Okay another weird sound question

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love2fly

love2fly

Flying the Mountains of the NW
Joined
Sep 7, 2004
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507
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2,142
Okay let me start with what is taken place here. Today I was on the freeway and from around 60-65 mph a rotational sound develops something like a low hum that proceeds to grow in sound the faster I go but stays the same as a semi loud hum that seems to take place 180 of a rotation evenly. When I hold it steady at 60-65 mph with the accelerator pedal then remove my foot or back off the accelerator lightly the sound with disappear, then when I add power again the sound returns. I have ruled out tires as the sound changes, and with tires it would continue. I had the driveline balanced so I kind of think that would not be it. I was thinking that the transmission bearing maybe the culprit when it has a steady load on it and goes away when slightly removing the power. That’s the only theory I have other than maybe also the engine crankshaft or flywheel is out of balance. Any suggestions where or what to check.
Thanks
 
Check your rear diff pinion nut, they can come loose and cause your symptoms. Also ANY play in the u joints will cause issues. Can also be differential pinion bearings or carrier bearings going.
 
I have the exact same issue in my BJ74. Keen to check out the suggestions.
 
Good suggestions, the nut on the diff is defiantly tight and the U joints are all new. When the drive shaft was built I installed new U joints at the same time, this was not to long ago. Also I pulled the rear diff 3rd not long ago for RR and set the backlash. The gears and bearings were in super condition. For experience this does not mean they are not failing now for some reason so I will check them all again and for the diff I will put it up jack stands and run the truck up to RPM and see and listen for some rotational hum sound with a stethoscope. I read on a ford truck web site that someone had problem similar to this and it turned out to be the pinion input bearing as you mentioned on the diff but it was more constant.
I took it out again for a high speed drive and does the same (60 mph and above), let off the gas and its gone, I put it in neutral and coasted as far as possible and it pretty much dissipates when the speed drops under 55 mph.
 
You can pull the driveshaft and the axles so there is no load on the ring and pinion,then spin the pinion by hand and check for any play. Pinion should be silky smooth with just a bit of backlash.If it feels rough or has play.most likely a pinion bearing,any play at all will transmit alot of noise under load.
 
Right now I am going to leave a load on it with wheels installed and try the wheels up approach. The sound is very distinctive so it should show it ugly head at RPM at one end or the other. If that does not work will start focusing in on the diff and trans. I remember before I reinstalled the 3rd I checked the bearings on the pinion several times feeling that they were more than adequate to go back in, smooth. That part was easy, finding strange sounds is the hard part.
 
Spoke to mate recently who told me that caster wedges need to be installed in the rear of lifted vehicles as well as the front. Otherwise you get a vibration around 100km/h.
 
cult45 I have wedges in the front spring pads for a re-arcing of the front springs but not the back pads as the angle is dead on for the drive line. The truck is not lifted as it is all stock. Its interesting and will check into it a bit more. Have not had a good day to do the wheels up check, hopefully maybe tomorrow.
Cheers
 
Okay update - sorry for the long wait. Very long work hours.
Today had some time to put the old gal up on jack stands under all four wheels in a safe area. We (good to have two for safety) ran it up to the 2800 rpm were that the sound usually starts at when driving ( @ 55 mph) we had no sound at all and even took it up higher to where we were comfortable and still no sounds. We even had a automotive stethoscope to listen in on the diff while running the gears, nothing.
Of course this is without a body load on the vehicle axles or ground so this is not a complete true actual diagnose, but it did reveal a few items if nothing else. One was the driveshaft even being new (replaced center tube shaft) had a very, very slight bit of wobble along its length when viewed as the wheels were in motion. It has been balanced so not to sure as if his would be a major concern . The other item that we found was at each end of the driveshaft at the u joints that when a push and pull check is employed we get a very slight bit of play on the inner shaft to cap around less than 1 mm if even that and only on one of the inner u joint shafts on both ends. This can be possibly a contribute to the problem but the noise is so pronounced when driving that it's hard to believe this could be it.
I checked the exhaust hanger and other items that could possibly conjure up noises or vibrations but found nothing. Checked the wheel bearings on all fours and found nothing of course the rear is a full float rear end with the inner bearings. Took the old rig out and drove at the noise speed and took some corners to see if the noise got louder or went away but it stayed the same regardless. Whatever it is it needs the weight of the truck on the ground. The sound again is a rotational very steady sound as if at every 180 degrees of 360 degrees it makes a one second hum or vibration over and over again and goes away with a lot or even a slight release of the accelerator pedal. :hmm: :meh:
 
Gotta remember that the driveshaft is rotating at 4.11 times the tyre, and if the tyre is doing 100km/h then that driveshaft is absolutely flying. So even a small amount of play/slop will be pronounced.
 
I realize that, that's why I took a better and closer look at the driveline a bit ago. I found that the slip yoke had some play also just enough to make me think at the high speed the combination of the very slight wobble of the driveline, slight bit of play in the u joint, and a slight bit of play at the slip joint adds up and can be the posing issue.
The part where I remove my foot from the accelerator gives me a gut feeling that the torque from the driveshaft when released takes the pressure off a component in or on the driveline rendering it near quiet, but it could be the pinion bearing also while under load. Tried to make a video of the sound on my cell but the sound of the cruiser is noisy anyway.

Thanks
 
Found this interesting bit of information on doing some tests to help diagnose problems such as I have. one highlighted in yellow sounds much like the situation I am experiencing.
This maybe of a help to others also.

Vehicle Preparation
Unlock the front hubs and back up approximately 20 feet to make sure of hub disengagement if the vehicle is a 4x4.

Remove any externally mounted accessories such as luggage racks, or magnetic base or the antenna which may cause wind noise that interferes with NVH diagnosis.

Use a tachometer.

Note the fuel level. Some vehicles change in their response to various excitations when the fuel level changes. If the customer mentions that the concern does not occur all the time, this might be a factor.

Try to duplicate the conditions with the customer present, particularly the speed and throttle operation. It is not uncommon to find concerns which the customer didn't notice so it is important to identify the specific concern causing the complaint.

Find the speed where the concern is most severe.

Turn the air conditioning system off and on to isolate air conditioning system impact on the noise. Accelerate gently through this speed to a few mph above it and then coast back down a few mph below it and note if the concern changes character when driving through or coasting down.

Repeat this procedure if necessary to get a feeling for the behavior. Then drive about five mph above the speed, put the transmission in neutral and coast down. Note any change in behavior.

Try "floating" the driveline by backing off slightly on the throttle at the problem speed. The idea is to unload the axle gears and the universal joints as much as possible. This test is difficult to master and sometimes it helps to test on a slight downgrade so that gravity is counteracting the aerodynamic drag.

If the concern does not change in all these modes of operation, the cause may well be driveline imbalance since the imbalance is not changed by the throttle position.

If there is a distinct change in the character or intensity between the drive and coast modes of operation, the concern is not likely imbalance but is most likely due to the axle or the universal joints since they are sensitive to the load on the driveline. (The axle pinion gear teeth are machined on two separate machines. One machine does the drive side of the teeth, another does the coast side. Hence there can be a great difference in performance between driving and coasting in gear.) If the noise and/or vibration goes away when the driveline is "floated" or when coasting through the speed range in neutral, the diagnosis is strengthened. Driveline imbalance does not go away in a neutral coast, but axle and joint concerns may.

To become familiar with the symptoms of imbalance and to determine if driveline imbalance exists on the vehicle, intentionally imbalance the driveline. This can be done by installing three hose clamps with screw heads aligned on the rear of the driveshaft. Test drive the vehicle again. If the same vibration is still present but now intensified, the concern is driveline imbalance. If a new vibration is now present as a result of the intentional imbalance, the original condition would not be caused by driveline imbalance.
 
Okay things are getting a little more complicated as far as the noise goes. I did a wheels up check again and ran the rear wheels while I checked the drive shaft for play or run out. I set it up with a fixed rod barely touching the DS so I could film with my cell any movement. Seems as it has about a 1mm of movement while turning at low speed. Being the DS center tube was built at a local shop that specializes in driveline, and differentials along with race car builds.
I should mention that we did a another high speed drive with the tires now rotated and balanced, u joints lubed and still get the hum @ 55 or above.
So back the driveline shop and talked with the gent that did my driveline rebuild. He was very helpful and said to bring the driveline in to check the balance when I can. He also said that all drivelines will have a small amount of play regardless. He also checked the u-joints to see if they were the crappy types that can be found on the market, lucky I have the good kind and they also passed his inspection as did with me.
When I decided the hum sound along with the speed that is starts at, and if I go to a coast or neutral or let off the gas around 2800 rpm he right away ruled out the differential pinion gear for a number of reasons.
He asked me to while parked to run the engine up to the known rpm were the sound starts which we did and very faintly we both could hear a Humming/droning noise while at the given rpm, very faint and one really has to listen but it was there. I asked if this would intensify when driving and was told oh yes. He asked me if I have done any repairs to the distributor or electronic system, yes we replaced the dizzy with a Trollhole electronic unit. He said that this could be the reason for the sound I am getting possibly from the distributor system, coil, cap, plugs and so on. Ask me if it made this hum before the new dizzy was install, it did not. Remember this guy works on race cars also, a land cruiser engine is entry level for him, doesn't make him a rocket scientist but well versed in engines.
So with that all said other than a pulling the DS just to be sure, now I am told the engine has a high speed balance problem that really could be anything but he thinks it the dizzy or related parts but still not going to rule out the DS.
So with that said I have to ask some of you guys and gals out there if you own a dizzy from Trollhole would you please do a from a parked position (no driving) and take the engine speed up to 2700-2800 rpm and listen hard for a Humming/droning (rotational) noise and post your findings. Maybe it's just my rig. This is not a slam or a negative in anyway on Trolholes dizzy's that he sells just to make sure that is clear.
So yeah this is getting interesting to say the least. I also am going to check the harmonic balancer to see if any of it is deteriorating, fan belts also.
Thanks:worms:
https://youtu.be/UJfixj2YNvQ
 
Last edited:
Well strange noise watcher fans, seems like this little @&$* is kicking my brain cells or what cells are left. Shaft was balanced again and u joints were checked at the same time, a little out of balance but $42 later no change. Took a test drive with a Toyota tech, he was all over it but he could not find the issue. Sound again is at around 55 mph a rotational drone steady sound comes out of nowhere ( it really sounds light a mud tire on pavement but with a rational brake in the sound) - no vibration.
Ran the engine at RPM and it's not a harmonic balance or the dizzy or power steering as told by the Toyota tech.
All tires rotated and balanced
Removed both rear axles-turned diff pinion yoke fast no noise just standard parts moving sound-no nothing
Checked bearings -all good
Ran engine while all wheels were on jacks and stethoscope the E brake and hub for bearing noise-nothing
Drive at 55-60 put the clutch in -goes away
Drive at 55-60 swerve left or right -no change
Drive at 55-60 put in neutral and coast-no change
Drive at 55-60 checked all four wheel hubs for hot to touch-warm but not real hot
Next is-
Drive 55-60 jump out and claim the insurance- it's that bad
 
If you want to just hear you trany, put the TC in neutral and run through your gears. Any of the listing methods will work or a stethoscope.
 
so, the only time the noise goes away is with the clutch pedal held down? almost sounds like the throw out bearing or something in the clutch.

still sounds much like a pinon bearing to me



love2fly said:
Ran engine while all wheels were on jacks and stethoscope the E brake and hub for bearing noise-nothing
Drive at 55-60 put the clutch in -goes away
Drive at 55-60 swerve left or right -no change
Drive at 55-60 put in neutral and coast-no change
Drive at 55-60 checked all four wheel hubs for hot to touch-warm but not real hot
Next is-
Drive 55-60 jump out and claim the insurance- it's that bad
Click to expand...
 
If the noise goes away with the clutch in. it may be your throwout bearing is the culprit
 
shawnfj40, Landpimp we did that check on the gears, nothing out of the ordinary. The clutch was also found not the be the culprit, as when we ran the truck up to RPM while on jack stands I used a stethoscope in that area, no typical TO bearing sounds were heard with clutch in or out and while shifting the gears. also as stated at the beginning of this post the sound will go away when not just the clutch is depressed but when the throttle is slightly released or backed off.
I got an email from a gent on a other 4x4 web site and asked if I had a snorkel install which I do, said that his at times will make a strange noise at high speeds as the air is being sucked into the snorkel, so removed the tube from the air cleaner housing and no still there.
I now at the point where I just take the whole rear end off and rebuild it.
Thanks guys
 
You hAve stated alot of things that are not that all that easy to follow. Your last post seemed to be what was the most current, so I went with that for a diagnosis.

Maybe some ear plugs would be the best course of action at this point.
 
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