Constant driveline whirring

Ok, first the background...
so I put my 88 MJ together using ...
97 TJ 4.0L
95 XJ AX15
93 XJ NP242
95 ZJ LPD30 (3.73) w/ CV shafts
94 Explorer 8.8 (3.73 LSD)

After initially getting it on the road, the hydraulic clutch line failed and I wound up driving on the starter to get going for 8 blocks and three intersections (not a good day).

Since that time there has been a constant whirring noise not unlike the sound heard when reversing with a straight cut reverse gear.
The sound is constant, only changing with road speed. It does not go away in neutral, does not go away or chnge with the front driveshaft removed. When I shift to full time 4wd then it gets louder on deceleration, back to normal on coasting and acceleration.

There is no issues with shifting, either the 242 or the AX15, and the whirring makes no change in pitch or frequency 1-5th, but tire and road noise drown most of it out after I hit 4th (about 70-80km/h or so).

All interior carpet/insulation has been removed and the driverside floor pan has a fair size hole rusted through (pans on the way, but wanted to include all info).

My thoughts lead to the transfer case (the internal gear differential inside the 242 is my prime suspect), but the front and rear axles, and transmission were all of used stock, nothing new. I have from my understanding ruled out pinion bearings and the front driveshaft 's one was removed nd the noise does not cycle with accel/deccel.

Any other ideas, other than the background noise there are no other issues that present themselves. Other than a slightly low hunting idle the truck runs and drive beautifully, having recently run from Duncan to Castlegar and back again (about 750km each way through some severe heat and mountain passes) with no change in the situation.

Thanks for any advice.

In my XJ, the OEM front driveshaft was barely long enough at ~4" of lift and a NP242 with a HP D30. The NP242 is longer than a 231 by a 1/2" or so.
Measuring and ordering an aftermarket shaft fixed my issue.

The other idea I have for you is the 8.8 rear. I have oem 4.10s in mine, which are notoriously noisy. Lucas 75W-140 quieted it right down. The 75 is the important part in this case.

Other than that, perhaps you need a SYE. The planetary gear setup inside the 242 doesn't come into play unless you have it in full time. In regular 2wd it's just like a 231. Running it without a front driveshaft really works that portion of it. It's possible that an bearing is going bad.

The front shaft is of a correct length, as is the rear driveshaft. I have no worries about either at this time regarding both length, or angle. The MJ's longer rear shaft eliminates the need for an SYE, so I have no bothered to pursue that direction yet.

The noise is present with, or without the front driveshaft with no change to the noise, which from my understanding, eliminates that as a possible suspect.



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As for the gear in the 242, it was not the Planetary assembly on the input side that I was referring to, but the actual gear driven differential assembly off the rear on the output side (the means of allowing full time 4wd), that I was meaning.

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https://youtu.be/WWLHmMg39KA

This is what it sounds like.

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That sounds more like "tire" whine.

I know, it's hard to capture it, but the tire noise is lower, more drummy, this is an underlying gear whine. Sadly don't have a set of road tire to isolate the tire noise.
The gear noise starts in about 5km/h you can hear it best at each stop (as I come to a stop).

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Well I can't hear anything that is not at tire/axle rpm(not driveshaft @ 3x the speed). So maybe low diff fluid, it doesn't seem loud enough for bad wheel/carrier bearings. Bad suspension bushings will transmit the sound into the chassis.

Might try removing the shifter boot so you can get closer to the sound?

Another thing to try is getting the transfer case into neutral while at speed and coasting down.

Also you didn't say whether the noise changed in rpm when going into 4LO.

Bushings in front end are new.

Not sure how easy it will be getting the tcase into neutral at highway speeds from 4PT ... Not arguing just didn't think it would shift at those speeds. Have to try that one next.

When I had the front driveshaft out I ran through all ranges with no real discernable difference, but oI only used 4lo on a back road while pulling my quad/trailer to the trailhead.

I'll try and capture some of the fun sounds associated with 4PT use tomorrow.

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If there is no difference in 4LO, then it's the output shaft side of the t-case.

Devilfrog said:

All interior carpet/insulation has been removed and the driverside floor pan has a fair size hole rusted through (pans on the way, but wanted to include all info).

Click to expand...

You definitely hear a lot more gear whine once you pull out the carpet.

Have you tried jacking up all four wheels and placing jack stands under both axles so it can be run in gear, in place?