weird driveline vibration!

Joined
Sep 7, 2022
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2
Location
nashville, TN
Hey yall, first time poster here.

I have a 93 fzj and i love it very much. Been baselining things since I got it back in March of this year.
The odometer stopped working a month after buying it at 168,xxx. Pretty nice, decently low miles example.

It has the common 2.5 OME suspension setup with coils and shocks. running stock LX450 16' wheels with 315/75 Nittos.

I noticed a driveline vibration a few weeks after getting it, but its weird because its only under throttle. if i let off the throttle and coast, it goes away. As soon as Im back on the
gas, it vibrates again. It happens between 30 mph and about 70mph. had a bad clink from a busted u joint in the rear so i replaced both rear u joints and its still there. I havent replaced the front u joints yet and thats next on the list. Its not engine related because it doesnt coincide with rpm's. Could it be slip yokes or an unbalanced drive shaft?

any help is appreciated!
 

desmocruiser

SILVER Star
Joined
Dec 17, 2005
Messages
1,620
Location
Big Orange Country, TN
Welcome!

Addressing the front DS would be next, I have had to balance one in the past along with new U Joints to smooth it out.

As you probably already have read 80’s have common driveline vibration if the caster hasn’t been addressed correctly after the lift and even sometimes after a few years if corrected with bushings, it seems there is some settling with age that takes them back out of spec. This typically happens when you lift the throttle, but every 80 seems a little different in the symptoms they exhibit.

If the DS service doesn’t resolve it, have an alignment performed to determine current caster. If it isn’t in spec, pursue new bushings or most preferred caster plates or if willing to spend extra money a set of arms from delta vs etc.

I mention this with the assumption bearing pre load in the front and condition of bearings front and rear have been properly addressed as a part of initial baselining? If all is good there and these steps don’t remedy beyond it can get into differentials, trans, and transfer case issues.

Good luck finding and resolving quickly, search on this forum will usually reveal your aren’t the first with the issue.

Enjoy, the 80 series journey it is worth it!
 
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Joined
Apr 14, 2016
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2,364
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Oregon
Lock the transfer case and pull the front driveshaft to verify that it's the cause of the vibration (it probably is).

Some people get lucky with the 2.5" lift, some don't. The broken-back arrangement of the front driveshaft is really uncommon and you have a balancing act between caster and smooth driveshaft operation.

A digital angle finder is a good thing to have to keep track of how your driveshaft angles are changing with modifications.
 
Joined
Jan 12, 2016
Messages
261
Location
Australia
rear DS slip joint - separate & clean out old grease and re grease.
I had what sounds exactly what youre describing and it was old hardened grease in the slip joint. after cleaning it and regreasing with Moly Gr its been perfect ever since

also, make sure the rear DS is in phase etc - lots of info on these as the front is 90deg out of phase and rear in phase
 
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Joined
Aug 13, 2015
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749
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SF Bay Area, CA
I feel like I'm always chasing driveline vibrations..

Agree with an earlier post, lock the TC and pull the front shaft and see if its still there. If so, put the front DS back in and remove the rear DS and see if it goes away then.

Next I would check for loose bearings on front and rear.
 
Joined
Sep 7, 2022
Messages
2
Location
nashville, TN
I feel like I'm always chasing driveline vibrations..

Agree with an earlier post, lock the TC and pull the front shaft and see if its still there. If so, put the front DS back in and remove the rear DS and see if it goes away then.

Next I would check for loose bearings on front and rear.
That’s my next move, for sure. I’ve checked bearings, and had some play in the front left lock nut and got that taken care of. I did that when I put the new wheels and tires on a few weeks ago.

I replaced the u joints in the rear and greased the slip yoke in the rear. I didn’t use the grease fitting seeing as how it’s broken off. 🤣

Greased the front shaft and slip yoke and they all accepted grease but I’m sure those joints weren’t replaced when the lift was installed.

Thanks for the advice, y’all.
 
Joined
Jul 4, 2020
Messages
198
Location
Raleigh, NC
exact issue on my 94LC- cruising speeds only on throttle caused an odd whirr vibe... went away when i removed the front shaft. Ordered a TW DC shaft and it was like butter after- minus the tire tread noise....
 

RAYJON

Get a bigger hammer..
Joined
Oct 20, 2005
Messages
1,943
Location
Reno NV
normal 80 issue, make sure the front shaft is clocked correctly( yokes 90 degrees off). u joints (use good ones or you will be doing it again soon) slip yokes can get stiff or warn out, if all that checks out check pinion bearings for play(rare), you may have to put a double cardigan front shaft in to cure it.. if you wheel it and have smacked a shaft you may need a local driveshaft shop to straighten and rebalance it.. good luck, if all else fails go pro underneath will help isolate where it is..
 
Joined
Apr 14, 2016
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Oregon
make sure the front shaft is clocked correctly( yokes 90 degrees off)

Depends on the year.

Edit: I had to double check. I thought it was 95+, but it's actually '93+ that *definitely* should be 90 degrees out. '91 & '92 *may be* in phase from the factory, but nobody knows for certain.
 
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Joined
Aug 13, 2015
Messages
749
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SF Bay Area, CA
That’s my next move, for sure. I’ve checked bearings, and had some play in the front left lock nut and got that taken care of. I did that when I put the new wheels and tires on a few weeks ago.

I replaced the u joints in the rear and greased the slip yoke in the rear. I didn’t use the grease fitting seeing as how it’s broken off. 🤣

Greased the front shaft and slip yoke and they all accepted grease but I’m sure those joints weren’t replaced when the lift was installed.

Thanks for the advice, y’all.
If you do pull the shafts might as well separate the yoke while it is out, clean out the old grease and put new on the splines and in the yoke. When I did this I removed the zerk on the yoke when re-installing the shaft to let grease push out if needed do avoid over filling it.
 

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