Driveline noise/drone/vibration

[Big_John]

I'm having a bit of an issue with a driveline noise. The car is a '65 Chrysler 300L. Auto trans, 413 engine.

It has the driveshaft with a constant velocity double u-joint at the front with a single u-joint at the rear. It does not have the "ball and trunnion" driveshaft you see on some cars. It also has 3.23 gears.

Looks like this:

Here's the issue... Up to about 52 MPH it's smooth. Over that, it gets a this noise that is kind of a rumble with a slight vibration. Coast and acceleration is noisy, but get it in that sweet spot were it not doing either and it quiets down. This seems to vary in noise a bit, but the 52 MPH is pretty much where it starts. It disappears at faster speeds, anything over around 65 MPH.

I had some rear noise when I bought the car. I replaced all the bearings in the rear, axle, pinion and carrier bearings. The sure-grip was missing and I replaced that. I understand the original rear axle was swapped out a while ago. The PO had someone work on the rear, and they installed a used set of 3.23 gears. Changing the bearings silenced the low speed bearing noise. The pattern on the ring gear when I checked it looked OK and the backlash was set t what it was before, which was well in spec. Ring gear face run out on the new sure-grip was minimal and well within spec.

I probably ought to add that I'm not very good with figuring out noise. My hearing just isn't the best, never was and not getting better as I get older.

My first thought was the rear. The gears being used, then moved to the new sure-grip unit, are suspect, but I hear no howling or typical gear noise.

The driveshaft u-joints all seem tight. I didn't see any signs of missing balance weights. It does seem like this is more of a driveshaft issue. My thoughts are to pull the driveshaft and have it checked at a local driveshaft shop.

I haven't checked angularity yet. I need to get the car up on the lift and poke around with that.

Any thoughts?

 

[68PK21 440.6bbl]

Tight joints are not good, vehicles that sit unused for awhile can have the joint grease harden up especially if contaminated with moisture from sitting out in the elements (heat/cold/freeze cycle) and can cause binding at certain rotational speeds. Re-greasing if fittings are present may not solve the problem as water contaminated grease can be like hardened glue. Checking on the car is pretty much useless unless the joints are obviously toast.
Those type of driveshafts need to be removed and all joints should 'flow' freely with no binding or 'spot' binding.

Have you ever had this driveshaft apart by yourself John? These type need to be marked (indexed) before disassemble to keep balance upon re-assembly.

.

 

[Rainy Day]

Check your pinion nut to ensure it's not backing off.. When loose they typically make a drumming or drone noise at lower speeds and coasting.
Once that is done, I'd focus my attention on the driveshaft/Ujoints. GL

 

[Blusmbl]

Rear springs losing arch? Could be pinion angle. Also agree it’s worth pulling the driveshaft and have it checked for balance.

 

[Big_John]

Tight joints are not good, vehicles that sit unused for awhile can have the joint grease harden up especially if contaminated with moisture from sitting out in the elements (heat/cold/freeze cycle) and can cause binding at certain rotational speeds. Re-greasing if fittings are present may not solve the problem as water contaminated grease can be like hardened glue. Checking on the car is pretty much useless unless the joints are obviously toast.
Those type of driveshafts need to be removed and all joints should 'flow' freely with no binding or 'spot' binding.

Have you ever had this driveshaft apart by yourself John? These type need to be marked (indexed) before disassemble to keep balance upon re-assembly.

.

The car has sit for a while, although it was inside and dry. That sounds like a good possibility. I did have the driveshaft out last year and did a quick overall check for bad u-joints. When I said "tight" I meant there was no play or slop.

I've never had one of these apart, so I'm glad you pointed that out. Makes me wonder if that was done in the past.

 

[Big_John]

Check your pinion nut to ensure it's not backing off.. When loose they typically make a drumming or drone noise at lower speeds and coasting.
Once that is done, I'd focus my attention on the driveshaft/Ujoints. GL

That's easy enough to check!

 

[Big_John]

Rear springs losing arch? Could be pinion angle. Also agree it’s worth pulling the driveshaft and have it checked for balance.

The springs were replaced before I got the car and they look good. I do want to check the angle though.

 

[Blusmbl]

The other quick and dirty thing to try is to pull the driveshaft, rotate it 180*, and reinstall. Sometimes that helps since the balance really includes the pinion and flange as well.

Also, meant to say if it's always there regardless of throttle position it's probably balance related. If it changes based on load it's more likely to be angle or possibly the u-joints themselves.

The angle finders are super cheap these days, I bought a $30 Milwaukee one that measured as identically as a friend's $300 Mitutoyo digital protractor.

 

[Big_John]

The other quick and dirty thing to try is to pull the driveshaft, rotate it 180*, and reinstall. Sometimes that helps since the balance really includes the pinion and flange as well.

Also, meant to say if it's always there regardless of throttle position it's probably balance related. If it changes based on load it's more likely to be angle or possibly the u-joints themselves.

The angle finders are super cheap these days, I bought a $30 Milwaukee one that measured as identically as a friend's $300 Mitutoyo digital protractor.

I have a decent digital protractor that will work great.

It does change based on load, and the sound even changes a bit. Hmmm....