Chasing vibrations - what should I try next

M

mikerhyne

NAXJA Member # 1375
Location
Aurora, CO
Okay first here is the important details on my rig:
1998 with AW4 that I have owned for just over 2 years and I have done/had done everything listed

-NP231 rebuilt with Teraflex SYE kit
-New stock style motor and tranny mounts, no TC drop
-4.56 gears D30HP & 8.25 open for the axles gears done about 2 years or 6000ish miles ago with new bearings
-Front axle: New unit bearings (Timken), new spicer u joints, new ball joints, power stop slotted rotors and pads (getting a high speed noise from them recently but not too worried about that)
-Rear axle: No idea on age of wheel bearings, just replaced drums, pads and all brake hardware (chasing pulsing rear brakes too but not too worried about)
-Lift: RE 3.5" with full arms, new springs, double sheer track bar and brace, steering box brace (Durango box), and disconnects.
-Cooper ST Maxx tires balanced multiple times

Okay so my issue (the one I'm most worried about) is vibration at high speeds which is noticable/annoying at 65+. Right now I'm not running a front shaft but I get more vibration when it is in that pulsates too. With just a rear shaft in it is more like a groan under power that goes away off power.

My issues started around when I had the gears done but at the same time I swapped out the rear springs (was lifted with blocks, add a leaf and shackles), did the SYE and tcase rebuild, had the front shaft rebuilt and got a new rear shaft locally (rear shaft was crap and ended up as scrap after it was "fixed" but that is another rant). I say around since it is only at higher speeds that you can hear/feel it and when I did all of this work it had very noisy MTRs on it so it was hard to hear at highway speeds. I really started hearing and feeling this when I pulled off the MTRs and put on new tires since they are much much quieter and smoother.

Here is what I have tried:

Taking back to the gear guy and he says everything is good with what he did.

Swapping around axle shafts fronts to rear. I have front and rear Woods shafts and a rebuilt/balanced stock front one. I have run the front shafts in the rear and no change in my vibrations. I have even rotated the yoke around trying to see if I could impact the balance of the shaft and that didn't change anything.

I have shimmed the rear axle all the way both up and down to the point where I get very clear vibrations from the angles. Right now it's about 1 degree different with the pinion lower.

What should I try next? I have some ideas but want yours first :-)
 
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Oh and I have G2 diff covers. I have even played with the amount of gear oil in there and I think that changes the noise slightly. However that could just be wishfull thinking.
 
That groan under power is your ring and pinion if it's not the u joints in your driveshaft. You need to find a new gear guy if he doesn't know that. What gears were installed? What weight oil are you using in the diff? If the oil in your diff changes the noise, then it's definitely not your driveshafts. But, the vibes at 65+ and groaning are two different animals. You should search more on driveline vibes so you can get all the right procedures for adjusting your pinion angles.
 
dan1977p,

Could the groaning in the gear create a felt vibration at the higher speeds? Additionally could/would that gear groan translate as a vibration through the drive shaft?

I have played with the pinion angles many times and while I can create additional vibration on acceleration or deceleration I cannot get rid of the primary groan/vibration.
 
If you think the vibes are coming from the primary, you should check all the bearings and check the axle shafts for straightness. I'd love to see a video of the primary vibrating when the rear ds is removed. I'm still of the mind that the groan and vibration are two totally different animals and should be dealt with differently.
If the gears are good quality and are set up properly, the groan should go away. It may not if the bearings are shot. Did your gear guy tell you what your pinion preload, backlash and pattern were? I guess if your pinion preload was way too low, it could help introduce driveshaft vibes and cause groaning. All this to say, I'd get someone else to check your gears first and while they are in there, refill it with 85-140 gear oil, esp if you wheel or tow with it.
 
What do you mean by the primary? I have tried to video it but at those speeds the vibration messes with the camera's picture too. When I put it on stands it unloads to one side.

I'll find out what gears I have since I can't remember. The oil is the stock weight for towing whatever that is.

I have been thinking my next steps are:

Check the axle shafts - that could be related since I'm getting pulsing brakes.

Have someone check the gears

Take all 3 shafts somewhere and have them checked
 
Sorry you said primary and I reverted to motorcycle terms. I meant diff everywhere I said primary. If you have a long straight edge, you can check the shafts yourself. Or you can roll them and see if they wobble.
 
So the gears are most likely Yukon but maybe Motive Gear. I took video this morning of the driveshaft at the axle up to 80MPH just got to get it from the camera to my phone or home computer since I can't upload from my work computer... I'll get that out there tonight. No crazy vibrations are apparent and with the suspension moving it may be hard to see. I might try putting the camera on the axle looking up the shaft.
 
Vibes that start at 45mph and up are normally associated with driveshaft balance.
 
Funny you posted that question. I have been out going through all the shims I have. All of them are RE. The 8 degree shim was what I have been running as it makes the pinion 1 degree lower. Then the 6 degree shim is 3 degrees lower and then the 4 degree shim makes it 5 degrees lower.

I ran the 6 degree for quite a while too but don't feel a difference between the 6 and 8.

Seems like I need a lot of shim...
 
So yes I took pictures of the 8 and 4 degree shims and clearly was tired when I made the post about the angles I found last night.

8 degree shim puts the pinion to shaft angle 2 degrees higher wrong direction. This configuration doesn't change my primary noise but might create some one the gas vibrations but I can't really hear them over the primary issue. Pics:

https://goo.gl/photos/9y9W5DBj1451vyis6
https://goo.gl/photos/bEBWzTygK4ZvFQW57
https://goo.gl/photos/CWf9kp3V9SEp9ccm9

4 degree shims put the pinion 5 degrees lower which is too low. Pics:

https://goo.gl/photos/2MxBjcpm9P6fWWTk6
https://goo.gl/photos/dnoJg2tSmmCTxhpXA

I will be going back to the 6 degree shim since that is pretty close to the desired 2 degree difference before I drive it again. However the shimming never changed the primary noise which I'm really thinking is gear/axle related but I'd love to hear some cheaper ideas or things to try. If I get someone to get into the axles and it's anything major I will do selectable lockers or different axles... I'd rather not spend that money right now as I'd rather just feel like I can go have fun in it without something blowing up on me.
 
I wish I had that many different shim combos so I can get mine perfect before burning new leaf mounts. I think it's good that you're looking at the two issues separately. Once you get the vibes right, you can focus on the howling gears.
Some gears are just loud. Mine are. They are USA standard and have been howling for the last 5k miles and took about that many to start making a little noise. I'm suspecting my pinion preload opened up way more than expected but they are also cheap gears and cheap gears make noise. I've heard of folks running loud gears for 50k miles with no issues so you may be good if you can deal with the noise.
 
I also have 2.5 degree shims - shims are way cheaper than new gears. I can deal with the noise I have when my front shaft is out. However to complicate issues when I have both shafts in the 2 vibrations/groans interact with each other and pulsate and that is really annoying and concerns me of what else is going to break after time. It's to the point where I have not wheeled it this year since the front shaft has only been in recently to try to solve this and for a couple snow storms. So I have the same issue in both ends. With the front shaft out I don't think the noise from the gears is audible. I think the noise/groan/vibration from the gears transfers to the shaft and thus to the rest of the vehicle.

I guess I'll take the 2 Tom Woods shafts to be balanced just to be sure. I have a feeling it's the gear set up.
 
Here is an update from everything I've done to solve this. I took the shafts to another drive line shop and they were out of balance about 1oz at the slip yoke where there was already a ton of weight. So the replaced the yokes and balanced them. This seems to have solved the rear vibrations/noise that I was getting and made the front way better. I have the rear pinion set 1.35 degrees below and the front is 2.5 below.

Who knew I would get bad shafts from a local shop and then bad shafts from Tom Woods. It's been a barrel of fun chasing my tail on this but at least it is acceptable now.

Thanks everyone!
 
I am happy you resolved the problem.

I too received a bad rear shafts from Tom Woods. The "U" joints were out of phase. Spent many frustrating hours chasing and re doing everything else but the shaft.
 
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