Front DC drive shaft vibration: (1 Viewer)

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Rick, true, but your skillset and the average person on this list is not the same. We suggested to John to add packers since this is the easiest way for him to change the front pinion angle. It is really difficult to compare lift measurements since we do not all start at the same place. If these were all brand new trucks, then yes, one can say that xx measurement rom hub center to flare is yy over stock. But we can not since suspensions sag over time.

Also, the lip is not totally square, some people do not get it dead center of the hub, some people do not have the tape totally vertical etc etc. Unless a strict guideline is set and everyone follows it, I always felt that measurements are probably one accurate to +- 1/2" anyway.

I know you went to great lengths to get your truck dialed in to spec and 100% right, and I wish that was in the capabilities of most people, but in reality it is not. We on the other hand have tons of experience with different setups and I know that in John's case the setup can be dialed in to be vibration free. And yes, this is probably only going to happen when things are 100% correct.

Driving with either shaft removed, and/or using chassis ears is the best way to locate the noise/vibration. However removing a drivehaft also changes the dynamics of the loads on the rotating parts. So in a lot of cases, it means you have to get the front and the rear dialed in at the same time.

I have not personally found that when you have a front shaft that vibrates, that adjusting the rear fixes it. Pretty much you need to get either vibration free individually, to ensure a vibration free ride.
 
Would not the basic approach be to 1) know what are the proper driveline line angles for pinions, u joints, driveshaft and transfer case output flanges, 2) measure actual angles, 3) adjust axles to achieve acceptable angles?

What are the acceptable max u joint angles? For non CV driveshaft, what is is max acceptable difference in angles between u joints on the same shaft?

Seems that this approach would eliminate any guess work regarding driveline geometry.
 
Rich said:
Would not the basic approach be to 1) know what are the proper driveline line angles for pinions, u joints, driveshaft and transfer case output flanges, 2) measure actual angles, 3) adjust axles to achieve acceptable angles?

Yes, but the front of the 80 is not like a 3 or 4 link where you can make the links adjustable and just get the angles dialed in.
 
Rich said:
Would not the basic approach be to 1) know what are the proper driveline line angles for pinions, u joints, driveshaft and transfer case output flanges, 2) measure actual angles, 3) adjust axles to achieve acceptable angles?

What are the acceptable max u joint angles? For non CV driveshaft, what is is max acceptable difference in angles between u joints on the same shaft?

Seems that this approach would eliminate any guess work regarding driveline geometry.

A little info on driveline setup;:D

http://www.pirate4x4.com/tech/billavista/PR-shaft/index.html
 
Christo, all I'm trying to do is help people to understand that this sort of problem doesn't mean going with a gut feeling or the one with the highest probability. These things can be identified, the solution might be a little difficult though.

After my initial lift and correction I then took some readings. My solution was to raise the vehicle 30mm and rotate the axle another 2*. However either one or the other probably would have gotten the pinion angle close enough to spec. to avoid vibrations.

These threads remind me of the initial P401 threads years ago. Everyone was shouting VSV for the fix. Now years later people have developed the skill set to diagnose and identify the problem and avoid heartache and wasted expenses. I hope these drive line issues get there someday also.
 
Rich said:
Would not the basic approach be to 1) know what are the proper driveline line angles for pinions, u joints, driveshaft and transfer case output flanges, 2) measure actual angles, 3) adjust axles to achieve acceptable angles?

What are the acceptable max u joint angles? For non CV driveshaft, what is is max acceptable difference in angles between u joints on the same shaft?

Seems that this approach would eliminate any guess work regarding driveline geometry.

Tools R Us said:
Ok, having reviewed the informative tutorial on driveline geometry linked above, it looks like for a non-cv driveshaft the u-joints need to be within .5° of each other. And for a cv driveshaft, the non-cv u-joint needs to be within .5° of 0°. And, just to make the setup a bit more challenging, those targets need to be achieved when the truck is at cruise throttle. So, with the truck sitting static, an allowance of 1°-2° needs to be made to accommodate the fact that the rear pinion rotates up and the front pinion rotates down approximately 1°-2° at cruise.

Sounds simple enough for the rear, and as Christo points out, a bit more challenging for the front, given the inability to independently set caster and pinion angles.
 
landtank said:
Christo, all I'm trying to do is help people to understand that this sort of problem doesn't mean going with a gut feeling or the one with the highest probability. These things can be identified, the solution might be a little difficult though.

I hope these drive line issues get there someday also.

Rick, thanks faor taking part in this discussion. I appreciate all the testing, measuring and education that you do on the board. It seems like ery discussion on this topic has you explaining it over and over.

Yes I wish everyone lifting their truck had your knowledge and understanding. What I wish more is that 80's had a front end that allowed for easy adjustable caster and no vibration issues when lifting them. Unfortunatelly it does not.

5 years ago, 2.5" was a huge lift, 4" was enourmous and 6" was unheard off and was only for the crazy people. Trucks were also newer and we did not have these issues. If you were the average customer calling us, you will find we talk more people out of tall lifts than we talk into it. We have come to think that lifting a 80 is a trivial matter and there are no affects to it. Well, sorry it's not. It is extremely important for people to realize that when the go on this patch of modifications, that although vendors try to give cookie cutter solutions, a lot of times you might have to mix the dough and understand what kind of cookie you are baking.

We strive to give a out of the box solution that works. Sometimes if does not due to a variety of reasons. For example, we will not insall a 2.5" lift without caster bushings. Period. Even though people on the internet say it is ok.

We will not install 850J's without additional caster correction, even though the people on the internet say it is ok. Etc Etc.

I should get a 1800fixyourcaster number and send it to your phone. That way we can get more done at the shop :D
 
Rich said:
Sounds simple enough for the rear, and as Christo points out, a bit more challenging for the front, given the inability to independently set caster and pinion angles.


This is where ride height plays a large role. For the most part caster needs to take a back seat to pinion angle to get a vibration free truck. It's when you rotate the axle for caster that you now transition from needing the stock shaft to a DC shaft. If you find yourself in some middle ground where neither shaft will work well you need to either

rotate the axle for less caster and use a stock shaft.

lower the truck and use the stock shaft.

rotate the axle for more caster and use a DC shaft

lift the truck to get less angle at the pinion and use the DC shaft.

While the second one may look like it's going in the wrong direction the solution might be as simple as a bumper and winch which is already in the works and just needs to be moved to the head of the line.
 
OK Experts. I'm back. The truck got it's 4.88's and ARB lockers. Here's the latest:

Drove home....many different speeds....hwy and street....VIBRATION IS DOWN 50% since the gears and lockers? :confused: :confused:

That pulsating noise that was REALLY annoying....HMMM HMMM HMMM is GONE. Here's what's left:

Low frequency vibes throughout the speeds. It's worst and with some added rhumble at 40-50MPH then smooths out from there up....though the faster you go, the more the "normal" vibration is there.

Vibes are WORSE whenever on the gas and near-gone when coasting/off tha gas. :confused:

TOMORROW...the front gets trim-packed 20mm to tune-in that front pinion angle. I'll report back afterwards.

MEANWHILE...any ideas on why the vibration dropped way down after that work?

THANKS!
 
This will be the 7th post in this thread telling you to try it without the rear drive shaft and tell us what happens.
 
Romer said:
This will be the 7th post in this thread telling you to try it without the rear drive shaft and tell us what happens.

FYI Romer....the shop was supposed to install just the front and test. They didn't. They put them both in. So, at this point, we'll try the 1-inch first then the front shaft if needed. :)
 
When you did the lift did someone separate the drive shafts? One or both maybe out of phase. This will cause a vibration.
 
TinBox said:
When you did the lift did someone separate the drive shafts? One or both maybe out of phase. This will cause a vibration.

Nope. But now it's yes because they were out for the gear/locker install.
 
ShottsUZJ100 said:
OK Experts. I'm back. The truck got it's 4.88's and ARB lockers. Here's the latest:

Drove home....many different speeds....hwy and street....VIBRATION IS DOWN 50% since the gears and lockers? :confused: :confused:

That pulsating noise that was REALLY annoying....HMMM HMMM HMMM is GONE. Here's what's left:

Low frequency vibes throughout the speeds. It's worst and with some added rhumble at 40-50MPH then smooths out from there up....though the faster you go, the more the "normal" vibration is there.

Vibes are WORSE whenever on the gas and near-gone when coasting/off tha gas. :confused:

TOMORROW...the front gets trim-packed 20mm to tune-in that front pinion angle. I'll report back afterwards.

MEANWHILE...any ideas on why the vibration dropped way down after that work?

THANKS!

Your driveline angles are changing as you get on and off the gas. A little extrapolation will tell you which direction your angles need to change, based on what's happening when you accelerate and decelerate.

I wonder why you would make more changes (adding height to the front) before you remove the rear shaft and check that scenario out? When troubleshooting, it's always best to make as few changes at a time as possible, fully exploring the ramifications of each modification before adding more factors to the situation.

-Spike
 

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