60 Vibration under load

[Boulder Cruiser]

Alright so I’ve done some searching and found some info but I have a pretty unique situation and wondering if you guys can help me figure this out. It’s kind of driving me crazy.

85 fj60 Cummins R2.8 H55F and split T-case.
I have a bad vibration starting at the top of 3rd gear, when I put it in 4th the vibration gets 10x worse and shakes the whole truck. I can feel it in the seat, pedal, wheel, mirrors shake, etc. 5th is the same. If I stay out of boost it’s fine.
It’s a strong rotational vibration. If I floor it through 4th and 5th the vibration is not as bad. Driving uphill it gets really bad. Coasting it goes away.
I pulled the rear driveshaft assuming I needed Ujoints. NO change. Ujoints have about 4k miles, along with a balance. The T-case was removed and inspected around the same time.
No play anywhere that I can feel. I put the truck on the 2 post put it in 4th and ran it. At a certain RPM (22-2300) I hear a nasty grinding noise, it comes and goes, then stays for awhile even while coasting and sounds slightly worse actually during decel. I have a video but don’t know how to post it.

So now I’m thinking rear output bearing BUT wouldn’t it have changed or gone away with the driveshaft out? I drained the gear oil and nothing but a little fine material on the magnet, the oil is shimmery but no larger pieces.

Any help or ideas would be much appreciated! I’m kinda stumped and don’t want to just throw money at it.

 

[Boulder Cruiser]

I am officially a YouTuber….video of noise…

 

[IoN6]

Hard to tell in the video, especially since the suspension is unloaded. But it looks like the axle end is pretty much straight but the tcase end has a decent angle to it. Non-CV shafts, the axle/tcase flanges should both be parallel. CV shaft, the non-CV end of the driveline should be straight.

I would stop driving it until you get it sorted. Driveline vibes are super hard on pretty much every component.

 

[IoN6]

Good video on what happens when the angles are not in phase (as I would call it).

 

[Boulder Cruiser]

The truck has a 2.5 OME lift. Pinion angles look good to me when the truck is on the ground. Also, no change with the rear driveshaft out.

 

[FunkyYota]

Any Slop in the slip?

 

[Boulder Cruiser]

I’ll check today.

 

[SteveH]

Pinion nut tight on rear diff? - that haunts more than a few on this forum.

 

[Boulder Cruiser]

I saw a couple of threads about that. I was hoping it would be that. Am I wrong in assuming it’s not that since there’s no change with DS out? I had ruled it out, there’s also no play there.
Seems like no one is worried about the noise coming from the T-case. If I had to put a sound to what I’m feeling it would be that.

Would preload or a bad output bearing cause these symptoms with the DS out? I’ll hopefully be putting a new output bearing in today since it’s cheap and easy.

Pinion nut tight on rear diff? - that haunts more than a few on this forum.

 

[IoN6]

The truck has a 2.5 OME lift. Pinion angles look good to me when the truck is on the ground. Also, no change with the rear driveshaft out.

The flange on the pinion looks to point directly at the tcase. But it could just be the angle of the dangle.

Am I wrong in assuming it’s not that since there’s no change with DS out?

IMO, it would still make the noise. Maybe just not as bad. Since the pinion is turning with the wheels. Unless you dropped the DS with it on the lift...

 

[Cruisertrash]

Engine or transmission mounts? That might cause some internal torquing between the two and make nasty scraping sounds as parts get off center from one another. I had that experience (with just a little shaking) at the driver's front motor mount on my 2F. Separately, I also had vibes after my OME install and it turned put to be an out-of-phase rear drive shaft - easy to overlook (thanks PO!).

 

[powderpig]

This is terrible way to test the drivetrain. Put some 12k lb jack stand under both the front and rear axles and do the same test.
With the drive line way out of it proper driving angles, you will not be able to tell what really is happening.
With the axles supported , you are then in at least the same angles you would be going down the road. Then one can also lay(done this many
times, with the 12k jack stands) under the cruiser with a stethoscope, and listen to the t-case to pinpoint where the noises are.
I would guess some of those noises will go away with the axle supported.
If the t-case is making the same noises with the axles supported, then YES, I would suspect something inside the case.

Or find a shop with a set of Chasis Ears to attach all around the t-case/ tranny, With two people, drive the cruiser, Make the noise, and the person listening can listen to different parts of the t-case/tranny combo and pin point the noise.

On the lift like you have it is far more deadly than putting them on heavy duty jack stands.

 

[nakman]

Did you actually drive around without the rear driveshaft? Or just pull them to inspect the joints and reinstall? Have you driven in FWD to confirm the noise is still there?

 

[Boulder Cruiser]

This is terrible way to test the drivetrain. Put some 12k lb jack stand under both the front and rear axles and do the same test.
With the drive line way out of it proper driving angles, you will not be able to tell what really is happening.
With the axles supported , you are then in at least the same angles you would be going down the road. Then one can also lay(done this many
times, with the 12k jack stands) under the cruiser with a stethoscope, and listen to the t-case to pinpoint where the noises are.
I would guess some of those noises will go away with the axle supported.
If the t-case is making the same noises with the axles supported, then YES, I would suspect something inside the case.

Or find a shop with a set of Chasis Ears to attach all around the t-case/ tranny, With two people, drive the cruiser, Make the noise, and the person listening can listen to different parts of the t-case/tranny combo and pin point the noise.

On the lift like you have it is far more deadly than putting them on heavy duty jack stands.

Sounds good, I’ll do that and report back.

 

[Boulder Cruiser]

Did you actually drive around without the rear driveshaft? Or just pull them to inspect the joints and reinstall? Have you driven in FWD to confirm the noise is still there?

I drove around in 4wd with the rear DS out. No change in vibration.
As far as the noise I don’t don’t if it’s there without the DS I didn’t hear the noise until yesterday when I put it on the lift. I pulled the DS a couple weeks ago then reinstalled.

 

[Boulder Cruiser]

Engine or transmission mounts? That might cause some internal torquing between the two and make nasty scraping sounds as parts get off center from one another. I had that experience (with just a little shaking) at the driver's front motor mount on my 2F. Separately, I also had vibes after my OME install and it turned put to be an out-of-phase rear drive shaft - easy to overlook (thanks PO!).

The swap was done 4k miles ago so it’s all new. The motor mounts and tranny mounts look good I don’t see any abnormal movement, cracked bushings or anything.

 

[rckhound]

I am wondering if your flywheel is loose?

 

[ccslider]

I know you took the rear shaft out and it didn't change vibs but I think you're supposed to have the slip joint at the tcase not the diff.

 

[Boulder Cruiser]

Alright finally had time to mess around with it today. I put it on jack stands and could not replicate the noise. I did hear some chatter but I don’t think it was anything bad. I did end up replacing the output shaft bearing since I had already bought it. (Turned out to be a pain getting the old one off). It’s done now, everything is tight and preloads are to within spec. Also checked the rear pinion nut and it’s also within spec.

NO change in vibration.

@rckhound i had thought this originally I pulled the flywheel cover off and ran and it appears fine. Anyway other way to check that beside pulling the trans?

@ccslider I changed the orientation today

 

[rover67]

how far are you from sugarloaf? i'd put an ear on it for ya.