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Unread 05-05-2013, 12:52 PM   #1
mpzj
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Pulsation in overdrive

97 Grand Cherokee, 4.0l.

When it drops down into the overdrive gears at high speed, there is a steady pulsating sound until I kick back into a passing gear.

Any Ideas? Ive already searched but didnt find anything helpful.

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Unread 05-05-2013, 01:43 PM   #2
JasonStebbins
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Could be the torque converter lock solenoid is fluctuating/not holding pressure or the torque converter itself. Have you done a torque converter stall test?

Look at your pulleys while idling, do any of them wobble?

Is your transmission fluid clean and at the proper level? Original transmission mount?

Could also be a wheel/tire defect or driveline imbalance, how are the U-joints?

Try cruising up to 50mph or so, then shift into neutral and let it coast down to see if you still feel vibration. If you do then it's probably not the torque converter since it's disengaged.
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Unread 05-06-2013, 02:43 PM   #3
ratmonkey
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do the rpms jump 200-300 in time with the pulsing?
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Unread 05-10-2013, 06:55 PM   #4
mpzj
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They do not jump. The pulsing goes away if i let off the gas.
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Unread 05-10-2013, 10:02 PM   #5
ratmonkey
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transmission output bearing.
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Unread 05-11-2013, 08:44 PM   #6
StellaTheZJ
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I've been chasing this for years!! Ratmonkey, how certain are you that it's the transmission output bearing? Is this something that a lot of people (except me and the OP ) just know about Jeeps? I took my ZJ to a local driveline shop I've dealt with a few times (getting driveshafts made) and they had no suggestions... is this thrumming something you personally have cured with a tranny output bearing?

I'm at the point with this that replacing likely culprits (motor and tranny mounts, u-joints, fluids, driveshafts, diff gears and bearings) has been tried to no avail, and I was about to try rebuilding the transfer case to eliminate the bearings in it (I've already changed the transfer case slip yoke bushing, and that made no appreciable difference). But I haven't replaced any bearings in the tranny, sounds like maybe it's time!
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Unread 05-12-2013, 06:01 AM   #7
ratmonkey
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It's the main diagnosis for that kind of problem in the factory service manual.
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Unread 05-12-2013, 10:13 AM   #8
StellaTheZJ
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Ratmonkey, thanks for passing this along. You are the first person in many threads who has suggested the tranny output bearing!
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Unread 05-12-2013, 11:31 AM   #9
ratmonkey
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It's not common, but is a source of noise/vibration in that situation.
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Unread 05-15-2013, 12:31 PM   #10
um7267
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i have the issue, but im almost positive that the transmission mount is the cause, i can see through the rubber. which leads me to believe the torque is making the front leak since the transmission is free to have some wiggle room, however ebay has them for around 25 so im ordering it today
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Unread 05-15-2013, 03:03 PM   #11
ratmonkey
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having a bad mount won't make anything about the transmission leak. it won't move relative to the motor or anything that would effect the front seals.
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Unread 05-15-2013, 03:20 PM   #12
KJK
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Your overdrive sun gear and/or planetaries could be highly worn. These only come under a load when the overdrive is engaged.
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Unread 05-15-2013, 03:44 PM   #13
tucsonzj
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interesting reading this. I get a harmonic pulse (0 rpm change) when in overdrive around 65mph. Haven't noticed it since I had the lift put on though.
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Unread 05-15-2013, 03:57 PM   #14
speedbucket
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i've had this same thing for 75k miles with no change in ti
wwwwwwwwwwwwwwwwwwooooooooooooooooooooooooooowwwww wwwwwwwwwwwwwwwwoooooooooooooooooowwwwwwwwwwwwwwww ooooooooooooooowwwwwwwwwwwwwwwwwwooooooooooooooooo ooowwwwwwwwwwwwwwwwooooooooooooooooowwwwwwwwwwwwww wwwww
sounds like that^ no rpm change no felling in the seat, i just figured it was harmonics of the drivetrain. it makes me sleepy
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Unread 05-15-2013, 04:01 PM   #15
tucsonzj
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Quote:
Originally Posted by speedbucket View Post
i've had this same thing for 75k miles with no change in ti
wwwwwwwwwwwwwwwwwwooooooooooooooooooooooooooowwwww wwwwwwwwwwwwwwwwoooooooooooooooooowwwwwwwwwwwwwwww ooooooooooooooowwwwwwwwwwwwwwwwwwooooooooooooooooo ooowwwwwwwwwwwwwwwwooooooooooooooooowwwwwwwwwwwwww wwwww
sounds like that^ no rpm change no felling in the seat, i just figured it was harmonics of the drivetrain. it makes me sleepy
Yup sad part is, the letters made my head repeat the sound. If there's any vibration from it, its drowned out from the speakers (nothing extreme). I assumed the same, its nothing. Not really wanting to have my od torn down and replaced parts for 0 reason.
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