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Unread 02-04-2008, 09:06 PM   #1
93GrandZJ
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What causes driveline vibration (idle) and a buck board ride?

My 93 4.0 has had a vibration at idle - either in park or in gear - for quite a while now. I changed the trans mount and it seemed to get worse, not better. I have not changed the motor mounts yet but I don't have any flex in the engine when I rev it, so I don't think they are bad.

What else would cause a vibration?

Also, it has 205K on it now and I am still riding on the original suspension, less the shocks which were changed 10K or so ago. It rides like a buckboard. I really did not notice it until I started driving our XK.

I want that smooth, stock Cadillac ride it used to have back. How can I do this and what are the components you recommend I change out? I think the rear springs are shot as it tends to list to the left rear corner (you can see it droop a little).

Thank you.

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Unread 02-04-2008, 09:23 PM   #2
driabyor
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there are alot of things rotating . you maybe able to narrow it down by listening various area of the engine.
Does it seem to idle normal. ... fuel filter, clean iac and throttle body....
is the a/c cycling, that will cause an engine to idle rough
you didn't mention which engine...
harmonic balancer could be bad..
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Unread 02-04-2008, 09:29 PM   #3
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flexplate-torque converter cracked or loose......
engine misfiring maybe . shorted sparkplug wire could cause it to idle poorly.
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Unread 02-04-2008, 09:36 PM   #4
CMARJEEP
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i dont think the 4.0L has a harmonic balancer which is what gives it its rough idle...
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Unread 02-04-2008, 09:40 PM   #5
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Quote:
Originally Posted by cmarjeep View Post
i dont think the 4.0L has a harmonic balancer which is what gives it its rough idle...
connor speaks the truth.
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It's threads like this that make me wonder why people lift there jeeps
its comments like this that make me wonder why some people are jerks.

build thread:http://www.jeepforum.com/forum/f197/...ndard-1056365/
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Unread 02-04-2008, 09:45 PM   #6
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if you contact kolak i think he can set you up with some new coils and shocks....
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Unread 02-04-2008, 09:58 PM   #7
driabyor
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ok vibration damper....
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Unread 02-04-2008, 11:29 PM   #8
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The I-6 is a very strong motor, but yes the I-6 motor tends to put out some excess vibrations at Idle and low RPM. Is is due to the Inline design. This is why those clever germans put a counterbalance shaft in their inline engines. First off bear in mind that the original design is 25 years+ old. Also keeping it simple keeps the production costs down. The 4.0 I-6 in the jeep does not have the counterbalance so it vibrates. -jgcfan


GO IN ANY JEEP THAT HAS THE SAME ENGINE AS YOURS. IT WILL MAKE THE SAME VIBRATION AS YOURS ( SOME A LITTLE MORE NOTICABLE AND VICE VERSA)


IM 3 FOR 3 ON THAT.

QUOTE ME.
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Unread 02-05-2008, 12:20 AM   #9
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Quote:
Originally Posted by cmarjeep View Post
i dont think the 4.0L has a harmonic balancer which is what gives it its rough idle...
Go to Wjjeeps.com/serpentine.htm
Under "4.0L Engine," the photo on the right clearly shows the harmonic balancer on the front of the crank.
I can't say, in 45 years or so of playing with engines I've ever seen an automotive engine without one.

At idle, my first guess would be a misfire, and its occurring right after mount was changed can be purely coincidental.

But where'd you get a GC with a "Cadillac ride"???
Yours would be the first!
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Unread 02-05-2008, 11:23 AM   #10
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It is your motor mounts I am pretty sure. The vibration in my '94 was driving me f'n insane. I could hear every damn plastic interior part creak and vibrate.

Anyways I tried to check the motor mounts in the same fashion as you did. I did not observe any engine rocking on the mounts when I gave it gas. I had them changed out anyways... Thing freakin' idles like new, I can barely feel any vibration at all now. Best satisfaction a repair has ever given me.

As for your harsh ride I know the answer to that because I started on that as soon as I fixed the mounts. The bushings in the control arms are all shot. Either replace them or buy new control arms with bushings already pressed in (sell for 35 each at discountjeepparts). Rubber bushings (just like what was on there stock) will be the softest but last the least. However, make sure you order rear upper control arms for a TJ not a ZJ when ordering on such sites as they have the rear uppers improperly cataloged for the ZJ's. Ask me how I know...

Then replace your stabilizer bar bushings on the front. What type of shocks did you get, perhaps they are toward the stiffer side. You can replace the rear coils by jacking up the rear and then jacking up the opposite side of the axle to cause it to flex and allow for you to pull out the spring on the other side.

Good luck!
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Unread 02-05-2008, 11:52 AM   #11
93GrandZJ
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Quote:
Originally Posted by driabyor View Post
Does it seem to idle normal.
yes

Quote:
fuel filter, clean iac and throttle body
yes

Quote:
is the a/c cycling, that will cause an engine to idle rough
no

Quote:
you didn't mention which engine
4.0
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Unread 02-05-2008, 11:59 AM   #12
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Quote:
The vibration in my '94 was driving me f'n insane. I could hear every damn plastic interior part creak and vibrate.
exactly

Quote:
Anyways I tried to check the motor mounts in the same fashion as you did. I did not observe any engine rocking on the mounts when I gave it gas. I had them changed out anyways... Thing freakin' idles like new, I can barely feel any vibration at all now. Best satisfaction a repair has ever given me.
will do - how long of a job is it? any one store better than the other for parts (eg. autozone over advanced)

Quote:
As for your harsh ride I know the answer to that because I started on that as soon as I fixed the mounts. The bushings in the control arms are all shot. Either replace them or buy new control arms with bushings already pressed in (sell for 35 each at discountjeepparts). Rubber bushings (just like what was on there stock) will be the softest but last the least. However, make sure you order rear upper control arms for a TJ not a ZJ when ordering on such sites as they have the rear uppers improperly cataloged for the ZJ's. Ask me how I know...

Then replace your stabilizer bar bushings on the front. You can replace the rear coils by jacking up the rear and then jacking up the opposite side of the axle to cause it to flex and allow for you to pull out the spring on the other side.
this is exactly what i was looking for - estimate how much to do this?

Quote:
What type of shocks did you get, perhaps they are toward the stiffer side.
The cheapest monroe's that were on sale - the "yellow" ones.

Quote:
Good luck!
Thank you very much. Sounds like this should get it back to riding smooth again.
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Unread 02-05-2008, 12:14 PM   #13
93GrandZJ
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Originally Posted by Redbob View Post
But where'd you get a GC with a "Cadillac ride"???
Yours would be the first!
ok, Cadillac ride for a Jeep. I remember the first day I drove it - very nice ride for a vehicle that size and style... would like it to ride like that again.
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Unread 02-05-2008, 12:18 PM   #14
93GrandZJ
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Quote:
Originally Posted by gomes512 View Post
buy new control arms with bushings already pressed in (sell for 35 each at discountjeepparts).
do you have a link? the ones i see are 200+
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Unread 02-05-2008, 12:24 PM   #15
driabyor
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pick something other than monroe... the ride is really harsh at first, this after a few months mush. like rocks side to side too much. They evidently are slow to respond. They aren't wore out. I can push down on a corner and it does bounce but one time. It' just not a great ride feeling when every car that goes by rocks you. When I'm stopped in a left turn lane ,waiting, the passing cars almost rock you to sleep...
I don't know what I going with next time but it won't be monroes'
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