Drivetrain Rattle in 4th & 5th - JeepForum.com
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post #1 of 50 Old 09-03-2017, 06:24 PM Thread Starter
Louie4
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Drivetrain Rattle in 4th & 5th

As the title says, I'm hearing a rattling type noise when cruising in 4th gear at 40 mph and in 5th when cruising a little over that. I also hear it more when I downshift into those gears. It sounds like it's coming form the t-case or the AX-15. I'm not sure though which nor know of any sure fire diagnostics short of taking those components out. Here's some things I do know:

-Front driveshaft rebuilt
-Rear driveshaft rebuilt
-NP231 has a AA SYE not installed by me, but a buddy. Came out of a '95 YJ.
-AX-15 has well over 320k miles so who knows.

I wish I had a better description of the noise. It's to the point where I feel if I let it go there will be a failure, possibly catastrophic.

Some methods of diagnosis I had was:

Remove front driveshaft and drive it similarly
Remove rear driveshaft and drive it similarly

I also put the t-case in neutral and put the AX-15 in 4th and 5th and listened. I have no idea if that's a good idea or not. But I thought I heard the faintest sound of what I was hearing.

Any thoughts or idea?


Lou

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post #2 of 50 Old 09-05-2017, 06:51 AM Thread Starter
Louie4
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Another idea that is probably less safe is to put the rear axle on jackstands and put the transmission in 4th and 5th. Maybe some load on it will present the problem.

Lou

I have a jeep...and it is modified...I win.

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post #3 of 50 Old 09-05-2017, 09:55 AM
gotswap
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Tcase chain loose and slapping around maybe?
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post #4 of 50 Old 09-06-2017, 09:02 AM
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When "cruising in 4th or 5th", does changing the throttle make the noise change? What I mean is, does accelerating lessen the noise? Does decelerating change the noise?

Those actions would change the tension on the TC chain. If it rattles the same when climbing a hill as it does when coasting, probably not the chain. But it would be not too be a job to pull the rear case half and inspect the chain for slop and the case for sign of rubbing.

Does slightly riding the clutch change anything? Like TO bearing type stuff?
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post #5 of 50 Old 09-06-2017, 09:53 AM
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can you descirbe it better? is it a resonance rattle? a metall on metal rattle? drivehaft hitting a muffler rattle?

to my knowledge. bearing issues related to the trans input/output shafts will show up as vibes. loose chains show up like a knock or a valve tap (loud).

First thing I would start doing is getting my baseline for diagnosing. Is it speed related or rpm related? If speed, does changing rpms reduce or increase the noise? or no change? Does it still happen if turn the engine off and leave in gear? Does the pitch change allowing you to listen for the location of the noise while coasting and engine off?

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post #6 of 50 Old 09-06-2017, 10:45 AM
mike134
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How old are the engine and transmission mount bushings? It might just be vibration making its way to another component unrelated to drivetrain.
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post #7 of 50 Old 09-06-2017, 06:28 PM Thread Starter
Louie4
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Quote:
Originally Posted by gotswap View Post
Tcase chain loose and slapping around maybe?
Potentially. I think removing the front driveshaft and driving around will help tell.

Quote:
Originally Posted by bpounds View Post
When "cruising in 4th or 5th", does changing the throttle make the noise change? What I mean is, does accelerating lessen the noise? Does decelerating change the noise?

Those actions would change the tension on the TC chain. If it rattles the same when climbing a hill as it does when coasting, probably not the chain. But it would be not too be a job to pull the rear case half and inspect the chain for slop and the case for sign of rubbing.

Does slightly riding the clutch change anything? Like TO bearing type stuff?
So...the noise goes away (as best I can tell) when accelerating under load. It's most noticeable when letting off the gas and coasting in 4th. Not as bad in 5th. I have a locker in the front D30 which causes the front driveshaft to spin which leads to the t-case chain spinning.

Quote:
Originally Posted by cKruzer View Post
can you descirbe it better? is it a resonance rattle? a metall on metal rattle? drivehaft hitting a muffler rattle?

to my knowledge. bearing issues related to the trans input/output shafts will show up as vibes. loose chains show up like a knock or a valve tap (loud).

First thing I would start doing is getting my baseline for diagnosing. Is it speed related or rpm related? If speed, does changing rpms reduce or increase the noise? or no change? Does it still happen if turn the engine off and leave in gear? Does the pitch change allowing you to listen for the location of the noise while coasting and engine off?
It's speed related. 40 mph is where it's most noticeable...coasting in gear. I haven't tried killing the engine and listening yet. The noise is like a tap almost but internal. I'm leaning towards the t-case.

Quote:
Originally Posted by mike134 View Post
How old are the engine and transmission mount bushings? It might just be vibration making its way to another component unrelated to drivetrain.
Engine mounts are Brown Dog, the trans mount is an aftermarket poly performance. I plan to get a new skid and change the trans mount back to stock. I don't think those are the culprits though.

My first instinct was the t-case. But I know it's not as old as my transmission...but I can't imagine a transmission making the noise I'm hearing. I would assume the transmission would eventually grind and squeal and have trouble shifting.

I will say, I do have some dark ATF on the seam of the t-case but when I pull the fill plug, ATF comes out. SO I know it's not low on fluid.

Next step is removing the front shaft.

Lou

I have a jeep...and it is modified...I win.

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post #8 of 50 Old 09-06-2017, 07:40 PM
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Can you hold your phone down below the rockers while driving and record the sound?

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post #9 of 50 Old 09-08-2017, 04:37 AM Thread Starter
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Quote:
Originally Posted by cKruzer
Can you hold your phone down below the rockers while driving and record the sound?
No.

Between the wind and tire noise...It would be a wash and with my luck I would drop my phone and drive over it.

Instead I unbolted the axle side of the front driveshaft and zip tied it to the frame. That doesn't sound good after typing it out but it's temporary. I wrapped the u-joint caps with duct tape. We'll see if the noise goes away.

Lou

I have a jeep...and it is modified...I win.

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post #10 of 50 Old 09-08-2017, 06:19 AM Thread Starter
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Well, drove to work and it didn't make a lot of change in the noise. It's almost like a roaring noise at times. So, the front driveshaft isn't spinning which to me eliminates the chain. It also makes me think it's a bearing of some sorts.

At this point, maybe I should pull the cover off the t-case?

Lou

I have a jeep...and it is modified...I win.

YJOTM July 2012
YJOTM February 2014


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post #11 of 50 Old 09-09-2017, 09:59 AM Thread Starter
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I drained the t-case. The fluid was dark but not burnt. I think I changed it a year or so ago so I may investigate it further.

At this point I can take the back half off the t-case or pull the whole thing. I'm leaning more towards the t-case because I have no issues shifting gears and no grinding from the AX-15.

Lou

I have a jeep...and it is modified...I win.

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post #12 of 50 Old 09-09-2017, 12:12 PM
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I would say that you might as well pull the t-case and work it on a bench Louie. Another reason to drop it is if you find out its not in the tc and you deside to tear into the trany I find it easer to drop the trany with the tc off already.

Jim...

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post #13 of 50 Old 09-09-2017, 01:01 PM Thread Starter
Louie4
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I would say that you might as well pull the t-case and work it on a bench Louie. Another reason to drop it is if you find out its not in the tc and you deside to tear into the trany I find it easer to drop the trany with the tc off already.
Point taken. I will unbolt the shifter and driveshafts and drop it like it's hot.
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post #14 of 50 Old 09-09-2017, 05:06 PM
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I feel your pain. I have to drop my tc Sunday as well to check for a slipping chain. Its like number six on my list of things to do tomorrow.

Jim...

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post #15 of 50 Old 09-09-2017, 06:32 PM Thread Starter
Louie4
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I hear ya. Mine is whenever I can spare some time. I have to put in spurts of time in between work and family time.
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Lou

I have a jeep...and it is modified...I win.

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