Roaring sound at 60mph

[Fwdstuck]

I've got a 78 class c with a 440 727. When I get it up to around 60 mph (maybe a little below) it will start to have roaring sound and I feel it in the floorboards and it quits when I let off the gas. I don't feel it in the steering wheel or the petals. It has new tires all the way around that are balanced. I thought it might could be the rear-end cause it quitting when I let off the gas but I could be wrong.

[Rickf1985]

Could it be the radiator fan clutch? Fully engage they sound like a jet taking off. Yours could be a centrifugal type that engages at higher speeds or it could be a thermostatic type and the engine is getting hot and the fan is engaging. Or the clutch could be bad and staying engaged.

[Fwdstuck]

I've troubleshooted it to be the fan clutch or the carrier bearing. Seems like the sound has more of a bearing roar and you can fill it in the floorboards pretty good. I pushing towards the carrier bearing cause greased all 3 u joints and spayed wd-40 around the bearing to try and troubleshoot and sound was smoother and not as loud for a short time. The fan clutch when spun by hand was smooth, not to loose and not to tight.

[Rickf1985]

It is simple to find out, Take it up to 60 mph when it starts to roar and pop it in neutral, Now rev the engine pretty high and if the roar comes back it is the fan. If not it is in the driveline. If it only does it under acceleration another place to look is the pinion bearing in the rear. If the carrier bearings are bad enough to roar then they should be smoking hot when you stop. Bearings pretty much always vibrate and not roar but I never rule anything out.

[Fwdstuck]

I finally got around today and done that test and it's not the fan clutch. It'd something in the driveline.

[Rickf1985]

I would park it on relatively smooth ground and block both sides of the the rear tires, front and back of the tires so there is no way it can roll and then put it in neutral and crawl under there and start at the front and start twisting the drive shaft and looking at the u-joints. Any play at all in the cups is a bad joint, any rust coming out of a cup is a bad joint. At the support bearing shake the shaft up and down and see how much play you have. You should have a little but not a lot. When you put it in neutral at speed did the noise stay there until it slowed down or did it go away as soon as you went into neutral? Another thing you can try if you have a laser temp gun is go for a ride and then jump under there (wheels chocked) and check all the ujoints and center bearing for excess heat. They will be normally warm but if it is bad it will be a lot hotter than the others. The one on the rear differential will be hotter since the rear gets hot BUT, If the front nose section of the differential is substantially hotter than the main housing then you could have a bad pinion bearing. This will usually make more noise under power and get quiet as you let off.

[ClydesdaleKevin]

REPLACE THAT CARRIER BEARING NOW!!!


Don't drive another mile until you do!  The part is cheap...the destruction it can cause is NOT!!!  A couple of winters ago, our carrier bearing seized while driving on the highway.  It exploded violently, twisting the driveshaft like a pretzel and breaking both sections...AND it cracked our "bullet proof" transmission housing like a walnut shell!  We ended up with the RV we have now because of it.


Don't take any chances with such a cheap part!  And at least inspect your U-Joints while you are at, and replace them if they are even a little bit suspect...again, a cheap part to protect very expensive parts!  Check your fluid in your differential as well, but that should be done before any long trip.


So yeah...Replace that carrier bearing!!!


Kev

[FarPoint]

Good advice! Now Iââ,¬â,,¢m gonna replace mine. Iââ,¬â,,¢ve also had a transient driveline noise I canââ,¬â,,¢t diagnose. And  have had a driveshaft let go (in a pickup) - very glad it happened at low speed.