Possible Input Shaft Bearing Issue

M

Mercury

TJ Enthusiast
Joined
Jul 18, 2018
Messages
227
Location
Louisville, KY, USA
Good morning, all.

I'm trying to diagnose a new sound (as if there weren't plenty of sounds already) coming from my 1999 Jeep Wrangler 4.0 TJ. A few days ago I started hearing this almost asynchronous grinding/whining sound when I have the vehicle in gear and giving it gas. It would occasionally chirp when held at constant speed, though I think that's from hitting small inclines where the load increases, though listening very carefully yesterday it almost seemed like I could very faintly hear it when not under load, but this could be in my head. The sounds cuts out when I'm decelerating and when the clutch is pressed in.

From my several hours of googling and searching it seems like it might be the input shaft bearing. I'm not seeing much in the way of write ups, which worries me. My questions, if anyone can help:
  1. Do I have to pull out the trans to change this? It seems like this might be a full tear-down situation, which is far, far outside of my budget at the moment.
  2. Is there any way to confirm it's the input shaft bearing and not something else? Could something else cause similar symptoms?
  3. How long can I drive it like this? I know any figures would be estimates, of course, but as I'm having to very very quickly move out of a bad situation I'm in and this being my only means of transportation for a while I'm sort of stuck without a vehicle if this goes down.
  4. If I do have to have the transmission pulled out, is there anything else I should have done while in there? If I have to go through the costs associated I don't want to pull this out again for a while.
I was in the process of trying to deal with a minor head gasket leak and really don't want another massive repair.

For reference:

4" lift kit, 33 x 12.5 tires
Ford 8.8 rear end
Driveshaft with low-mileage u-joints
 
Input shaft bearing noise is very common in the TJ and is normally only noticed with the vehicle in neutral and the clutch disengaged. My NV3550 has been making noise for years. I don't worry about it.
 
Last edited:
See if you can recreate the sound in 4Hi, Neutral (transfer case neutral), and in 4Low. If you can, it's likely transmission noise, and not transfer case noise.

First, check the fluid and fluid levels in the transmission and transfer case. Bad or low fluid will accelerate bearing wear. If you haven't changed it in a couple years, it may be worthwhile changing the fluid regardless.

The transmission uses a specific type of gear oil. Many on the forum will recommend Redline MT-90. Though it is more expensive than most, it is one of the best performing fluids on the market.

The transfer case uses generic ATF+4 automatic transmission fluid.
 
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CodaMan said:
Input shaft bearing noise is very common in the TJ and is normally only noticed with the vehicle in neutral and the clutch disengaged. My NV3550 has been making noise for years. I don't worry about it.
Click to expand...

Only thing is it's fairly loud. So far it doesn't seem like it's impacted driveability, just loud.
 
Steel City 06 said:
See if you can recreate the sound in 4Hi, Neutral (transfer case neutral), and in 4Low. If you can, it's likely transmission noise, and not transfer case noise.

First, check the fluid and fluid levels in the transmission and transfer case. Bad or low fluid will accelerate bearing wear. If you haven't changed it in a couple years, it may be worthwhile changing the fluid regardless.

The transmission uses a specific type of gear oil. Many on the forum will recommend Redline MT-90. Though it is more expensive than most, it is one of the best performing fluids on the market.

The transfer case uses generic ATF+4 automatic transmission fluid.
Click to expand...

Yeah, it's about time I do.

Shoot, I should have mentioned that the Jeep sat idle for over a year. Just changed out the oil, checked the fluids in the diffs (the rear end was about a quart low, the front end is foul and I think it's going at some point). I haven't checked the trans and diff, which should have been one of the first things.
 
CodaMan said:
Input shaft bearing noise is very common in the TJ and is normally only noticed with the vehicle in neutral and the clutch disengaged. My NV3550 has been making noise for years. I don't worry about it.
Click to expand...
Agreed! Mine is noisy until clutch engaged. Sounds just like regular old roller bearing noise.
 
brewtus98 said:
Agreed! Mine is noisy until clutch engaged. Sounds just like regular old roller bearing noise.
Click to expand...

I hope this is the case. Transmission/transfer case repairs are an expense I'd rather save for a while. I have to replace the head gasket already 🙄

Have to get some of my tools from storage and I'm going to drain and replace the tranny and trans case fluid. I'd love to get redline, but my budget is thin, and $80 to refill is out of my range. Is there a respectable alternative? I think I was using syncromesh before, but it's been a while.
 
Alright, ran some tests:

4wd high - noise present

trans case neutral - no noise

4wd low - noise present

When I let off the clutch in neutral and coast (while driving) it seems to occasionally chirp.

New issue: do you know the sound that an old baseball card in the spokes of a bicycle wheel sounds like? I have that now, seems happen in the exact same conditions, when the clutch is released, in gear, and under load. I can feel it in the gas pedal.

I can't check the transmission fluid because the nut seems to be overtightened and I need my break bar to get it loose.
 
Steel City 06 said:
See if you can recreate the sound in 4Hi, Neutral (transfer case neutral), and in 4Low. If you can, it's likely transmission noise, and not transfer case noise.

First, check the fluid and fluid levels in the transmission and transfer case. Bad or low fluid will accelerate bearing wear. If you haven't changed it in a couple years, it may be worthwhile changing the fluid regardless.

The transmission uses a specific type of gear oil. Many on the forum will recommend Redline MT-90. Though it is more expensive than most, it is one of the best performing fluids on the market.

The transfer case uses generic ATF+4 automatic transmission fluid.
Click to expand...

I checked the fluid levels in both the transmission and the transfer case and both were low and dingy oil. I'm a terrible Jeeper. I replaced it all (I couldn't afford the redline stuff, but I'm going to get it in two weeks. It *feels* like it's a bit smoother, but the whining is still there and the baseball card in the spokes thing is still there.

I know the oil in my front diff is pretty bad, I just haven't had a chance to fully drain and replace, but I'll do that tonight.

Any other possibilities?
 
Topped off the fluid in my transmission which was about a quart low, completely changed out the oil in my transfer case which looked low when I drained it. The squeal and the weird clinking have not improved.
 
Steel City 06 said:
I would look up a few videos of transfer case chain noise and see if that describes anything.
Here are a few I came across quickly:

Click to expand...

Thanks for those. That's not the sound, it is a loud clanking to the beat pattern of a stick hitting wheel spokes, increasing the faster I go.

I went to AutoZone and one of the guys came out and tried to help me figure it out. He said it look like it was when the rear drive shaft engaged the rear differential that it started the clank. he wasn't very sure, though, so it's still up in the air. But it does seem to come from around the rear driveshaft.
 
Mercury said:
Thanks for those. That's not the sound, it is a loud clanking to the beat pattern of a stick hitting wheel spokes, increasing the faster I go.

I went to AutoZone and one of the guys came out and tried to help me figure it out. He said it look like it was when the rear drive shaft engaged the rear differential that it started the clank. he wasn't very sure, though, so it's still up in the air. But it does seem to come from around the rear driveshaft.
Click to expand...
Take the rear driveshaft out and drive around in 4WD (essentially front wheel drive) and see if the noise goes away.

(Make sure you use the parking brake when disconnecting the driveshaft.)
 
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Mercury said:
Good morning, all.

I'm trying to diagnose a new sound (as if there weren't plenty of sounds already) coming from my 1999 Jeep Wrangler 4.0 TJ. A few days ago I started hearing this almost asynchronous grinding/whining sound when I have the vehicle in gear and giving it gas. It would occasionally chirp when held at constant speed, though I think that's from hitting small inclines where the load increases, though listening very carefully yesterday it almost seemed like I could very faintly hear it when not under load, but this could be in my head. The sounds cuts out when I'm decelerating and when the clutch is pressed in.

From my several hours of googling and searching it seems like it might be the input shaft bearing. I'm not seeing much in the way of write ups, which worries me. My questions, if anyone can help:
  1. Do I have to pull out the trans to change this? It seems like this might be a full tear-down situation, which is far, far outside of my budget at the moment.
  2. Is there any way to confirm it's the input shaft bearing and not something else? Could something else cause similar symptoms?
  3. How long can I drive it like this? I know any figures would be estimates, of course, but as I'm having to very very quickly move out of a bad situation I'm in and this being my only means of transportation for a while I'm sort of stuck without a vehicle if this goes down.
  4. If I do have to have the transmission pulled out, is there anything else I should have done while in there? If I have to go through the costs associated I don't want to pull this out again for a while.
I was in the process of trying to deal with a minor head gasket leak and really don't want another massive repair.

For reference:

4" lift kit, 33 x 12.5 tires
Ford 8.8 rear end
Driveshaft with low-mileage u-joints
Click to expand...
Has the engine, transmission ever been separated. I has a similar sound last fall, more than a year after a new engine was installed. My mechanic found a spacer thing missing between the two. Concensus was when the engine/transmission were separated the spacer stayed with the old engine and in reassembly the noise developed once something moved enough to generate the noise. Thankfully the shop lived up to their reputation and did the fix under warranty.

They only made the discovery by referring to the online schematic. They are worth every penny I pay them !!!
 
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Mercury said:
  1. Do I have to pull out the trans to change this? It seems like this might be a full tear-down situation, which is far, far outside of my budget at the moment.
  2. Is there any way to confirm it's the input shaft bearing and not something else? Could something else cause similar symptoms?
  3. How long can I drive it like this? I know any figures would be estimates, of course, but as I'm having to very very quickly move out of a bad situation I'm in and this being my only means of transportation for a while I'm sort of stuck without a vehicle if this goes down.
  4. If I do have to have the transmission pulled out, is there anything else I should have done while in there? If I have to go through the costs associated I don't want to pull this out again for a while.
Click to expand...
1 likely yes.
2 many choices, this is an online diagnosis. it would be a shooting starbto guess it right
3 in my case, likely forever
4 rear main seal ? clutch ? throw out bearing ?

but on a budget, just git 'er fixed
 
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Steel City 06 said:
Take the rear driveshaft out and drive around in 4WD (essentially front wheel drive) and see if the noise goes away.

(Make sure you use the parking brake when disconnecting the driveshaft.)
Click to expand...
I agree, you may be chasing two or more issues, with the card-in-the-spokes being a "new" issue (possibly U-joint). Disconnecting the rear DS eliminates two (or three) U-joints and the rear differential to narrow things down. Don't let the ends fall off of the U-joints while disconnecting...tape can be your friend for keeping them in place while they are unbolted.
Also, take a good look underneath just to make sure you didn't pick up a stick or some road debris that is literally acting like a card in the spokes/driveshaft.
If the click is a U-joint, do that ASAP so you don't run the risk of having it bind and break something expensive like your transfer case or the shaft itself.
If you have jack stands, you can also jack up both sides of the rear of the TJ and place it on the stands. Then put it in 1st gear in idle and lay down next to it to see what you can see/hear as things turn. DO NOT get under the vehicle in this configuration...I don't want to hear about the guy who ran himself over with his TJ! 🤨
 
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