tcase chain rubbing or tranny noise?

- '91 XJ
- 4.0 HO
- AX15 MT
- NP231 TCase
- 235k miles

Ok ... yesterday I noticed a noise ... sounds exactly like a chain rubbing. I'm at a stop light, manual AX15 in neutral, and I let out the clutch ... noise is there. Push in the clutch ... noise is gone. Let out the clutch ... noise is there again. Coming from the area of tranny/tcase.

Seems to me like the tcase chain shouldn't be moving when the tranny is in neutral, right? Tcase is still in 2H.

Anything else It could be? Tranny bearings?

Thanks.

i know you can open up the drain hole on the t-case, stick your finger in there and feel the chain. check if its loose.

So you are doing this with the tranny in neutral? If so, your problem is the throw out bearing.

old_man said:

So you are doing this with the tranny in neutral? If so, your problem is the throw out bearing.

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When I push the clutch in (engaging the throwout bearing) the noise goes away ...

If the transmission is in neutral, nothing in the transfer case is moving.

When the clutch is engaged, the throwout bearing "floats". If it's starting to fail, it may be rattling. When you disengage the clutch, the bearing bits lose all of their freedom of motion.

ChiXJeff said:

If the transmission is in neutral, nothing in the transfer case is moving.

Click to expand...

Yeah ... that's what I was thinking too ... if it didn't sound so much like a chain, wouldn't have even asked that.

ChiXJeff said:

When the clutch is engaged, the throwout bearing "floats". If it's starting to fail, it may be rattling. When you disengage the clutch, the bearing bits lose all of their freedom of motion.

Click to expand...

So ... you're saying when the clutch is engaged, the throwout bearing is still pressed up against the spring splines of the pressure plate? But not enough to disengage the clutch? That would be great if it's just the throwout ... I was planning to do a clutch job anyway. A much easier fix than rebuilding the trans.

Thanks for the help, and keep them coming.

No. When the clutch is engaged, the throwout bearing should not be touching the fingers, hence "free play." The components of the throwout bearing are not compressed together, if there's significant wear, they can rattle against each other.

Ok ... so you're saying the throwout bearing can rattle when not engaged, but get quiet when engaged? I see how that could work ... but I don't know ... I replaced the entire clutch kit only about 45k miles ago. And the noise doesn't sound like loose rattling ... sounds like a steady, driven kind of garble. Maybe the input shaft bearing on the tranny? That has 235k miles on it.

I'm planning to pull the tranny anyway ... so I guess I'll just have to examine everything. I was planning to throw in a new clutch kit while it's all out. I'm also swapping out the plastic clutch hydraulic line with the "quick disconnect" for a metal line with a threaded union.

I sure do hope it's just the throwout.