Mystery noise from BJ70 (1 Viewer)

[Estancio]

OK, I'm sure someone on this forum can help...

My 1987 BJ70 (465,000km and mostly original) has developed a low pitched rhythmic noise that comes on about 50mph (in either 4th or 5th gear), subsides by 55-60, and appears again at 65mph. It is a steady noise like a pulsing, droning sound, and at 50mph it counts out to just about 120 times per minute. Been slowly developing during the past 6 months. Cannot locate the source of the noise and it is driving me zonkers....

TRIED TO DATE -- Checked all drive shaft u and slip joints. Nada. But just to make sure, I removed each drive shaft and ran without rear and then without front. No change at all in the noise. Checked all fan belts and all associated pulleys and bearings (water pump, idler pulley, alternator, and steering pump). Nada. Checked out fan clutch. Nada. Checked free play in all 4 wheels. Nada. Even replaced front spring bushings to be sure. Nada.

CLUES: When I hear the noise at 50mph and push in the clutch, or shift to neutral, the noise mostly goes away. I also notice that in gear when heading downhill, the noise lessens. I cannot replicate the noise by reving the engine when stopped. Does not appear at all when idling at any rpm.

SUSPICIONS: Could it be worn motor mounts? Could it be exhaust system vibrations? Could it be related to the original clutch? Could it be something in rear axle that eases off when no power comes from engine?

PLEASE POINT ME IN SOME USEFUL DIRECTION.....

 

[AlbertoSD]

Have you considered the throw-out bearing on the clutch system?

 

[Estancio]

My experience with bad throw out bearings is that they create a much higher pitch squeal, one that is not related to road or engine speed.....

 

[cruiserdan]

Transmission input shaft/bearing? Counter shaft/bearings? With close to 300,000 miles on it I can see that.

 

[Gun Runner 5]

My experience with bad throw out bearings is that they create a much higher pitch squeal, one that is not related to road or engine speed.....

Most of the time a bad throw out bearing is only evident when the vehicle is stopped. (Sounds like a pulley squealing and is generally not loud enough to hear at road speeds)
At least that was the case when mine went bad.

 

[kbushnz]

Could be the output bearing in the transfercase... Grab the companion flange the drive shaft bolts to and give it a wiggle.

 

[roscoFJ73]

I also say the T/case. Mine had similar symptoms(the low pitched rhythmic noise) that was driving me crazy. Mine seemed to come and go at lower speeds also but at lower decibels,eg 30kph 60 kph 90 kph.
So it got louder the higher the speed.

Disappeared after a rebuild. If you can find a gearbox mechanic with a stethoscope for gearboxes you maybe able to track it down more accurately.
All of the components died before 300000klms on my FJ73 ,including gearbox t/case F and R diffs and engine from suspected lack of oil changes.

 

[Estancio]

Could be the output bearing in the transfercase... Grab the companion flange the drive shaft bolts to and give it a wiggle.

The output is very tight in the TC. No excess movement in output flange.

 

[Estancio]

I also say the T/case. Mine had similar symptoms(the low pitched rhythmic noise) that was driving me crazy. Mine seemed to come and go at lower speeds also but at lower decibels,eg 30kph 60 kph 90 kph.
So it got louder the higher the speed.

Disappeared after a rebuild. If you can find a gearbox mechanic with a stethoscope for gearboxes you maybe able to track it down more accurately.
All of the components died before 300000klms on my FJ73 ,including gearbox t/case F and R diffs and engine from suspected lack of oil changes.

Will see if my best local toyota mechanic can isolate that noise with his stethoscope. Last time I gave him a noise problem, he came up empty....and that time it turned out to be tires.

 

[BobBJ74]

My BJ74 develops that droning noise at 2400rpm in 5th gear road speed 70mph. No noise in 4th gear at 2400rpm. Rebuilt engine, gearbox, transfer, new exedy clutch kit and new uni joints in drive shafts about 12,000 km. Think it might be from front axle, maybe bearing on the way out?

 

[Estancio]

BobBJ74, my BJ droning is worse at 2200rpm. But sounds very similar to what you describe.
Interesting that you don't get it in 4th at the same rpm. I'm still thinking mine is some mysterious combination of ENGINE and MECHANICAL noise that get amplified at certain speed/engine combinations.

 

[BobBJ74]

I don't get the noise when oils are cold eg; short trips. only on highway with power on and road speed 70mph plus. Going to remove front drive shaft and see if that fixes it.

 

[Estancio]

I already tried pulling my drives shafts one by one...and it made absolutely no difference on mine.
Let me know what you discover with yours.

 

[BobBJ74]

Well Estancio, A mechanic friend of mine told me that if a wheel is out of balance it can cause vibration at between 60 to 70mph and also to check wheel bearings for proper tightness. Another thing he mentioned was if drive the shaft splines are worn it will sag a little and this can cause vibration too. But you checked this.
I removed my PTO winch and ARB bumper for re-powercoating, with about 240lbs load gone from the front end the droning noise is gone? Wheel bearings checked out good, so I will have to keep looking for source of noise. Any luck on your end?

 

[Estancio]

Thanks BobBj74. I have in fact noticed some slight wear in the rear drive shaft splines...but as mentioned previously, when I removed the rear drive shaft completely, the noise was still there. I have not found sourse of my noise, and still looking.