Vibration after installing a new front diff (1 Viewer)

[digitalmarker]

Hey guys, I recently replaced the front diff on my 99 with a "stronger" 2001 unit with about 180k miles from a junk yard (non-accident vehicle). I replaced the front bushing before installing, but left the other two mounts with integrated bushings since they looked/felt intact when I reinstalled the new diff. While this upgrade took care of the grinding/whining sounds I was getting from the old diff, I am now experiencing a new issue.

When accelerating and the transmission is approaching a shift point, I am feeling a buzzing type vibration in the floor with my left foot. The vibration intensifies as the RPMs get higher, and subsides when it shifts into the next gear. It is most pronounced when shifting into 4th gear, around 55MPH. Once I get into a cruising speed and no longer pushing on the gas, the vibration is not really noticeable.

Any ideas what could be causing this before I pull the axles again and try to poke around? Is it an install-related issue, or a potential problem with the "new-to-me" diff?

 

[KliersLC]

I can't offer any specific suggestions, but that sounds like something rotational is loose or improperly installed.

Things I'd check

1. Driveshaft flange bolts on both ends
2. Did you separate the two halves of the Driveshaft? If so, can you verify that they were put back together in the correct phase?
3. Make sure U-joints move freely and smoothly in all directions.
4. Check install of CVs to ensure they are seated correctly.
5. Check for play in the pinion bearing--just because the parts truck wasn't wrecked doesn't mean the diff was in tip-top shape.

If all of that checks out, you may be in the unenviable position of just having to wait till it gets worse in order to find it.

Good luck.

 

[digitalmarker]

Thanks for the suggestions.

I can't offer any specific suggestions, but that sounds like something rotational is loose or improperly installed.

Things I'd check

1. Driveshaft flange bolts on both ends
2. Did you separate the two halves of the Driveshaft? If so, can you verify that they were put back together in the correct phase?
3. Make sure U-joints move freely and smoothly in all directions.
4. Check install of CVs to ensure they are seated correctly.
5. Check for play in the pinion bearing--just because the parts truck wasn't wrecked doesn't mean the diff was in tip-top shape.

If all of that checks out, you may be in the unenviable position of just having to wait till it gets worse in order to find it.

Good luck.

Thanks for the suggestions and a reply.

1. flange bolts are good (read below)
2. did not separate the driveshaft, phasing is same as it was before
3. u-joints on the pinion flange end seemed fine. Not sure what I was testing for but there didn't seem to be binding. One thing to note is I greased the u-joints after reinstalling the new diff - maybe 5-6 pumps into each zerc. These have not been greased for quite some time, so I figured it was a good time to do it. Not sure if doing that could have caused an issue.
4. CVs are in properly on both ends. I tried wiggling them last night and they move about 1/8" in and out of the diff so they seem to be properly seated.
5. No lateral play, I can wiggle it a bit left to right but no up/down or lateral movement.

Based on a suggestion from a FB 100 series group member, I disconnected the driveshaft from the pinion flange and rotated it 180* last night.

The vibration/buzzing sensation subsided quite a bit. Still not completely gone, but definitely quieted down a bunch. Still feel it the most at the higher speed, going into 4th gear.

Does this suggest the front driveshaft could be a culprit?

 

[KliersLC]

Thanks for the suggestions.

Thanks for the suggestions and a reply.

1. flange bolts are good (read below)
2. did not separate the driveshaft, phasing is same as it was before
3. u-joints on the pinion flange end seemed fine. Not sure what I was testing for but there didn't seem to be binding. One thing to note is I greased the u-joints after reinstalling the new diff - maybe 5-6 pumps into each zerc. These have not been greased for quite some time, so I figured it was a good time to do it. Not sure if doing that could have caused an issue.
4. CVs are in properly on both ends. I tried wiggling them last night and they move about 1/8" in and out of the diff so they seem to be properly seated.
5. No lateral play, I can wiggle it a bit left to right but no up/down or lateral movement.

Based on a suggestion from a FB 100 series group member, I disconnected the driveshaft from the pinion flange and rotated it 180* last night.

The vibration/buzzing sensation subsided quite a bit. Still not completely gone, but definitely quieted down a bunch. Still feel it the most at the higher speed, going into 4th gear.

Does this suggest the front driveshaft could be a culprit?

It certainly seems like it. Based on that info, I'd try the following.

1. Did you grease the slip yolk? If so, verify that it will freely travel in both directions past the normal spot where it rides. Even better, remove the grease zerk and push some grease back out.
2. If moving 180 helped that much, it could be due to one of two things--either your manipulation of the driveshaft while moving it 180 alleviated some pressure (see above) or the orientation of the shaft to the pinion flange matters. (I don't see why it should, but there are many things that I don't know.) If the orientation does indeed matter, then maybe rotate it one position at a time till you find the sweet spot.

 

[digitalmarker]

It certainly seems like it. Based on that info, I'd try the following.

1. Did you grease the slip yolk? If so, verify that it will freely travel in both directions past the normal spot where it rides. Even better, remove the grease zerk and push some grease back out.
2. If moving 180 helped that much, it could be due to one of two things--either your manipulation of the driveshaft while moving it 180 alleviated some pressure (see above) or the orientation of the shaft to the pinion flange matters. (I don't see why it should, but there are many things that I don't know.) If the orientation does indeed matter, then maybe rotate it one position at a time till you find the sweet spot.

Thanks. Will give a shot tonight. Also confused as to why the rotation of the driveshaft by 180 (and not 90*?) made a difference. Will drive it around some more and see if there is improvement.

 

[KliersLC]

Thanks. Will give a shot tonight. Also confused as to why the rotation of the driveshaft by 180 (and not 90*?) made a difference. Will drive it around some more and see if there is improvement.

I personally don't think that the flange orientation has anything to do with it--as far as I know, the flange, pinion shaft, and pinion gear are all uniformly round and balanced. However, as stated above, there are many things that I do not know.

Side note: I misread your info on the pinion bearing---Are you saying that there is some "in/out" movement but nothing left/right and up down, or some rotational play?

Also, for the U joints, you just want to make sure that each joint can move freely through each axis of movement without any binding.

 

[digitalmarker]

I personally don't think that the flange orientation has anything to do with it--as far as I know, the flange, pinion shaft, and pinion gear are all uniformly round and balanced. However, as stated above, there are many things that I do not know.

Side note: I misread your info on the pinion bearing---Are you saying that there is some "in/out" movement but nothing left/right and up down, or some rotational play?

Also, for the U joints, you just want to make sure that each joint can move freely through each axis of movement without any binding.

No in-and-out movement. Just some movement left to right. But nothing that makes the flange feel wobbly or off-axis. Just normal left to right rotation.

I am going to drive the truck for a bit more - had a few short drives today and not feeling it at low speeds, but haven't been on the freeway or at high speed yet. Going to try to drive around a bit more and see if it persists. If it does will mess with u-joints again and potentially rotate the shaft 90*.

 

[digitalmarker]

Update on my issue. I took the truck on a long drive (300 miles) with the family, and felt a ton of vibration through the floor/pedal, as described in the original post. The worst of it comes as it's approaching 4th gear around 60mph, and then increases significantly after 70mph.

I pulled both drive shafts separately, and it seems the issue is coming from a rear drive shaft, which is less than 3 years old. The vibration is definitely there when I only had the rear drive shaft in place, and I did not feel it when driving in "front wheel drive" only mode.

I took the zerc out of the slip yoke and pushed out all of the extra grease, given that some folks said over-greased slip yokes can create vibrations because the driveshaft can't compress. With the grease pushed out, the amount of vibration has gone down quite a bit, but definitely still there. Specifically it happens as I the transmission is shifting up around 35mph, then goes away, then comes back as it shifts into 4th around 60mph, and then progressively gets worse around 70mph.

The vibration goes away entirely as soon as I take my foot off the gas.

What else could I check for before trying to replace the rear drive shaft? The u-joints seemed fine on both ends, the extra grease has been removed, the slip yoke seems to compress fine. The rear shaft itself is practically brand new, was installed by a shop a few years ago.

What's making this even more strange is that this issue started after the new front diff was installed, so not sure how/why it would affect the rear drive shaft.

What else could be causing this? Wheel bearings? Transfer case? Anything else?

 

[KliersLC]

Update on my issue. I took the truck on a long drive (300 miles) with the family, and felt a ton of vibration through the floor/pedal, as described in the original post. The worst of it comes as it's approaching 4th gear around 60mph, and then increases significantly after 70mph.

I pulled both drive shafts separately, and it seems the issue is coming from a rear drive shaft, which is less than 3 years old. The vibration is definitely there when I only had the rear drive shaft in place, and I did not feel it when driving in "front wheel drive" only mode.

I took the zerc out of the slip yoke and pushed out all of the extra grease, given that some folks said over-greased slip yokes can create vibrations because the driveshaft can't compress. With the grease pushed out, the amount of vibration has gone down quite a bit, but definitely still there. Specifically it happens as I the transmission is shifting up around 35mph, then goes away, then comes back as it shifts into 4th around 60mph, and then progressively gets worse around 70mph.

The vibration goes away entirely as soon as I take my foot off the gas.

What else could I check for before trying to replace the rear drive shaft? The u-joints seemed fine on both ends, the extra grease has been removed, the slip yoke seems to compress fine. The rear shaft itself is practically brand new, was installed by a shop a few years ago.

What's making this even more strange is that this issue started after the new front diff was installed, so not sure how/why it would affect the rear drive shaft.

What else could be causing this? Wheel bearings? Transfer case? Anything else?

Is there vibration with both shafts installed, AND the center diff locked? If not, I wonder if it is indeed a transfer case issue that only manifests when the CDL is unlocked. If there is still vibration, that definitely isolates the rear shaft, but like you said, that doesn't make sense. It could be a coincidence, however unlikely....

 

[digitalmarker]

Is there vibration with both shafts installed, AND the center diff locked? If not, I wonder if it is indeed a transfer case issue that only manifests when the CDL is unlocked. If there is still vibration, that definitely isolates the rear shaft, but like you said, that doesn't make sense. It could be a coincidence, however unlikely....

Is it safe to drive at high speed with the CDL locked? I have never had a need to lock it on this truck. If the vibrations go away with the CDL locked and both shafts in, that means the TC is the issue?

 

[KliersLC]

Yes, you can run it at speed. IIRC, the manual lists the top speed with CDL locked as 55, but the more I think about it, I think that might have been in the 80 series. Either way, I've run both an 80 and a 100 well in excess of 55. Do a couple tests activations at low speed if it will make you more comfortable--just limit your tight turns.

As far as what that means, it is tough to say--that would certainly make me look at the TC a little harder, but I wouldn't tear into the TC until I'd tested for vibrations with known good shafts. You checked the rear axle pinion bearing for play I assume? Unlikely culprit, but couldn't hurt to check.

 

[digitalmarker]

Yes, you can run it at speed. IIRC, the manual lists the top speed with CDL locked as 55, but the more I think about it, I think that might have been in the 80 series. Either way, I've run both an 80 and a 100 well in excess of 55. Do a couple tests activations at low speed if it will make you more comfortable--just limit your tight turns.

As far as what that means, it is tough to say--that would certainly make me look at the TC a little harder, but I wouldn't tear into the TC until I'd tested for vibrations with known good shafts. You checked the rear axle pinion bearing for play I assume? Unlikely culprit, but couldn't hurt to check.

There is side-to-side movement, but nothing lateral/off axis. The side to side movement is similar to the movement in the front, and similar to the amount of movement I have on my 80 series.