1992 Rear Driveshaft Vibration at Highway Speeds (1 Viewer)

[DesertCruiser80]

Hey MUD,

I just got back from a nice camping trip in the mountains and noticed a few things so I thought I'd pick your brains. 1992 FJ80, 3FE and A440F.

1st: Gear Whine in 1st
My cruiser has had this since day 1 when I got it 2 years ago. Basically it sounds like a high pitch whine that gets higher as rpm's go up, then go away in any other gear. It is present in 4-LO and 4-High so that to me indicates its in the tranny or in the high range side. Does anyone else have this whine? And does this mean the tranny has an issue?
Normal and common.

2nd: Vibration at highway speeds when at partial throttle
This one is...hard to describe. Basically, if I give enough gas to maintain speed, but not enough to noticeably accelerate, I feel a fast, thumpy vibration, through the floor and pedal. If I completely release the throttle, it goes away. If I give it enough gas to accelerate, it goes away. Speeds that I noticed it were around 60-75 mph. I recently did some mods that may be in play here: OME 2.5" lift, 4.56 diff gears, and slapped on 295/75/16 KO2's. Any clue as to why I'm getting the vibration?

Driveshaft is worn. Further discussion below.

3rd was my mistake: Over rev damage to 3FE?
I mis-shifted going up a hill, went into N instead of 3rd. Speed was about 60mph. Revs instantly went way up. Noticed within a second and shifted back into D. Drove another 50 miles at highway speeds without any indication of damage. Am I safe?
No damage.

And of course, THANK YOU! This trip wouldn't have been possible without the knowledge and support found here!

 

[APTFN]

Can't speak to the other two, but regarding #1, my 91 FJ80 whines in first gear as well. Not sure if that's normal either.

 

[Michael Hanson]

Hi, Sounds like the torque converter is starting to go. Mike

 

[jonheld]

1. Whine in 1st gear. My 91 FJ80 had this since I drove it off the dealer's lot in 1991. Your transmission is fine. Do regular passive drain/refills once in a while.

2. Driveline buzz when coasting at highway speeds is a sign of worn slip yolks on one of the drive shafts. There should be ZERO rotational play between the 2 halves.

3. Over revving on a 3FE will have no effects unless you're above red line for an extended period of time, and even then, probably nothing will happen. Of course, I'm assuming you have motor oil in the engine.

 

[DesertCruiser80]

So I got around to checking the driveline buzz and confirmed the rear shaft slip yoke had rotational play. Enough to hear nice metallic ping sound when I spun the halves against each other. Having a shop take a look at the shaft soon. Front driveshaft slip yoke was nice and tight, no play.

As a side note, I did notice that I could spin the shafts, and therefore the pinions, a good amount. Maybe 40-50 degrees? (Hard to estimate, I can take a video if needed). I was reading previous threads about this, but couldn't find a definitive answer. I did understand that the motion is the sum of all slop in the axle and that some slop is normal. I also understand that it is not the diff backlash since this is normally thousandths of an inch. Note, both front and rear pinions had similar amounts of play.

I guess my question is how much play is normal/expected here? I want to make sure that the diff rebuilds and installs were done properly.

 

[DesertCruiser80]

Had a shop look at the driveshaft today and they said they would replace the u-joints, clean out the slip yoke splines, and regrease everything; that would solve 95% of it. They also said the slip yoke play was the result of infrequent greasing and that it should have minimal play.


What is the usual remedy for this issue? Would cleaning and regreasing the slip yoke fix this vibration issue?

 

[DesertCruiser80]

I took off the rear shaft to service it and thought to take a drive to confirm the problem was isolated to the rear shaft. I know you can drive with one shaft by locking the center diff. However, I made some mistakes in the process. I turned the cruiser on, threw it into R, then tried to lock the diff. I heard the awful noise of gears grinding. Unselected the center diff lock button, then tried to place it back into P and heard more gears grind. Threw it into N, turned it off, locked the center diff, then turned it back on. Drove like a charm and no vibration which confirms the issue is in the rear. How badly did I damage the T-case and tranny? I know it takes a special kind of person to grind gears in an automatic...

 

[jonheld]

I took off the rear shaft to service it and thought to take a drive to confirm the problem was isolated to the rear shaft. I know you can drive with one shaft by locking the center diff. However, I made some mistakes in the process. I turned the cruiser on, threw it into R, then tried to lock the diff. I heard the awful noise of gears grinding. Unselected the center diff lock button, then tried to place it back into P and heard more gears grind. Threw it into N, turned it off, locked the center diff, then turned it back on. Drove like a charm and no vibration which confirms the issue is in the rear. How badly did I damage the T-case and tranny? I know it takes a special kind of person to grind gears in an automatic...

The transfer case gears are not made of eggshells and dove feathers. You did no damage.

 

[DesertCruiser80]

Copy that, Jon! Now I know, lock before starting engine.

 

[jonheld]

Copy that, Jon! Now I know, lock before starting engine.

As long as you start with the transmission in park, there will be no spinny bits, even with the engine running.
You shifted the transmission into gear which set everything in motion in the transmission and transfer case. You tried to lock the center diff and because the rear driveshaft was removed, the rear output shaft of the transfer case was spinning. The grinding was the locking collar for the center diff trying to catch the teeth.

When you went to put it in park, the transmission and transfer were in motion and the grinding was the parking pawl of the transmission trying to grab.

In both cases, there was no real "load" on the system, just the inertia of the spinning bits and you backed off when you heard the sounds. I agree that it is an uncomfortable sound, but the possibility of damage is negligible. If you have ever seen the inside of your transfer case, you'd understand.

 

[DesertCruiser80]

As long as you start with the transmission in park, there will be no spinny bits, even with the engine running.
You shifted the transmission into gear which set everything in motion in the transmission and transfer case. You tried to lock the center diff and because the rear driveshaft was removed, the rear output shaft of the transfer case was spinning. The grinding was the locking collar for the center diff trying to catch the teeth.

When you went to put it in park, the transmission and transfer were in motion and the grinding was the parking pawl of the transmission trying to grab.

In both cases, there was no real "load" on the system, just the inertia of the spinning bits and you backed off when you heard the sounds. I agree that it is an uncomfortable sound, but the possibility of damage is negligible. If you have ever seen the inside of your transfer case, you'd understand.

I have, I was watching OTRAAM's Terrain Tamer Gear Install video last night afterwards trying to see where the hell it was grinding. I understand (for the most part) how the T-case works. Is the locking collar what "selects" a gear? And if that collar and the teeth it meshes with are roasted, then that t-case essentially can't stay in gear, correct?

 

[jonheld]

I have, I was watching OTRAAM's Terrain Tamer Gear Install video last night afterwards trying to see where the hell it was grinding. I understand (for the most part) how the T-case works. Is the locking collar what "selects" a gear? And if that collar and the teeth it meshes with are roasted, then that t-case essentially can't stay in gear, correct?

First of all, I am by no means a seasoned transfer case person. I've assisted in a tear down of a grand total of 1 for a rebuild. However I can say with certainty that watching a video and actually holding these parts in your hands are 2 VERY different things.

The locking collar is called a "clutch sleeve". There are 2 of them. One for high/low and one for locking the center diff. They each get moved by shift forks. The one for the CDL gets moved by a shift fork that is moved by the center diff actuator.
It engages and locks the front output shaft to the center diff so both output shafts turn together. It is a sliding hardened steel ring that engages with the base teeth of another gear.

It would take a significant amount of force to damage these parts. The fact that your truck moves under its own power and with no additional noises tells you that you're most likely OK.

 

[BILT4ME]

If you heard and felt a LOUD BANG
PING!
Crunch, crunch, grind, crunch, grind........

Then I'd say you have a problem.

If all you heard was GRRRRTTTT! GRRRRTTTT!

Then I'm guessing you're OK.

It was the sleeve trying to engage moving gears and bouncing off the tips of the teeth as well as the parking pawl trying to engage a freewheeling shaft.

They are designed to take a few hits like that, but not engage.

If you are really concerned, drain your T-Case and refill. If the oil is glittery like Barbie, then maybe. If there are chunks, then you have damage.

 

[DesertCruiser80]

GRRRRTTTT! GRRRRTTTT!

Love the onamonapia! @BILT4ME . Yes is was only "GRRRT GRRRRT".

I also found another video of a guy showing a gear set from a Civic that had been grinding so much the base teeth were rounded and wouldn't allow the gear to be engaged. All this to say I have a decent understanding of where the grinding happened.

And thanks for the info both you and @jonheld . I'll take a look at the oil, I have a few quarts of gear oil lying around...

 

[DesertCruiser80]

Changed and inspected the t-case oil. Clean and glitter free. Barbie would be disappointed. The drain plug magnet was unremarkable, oil in pan was clean to the eye. Did some swipes with my finger to see if I could catch anything. Even with a flashlight, nothing I could see. I wiped the last bit of oil after pouring the pan into a holding container and managed to get some debris. (See pic). The drain pan wasn't spotless before this so some of that might just be old crud. I think we're clear, no?

Now back to the driveshaft...

 

[BILT4ME]

Changed and inspected the t-case oil. Clean and glitter free. Barbie would be disappointed. The drain plug magnet was unremarkable, oil in pan was clean to the eye. Did some swipes with my finger to see if I could catch anything. Even with a flashlight, nothing I could see. I wiped the last bit of oil after pouring the pan into a holding container and managed to get some debris. (See pic). The drain pan wasn't spotless before this so some of that might just be old crud. I think we're clear, no?

View attachment 2654252

Now back to the driveshaft...

Looks good, no worries.