Transmission or Tailshaft humm??

[79dentside]

Hello, got a question. I am experiencing a humm/howl at 45 that fades in and fades out about 50 mph. I originally thought it was rear end, but it seems to not be. I got the truck off the ground and ran it through the gears and I went around with a stethoscope and it was QUIET. Quiet at the pinion, quiet at the carrier bearings, quiet at the back left wheel bearing... I put new wheel bearings in because the back right went bad. I thought surely this was my noise, nope. Still howls between 45-50ish

I am wondering if it is transmission noise because the rear end was rebuilt at some point (not saying it can’t be the culprit) If I accelerate it howl at45, if I decel it howls, but there is a break in sound when I take my foot off the accelerator for a second.

The noise also is not existent at 45-50 if I am in second gear (manually shifting it).

To me it sounds like a resonance thing, but I’m not sure. In second gear it doesn’t make the noise, in 3rd it would

Also, the tailshaft spline deal-io; that the driveshaft splines onto, has some metal mixed in with the trans fluid which made me wonder. The trans fluid on the dipstick is stupid clean, it’s looks like it’s brand new.

I don’t know, I just was looking for a sounding board. I don’t want to grenade something because I neglected a noise. Thanks!!

 

[Goldie Driver]

U joints on the back driveshaft ?

I had a weird drone 55 up on the speedo, so 65 ish real life that would go away below that and was accompanied by a minor seat of the pants vibration.

Just popped up one day.

Turned out to be a dried out u joint.

Never would have guessed that.

Anyway, worth a look.

Best of luck!

Britt

 

[79dentside]

U joints on the back driveshaft ?

I had a weird drone 55 up on the speedo, so 65 ish real life that would go away below that and was accompanied by a minor seat of the pants vibration.

Just popped up one day.

Turned out to be a dried out u joint.

Never would have guessed that.

Anyway, worth a look.

Best of luck!

Britt

You might be onto something... flipping the driveshaft made it worse. I Had the transmission out to put a converter and flexplate in and didn’t mark what direction I had the driveshaft mate to the pinion, so I flipped it tonight.

 

[79dentside]

I just went to the car wash to clean the bottom side up. She was an old farm truck so mud was all over the underside. I went ahead and sprayed the u-joints and EVERYTHING else with the power washer and my noise was about 90% gone, I really couldn’t hear that much at all for a few minutes. I’m thinking I need to slap some u-joints in her first.

On a side note... I’m pretty sure I just discovered something.... She definitely has a new frame in her or the frame has been wire brushed and treated/coated... She’s a 1979 and that frame don’t look 40 years old.

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[AuroraGirl]

beings your bed looks like what it does, i would agree. BUT if the bed had a similar patina, id just say well maintained.

 

[AuroraGirl]

also if not for the drone being variable on the things you said, i would have said tires or engine/trans mounts

 

[ali_c20]

I don't think the tires are the reason...my tires whine and it gets louder the faster you go, it never stops except the wheels are in the air Does it make the noise when jacked up and while driving or only when it's on the ground/ under load? As it howls in 3rd gear only I think the transmission is the source. How old is your atf?

 

[AuroraGirl]

I don't think the tires are the reason...my tires whine and it gets louder the faster you go, it never stops except the wheels are in the air Does it make the noise when jacked up and while driving or only when it's on the ground/ under load? As it howls in 3rd gear only I think the transmission is the source. How old is your atf?

i didnt say tires were the reason. but i would consider fluid a good investigation source. a non llockup trans in 3rd maybe has some pressure issues that could be from flow or just wear. I have a C6 that liked to be choppy in 3rd gear, turns out it had plenty of ATF but i think a little too much thicker lucas or other additive was moving inside like molasses.
because fresh type F made it work fine

 

[79dentside]

I don't think the tires are the reason...my tires whine and it gets louder the faster you go, it never stops except the wheels are in the air Does it make the noise when jacked up and while driving or only when it's on the ground/ under load? As it howls in 3rd gear only I think the transmission is the source. How old is your atf?

Nope, when I had someone manning the truck while it was hoisted in the air, no noise at all.

The transmission fluid looks brand spanking new. Truck has all new fluids front to rear. Everything is new and it wasn’t me. The previous owner used it as a farm truck and kept great care of it. Before him, the truck had an engine swap, a rear end rebuild and some other things. I believe the tranny has been gone through too, it has a shift kit in it. It has no problem barking both the tires when it shifts to second gear.

Any ideas why it would be quieter when I power washed it with soapy water? That is just strange to me other than the fact that It could have added some temporary lubrication until it dried up. It has a new rear u-joint, the front may be original...

Like I said, flipping the drive shaft made it way worse. I’m just hoping to catch a problem before a big issue occurs. Thanks!

 

[Frankenchevy]

I’d try the u joints. Try to keep the slip yoke, diff yoke and driveshaft all phased as they were before you swapped the u joints. If you’re really anal retentive, you’ll want to rebalance the driveshaft after new joints are installed. Ask the shop how much they’d charge to do the whole thing joints and all—it may be cheaper than you think.

If that doesn’t remedy it, there is a race in the tail housing that’s fairly painless to change. The slip yoke on the front of your driveshaft rides in it.

The struggle is real. I chased a harmonic for a while. Next on my list is rebuild my transfer case. If that doesn’t fix it, I was planning a 4l80 swap anyhow.

 

[79dentside]

I put a u-joint in it, now both are new. The noise has drastically gone down. Like 60-80% easily. BUT it’s technically still there. If you have the windows down, radio off, you can hear a faint remanence of the noise while driving. If you let off the gas it stops for a moment, Then comes back as it did before, but it’s almost gone. I think I had 2 noises. Front u-joint was definitely shot. I greased the inside of the splines too that go into the output shaft and that’s where I found my metal gritty-ness. It’s within the spline, not the tailshaft housing.

Maybes I have another issue. It is barely audible, but I can hear it.

 

[AuroraGirl]

worth looking into how your trans mount is.. maybe when torque is applied it moves the trans to an angle that causes some drone, goes away under no or different load.

 

[79dentside]

worth looking into how your trans mount is.. maybe when torque is applied it moves the trans to an angle that causes some drone, goes away under no or different load.

I can move the transmission up off of the cross member a little just by pushing up on the tailshaft. Never thought about that, but maybe that is an issue too Hahaha.

I appreciate the help, I learn so much from you all!

 

[AuroraGirl]

I can move the transmission up off of the cross member a little just by pushing up on the tailshaft. Never thought about that, but maybe that is an issue too Hahaha.

I appreciate the help, I learn so much from you all!

I only say it because mine is literally smacking ****

 

[79dentside]

Little report back to you all. The exhaust on the truck has a grumble to it and was masking the noise if I had it in second gear as opposed to third gear at 45mph. I did confirm that it will do it in second or third.

Even though I didn’t hear ANY rear end noise while it was hoisted, what’s the likelihood of this being like a pinion depth issue/backlash? Maybe with the bad u-joint, that somehow resonated more noise through the driveshaft? If that’s even possible?

Why I ask is the 3.42’s were upgraded to a 4.10 ring/pinion 2 owners ago. Since it does it on the accel and decel situations with a quick break in noise, I wonder if it’s like a pinion depth issue? Gears look fantastic, I’ve been in the rear end 2 times since I’ve owned it. I am not well versed in rear ends, but My mind is wandering around on what all it could be.

Thanks!