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Loud Roar from Underside


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When my 1988 Comanche reaches 57.5 MPH a vibration and noise comes from underneath. It vibrates my seat. At 70 MPH it runs smoothe with no noise or vibration. This is something that does not happen all the time. BTW there is NO steering wheel movement. ANY suggestions would be appreciated. My first Comanche so I am clueless.

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Forgot to mention, my Comanche is 2 WD. I also retired it on Friday - still vibrates. I will look up Spicer (?) U loins and install them. I'll get back to you guys. ALL help is appreciated.

Slimjater

the 2wd drive shaft has some funky outer tube connected by rubber that has been known to cause vibrations. If this is the case you can only fix it by replacing the drive shaft. Keep this in mind if you remove the u-joints and the look good. My 2wd had this problem and it was fived with a bew shaft.
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Could it be the dreaded "Death Wobble"?

 

You need to read about it.

Search this forum.

Trust me, that ain't Death Wobble, if you get THE death Wobble, you are not in the least bit confused about what it was. And you need new gonch.

 

Check for "lumpy" tires .... Just recently eliminated a horrible Wobble in my MJ... Had a front Tire with a broken/breaking belt (had uneven shape to the tread) And that started an episode of death Wobble one trip to work. Damn near tossed me off the road, not fun. Replaced the fronts, but still had a nasty wicked vibration at 100 km/h (around 65mph) ... Recently replaced those tires and fixed my wobbling vibrations. Been running these tires for over a year and a half, no issues until the last two months. Not bad for a $60 set of TJ take offs. Still have great tread, just past their time.

When it was just the rear the truck would shake during vibration, started at 100 km/h and would die off about 120 km/h. No vibration through the steering wheel, mostly in the seat.

General rule is if you can drive through it, tires, if it happens at specific speeds, tires ....

If it can be heard/felt at all speeds, driveline .... Sometimes it takes a bit of time and patience to fell the low harmonic from a bad driveshaft, but if it is the driveshaft you will be able to feel even a slight vibe at low speeds.

A bent wheel will act similar to a driveshaft ... and wag the dog as it were at speed.

Move the tires around or swap another set on if available, if the harmonic (feel of, and onset speed of the vibe) changes, you have your cause.

If no change move on to ujoint and shafts.

 

Just my opinions

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I've experienced "Death Wobble" a few times in my 88 Comanche Chief, and I know what it is like.

Almost a life changing experience.

 

It reared it's ugly head one time when I was on the freeway pulling a trailer with a yard tractor on it.

60 mph in the right lane on a long sweeping curve to the left....this with a transfer truck immediately on my  left.

One bump in the pavement and away it went.

I thought I was a goner for sure.

Luckily, there was a right side safety lane and I was able to coax the truck over into the lane and slow down until it stopped..

 

It's scary as he** if you're in a tight spot.

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Forgot to mention, my Comanche is 2 WD. I also retired it on Friday - still vibrates. I will look up Spicer (?) U loins and install them. I'll get back to you guys. ALL help is appreciated.

Slimjater

the 2wd drive shaft has some funky outer tube connected by rubber that has been known to cause vibrations. If this is the case you can only fix it by replacing the drive shaft. Keep this in mind if you remove the u-joints and the look good. My 2wd had this problem and it was fived with a bew shaft.

 

WOW!!! I never knew that :eek: , thanks for posting that I might need a new drive shaft myself.

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  • 2 months later...

Well guys, I've almost done it all. Replaced u-joints, ring & pinion, axle bearings and brake shoes. I have had three mechanics inspect the noise. Yesterday,  had a new drive shaft made and the roar, vibration & whine are still there. Found a junk yard and ordered new differential and drive shaft. Is there ANYTHING else I can buy to add to the already $1,500.00 spent?

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I forgot to mention that the U joints are tight. Transmission mout looks good and solid. Put jack under tailshaft and the whole truck lifted up. I would look up "Death Wobble" if I knew how to search on this forum. Any help on searching.

 

2WD w. auto AW4 transmission? Inside the AW4 tail extension there is a bushing in front of the oil seal that the drive shaft slip yoke rides in. I was getting similar harmonic vibes as you are, though not as severe. It turned out to be an egged out bushing causing it. It's about a ~$4 part and is available from most online transmission sites.

 

http://comancheclub.com/topic/33041-2wd-aw4-extension-housing-bushing-replacement/#p344650

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  • 2 weeks later...

Well, Maybe I made a mistake. I DID replace and rebuild the Dana 35. Put in a used drive shaft and cured the biggest part of the problem Still shakes at 60-70. Found that the drive shaft where it goes into the tranny is loose. I'll do the bushing next. Any idea what the part number my be? By the way, if you have a DS built, make sure the maker can BALANCE it!

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From an older post:
 

Are you referring to the bushing and seal on the AW4 2WD tailshaft extension piece? I did this awhile back, and it was cheap. Ordered the parts from Transmission Parts USA as follows:

1. 94401, Jeep AW4 tailshaft extension housing seal, 1987-on, $3.04
2. 76635 A340, AW4, A40 38mm transmission extension housing bushing, $2.59
3. 94635A A340, AW4 35mm extension housing bushing, $4.10

$10 for a local machine shop to change the bushing.

I ordered the two bushings because I wasn't sure which one went in my 91 (it could have been either). For your 96 it would be the 38mm bushing.

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