Rear driveshaft goes grrrrrr (1 Viewer)

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Darwood

Darwood

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Alrighty,

This weekend I put the 6 inch Slee springs on and I'm trying to tune the rear drive shaft. So with my front drive shaft removed I still get some drive line vibes from the rear shaft, however it is only when I just barely touch the throttle. If I accelerate or decelerate I get no vibrations.

Right now both the output shaft and the pinion are in parallel and if anything the pinion is about 1/2 a degree lower than the output shaft which should be where I want it since the pinion will tend to rise on acceleration.

Since the vibration doesn't happen at either deceleration or acceleration I'm stumped as to what to do. Could I need new U joints? Or is this something I have to live with unless I go with a CV joint driveshaft? Is there anything I can fix by adjusting the angle and if so which way do I adjust it?
 
So here's ny .02 since you got no replies, I'm a computer geek so take it for what it's worth. As I understand it, the rear pinion torques upwards when you accelerate, and torques downwards when decelerating quickly. This would lead me to believe that in your case that when the pinion shifts under acceleration the angle at which comes to is too "off" and vibrates. From this I would say that you need to compress the adjustable arms a bit to get it to point down a bit more.

This obviously could just prove to give you vibrations on deceleration since that angle will be increased in the same move. Good Luck.

There are some that are of the opintion that u-joints "form" themselves around the angle they are installed in...and changing that angle drastically would upset that. Only $100 to test. ;)
 
Just out of curiosity, when you say you get the vibration when you barely touch the pedal, is that only when starting off from stop or when you touch the pedal at any speed?

If your pinion and T-Case output shaft are within 1/2 degree of each other, then the geometry is not likely the direct problem. One thing that may be worth looking at is the T-Case/Tranny mounts. The parallel geometry will cancel out the rotational vibration in the shaft, but that depends on the T-Case and Axle being able to constrain the shaft. There is a fair bit of coupled force acting on the Axle and T-Case as that driveshaft spins at those angles.

I could see this being a situation where hard accell/decell is enough force to lock out the drivetrain against the mounts one way or the other thereby constraining the driveshaft, but under very light throttle the entire drivetrain is essentailly under 0 load and floating on the mounts. With the whole drivetrain floating on the mounts, the shaft is not completely constrained and the result is vibration.

Just a WAG from an engineer with some driveshaft experience.

Oh yeah... a note on CV driveshafts. A CV driveshaft will not work on a four-link rear unless you put a CV at both the top and the bottom. With a CV driveshaft that has the CV at the T-Case output, to get proper geometry, you must have the pinion pointing directly at the CV joint. If the pinion angle is not within a degree or so of being inline with the driveshaft, you will have just traded one vibration problem for another. The CV shaft at the top is... just like the name says... constant velocity. The U-Joint at the bottom only turns at a constant velocity when there is 0 angle on it. If you have any angle on the u-joint it will accellerate and decellerate twice per revolution, while the CV joint trucks along always at a... you guessed it... constant velocity. Result... nasty vibration if the u-joint has any angle on it.

Chris
 
Right on, a driveshaft engineer! :D

Care to guess on why the rear shaft is in phase and the front is out of phase on an 80? On a stock truck the front shaft has very little angle, but lifted it looks like a sure bet for vibration?

Pirate has a little light reading on driveshafts. :D
http://www.pirate4x4.com/tech/billavista/PR-shaft/index.html
 
Thanks for the replies!

I get the vibration when I barely touch the petal at any speed however the greater the speed the more obvious the vibration is.

I also have some more information that makes my situation more interesting. With my front driveshaft connected I also get vibration on deceleration. This does not occur when I have the center diff locked without the front driveshaft. I also just recently learned, by the advice of Christo, that with the front driveshaft connected I can get rid of the deceleration vibration by engaging the center diff lock. When I do this it behaves as mentioned before.

As Safado pointed out this should mean that my pinion needs to be raised... however if my u joints are trashed then my vibration could be because of that reason as well?

Thanks
 
Ok more info,

This past weekend I decided to change out the u-joints in the rear driveshaft with the help of rockclmbr. All I can say is that is a lot of work. Anyway while I had the rear shaft off I drove around for a bit with only the front shaft. The test drive resulted in a very quiet drive. So now I'm confident (mostly) that my vibrations are from the rear driveshaft.

Like I said we replaced the u-joints in the rear shaft, however after we got the shaft back on it was quiet for about 2 minutes. After that the vibration on decelleration came back. Also I think I had a slight vibration under power so I lowered the pinion about a half degree to a degree. I think this solved the under power vibration.

So now it looks like I just might need a CV rear shaft. One thing I did notice about the stock rear shaft is that the yokes did not line up perfectly. The shaft would kinda wobble a bit on the ground when it was set on it's yokes. I checked the spines and they seemed fine; no damage. If I rotate the splines one spline forward or back the yokes get more out of alignment. Could the fact that the yokes aren't perfectly aligned cause the vibrations on decelleration? Is the misalignment normal, or is this some sort of manufacturer defect that only causes problems at higher angles?
 
One thing I did notice about the stock rear shaft is that the yokes did not line up perfectly. The shaft would kinda wobble a bit on the ground when it was set on it's yokes.
Click to expand...

Did you try turning it 180 degrees?

I checked the spines and they seemed fine; no damage.
Click to expand...

Do you have any play in the splines?
 
Tools R Us said:
Did you try turning it 180 degrees?
Click to expand...

I thought about it but haven't tried yet. I might try it to see what happens. I messed up the placement of a zerk when I replaced the u-joints so turning 180 won't make that any worse.

Tools R Us said:
Do you have any play in the splines?
Click to expand...

No, I didn't feel any play in the splines.
 
The front u joints are not in phase becuase the front pinion and tranfercase output shafts are not parallel. The are both angled upward.
 
Rich said:
The front u joints are not in phase becuase the front pinion and tranfercase output shafts are not parallel. The are both angled upward.
Click to expand...

Yes that is correct. However we are talking about the rear shaft. :cool:
 
Rich said:
I was answering the question in post number 4.
Click to expand...

Which is why we have the quote feature.
 
Darwood have you had the driveshaft balanced?

did you read scottM's comments about u-joint phasing in that redux thread? His explanation seems to raise the possibility that playing with the phasing by a few degrees might allow you to compensate for slight angle differences between the pinion and t-case outputs. I am not sure if it would work myslef but it's something to think about.

Also, el jefe's tranny mount idea is a good point. If the mounts are worn your mounts may be bouncing when in gear but not under load.
 
Thanks semlin,

My tranny mounts look pretty good. I don't think they are the problem. I read ScottM's comments and that could be something to look at. The only problem is the spines in the rear shaft are such that from one spline to another you probably get a good 10 degrees of change. That might be too much.

This weekend I played with my rear control arms a bit and was able to quiet down the drive shaft a bit by lowering the pinion. I still get decel vibes but they are less. The neutral vibes seem to be mostly gone. Even though el jefe recommends against a CV rear shaft I think it might be the only way to get rid of the vibes.
 
Darwood said:
...This weekend I played with my rear control arms a bit and was able to quiet down the drive shaft a bit by lowering the pinion. I still get decel vibes but they are less. The neutral vibes seem to be mostly gone. Even though el jefe recommends against a CV rear shaft I think it might be the only way to get rid of the vibes.
Click to expand...

I'm not recommending AGAINST a CV driveshaft, just letting you know that you will have to rotate your pinion up to be inline with your driveshaft. Just throwing a CV shaft in without adjusting the pinion angle up will be a source of vibration. Here is a diagram of the proper allignment of a CV driveshaft. You really just need to get the pinion within a degree or 2 of the driveshaft.

I am actually pretty surprised that the 80's did not come from the factory with front CV driveshafts. The radius arm configuration is the ideal setup for a CV driveshaft on the front. The pinion points directly at the transfercase through the entire arc of motion as the suspension cycles.

Chris


cv_angle.gif
 
ElJefe said:
I'm not recommending AGAINST a CV driveshaft, just letting you know that you will have to rotate your pinion up to be inline with your driveshaft.
Click to expand...

Oh ok, I gotcha now. With Slee's upper control arms rotating the pinion up is an easy task.

I agree it's strange that Toyota didn't put a Double Cardan shaft on the front yet they were fine with a Double Cardan on the rear of the extra cab Tacoma (I think this is where they put it. I don't have my Tacoma anymore to check). I guess they figured the out of phase front shaft would work as well which in turn would save them money since that requires only two spiders instead of three, not to mention the Double Cardan and the internal ball.
 
ElJefe said:
...A CV driveshaft will not work on a four-link rear unless you put a CV at both the top and the bottom... Chris.
Click to expand...
Chris, are you saying that in order to use a cv driveshaft on the rear axle of a '80 series Cruiser that it must have cv joints at both the transfercase and the rear axle? Is that doable with double carden cv joints? Intuitively, it seems to me that such a setup would "flop" around. Or would one need to use the style of CV joints used in independent suspension rear ends. Are they made strong enough for offroad driveshaft use? I thinking even if they were strong enough, damage to the rubber boots would be problematic.
 
Rich said:
Chris, are you saying that in order to use a cv driveshaft on the rear axle of a '80 series Cruiser that it must have cv joints at both the transfercase and the rear axle? Is that doable with double carden cv joints? Intuitively, it seems to me that such a setup would "flop" around. Or would one need to use the style of CV joints used in independent suspension rear ends. Are they made strong enough for offroad driveshaft use? I thinking even if they were strong enough, damage to the rubber boots would be problematic.
Click to expand...

Actually I was more thinking out loud on how you would get a CV driveshaft to work on a cruiser with the stock 4 link rear suspension setup. Having a CV at the top and bottom would correct for not having the pinion angle in line with the driveshaft with the stock 4 link rear. This is definitely NOT the ideal situation though...

The best way to implement a CV driveshaft on a cruiser would be to use a shaft that had a CV at the transfer case and a standard U-joint at the pinion, and use Slee's adjustable links to angle the pinion to be inline with the driveshaft. The key with a single CV shaft is the adjustable links that allow you to set the pinion angle.

Chris
 
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