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Troubleshooting rear suspension problem - 1937 Packard 120


Ken_P
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Trying to troubleshoot what I hoped would be a simple suspension problem. Unfortunately tear down didn't reveal any problems!

 

1937 Packard 120, HPOF car, 54,xxx original miles. I've owned the car for 7 years (time flies!) and I've spent time each year improving it mechanically and cosmetically while keeping it original. I also often work in fits and starts because of my career, moving, young family, etc...

 

The problem: the car would "clunk" from the rear of the car upon takeoff. It initially sounded like a u-joint to me. They felt fine, but I replaced them anyway. No change. The exhaust is also really tight where it goes through the X-frame, but the noise seems more substantial, and the exhaust was inspected several times and doesn't appear to be the problem. Finally, this spring, I had a helper look under the car while we tried to re-create the noise. Found there is significant pinion rotational motion, especially if taking off in reverse, subsequently stopping, and then taking off in first gear. This rotation of the pinion corresponded exactly to the clunk.

 

I thought the problem was solved - a broken shackle, shackle mount, or leaf spring. The problem is, I've taken apart the entire rear suspension, and other than breaking a shock link (argh!) and cleaning off 85 years of grease buildup, I haven't found any smoking guns. I removed the leaf springs, carefully removed the gaiters, and cleaned everything up.

 

The only issues I've found so far:

 

1. With the axle removed but the springs still attached, the passenger leaf spring seemed to have slightly more lateral motion than the drivers side.

2. Both leaf spring bushings (on the forward eye of the spring, opposite of the shackle) appear to have some wear, although there is no wobble that I can see with a prybar through the hole.

3. Upon disassembly, it was apparent that the passenger rear wheel was contacting the inner fender occasionally (rub marks) and there was grease from the passenger side shackle on the fuel tank, both indications that the entire axle assembly is moving left, relative to the frame.

4. The passenger leaf spring is about 1/4" taller than the driver's side spring when they are upside down and side by side off the car, fully unloaded. Exercising the spring (me standing on them and cycling a few times) changes nothing.

 

No cracks that I've found anywhere, the mounts are solid, shackles are solid, etc. etc.

 

I can source new leaf springs, but I hate to just throw parts and money at the car without finding an actual problem.

 

Both springs are the same part number, so right now I'm tempted to swap the two leaf springs side to side, re-assemble, and see what I find.

The car rides well, perhaps a bit harsher than my previous Packard (37 115), and wallows a bit on larger bumps. Again, just trying to solve the "clunk".

 

Anyone have any ideas? Thanks in advance!

Edited by Ken_P (see edit history)
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A local spring shop can rearch your springs to like new condition. They can also add a leaf if they are sagging. Easier and cheaper than buying new springs, and you keep the original parts/

 

Have you checked for play in the crown gear and pinion? With the car jacked up can you turn the rear wheel very far without turning the drive shaft or the opposite wheel? It's not unusual to develop some slack in this area. It usually does no harm except, for the klunk you describe and some gear whine at speed. The slack can be adjusted out but you have to take the differential apart to do it. Unless it's real bad it may be best to live with it.

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Hi Ken

 

Not sure if this will help or not. I have a '36 120 which I first got back in 1978 when it had 69,000 miles. It now has almost 105,000. During that time it has had a rolling mechanical restoration and cosmetic upgrades and is mainly a driver, not a show car.

 

Like you I have had the rear springs re-arched (back end sagged), replaced U-joints (one wore out) and replaced the rear spring rear shackles (also worn). But the only actual work on the rear axle has been to replace the outer oil seals when redoing the brakes.

 

Mine will also "clunk" when shifting from forward to reverse and back. There is similar play in the pinion input shaft that does feel like more than you might expect. These Packards use hypoid rear ends which have the pinion input shaft mounted lower relative to the crown gear then most cars which also requires a different spiral on the gear teeth than most. This allowed for the flatter floor inside. It may be a side effect of this different design of gear set that they may have or develop a bit more "play" between the pinion gear and the crown gear. I don't know what the original gear setting specifications are, the manual is sometimes a bit vague about some of that data.

 

So far I have not tackled my rear end, In part I don't really want to open it up as the "clunk" is the only issue. There is no gear whine going down the road and no other issues that have given me any concern. So unless there is a change in the sound of the rear end, I'm not planning on taking it apart any time soon. I just take my time when shifting from forward to reverse and don't over rev the engine when starting off. Once going forward and the play is taken up in the gears there is no further sound from the rear end.

 

If there is no other issue with yours you may want to consider leaving it alone until such time as the sound changes.

 

Drive Safe

Jeff

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Jeff and Rusty, thanks!

 

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.

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Hi Ken

 

Some updated information on the Packard rear end.

 

I took my '36 out for a last fall spin before putting it away for winter storage on Friday. I happened to think about the rear end clunk issues and tried out some additional checks. This time there were no "clunks" when normally shifting between forward and reverse an moving the car, although they have happened on occasion.

 

I then crawled under after it was up on stands and looked closer at the rear axle. From underneath when turning the driveshaft back and forth there is an audible clunk when each "end" of the free play is reached. An approximate measure of the play by looking at the outside diameter of the shield behind the u-joint (and in front of the pinion in the axle) the free play measures about 1/8 to 3/16 inch rotation.

 

The Packard 120 data book does mention that there are two nuts inside the rear end that can be used to adjust the pinion to crown free play. It says that there will be more information in the Packard shop manual, however the 1936 manual doesn't say much about the rear end at all. It does note that pinion to crown back lash should be .003 to .005 inch free play. I have never had mine open to check and by the amount of driveshaft play I suspect that it may be a bit more than that now. The hypoid gear design is a "steeper" (semi-worm gear design) angle gear than the standard design so a small amount of back lash may equal a bit more shaft rotation than you would find on a standard gear tooth design with the same amount of back lash.

 

My car runs down the road fine with no sounds coming from the rear axle. So I will be leaving mine alone. But I did notice that I have some oil leakage out the pinion seal so a spring chore will be to drain and refill the rear axle lubricant as a precaution.

 

Note sure if this will help much, but it may provide a reference for comparison with yours.

 

Drive Safe

Jeff

 

 

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The play you feel on the driveshaft is almost certainly not in the gear adjustment. It will be in the spider gears and differential unit in general. What you are describing I would say is perfectly normal.  If it is quiet do NOT adjust the gears.  The play is just taking up the slack in the diff gears, which will have worn a little, and the cumulative effect of a little wear in the axle thrusts and the spider gear washers, if it even has them, is what you describe.  A pinion seal may be in order. 

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