42rle or 4.0L causing vibes on stock drivetrain? - JeepForum.com
 
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post #1 of 13 Old 08-06-2010, 10:13 AM Thread Starter
LJinNOLA
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42rle or 4.0L causing vibes on stock drivetrain?

I'm not so much looking for a cure (yet), but rather trying to determine if this is normal.

I have an 04 LJ and I get some slight vibes/hum when I'm in OD, at about 1600+/- rpm and 50 +/- mph.

I know that the 42rle and 3.73s (on 30x9.5) leaves something to be desired, but is the engine lugging causing these vibes or the transmission. I get it almost everyday driving up a long incline at 50mph, but if I turn off OD rpms jump, vibes go away.

Anyone else have this? Should I be concerned? and if yes, what to do?

I have no lift.


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post #2 of 13 Old 08-06-2010, 10:15 AM
jimkonow
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hmm....have you checked the mounts?

*edit*
motor and transmission mounts

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post #3 of 13 Old 08-06-2010, 10:15 AM
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Not a vibe, but merely the sound of the engine not being in it's power band and the stock t case skid is drumming the noise and making it louder. It's normal and I've had it since I bought my jeep then lifted it and nothing has happened.

I wouldn't worry about it.
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post #4 of 13 Old 08-06-2010, 10:25 AM
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Quote:
Originally Posted by LJinNOLA View Post
I know that the 42rle and 3.73s (on 30x9.5) leaves something to be desired, but is the engine lugging causing these vibes or the transmission.
its "supposed" to do that. bottom line is the 42RLE should have never been put behind a 4.0L. the engine is always out of the powerband, stock ratios are almost 1 whole point too high. 4.56s with 31s would be more reasonable with this tranny.

https://www.jeepforum.com/forum/f9/al...s-here-990762/


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post #5 of 13 Old 08-06-2010, 10:26 AM
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This has actually been researched. It was discovered that the stock t-case skid allows the frequency at that certain RPM range. It's not hurting anything but I bet that would be annoying.

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post #6 of 13 Old 08-06-2010, 10:27 AM
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I keep my OD turned off 90% of the time. Only use it at 60 mph +.
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post #7 of 13 Old 08-06-2010, 10:27 AM
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It is quite annoying
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post #8 of 13 Old 08-06-2010, 12:41 PM
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Yep, fairly normal and I had this when I was stock too. I now run 4.88's and 35s and wish I could go to 5.38's. I run with OD off all the time until I am cruising at least a constant 65+ mph

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post #9 of 13 Old 08-06-2010, 12:46 PM
Jerry Bransford
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Your engine is probably just lugging at such a low rpm. 1600 rpm is just too low of an engine rpm for a Jeep Wrangler at 50 mph.

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post #10 of 13 Old 08-06-2010, 12:49 PM
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Your engine is probably just lugging at such a low rpm. 1600 rpm is just too low of an engine rpm for a Jeep Wrangler at 50 mph.
or maybe the 42RLE shouldn't shift into OD at 38mph, and lockup in OD at 45mph...it should stay in 3rd until 53mph with 3.73s/30s.


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post #11 of 13 Old 08-06-2010, 12:58 PM
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Originally Posted by Unlimited04 View Post
or maybe the 42RLE shouldn't shift into OD at 38mph, and lockup in OD at 45mph...it should stay in 3rd until 53mph with 3.73s/30s.
Hah that too.

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post #12 of 13 Old 08-06-2010, 01:08 PM
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Quote:
Originally Posted by Imped View Post
This has actually been researched. It was discovered that the stock t-case skid allows the frequency at that certain RPM range. It's not hurting anything but I bet that would be annoying.
would that cause any problems of loosening bolts/nuts? I remember years ago a Detroit engine in a 379 Peterbilt would have a resident noise (i think that is what is called) that would shake off the alternator. folks had to go up to a 34 alt to get the fourth bracket. The frequency for that particular cubic space vibrated stuff to death?
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post #13 of 13 Old 08-06-2010, 02:41 PM Thread Starter
LJinNOLA
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Yeah it seemed fairly normal so I assumed others had it and I usually turn off the OD going up that incline, simply because I need the power and it DOES indeed get annoying. One of these days I'll probably go with some 4.88s and 33s so it will lug less then.

It does seem like it could easily be a frequency vibe from the t-case because it seems like the floor right under my feet is the strongest vibe.

I kept trying to hold out for a manual LJ, but my 04 was too good of a deal to pass up. I've lived with this for almost a year and a half, so I think I can keep living with it.

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