vibrtion, your suggestions

[benno440]

Hey guys, not sure if many of you saw my mopar mayhem video of me racing around the track, but since then I have gained a vibration that only comes on when going over 100 km/h and only seems to do it when I touch the accelerator pedal, for example if I am sitting on 100 km/h all is good if I accelerate I get a vibration through whole car, and then it goes away if I coast, feels like a whole body shudder sort of feeling.
any suggestions? front end is perfect and verified, alignment good and all parts are good. everything on my car is modified or new FYI.
just looking for suggestions on where to start looking

 

[747mopar]

Sounds like pinion angle issues... Lord knows I've been down this road. I say pinion angle because it can change depending on whether your coasting, accelerating or just cruising and it's usually only noticeable at certain rpm ranges. I know you've got a 4 link of some sort so I'd start with looking it over to make sure you didn't damage anything or wipe out a Heim's link. Since you say it only does it under acceleration I'd say your pinion is to high or there's slop allowing it to raise under load. I'm sure it could be allot of things but it sure sounds like pinion angle.

 

[benno440]

thanks man, I may be stressing too much, but could it may be a flywheel unbalance? as in a bolt came loose? I seem to always think of worse case or maybe something unbalanced in the engine or gearbox due to the accelerating causing vibration?
only reason I think that over the pinion angle wrong is being it is a heim joint 4 link so how could it suddenly come out of adjustment? but I will check this, 747 do you think jacking rear end up and running through the gears to see if I can see anything might help?

 

[badlite]

I would give the motor and transmission mounts a look at also.

 

[Meep-Meep]

Have you tried revving the engine to that same RPM in neutral?

 

[benno440]

Have you tried revving the engine to that same RPM in neutral?

I have as that's only around 2500-3000 rpm. and there is a slight vibration but feels more like just engine rumble sort of thing.
checked and regreased wheel bearings, everything is tight and spot on. im thinking it may be engine, gearbox, driveshaft or something

 

[747mopar]

thanks man, I may be stressing too much, but could it may be a flywheel unbalance? as in a bolt came loose? I seem to always think of worse case or maybe something unbalanced in the engine or gearbox due to the accelerating causing vibration?
only reason I think that over the pinion angle wrong is being it is a heim joint 4 link so how could it suddenly come out of adjustment? but I will check this, 747 do you think jacking rear end up and running through the gears to see if I can see anything might help?

If it is an angle issue it won't do it jacked up. Your right saying a 4 link is less likely to do it but since you were hammering on it it's possible that you bent or tweaked something. I only mentioned it because it sounds so much like the issue I had only mine was to low meaning my vibration was worse unloaded whereas yours is worse loaded meaning if it is an angle issue it's to high. Vibrations can be a real pain to track down!

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My line of thinking is if it's the motor or flywheel it should do it in neutral, if it's tires or wheels then it would be mph specific and not matter whether it's loaded or in coast but if it's driveline related then it will be sensitive to driveshaft rpm (mph) and will vary depending on whether it's under load or in coast. Bad motor or tranny mounts I would think you'd notice and not be just at high speeds?

 

[benno440]

update, I adjusted pinion angle down a couple of degrees, vibration is still there, if I sit on 100 km/h I cant notice it, if I sit on 120 kmh its bad, I can feel it really bad through the gearstick. low speed theres nothing

 

[Lets Roll]

Do you have a different set of tires and rims you can try? I've had some weird shakes that ended up being wheel issues.

 

[747mopar]

Sounds like the funs about to begin, like mentioned get wheels checked, check universal joints, have driveshaft looked at, check tailshaft bushing, etc and I'd put a gauge on your tranny and pinion to see where they're at just to be sure.

 

[benno440]

Do you have a different set of tires and rims you can try? I've had some weird shakes that ended up being wheel issues.

nah I don't, I might go get a balance done.

- - - Updated - - -

Sounds like the funs about to begin, like mentioned get wheels checked, check universal joints, have driveshaft looked at, check tailshaft bushing, etc and I'd put a gauge on your tranny and pinion to see where their at just to be sure.

will do, tailshaft bushing? which ones that?

 

[jim496]

The bushing in the tail shaft that the front drive shaft yoke rides on. grab the front of the drive shaft and push and pull from the side and then from underneath. I don't think its a wheel balance problem as it would vibrate if you are coasting or accelerating. It has to be a loading problem.

 

[benno440]

ahh yes the pipe bushing in the end of the trans, checked that all tight.

I think I found the problem, just measure each side of diff to square point on the chassis, the passenger side of the diff was sitting towards the rear 1 1/4" more than the driver side, so it has been crab walking a bit.
I will take for a test drive and see if it has gone

 

[benno440]

fixed woohoo.
slight vibration though when up around 4000rpm but bearable

 

[fmontez1]

What did you do to fix it? Loosen the leafs and move the whole thing over? I'm trying to visualize it. . . I'm having the same exact issue, and I had my driveshaft balanced already.