Squeal from Transmission

[gavin]

So I've been... fighting and dealing with... a vibe on the junk forever.
At this point, about the only thing I haven't done anything with is the transmission.

With truck off and transmission in N, rolling the vehicle forward or back I hear a high-pitched squeal coming from the transmission. Putting my ear or a stethoscope on the transmission pan verifies the noise is coming from the transmission.
Now it's not super loud, but can be heard clearly (if truck is not running anyway.)

It was rebuilt years ago, and I know the issue came some time after that, but I cannot be positive as to when exactly the issue started.

Questions...

#1 - squeal can't be good, right? Fluid is clean, though I haven't dropped my pan in forever. I do have an aftermarket pan with a drain plug and I have drained fluid to get a look at it.

#2 - can whatever is causing the squeal, also cause a fairly consistent vibration even when coasting in N?

#3 - what internals could be causing a squeal?

I'm pretty dumb... err, uninformed when it comes to transmissions.

4R70W

 

[BrooklynBay]

One time I installed a defective torque converter in my 1989 van, and it made a high pitch squeal which varied in sound as the engine RPM speed changed. This noise was the loudest when it was cold, but toned down as it warmed up. It always made the sound regardless of the temperature. Does the sound vary as you rev the engine? What about when it warms up?

 

[gavin]

It's mostly inaudible with the engine running. I have recently started hearing it when driving, but it's still barely audible. To the point where it's extremely difficult to hear even when coasting at 5mph.
I cannot hear it with the windows up.
I don't believe I can hear it when just idling.
If I remember correctly, the TC was not replaced with the rebuild.

 

[BrooklynBay]

How old are the wheel bearings? Sounds tend to travel, so the sound might travel through the AWD drivetrain. Did you check the fluid level in the differential?

 

[gavin]

Wheel bearings are good.
Squeal definitely comes from the transmission.
I verified by putting my stethoscope on the transmission pan.
I can hear it when engine off in N, tires in the air, and rotating them by hand.

Squeal has been there since at least 2008 (I found an old thread I started.)
Front and rear axles have changed twice, along with front and rear axle shafts, bearings, and transfer case.

 

[JK080]

Its not uncommon to hear a squeal from the sprags that are inside the transmission when the output shaft is rotated. This is not a sign of a problem and I wouldn't worry about it.

When assembling any transmission I usually turn the output shaft both ways and I can hear the sprags squeal when they freewheel or clicks from a mechanical diode like on the 4R75W trannys.


The sprag sound might be like a finger on wet glass..?

 

[gavin]

Its not uncommon to hear a squeal from the sprags that are inside the transmission when the output shaft is rotated. This is not a sign of a problem and I wouldn't worry about it.

When assembling any transmission I usually turn the output shaft both ways and I can hear the sprags squeal when they freewheel or clicks from a mechanical diode like on the 4R75W trannys.


The sprag sound might be like a finger on wet glass..?

Thanks. I was thinking it may be a non-issue, but as I stated I'm quite unknowledgeable with transmissions so wasn't sure.

I think that may be a good description of the sound.

 

[gavin]

squeal aside, is there anything in the transmission that could cause a consistent/constant vibration?

It's most noticeable and audible at slower speeds (10mph and under), but still noticeable at speed.
Felt in the floor board and steering wheel.
It's definitely rotational.

Literally everything else in the driveline has been replaced at some point or another, but the vibe persists.
Axle shafts, axle housings, differentials, wheel bearing/hub assemblies, driveshafts, u-joints, transfer case, have all been replaced, tested, or checked at some time or other.
I recently put 2* shims on the rear to get the pinion angle inline with the t-case output angle.

The only thing that hasn't been touched is the transmission.