Help with corner weight and vibration

[1972orangebeast]

Ok I'll start off by posting about corner weight, I got car on scales today and here were my results. FR 709 LR 675 FR 818 RR 719 , is it normal my right side is heavier? And the front to be 100lbs heavier? And rear to be 50lbs? Could any of this be a cause of a vibration at 70mph?

Now here are the problems I have been having sorry it's a little long

Sorry I know there are a lot of posts about vibrations and some seem similar to mine but like most of you know everyone seems to be a little different. I just wanted to post and see if I am over looking something simple or if my calculations are wrong etc.

The setup: I have a 72 Dodge Dart, stock 360 motor right now, ls1 t56, 50"x3" steel drive shaft with all spicer parts and solid joints, QA1 coilovers front and rear, rack and pinion, triangulated rear, 8.75 rear with 3:91 posi, wilwood disc brakes 12" all four corners, BFG kdw tires 245/35/18 f and 285/30/20 rear, and thats about everything I can think of at the moment

The problem: The vibration has changed a little but its always between 65-75 mph, it comes on pretty strong and i have not went faster due to the fact the sound and vibration get faster and harder. You can tell the sound is like going round and round, and seems to be directly from the rear of the car, it vibrates the shifter and you can feel it a little in the seat and wheel when its really strong. Also when you let off it feels like you are running over the rumble strip on the side of the road untill your under 55mph.

The background: So far I have had the weight of the driveshaft come off at the tranny end twice( the first time though i think it was unbalanced motor) but the second time car felt pretty smooth and then at 70 bang the weight came off and same vibration was back. The drive shaft has been built at 2 different shops in town, both reputable and build stuff for drag racers, i have had the drive shaft balanced prob 5 times now and doesnt seem to change except the most recent balance feels a tad smoother but still vibs at the same speeds. I have had my pinion and trans angles all over the place, I can adjust the trans from 1* point down to 1.6* point down( i can go lower but have some major fab redo xmem), the rear end has been any where from 2* pointing down to 2* pointing up and everywhere in between. The last try at it the trans is at 1.5* down, drive shaft is sitting at 1* down, rear end sitting at .7* up, and vibration seems to come in at 65ish, i did have the setup at 1.5* down, ds @ .7* down and rear @ 1.4* up and vib came in at closer to 73mph but that is the best I have been able to get it. Out side of all that I have had rear 2 tires balanced and checked for run out 3 times, fronts 2 times, axles are new and have barely gotten on the throttle to maybe at most squeal tires( i have a stock rv 360 motor..) , I thought maybe rear bushing in trans maybe bad cause there is a little play about .10-.20 but its not leaking any fluid into the rear seal or out of it which most guys said would happen if tail shaft bushing is bad, i have tried runout myself on the driveshaft and its no more that a few thousands, i have tried 4-6th gear and doesnt matter its still at same mph, also I have had the center section rebuilt, backlash set and bearings checked, i have had it on jack stands with drive shaft out and brought it up to 60-70 mph and its smooth.

At this point im just banging my head, I have dumped way too much into a steel shaft so far I would hate to have to buy a aluminum piece and not be the issue. I just dont know what else to check, I appreciate any and all advice. My next step is taking it to a shop but never sure who you can trust and things like this can take for ever and they just rack you big $$$$$ and possibly get you no where....

 

[72BBSwinger]

Do you have the right flywheel and balancer on that 360? Seems bad enough to throw the weight off the driveshaft, which is severe imo.

 

[furyus2]

If you had the drive shaft out, and it was smooth at the same m p h, it's probably from the drive shaft back.

 

[jos51700]

The car won't be even side to side. The entire drive line is not centered in the vehicle and if memory serves, it sits off to the passenger side. Look at the rear end pinion to be sure.

Either way, weight distribution is not the cause of your vibration.

I'd look at the drive shaft and find a third shop if they can't even weld weight on. You can put hose clamps on the shaft and re clock them to fine tune the shaft balance and see if it gets better out worse.

 

[1972orangebeast]

I bought a brand new 360 flywheel from brewers. I didn't think that weight would cause issue but just wanted to make sure that weight is correct. Vibration still a mystery, weight has not came off here recently, so seems to be on there pretty good. Outside of that I'm still lost. I'm going to take it to a shop and have them measure the angles and double check everything

 

[easyrider]

If this is a manual transmission, check the pilot bearing.

 

[1972orangebeast]

Ok so I cured 90% of the vibration!!! So here's what I found out, check with you driveline shops and make sure they are high speed balancing the shaft!! I had the drive shaft balanced again(the 5th time) and it fixed it. The shop that was balancing the shaft the majority of the time had a 500 rpm conputerized balancer, second place I took it to had one that spun at 4000 rpm, and this was the difference. I ruled out the second company a while back because they did balance the shaft for me once before but I think I had bad pinion angle, then when I changed pinion angle the shaft became too long or short and had to be rebuilt, which I took it to the closer shop which had the low rom balancer.

Still have some drone from exhaust to work out and loose bracket on exhaust but everything else seem to do fine at 80. I will say I have a high rom vib but hopefully that changes with my motor swap this winter. Thanks for everyone's help!

Few tips for anyone searching about driveline or driveshaft or speed vibrations
1.Don't change multiple things at once
2. Write down every combination you try(pinion angles, where shaft was built or balanced, etc)
3. Ask your driveshaft shop what rpm they balance at
4. And good luck!