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Ken, thanks for the tip. When I had the radiator redone it was supposed to be a “high flow” but modern style core. Perhaps that is the issue.

Mixture, valve lash & timing have all recently been checked.

Thanks again!

Long time, no post. I've been away for work for some of it, just busy moving and living life for some of it. I have been out in the car quite a bit, and the more I drive it, the better it gets.

I am working a long-standing problem, and hoping for some insight here.

When taking off, I would often get a loud "clunk". I initially suspected the cause as driveline u-joints. I replaced those, no change. Also new engine mounts and significant looks at the exhaust to make sure it didn't hit the frame. This spring, I had a helper look at the drivetrain when I was taking off. There is significant pinion motion when taking off, especially if transitioning from reverse to forward. That seems to be the source of my clunk.

I was assuming a rear suspension problem, and have begun disassembly and inspection, but so far I have found no smoking guns. I have both leaf springs off, gaiters removed, and while I'm still cleaning, I haven't found any cracked springs, broken shackles, broken shackle bolts, bad bushings, or any obvious problems. Other than chipping through 85 years of grease buildup, I was amazed how easily everything came apart.

I did find grease from the passenger side shackle on the fuel tank and rubbing on the passenger rear wheel well, indicating that the whole rear axle assembly is shifting to the left.

The ONLY issue I've found is that right rear shackle feels a bit looser than the left. With the axle disconnected from the leaf springs, I could get more lateral play out of the passenger leaf spring than the drivers.

Anyone experience this? How tight should the shackles be? Is it possibly just worn out leaf springs? The car has about 54k miles on it.

Thanks in advance!

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This doesn't give any specs on tightness or define the noise but maybe something in it could be applicable.

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Howard, that's helpful, thanks! I'll check both shackles and see if the passenger one was assembled incorrectly long ago.

Ken, there is a Service Letter that may apply. I recall it stating that a small amount of axle housing rotation during launch can result in the drive shaft needing to telescope just a bit (can't remember if shortening or lengthening) causing the sound.
The resolution was to change the angle of the rear axle just a bit by introducing tapered shims with just a couple degrees of angle.

Pat

Ken, there is a Service Letter that may apply. I recall it stating that a small amount of axle housing rotation during launch can result in the drive shaft needing to telescope just a bit (can't remember if shortening or lengthening) causing the sound. The resolution was to change the angle of the rear axle just a bit by introducing tapered shims with just a couple degrees of angle. Pat

Pat, thanks for that. I'll take a look.

Spent some more time this weekend on the springs. After cleaning everything up, still no smoking guns. There are some wear marks on each main leaf where the gaiters have rubbed for the last 85 years, but no cracks or anything that I can see. The ONLY issue that I have found so far, in addition to the right spring having more lateral motion when installed, is that the two leaf springs have a different static height. The passenger side leaf spring is about 1/4" taller than the drivers side.

I didn't take the frame height measurements discussed in the service manual before I disassembled, because I was expecting to find a broken bolt or spring mount.

I tore it down before I remembered that I'm supposed to have the car in a parade on Thursday. Based on that, and no obvious problems, I think I am going to trying swapping leaf springs side to side, and re-installing, using the shackle guidance above (my shackles do have the notches in the outer plate discussed in Howard's post), and see if the problem remains, shifts sides, or goes away completely.

I did find one problem - upon cleaning the u-bolts, it was evident that they were a little bit loose. I think this is what was allowing the axle to shift laterally. I also measured the leaf spring arch. Per Eaton spring, factory arch is 8-1/2". Passenger was at 8-3/4" and drivers was at 8-1/4".


I swapped sides of the leaf springs, reassembled everything, and got her back on the road. Clunk is still present, but much softer. I suspect the clunk is from the rear end as Jeff suggests. Perhaps it was made worse by the loose u-bolt, or it sounds the same and it's just my wishful thinking that it's better. Either way, I'm going to drive it!



I am also renewing the shock oil and installing new shock links. We'll see how she rides when I'm all done.

Drained and refilled the rear shocks with fresh oil, installed new shock links and bushings, and back on the road.

Got the links and bushings from Max Merritt. Caveat emptor, the links and bushings have to be ordered separately, and I ended up using my bushing washers and all nuts from the original shock links, to retain stock appearance. Very happy with the links, but the hardware they come with is nothing like the original.

I was surprised to find how little compression damping the shocks had. Rebound damping feels much better, and the car rides much nicer, so successful overall, just surprised.

Concerning the persistent clunk on takeoff:

One thing to check is the drive shaft slip joint, which is allows the driveshaft to telescope slightly when the car goes over bumps and when taking off from a stop. The splined shaft and sleeve need to be clean and well lubricated. Sometimes old grease can accumulate and prevent the parts from moving freely and having full travel, and an assembly that is not well-lubricated may bind under torque load and then release suddenly, making a clunk or bumping sound. It's also important that the slip joint be assembled correctly so that the u-joints will be "in phase". The Packard drive shaft has arrows on the slip joint extenion on the driveshaft and on the yoke to show when they are in correct alignment. Incorrect alignment can cause driveline vibration and rougher clutch engagement by causing the u-joints to fight each other each time the driveshaft revolves.

Mild occasional gear clash when shifting might be related to a dry transmission input shaft spline or a dry input shaft pilot bearing. (Or a worn synchronizer) Low mileage cars can have these conditions due to age, or in the case of prematurely worn synchronizers, a previous driver may have had the bad habit of not fully depressing the clutch pedal when shifting gears.