Hot Rods Driveshaft rumble, problem solvers unite!

There's usually more than one way to solve a problem...

So now the pinion is down .5 degrees relative to the engine/trans?

How much give does the rear suspension have?

 

So, how was the drive home??

 

It does this vibration at 75 mph in 3rd, 4th and 5th gear? Hmm...very intresting...The thinking is, the only things spinning at a constant at 75 mph in all gears is the driveshaft, rear end, wheels/tires.

I'm sure you have already changed the wheel/tire set up, right??

If you are rolling along at 75 in 5th gear and you are getting this vibration, what does it do if you gently increase the throttle, or decrease the throttle?

OK, now try to bear with me...Usually, if you have a driveshaft angle/phasing problem, the vibration kind comes in medium repe***ive waves...like wooom....wooom....wooom..., is that what you are getting?

Or is it more of a "rattle"...?

And, how intense is it? Is it like "hey man, do you feel that?" Or is it more like "oh ****, this thing is about to come apart?"

-Abone.

 

Dennys Drive shaft has the capability to spin the shaft to 10,000 RPM. Since all this started when you replaced the shaft.I still think that is your problem.

 

Just FYI - I work for Hunter Engineering that makes many of the tire balancers that are used worldwide and they only spin at 300rpm. And our heavy truck tire balancers spin at 150 so speed is not that critical.

 

It might sound dumb but you might check and make sure your wheels arent bent.

 

now that technology is cheap....put a video camera under there and see what's happening

 

Check to be sure that each end [joint X]of the new shaft is infact timed to each other,they must be timed dead on or they shake.
Seen that happen a few times when made just a small bit off time

 

IMO, twenty thou (0.020") total indicated runout (TIR) is way too much for a drive shaft, especially one that long.

Our race shafts are held to a TIR of three thou or less. They are thicker walled and smaller OD stuff, but the principle applies.

The greater the TIR, the harder it is to balance the shaft, and the more likely you are to have a harmonic whip (which is what this sounds like to me).

Personally, I would not run a drive shaft with more than five thou TIR, especially behind a motor that stout.

 

The drive home was much better, still not completely gone but I'm making moves in the right direction.

The rear suspension is pretty rigid, fabricated torque arm. I will add in another half degree of pinion up to make the angles cancel out completely. I'm going to ask the drive shaft shop to replace this one. I agree that the runout is too much and why I mentioned it.

The vibration was shake the mirrors so bad they were unusable, it was totally noticeable and felt like the rear was coming apart. Now it feels more like a wheel out of balance.

 

check your harmonic balancer...right before mine came apart i would have bet the farm it was driveline...would only do it at a certain speed .....it acted just like the u-joint.

 

Bulletproof1 could be on to something, been there before. Good place too look with an engine holdin that much coin, dont wont to sling one off and beat out the bottom end. Done it on a 4 banger, and it dont take long at high rpms.

 

No, he isn't on to something in my case. It is not engine or transmission, I have proven to myself it is sloppy workmanship from my drive shaft supplier(s) and nothing else.

 

Here's another dumb question. How much spline engagement do you have with the output shaft of the trans?