Driveline noise/drone/vibration

How old is gear lube, what weight is it. Fsm has quite a few notations that any gear noise should be followed by changing gear oil to rid of contamination and fill with recommended weight and have customer retest.. My differential builder recommends 85w/140 I know the factory typically recommended 75w/90.. worth a shot.
Valvolene 80W-90 with Ford LSD additive. Fresh this spring.

I had Triax 80w-90 in last year after I put the sure grip unit in. I had some awful chatter that was eliminated with the change this spring.

It's funny... Just today I remembered a friend from years ago talking about selling used cars at the dealer auction. Sawdust and bananas was the rear end fix.
 
The stars aligned for what is probably the last drive of the season. Stopped to vote and then we hit scenic route 20 for a nice ride. Too bad most of the leaves have already fallen... Bu I digress...

With Mrs. Big John in the car, the noise was noticeable 55 MPH ish... and then seemed to quiet down as the car warmed up. From there, I could get it to make a rumble type sound as I let off the gas at anything over 50 MPH. It wasn't constant though. This section of road is quite hilly so on and off the gas happened a lot.

We turned around and Mrs. Big John had a brilliant idea of letting her drive! (She likes driving this car anyway) . While it was quiet with me driving, her driving style, which tends to be a little more "on and off" than mine, got the noise going a lot!

So... It's a rumble, kind of like a bearing noise, but it's mostly under deceleration, but she also got it to do it on acceleration which was something it didn't do when I was driving.

To summarize:

There is no vibration now. We did solve that with the driveshaft rebuild.

The noise does come from the rear, but it kind of reverberates under the floor.

The noise does quiet a little as it warms up, but doesn't go away.

There is no noise at cruise, that is constant speed at any speed (I think I hit just under 70 MPH a few times on the drive)

The noise occurs under mild deceleration from above 45 MPH and under mild acceleration from about 45 to 60+ MPH.

The work done so far:

Replaced all 3 u-joints, 2 of them being in the double cardan front joint. The centering yoke assembly was also replaced. Driveshaft balance was checked.

The rear end was completely taken apart last year as there was some bearing noise. All the bearings in the rear were changed, including the pinion and carrier bearings along with the axle bearings. A sure-grip center section was added at this time.

All leaf spring bushings were also changed at that time.

I drove it minimally after that last year and had issues with chatter on turning, so I changed rear end lube and added Ford LSD additive this spring and no chatter after that.

I also drove it minimally this spring after the rear lube change.

Driveshaft angle was checked and while it could be optimized, I don't think it's the problem. About 5 1/2° down for the pinion.

The pinion nut was checked for tightness and is OK.

The trans mount is hard to really see, but it looks OK.

Conclusion:

I'm thinking it's the gears. According to the notes from the previous owner and my observations, the rear gears were used and swapped into this center section. I then swapped out the center carrier for a new sure-grip unit. I checked the mesh at the time and it looked OK, but not perfect. I did change a spacer under the pinion gear.

I'm going to also address the pinion angle. I can shim the rear up 3° and that should leave me with 2 1/2° down, which I think would be good.

Any thoughts?


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Could be either Pinion bearings... Or gear pattern is a little off. Are gears OEM known good quiet gears that you've heard run prior to sure grip, or used picked up when sure grip was added? You mentioned pinion shim, so I'd assume it is 742 or 741 case not 489.
 
Could be either Pinion bearings... Or gear pattern is a little off. Are gears OEM known good quiet gears that you've heard run prior to sure grip, or used picked up when sure grip was added? You mentioned pinion shim, so I'd assume it is 742 or 741 case not 489.
The pinion and carrier bearings were changed last year last year when I installed the sure-grip. I did that because it sounded like I had a bearing noise.

The gears were used and installed a few years before I bought the car. The PO parked it and didn't drive it much, if at all after that.

It is the 742. Gears have a build date of (ready for this?) 1959 but are OEM gears.

Thinking on this... I've been chasing a rear end noise of one sort or another since day 1 with this car. The bearing changes were made because the noise sounded like bad axle bearings and that did get rid of the low speed noise that was worse when turning. The vibration that started digging this rabbit hole this season has also been cured with the rebuild of the driveshaft. Hmmm....

I'm really wondering if I didn't get the gear pattern right, or the gears are just worn and noisy.
 
It would be nice if you had a complete known good pumpkin to swap in for a test. A bit of a mess for a test, but insightful.
I would do it.
Just like the car service centers do now, diagnosis by substitution. Only they leave the test parts on the car, and we get charged for them.
Anyway, good luck with this annoyance. I relate.
 
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