the RPM's,would that make it wheel hop for you could see it better??.

Maybe find somebody with one of these & mount it under the truck.
http://gopro.com/cameras/hd-hero-960-camera/
get a real time view of what's going on under there under power. under 200 bux

I was thinking like 1Gary, clutch chatter, suspension doesn't appear to flex and it's smooth under "normal" driving. Problem seems to be torque overloaded components.