Humming sound at high speed.

[rloaderro]

Picked up a '79 cruiser 2 days ago. So far so good. Yesterday noticed that at "high" speed (cruising at ~50) a humming sound kicked in - like a motor or a fan. Hard to describe. Every time I slowed down, just before pulling over to check it out, goes away. So, hard to diagnose. Right now it's pretty consistent - don't know if it's something rubbing, or even where to look. So posting this hoping someone has had some experience, but really any suggestions welcome!

 

[rockcod]

It could be your fan, or perhaps harmonics. What kind of tires are you running? You could have someone drive next to you to see if they can hear it.

Lets see some good pics of the whole vehicle, that color is close to what my Snotz project is going to be.

Good Luck!

 

[rloaderro]

I don't think it's the tires cause it's something that "clicks" on: shift to 4th, about 20-30 seconds later the sound starts, like a fan or motor - but I'm sure it's not the fan directly. This suddenly started last night - and has since been consistent. Gauges look good - not running hot. ATM I am concerned - just don't want it degrade into where I am worried.... or walking

Definitely will post pictures later today - thanks!!

 

[D'Animal]

As RockCod mentioned, it may be your radiator fan clutch. It is the finned metal looking thing that your white plastic fan bolts to.

 

[alkarich]

Wouldn't hurt to post in the diesel section as well.

 

[mudnyreye]

Could be pilot or throw out bearing goin south. How old is the clutch?

 

[rloaderro]

@mudnyreye

Couldn't tell you for sure. I know a lot of the motor was supposedly rebuilt just before I bought the jeep. Could this be a reason why it only affects a specific gear? Could you please tell me a little more about pilot or throw out bearings - how they wear, or why the humming sound could be caused by either of them... reading some things now: "If you allow the vehicle to Idle in gear with the Clutch pedal depressed, instead of shifting to Neutral gear, you can wear out the throwout bearing." good to know.

 

[grant5127]

I've come across a couple of de-funk vacuum pumps in the past that produced strange intermittent noises.....

 

[Fryedaddy]

Not always but pilot bearings normally tick if you have the car in neutral ideling.

 

[PressOn]

Does the noise change when in two wheel drive versus 4WD? Just curious because at speeds > 40mph in 4WD I get a high frequency hum (not real loud but rpm related) from the front differential area. In my case, gear lubs look fine but I need to look into it further.

Definately post in the diesel area as there are some B engine gurus that like to help. Good luck and that's one good looking diesel bay.

Jeff

 

[Pin_Head]

Run a Fourier transform analysis of the noise to deconvolute the wave form into its component resonances in the frequency domain. That should point you in the right direction as to what is making the noise.

 

[D'Animal]

Do I plug my laptop into the two prong slots in the glove box for that?

Run a Fourier transform analysis of the noise to deconvolute the wave form into its component resonances in the frequency domain. That should point you in the right direction as to what is making the noise.

 

[DSRTRDR]

Run a Fourier transform analysis of the noise to deconvolute the wave form into its component resonances in the frequency domain. That should point you in the right direction as to what is making the noise.

Do I plug my laptop into the two prong slots in the glove box for that?

they can be used for something else

I typically apply Principal Component Analysis, though, works better for the earlier models

my truck currently hums because the diamond plate at the bib is loose ; and it also hums when the rubber strips on which the hood rests wear out

 

[lostmarbles]

Does the noise change when in two wheel drive versus 4WD? Just curious because at speeds > 40mph in 4WD I get a high frequency hum (not real loud but rpm related) from the front differential area. In my case, gear lubs look fine but I need to look into it further.

Definately post in the diesel area as there are some B engine gurus that like to help. Good luck and that's one good looking diesel bay.

Jeff

Well spotted Jeff.

Yes it looks like the same 2977cc B-diesel I have so that would make it another 1979 BJ40.

Very nice and tidy too.

However I don't think the noise is related to the engine at all. I suspect it is "tyre-related" or "transmission-related".

The humm could well be normal. After all, having the cruiser for only a couple of days must mean "hardly knowing anything about its normal behaviour/sounds".



PS. Stick your head out the window while your driving and see if you can hear where the noise is coming from. If it changes according to the road-surface then it will be your tyres.

 

[rloaderro]

I think now it was the speedometer deteriorating. There's very little light in the cab, but during the day today I caught the speedometer needle going crazy while there was the humming sound. The speedometer has since more or less died and the noise has appeared to have stopped. Luckily the speedometer is an optional part since I doubt I'd take it past 50mph.

Does that make sense? I have to get a hold of some manuals to understand where things are and what.

 

[amaurer]

I think now it was the velocimeter deteriorating. There's very little light in the cab, but during the day today I caught the velocimeter needle going crazy while there was the humming sound. The velocimeter has since more or less died and the noise has appeared to have stopped. Luckily the velocimeter is an optional part since I doubt I'd take it past 50mph.

Does that make sense? I have to get a hold of some manuals to understand where things are and what.

A velocimeter would indicate speed and direction. You have a speedometer.

 

[rloaderro]

Fixed. If you remember seeing something besides speedometer please do your best to erase that event from your memory.

 

[fj404life]

Couldn't tell you for sure. I know a lot of the motor was supposedly rebuilt just before I bought the jeep.

Bought the what??????

 

[lostmarbles]

Fixed. If you remember seeing something besides speedometer please do your best to erase that event from your memory.

Erased!


Yeah. ...... Must have been your speedo cable or the speedometer itself. (I suspect the cable though.)

You may well find that your cable has been "kinked" during the recent work on your vehicle. This would then cause increased friction (as the cable turns within its sheathing) and probably then cause failure of either the cable itself or the worm gear that drives it.



PS. I don't think any BJ40s were ever fitted with fan-clutches. (My fan is solid-bolted to my waterpump pulley.)

 

[rloaderro]

Bought the what??????

Sorry - I made the same mistake in another thread. In Costa Rica "jeep" is a generic term for a 4x4 that is not a truck.