Hello, I need your help to diagnose a rumble.

My 4.0 (a 87 Wagoneer) did 2000km during the last 2 weeks of vacations.
Thanks and congratulations to my old lady.

the only issue is when the auto trans goes on 4th gear.
the car rumbles, becomes too noisy. This is a low pitched sound, like a vibration sound but the car doesn’t shake
So driving on the highway becomes … a pain for the family, not because of vibrations, but because it is too noisy

the shifting works well. Everything is ok on 1st 2d and 3rd.
maybe a bit slippery. But nothing that could be considered as a real issue.
it might just be the way old trans. do.

• on the highway, if I manually shift to 3rd and keep the same speed, the car revs (normal) but works perfectly with no rumble.
• if I go in Neutral the noise also globally stops
• if I slow down and the 3rd engages by itself, no rumble
• i didn’t try to put the transfer case in neutral while driving fast.

it is really when the 4th is engaged that this issue happens.

I visited 2 «specialists » who really didn’t help.
What would you advise to do in order to diagnose the problem ?

thanks a lot.

 

Additional information :

- oil level checked (not easy as it is almost transparent, it might be now a bit over the top, with no impact on the issue)
- trans mount is new
- wheels are recently balanced with 2 years old road tires
- kick down works ok


Wheel bearings will be checked again, but the noise would not be only in 4th, right ?
Driving at the exact same speed in 3rd solves the issue

 

 

 

how many total KMs do you have on the Jeep? Is the transmission original to the jeep?
Is the overdrive engaging? should be around the 60kph speed. You'll know it does as you can slightly feel it and you'll see your rpms drop from around 2,000 rpms to around 1400.

There are many variables here. Have to systematically rule each one in or out as the possible cause. The things you have checked already are good to look at... now time to look at additional items.

 

Thanks for opening the dance.
(btw sorry for my misspellings, I am French )

The car has 170 000km (108 000 miles).
Transmission seems to be original. As far as I can say, no significant off-road in its life

The 4th perfectly engages. (the 4th it is the overdrive, right ?)

What bothers me is that the noise is only in fourth and disappears when I manually engage the third keeping the same speed.
Maybe a bearing in the TC ? but why only ion 4th ?

 

If your transmission mount is new, did you replace the engine mounts at the same time?

I ask because I had a similar issue, but opposite. It made noise in 1-3 but stopped in 4th. I replaced the transmission mount and it got worse. The engine mounts solved it.

Does it happen at any speed? Could it be a resonant frequency from several worn out parts that are "singing the same song"?

 

I will change the mounts.

any other thing to investigate (in the trans or transfer case maye)

 

If it is an AW4 auto, it has 4 gears and a lock-up torque convertor that operates on 3rd and 4th gear under the right load/speed conditions

This manually locks the torque convertor very much like a manual clutch

If you travel on a level road at about 50mph in 4th, it should operate and your RPM will drop about 10%

feels like a 5th gear if you carefully count the gear RPM changes