LOST JEEPS :: View topic - Vibration at 45 after differential Swap

What is the pinion / driveshaft angle relationship look like with the the vehicle setting on the ground at rest?

Pinion angle should be pointing ideally slightly below the driveshaft angle.
As power is applied, the pinion angle tries to rise above the driveshafts straight line angle.
If the pinion angle rises above the driveshaft angle to much, weird vibrations can occur.
What you want is when power is applied is for the pinion angle to stay slightly below or at least in line with the driveshaft angle.
So, a slightly negative pinion angle pointing below the driveshaft angle at full rest is ideal.

If your still running the OEM boomerang, the soft rubber bushings on the body end have a lot of give in them which can contribute to the problem.
The IronRock rear upper control arm bushings are very hard, so they don't allow hardly any give when power is applied to the drive chain.

I hope this is not too confusing? :dizzy:

WWDiesel wrote:

I understand completely.

I appreciate both responses.

The rear transmission measures 89 degrees and the front of the pinion yoke reads 89 degrees. BUT that would give a 2 degree pinion offset in the UP direction. How to adjust for this? I don't mind getting the IronRock but I'm still concerned about those slotted holes for the trailing arms in this diff housing?

I will post the NVH app results later after I get them

vwroad87 wrote:

WWDiesel wrote:

Well if they are both 89 degrees, that would be a 0 offset which could increase to a negative offset when power is applied which would not be good.
Do you have any pictures of the slotted holes?

Yes I want to see the slotted holes for one
Plus some other things you have done

And finally here is the picture of the slotted holes in the rebuilt differential trailing arm horns?

After measuring my front and back from the center of the tires to the flare I have a difference of about 1.5 to 1.75 inches. I'm wondering in order to level this if a .500 clevis shim is correct for this difference? I have installed the OME kit, front and rear.

vwroad87 wrote:

The lift to spacer ratio is 2 to 1 with our IFS such that an added 0.500 inch at the coil over will yield 1.0 inch of lift at the hub. There's really no need to use spacers with a clevis lift, just ensure full contact between the strut fork clamp and the strut cylinder is maintained and torque the clamp to spec. Using this rule and depending on your particular equipment, you may not be able to add 0.500 of space. If the clevis doesn't give you enough, JBA sells 0.25 inch top plates that will give you another half inch of lift. Some like me have also installed a set of slightly longer KK/KA cast strut forks. These three things together are working for me, but I'm on some definitely sagged OE springs. YMMV.

Does leveling this way actually improve your driveline angles?

I have read online that the .5 inch spacers are not an issue to install? Hum?

vwroad87 wrote:

I have read online that the .5 inch spacers are not an issue to install? Hum?

There is no issue installing the .5 clevis spacers. Plenty of room for them on Bilstein struts, can't say for sure on other brands.
Even with the .5 spacers on mine with the Bilstein struts, the strut shock tube still sticks out below the clevis about 1/2 inch.

Author:	vwroad87 [ Sun Jan 27, 2019 3:34 pm ]
Post subject:	Vibration at 45 after differential Swap
Hi. I got a donor differential for my 2006 CRD. I rebuilt the doner with trutrac LSD and all new internal parts except gears which were in perfect condition. I setup the diff correctly (experienced rebuilder) and swapped them out. I rebuilt the prop shaft with new ujoints (experienced) correctly indexing the parts for balance. One wierd thing is that the new diff has slotted holes for the trailing arms and the previous one only had round holes. This made me suspect the pinion angle ( on a two ujoint system the output and input flange angles must be parallel) They are really close, within measurement error. One thing that did happen is I had to press one ujoint out with lots of force but the replacement fit fine so I don't think I "bent" the horn. Anyway around 45 I get vibration I didn't have _and_ it seems worse under load. Any suggestions welcome. UPDATE: Just bought NVH vibration app, 399.00 plus tax Gonna go test drive after I clean up the shop some more and the shots wear off. Will update this thread. Just Empty Every Pocket, I honestly have Stockholm Syndrome with this rig.

Author:	u2slow [ Sun Jan 27, 2019 7:36 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
Slotted holes? That sounds weird. Does it look pounded out? i.e. from loose bolts? Or intentionally done? Vibrating harder under load suggests the pinion is already a tad high, and load raises the pinion further. I would try shifting the diff to the other end of the "holes" (probably lowers pinion) and try another test drive. Its possible your axle came from a lifted KJ where somebody had tried to adjust the pinion angle. If you find the other position is the cure, you can probably weld some washers over the ovalled holes.

Author:	WWDiesel [ Sun Jan 27, 2019 8:23 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
What is the pinion / driveshaft angle relationship look like with the the vehicle setting on the ground at rest? Pinion angle should be pointing ideally slightly below the driveshaft angle. As power is applied, the pinion angle tries to rise above the driveshafts straight line angle. If the pinion angle rises above the driveshaft angle to much, weird vibrations can occur. What you want is when power is applied is for the pinion angle to stay slightly below or at least in line with the driveshaft angle. So, a slightly negative pinion angle pointing below the driveshaft angle at full rest is ideal. If your still running the OEM boomerang, the soft rubber bushings on the body end have a lot of give in them which can contribute to the problem. The IronRock rear upper control arm bushings are very hard, so they don't allow hardly any give when power is applied to the drive train. I hope this is not too confusing?

Author:	vwroad87 [ Sun Jan 27, 2019 9:55 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
WWDiesel wrote: What is the pinion / driveshaft angle relationship look like with the the vehicle setting on the ground at rest? Pinion angle should be pointing ideally slightly below the driveshaft angle. As power is applied, the pinion angle tries to rise above the driveshafts straight line angle. If the pinion angle rises above the driveshaft angle to much, weird vibrations can occur. What you want is when power is applied is for the pinion angle to stay slightly below or at least in line with the driveshaft angle. So, a slightly negative pinion angle pointing below the driveshaft angle at full rest is ideal. If your still running the OEM boomerang, the soft rubber bushings on the body end have a lot of give in them which can contribute to the problem. The IronRock rear upper control arm bushings are very hard, so they don't allow hardly any give when power is applied to the drive chain. I hope this is not too confusing? I understand completely. I appreciate both responses. The rear transmission measures 89 degrees and the front of the pinion yoke reads 89 degrees. BUT that would give a 2 degree pinion offset in the UP direction. How to adjust for this? I don't mind getting the IronRock but I'm still concerned about those slotted holes for the trailing arms in this diff housing? I will post the NVH app results later after I get them

Author:	WWDiesel [ Sun Jan 27, 2019 10:42 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
vwroad87 wrote: WWDiesel wrote: What is the pinion / driveshaft angle relationship look like with the the vehicle setting on the ground at rest? Pinion angle should be pointing ideally slightly below the driveshaft angle. As power is applied, the pinion angle tries to rise above the driveshafts straight line angle. If the pinion angle rises above the driveshaft angle to much, weird vibrations can occur. What you want is when power is applied is for the pinion angle to stay slightly below or at least in line with the driveshaft angle. So, a slightly negative pinion angle pointing below the driveshaft angle at full rest is ideal. If your still running the OEM boomerang, the soft rubber bushings on the body end have a lot of give in them which can contribute to the problem. The IronRock rear upper control arm bushings are very hard, so they don't allow hardly any give when power is applied to the drive chain. I hope this is not too confusing? I understand completely. I appreciate both responses. The rear transmission measures 89 degrees and the front of the pinion yoke reads 89 degrees. BUT that would give a 2 degree pinion offset in the UP direction. How to adjust for this? I don't mind getting the IronRock but I'm still concerned about those slotted holes for the trailing arms in this diff housing? I will post the NVH app results later after I get them Well if they are both 89 degrees, that would be a 0 offset which could increase to a negative offset when power is applied which would not be good. Do you have any pictures of the slotted holes?

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Author:	vwroad87 [ Sun Jan 27, 2019 11:40 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
WWDiesel wrote: vwroad87 wrote: WWDiesel wrote: What is the pinion / driveshaft angle relationship look like with the the vehicle setting on the ground at rest? Pinion angle should be pointing ideally slightly below the driveshaft angle. As power is applied, the pinion angle tries to rise above the driveshafts straight line angle. If the pinion angle rises above the driveshaft angle to much, weird vibrations can occur. What you want is when power is applied is for the pinion angle to stay slightly below or at least in line with the driveshaft angle. So, a slightly negative pinion angle pointing below the driveshaft angle at full rest is ideal. If your still running the OEM boomerang, the soft rubber bushings on the body end have a lot of give in them which can contribute to the problem. The IronRock rear upper control arm bushings are very hard, so they don't allow hardly any give when power is applied to the drive chain. I hope this is not too confusing? I understand completely. I appreciate both responses. The rear transmission measures 89 degrees and the front of the pinion yoke reads 89 degrees. BUT that would give a 2 degree pinion offset in the UP direction. How to adjust for this? I don't mind getting the IronRock but I'm still concerned about those slotted holes for the trailing arms in this diff housing? I will post the NVH app results later after I get them Well if they are both 89 degrees, that would be a 0 offset which could increase to a negative offset when power is applied which would not be good. Do you have any pictures of the slotted holes? You need to account for the angles being measured at the back of the transmission and the front of the pinion. That makes them opposite by 2 degrees. I post some pictures tomorrow but going to town now to walk the dog on his favorite loop and gather some NVH readings

Author:	tommudd [ Mon Jan 28, 2019 1:00 am ]
Post subject:	Re: Vibration at 45 after differential Swap
Yes I want to see the slotted holes for one Plus some other things you have done

Author:	vwroad87 [ Mon Jan 28, 2019 2:26 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
tommudd wrote: Yes I want to see the slotted holes for one Plus some other things you have done Okay, later today I wil get pictures. The OME lift gave the vehicle a slight downward rake, looks like the tire clearance in the back is about an inch to 1.5 inches higher than the front. The NVH app confirmed a 2nd order driveshaft vibration so it's either the trim height or the pinion angle (guess I didn't need to spend 399.00 to figure that out though). Appreciate all the input.

Author:	vwroad87 [ Tue Jan 29, 2019 12:43 am ]
Post subject:	Re: Vibration at 45 after differential Swap
Okay so the NVH app showed a 2nd order vibration at 0.36 amplitude. After measuring the drive angles again I added a 5/16ths shim above the transmission mount crossmember to lower the transfer case. Road tested again and measured a 0.06 amplitude 2nd order vibration, wow 84% improvement, not really noticeable in the wheel at 45-55 at all now, I can't tell at least. Gonna add 1/8 more shim tomorrow and post results. I have only installed the OME "lift" kit, no additional plates..... The front measures 4.5 inches of clearance above the 245/70R16 tires, the back 6 inches so the trim height changed allot after this lift. And finally here is the picture of the slotted holes in the rebuilt differential trailing arm horns?

Author:	tommudd [ Tue Jan 29, 2019 3:36 am ]
Post subject:	Re: Vibration at 45 after differential Swap
Measurements you have given us don't mean any thing at all Measure middle of the wheel to bottom of the flare, that is the only way we can tell exactly how much lift you have actually

Author:	WWDiesel [ Tue Jan 29, 2019 2:21 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
vwroad87 wrote: And finally here is the picture of the slotted holes in the rebuilt differential trailing arm horns? The picture you shared looks like someone was trying to adjust the pinion angle on a lifted vehicle by grinding those slots in the metal? If you have a "lifted" Libby and would like to be able to adjust the pinion angle, you can install the IronRock rear upper control arm using a custom mount that I developed for the KJ. It allows you to adjust the pinion angle as it has a threaded Heim joint as pictured below. The IronRock Arm was originally designed for the much larger and heavier WJ Cherokee and is super heavy duty and will be the last one you ever purchase for the Liberty. PM if interested.

Author:	vwroad87 [ Mon Feb 04, 2019 3:38 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
After measuring my front and back from the center of the tires to the flare I have a difference of about 1.5 to 1.75 inches. I'm wondering in order to level this if a .500 clevis shim is correct for this difference? I have installed the OME kit, front and rear. https://jeepinbyal.com/clevis-spacer-for-front-struts.html

Author:	WWDiesel [ Mon Feb 04, 2019 5:09 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
vwroad87 wrote: After measuring my front and back from the center of the tires to the flare I have a difference of about 1.5 to 1.75 inches. I'm wondering in order to level this if a .500 clevis shim is correct for this difference? I have installed the OME kit, front and rear. I have metal 1/2 (.500) clevis spacers on mine and it still has a slightly higher rear stance than front. I have Ironman springs though, not OME. Also, some simply use 2" conduit nuts stacked together to make the clevis spacers.

Author:	iakj11 [ Mon Feb 04, 2019 6:57 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
vwroad87 wrote: After measuring my front and back from the center of the tires to the flare I have a difference of about 1.5 to 1.75 inches. I'm wondering in order to level this if a .500 clevis shim is correct for this difference? I have installed the OME kit, front and rear. https://jeepinbyal.com/clevis-spacer-for-front-struts.html The lift to spacer ratio is 2 to 1 with our IFS such that an added 0.500 inch at the coil over will yield 1.0 inch of lift at the hub. There's really no need to use spacers with a clevis lift, just ensure full contact between the strut fork clamp and the strut cylinder is maintained and torque the clamp to spec. Using this rule and depending on your particular equipment, you may not be able to add 0.500 of space. If the clevis doesn't give you enough, JBA sells 0.25 inch top plates that will give you another half inch of lift. Some like me have also installed a set of slightly longer KK/KA cast strut forks. These three things together are working for me, but I'm on some definitely sagged OE springs. YMMV. Does leveling this way actually improve your driveline angles?

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Author:	vwroad87 [ Mon Feb 04, 2019 11:05 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
iakj11 wrote: vwroad87 wrote: After measuring my front and back from the center of the tires to the flare I have a difference of about 1.5 to 1.75 inches. I'm wondering in order to level this if a .500 clevis shim is correct for this difference? I have installed the OME kit, front and rear. https://jeepinbyal.com/clevis-spacer-for-front-struts.html The lift to spacer ratio is 2 to 1 with our IFS such that an added 0.500 inch at the coil over will yield 1.0 inch of lift at the hub. There's really no need to use spacers with a clevis lift, just ensure full contact between the strut fork clamp and the strut cylinder is maintained and torque the clamp to spec. Using this rule and depending on your particular equipment, you may not be able to add 0.500 of space. If the clevis doesn't give you enough, JBA sells 0.25 inch top plates that will give you another half inch of lift. Some like me have also installed a set of slightly longer KK/KA cast strut forks. These three things together are working for me, but I'm on some definitely sagged OE springs. YMMV. Does leveling this way actually improve your driveline angles? Trim height is changed by my lift, this lifted the transfer case too with respect to the differential. By shimming down the transfer case cross member by 5/16 I was able to reduce the vibration 85% by way of the NVH app. I have read online that the .5 inch spacers are not an issue to install? Hum?

Author:	WWDiesel [ Tue Feb 05, 2019 2:31 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
vwroad87 wrote: I have read online that the .5 inch spacers are not an issue to install? Hum? There is no issue installing the .5 clevis spacers. Plenty of room for them on Bilstein struts, can't say for sure on other brands. Even with the .5 spacers on mine with the Bilstein struts, the strut shock tube still sticks out below the clevis about 1/2 inch.

Author:	iakj11 [ Tue Feb 05, 2019 6:55 pm ]
Post subject:	Re: Vibration at 45 after differential Swap
WWDiesel wrote: vwroad87 wrote: I have read online that the .5 inch spacers are not an issue to install? Hum? There is no issue installing the .5 clevis spacers. Plenty of room for them on Bilstein struts, can't say for sure on other brands. Even with the .5 spacers on mine with the Bilstein struts, the strut shock tube still sticks out below the clevis about 1/2 inch. Yeah, my Rancho RS5764s don't have nearly that much tube to work with. Their design actually makes clevis spacers a challenge - note the reference bump on the tube and the way the metal plate above is flared. Time for different suspension!