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Unread 03-02-2014, 04:31 PM   #1
lildoggy
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1995 ZJ 
 
Join Date: Feb 2014
Location: Ft. Lauderdale, FL
Posts: 9
Help me solve my vibration - '95 ZJ 4.0

I was just gifted a sweet 1995 Jeep Grand Cherokee 4.0 AT. Actually the jeep runs great except for this vibration problem I'm unable to solve.
It cranks every time and seems real smooth. But when I shift it into reverse or drive it starts a vibration that feels under the seat running to the rear . No codes are showing up. I have the FSM and a Haynes manual. I first thought it was the mounts and they seem alright.
I tackled a new TPS having to remove the throttle body since the torx were stripped, cleaned the throttle body, adjusted the cables. The drive shaft seems fine too. There's no play in the shaft. T fluid seems ok, looks good and level. There was a quart of T fluid in the back and the it is ATF-4 so assume....
The thing is, there's no vibration driving, only on initial shift out of park and neutral and when it idles at a stop. Before I changed the TPS it was cutting out at stops and now doesn't but has the vibration.
I haven't opened up the transmission yet but will soon to change the fluids and filter. I know there's that governor solenoid in there right? Bands? But the manual reads like that should show up as a problem shifting and it shifts ok.
The manual also says something about the brake rotors but don't want to go there yet if anybody has other ideas. It s idling around 500 - 600 rpms and it seems if I run it up to just above that with the throttle in idle the vibration goes away. That was what made me think not rotors. IAC? Its supposed to run in open loop without reading IAC if it hasn't reached operating temperature so I didn't think that was it. I'd liike for it to give me just a little more rpms while idling just to smooth the issue out but thats also a gulp of gas wasted but would be fine if it did. I know its a jeep and have had a few - thats why it was givin to me. I don't expect it not to rattle and roll but this vibration will loosen parts and teeth. Anybody have any direction for me? I've read and read but won't give up.

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Unread 03-02-2014, 08:15 PM   #2
papitt
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1995 ZJ 
 
Join Date: Dec 2008
Location: Stephenville Texas 76401, Texas
Posts: 709
.. Put it in neutral an re-look at your U-Joints ..
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Unread 03-03-2014, 02:43 AM   #3
lildoggy
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1995 ZJ 
 
Join Date: Feb 2014
Location: Ft. Lauderdale, FL
Posts: 9
I thought driveshaft too

Thanks papitt, I'll take a look at that again as soon as the sun comes up. Will report back. I did see that the rear u-joint had a grease fitting but not the front one. It does turn so slightly when putting it in gear. I laid under it while I had a friend shift through all of the positions. I couldn't wiggle it though. It seemed solid but will check closer. That was my first thought along with the differential and missing weights or something on the DS. Nice to be able to crawl under a vehicle w/o jacking it up each time. Makes some things easier anyway.
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Unread 03-03-2014, 02:44 AM   #4
lildoggy
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1995 ZJ 
 
Join Date: Feb 2014
Location: Ft. Lauderdale, FL
Posts: 9
and to be honest. I didn't stay under it for a long time thinking brakes and friend who might get clumsy and run me over.
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Unread 03-13-2014, 09:49 AM   #5
lildoggy
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1995 ZJ 
 
Join Date: Feb 2014
Location: Ft. Lauderdale, FL
Posts: 9
Motor Mount

Well, so far I tackled the u-joints. Had bought them and they were cheap. Although they seemed fine I changed them anyway since I don't know the maintenance history of this jeep. The vibration still is there. I cleaned the throttle body and the IAC. One of the things that lead me to that was reading the FSM. I thought that a cold start the IAC didn't matter. What I was seeing was no change in RPMs when I turned on the AC. As a matter of fact the RPM's never change except upon throttle in my jeep. Right at 600.
But, just the other day looking for vacumn, I had a friend throttle it a couple of times and though I never saw the engine move when I did it. With a flashlight, I watched the mounts while he put on the gas in drive. I finally saw the drivers side mount raise and lower as if there was no rubber at all.
I've now ordered the mounts from Rockauto (they were so much cheaper than in the store I saved more than half price). I hate throwing parts unless I can find the problem but I bet thats it. It needs them anyway.
Should be here friday (fast shipping by them too) and I'll put them on and post results. Other than the vibration, the jeep runs great and doesn't look bad for the age of it so I'll keep going.
BTW, I did read all the FAQ's and plan to especially tackle those 12 steps in them.
Reading about the mounts scared me a bit since I'd read about the bolts breaking. Upon inspection of them I did see that washers had been placed where the load on those bolts were so that was a relief and told me somebody had taken care of this jeep properly.
If anybody hasn't read about those bolts I'd research that since they have a tendency to break off in the block.
I'm only adding that in case some nooby like me searches for motor mounts or vibration and reads this. Of course, it may not be the problem so I'll post when finished.
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Unread 03-13-2014, 06:29 PM   #6
dusterdude
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1996 ZJ 
 
Join Date: Jan 2012
Location: hopewell, va
Posts: 2,041
Hose the bolts real good with pb blaster
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Unread 03-14-2014, 09:27 AM   #7
PolkaPower
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1998 ZJ 
 
Join Date: Aug 2011
Location: The Abyss, MD
Posts: 15,735
Good luck with the rock auto mounts. You might find yourself doing it again in a year or so. You should get the Mopar mounts or the Iron Man mounts. I would also advise doing the transmission mount as well because they all affect each other.
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Unread 03-17-2014, 04:23 AM   #8
lildoggy
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1995 ZJ 
 
Join Date: Feb 2014
Location: Ft. Lauderdale, FL
Posts: 9
Vibration solved for my ZJ

The vibration was finally fixed with the replacement of the motor mounts. I did replace all of them but it was definitely the driver's side mount that was causing the extreme vibration when I shifted out of park or neutral. That vibration was felt through my seat and did seem to vibrate mostly the rear end area.
After I replaced that mount, I could see that there was no rubber at all between the center rod and the outer area of the mount so the motor would twist along with the drive shaft as the jeep was put under load. It was a pita to change since I was by myself. I had a hard time getting the center bolt out since nothing was holding it. It came out all the way to the threaded ends and I had to get a small sledge hammer and a flat prybar to bang it out and there's not much room in there to work. Putting the new one in was a matter of constantly adjusting my floor jack to line up the hole just right to get that center bolt back in. Thats where a helper would have been handy since I could see the hole from underneath lying just behind the front left tire. My floor jack was holding although from the front where I had the jack handle I didn't have a good view of the mount.
Dusterdude, yea, that PB Blaster did a good job, thanks. That stuff is great.
Polkapower, the price was right with those mounts from Rockauto and since I'm budgeting, the jeep was free and and I don't know what other expenses I'll see with this jeep, I went for the price. I'll be more than willing to do the job again with a better quality mounts when I see the jeep is running fine.
I appreciate everybody's input and especially this site. I plan to be here alot.
I don't know if anybody here has used it but there is a product that restores and preserves rubber well. Its called AT-205 re-seal. I think it strengthens rubber and helps restore old bushings and things (but it will eat plastic) and I'll be spraying it on the rubber there to see if it gives the mounts a longer lifespan.
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Unread 03-17-2014, 07:46 AM   #9
Skydmark1
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1998 ZJ 
 
Join Date: Apr 2007
Location: Northern, New Hampshire
Posts: 438
I have the exact same issue in my ZJ that I just purchased with 282k miles on it. I was thinking motor mounts and tranny mounts. I was also going to order the rock auto ones so I'd be curious to hear what you thought about them and how difficult a job this was to do. Might be tackling it in a couple of weeks.
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Unread 03-17-2014, 07:53 PM   #10
papitt
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1995 ZJ 
 
Join Date: Dec 2008
Location: Stephenville Texas 76401, Texas
Posts: 709
Guys don't worry about buying a more expensive motor mount... When I had my parts house .. All motor mounts were actually made by only one MFG. Even when I went to work for Chrysler theirs were also mfg by the same people.. So I'm going out on a limb an saying .. Your Rock Auto mounts are going to be just as good as your going to get.
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Unread 03-19-2014, 05:37 AM   #11
lildoggy
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Location: Ft. Lauderdale, FL
Posts: 9
The mounts I got seem alot better than the ones I saw at the auto parts store here locally and the price difference was less than half of what they charged even with shipping. They arrived within 3 days. I thought the transmission mount was the one that was gonna be a pain to do but it was the driver's side for me but I was working without help. It would have been much easier if I'd had a friend there. It took me most of the day to replace all 3 mounts but i have never tackled these before and just finding the right sockets for the bolt heads was confusing. It took me using a 17mm socket which I hadn't expected and as suggested I did PB Blast all of them beforehand and let it sit overnight. I considered replacing those bolts but they seemed good so I reused them all. If you haven't read about using washers under the heads do it as they're just long enough to bottom out right at the head so that if you haven't got them in all the way I've heard the heads can break off from the weakness the load places on the bolt shafts - thank you sticky facts for that.
Anyway, the mount replacements made all the difference in the world as I was thinking the transmission might need adjustment or be shot. It runs nice and smooth now and feels strong.
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