LS6427

iTrader: (2)

Problem found....2nd page....post #26..... Hope it helps someone else with this damn annoying vibration issue......


So it vibrates around 65 mph......but I noticed today if Im on the pedal steady speed its vibrating.....but if I lift my foot just a little bit it goes away. Then as gradually apply pedal again..it comes back. So....its most apparent under power.

Anyone have this issue and find what the cause was....?

Im putting it back up in the air on Wednesday to look around some more....but I haven't seen anything yet....

Can bad bushings in the torque arm cause vibration......?


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jblankenship

iTrader: (5)

driveshaft

Darth_V8r

iTrader: (4)

Dude, I feel for you. Chasing vibrations can really suck. In my case, there were several things, and none of them by themselves was the answer:

1. Removed the poly trans mount and replaced with a stocker

2. U joints were shot. I got a big improvement replacing the U joints

3. Pinion angles. You'll read lots on here about the right settings. I can't tell you what's perfect, but I can tell you that for me was to make the trans output shaft parallel to the yoke pinion. There are threads on how to measure this. After I made them parallel, the driveline was pretty quiet. I ended up tweaking to where the rear pinion is at 3.6 degrees and the transmission is at 4.1 degrees, giving me a -0.5 degree pinion angle.

4. After doing all three of the above, I still had vibrations, but the humming shaking thing was gone, and instead I could feel the individual pulses. AT 65 MPH, your driveshaft is spinning in the 60 Hz range, which is audible. Your tires spin at 17 Hz, which is inaudible. This led me to start looking on the wheel side. One morning, my rear axle locked up completely, and I ended up having to drag the car home, ruining a tire. Replaced that tire, and the rest of the vibes were gone. So, I also had a bad tire in there complicating things. Turns out there was a bubble underneath the tread.

Hope that helps

LS6427

iTrader: (2)

Can it be the driveshaft after years of having no issues...? Its a steel shaft I bought used like 9 years ago after my aluminum one broke. BUT....all of this vibrating did start after the driveshaft was reinstalled 1 1/2 years ago along with my new engine.
Should a DS be rebalanced before it goes back in....?


You saying to just buy new u-Joints....?

Which brand (part number) is best for a factory steel shaft....? I'll just do them this week.

The shop that installed my new engine put in a very good condition factory rubber mount.

All 4 tires are brand new on brand new rims.......But this was vibrating before I bought them all.

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BMR Tech2

iTrader: (5)

Text book pinion angle vibration. Your pinion angle is too high. As you are under load/power the rear rolls back and the pinion angle goes higher and gets into the range where it begins to vibrate. As you ease off the pedal, it relaxes down to a lower angle where it is more in line and does not vibrate. You can check the torque arm bushing, as a worn one will allow excessive rise in pinion angle. If the bushing is good, then it is likely you have lowered the car or made another change that has affected how the rear end is oriented in the car. If you have an adjustable torque arm this is an easy fix. If not, you will need to get creative.

Darth_V8r

iTrader: (4)

It helped mine. Mine were super loose, though. I'm not saying just replace them, but i'm saying check them out. if you're in doubt, replace them both. I used Lakewood greasables from AZ.

As to the pinion angle per both mine and BMR suggestion - mine was off, and I have the stock torque arm, transmission mount, and cross member. All non-adjustable. So, here's the deal on that. Measure your engine / trans angle using the crank pulley. Measure your rear pinion angle using the bearing cap on the yoke side of the U-joint with a socket as a spacer.

To adjust, I inserted rubber washers between the trans mount and crossmember, raising the transmission tail. This simultaneously reduced the trans angle from 6 to 4 and raised the pinion angle from 2 to 3.5. If I needed to go the other way, I would have inserted shims between the crossmember and the frame mount points. This would simulateously increase the trans angle and reduce the rear pinion angle.

Darth_V8r

iTrader: (4)

On determining if the U-joints are bad, here is how mine were. They U-joint could not support the weight of the yoke, so they had this "loose" feeling about them. There was also a flat spot at perfectly straight where I could feel it "click" into place and then back out of place.

After installing new joints, the yoke could stand out without being supported, and the click was gone

BMR Tech2

iTrader: (5)

Good advice

LS6427

iTrader: (2)

Darth/BMR,

Thanks a lot for the info.

Vibrations today were unbelievable.....had to slow down and make it stop. And my tranny.....coincidentally....started totally slipping in 1st gear and was hard to get it moving. All other gears shift fine.

My friend at a dealership (he does side work there on friends cars at night) is gonna take the car tomorrow.....he's gonna rebuild my tranny and then I will forward him all these recommendations to check while he installs new u-Joints. Torque Arm bushings are 17 years old.....so maybe I'll replace them while hes in there.....probably a dealer or discontinued part......LOL


Thanks again....

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LS6427

iTrader: (2)

Do I need two ujoints of the same part number.....front and rear...?

Moog PN 235 greaseable is all I find for a factory driveshaft. Or PN 234 non-greaseable........

http://shop.advanceautoparts.com/p/m...chTerm=u+joint

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Darth_V8r

iTrader: (4)

They are both identical. Up to you if you want greasable or not.

LS6427

iTrader: (2)

Cool thanks. I ordered 2 of the non-grease Moog 234's at Advance Auto website. Found a coupon code on Google.....got both for $31.00 store pick up.

Found a new Torque Arm bushing for $18.00 at my local PepBoys.

Hope these items fix this......its a crazy *** vibration......like the world is coming to an end when it hits hard. When my friend installs the rebuilt tranny and puit the new ujoints and TA bushing in....he will check the angles on everything. Should have it back by Thursday.

As you said in your post.....are these the angles we should target...? Is the goal "0" combined pinion angle....???

rear pinion is at 3.6 degrees and the transmission is at 4.1 degrees, giving me a -0.5 degree pinion angle.

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Darth_V8r

iTrader: (4)

It's rarely the same between cars. My suggestion is to set the rear pinion parallel to the trans tail shaft, which is zero. Then, test it out. Then, adjust toward negative pinion a little and see if it improves. By trial and error, you'll have to tune it in. If adjusting negative makes it worse, then adjust the other way.

I wish it were as easy as, "set it to x" but subtly differences between vehicles make it a bit tricky

LS6427

iTrader: (2)

So I assume my tranny guy who works at the dealership will know how to adjust the pinion angle with shims......?

Is shims the only way to adjust...?

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LS6427

iTrader: (2)

Darth,

If I get an adjustable UMI TA that has the tunnel brace mount......so no longer attached to the tranny.......does the tranny/engine pinion angle become meaningless....?

Then all we have to do is adjust the TA to "0" and its all done....?
Or do adjust the TA to match what the tranny/engine angle is and you are done...?

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Darth_V8r

iTrader: (4)

Not meaningless, but easier to adjust. You can adjust the rear without adjusting the trans. You still want to start with the trans angle matching the rear angle and make adjustments from there. If you keep the stock stuff, shims is the only option.

I wouldn't assume the transmission shop knows what to do. There are stories of GM not being able to stop the vibration at stealerships.

1 FMF

iTrader: (1)

not so much "pinion angle".
the correct terminology is u-joint phase angle.
on each end of the drive shaft is a ujoint, there is an operating angle at each end.
the forward end operating angle is that angle between the transmission tail shaft and the drive shaft. the rear end operating angle (i.e. pinion angle) is the angle between the drive shaft and axle pinion yoke.
those two operating angles need to be the same, such that the difference between those two angles = 0 = 0° phase angle = no vibration.
based on your description of how vibration is happening i would guess bad or cracked torque arm or bad bushing allowing the rear end to rotate under load. and possibly bad ujoint that when under load it's the ujoint causing vibration. or you have something not 100% with trans mount, or LCA/PHB holding the rear end in place which is causing the rear to move under the car and that ujoint phase angle is deviating from 0°. those are all things you should have checked. i put a strange s60 under mine and have an umi adjustable torque arm and with everything mounted and trying to rotate the rear with a jack i measure only 0.2° of deflection before lifting the car to give you an idea, so with the car on a drive on lift if you can rotate the rear more than 0.5° upward i would say your torque arm and/or mount is bad and you most likely have a "pinion angle" problem.

Darth_V8r

iTrader: (4)

I think the reason -0.5 degrees workers in my case is I'm getting about 1/2 degree of deflection under heavy load, so it lines up true when I run it hard. Then when it settles back to -0.5 on light to no load, the working angles are close enough that I don't pick up any vibes.

LS6427

iTrader: (2)

Cool info....thanks.....

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LS6427

iTrader: (2)

My buddy is a 1/4 mile guy....built his entire fbody sc'er set up and does all of his work on his car....engine R&R, rear-ends...everything. He has a private shop with a lift and does a lot of side stuff too.

He just works at a dealership as a tranny tech......but its cool the dealership lets him do side work there at night.....so he can use all the equipment.

I spoke to him tonight....he has the angle tool and says he knows how to do it all. He also mentioned shimming to get it right if we have to.....so he should be good to go.

I have used him for the last 14 years to do all my tranny rebuilds on my car. Does a great job........

Drop it off tomorrow...he said I should have it back Saturday. Tranny rebuild, reinstall my sway bar, rear brake pads, new ujoints and new TA bushing.

Crossing fingers for no vibration........

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