"klunk", what the heck was that? - I've been hearing and feeling a "klunk" noise when I take off in my 1930 Hudson

[timecapsule]

For several months I've been hearing and feeling a "klunk" noise when I take off in my 1930 Hudson.  It's coming from the rear of the car.  Imagine replacing the leaf spring shackle pin/bolt with one much smaller in diameter.  When you'd take off all those components (shackles, pin, leaf spring) would make a similar sound to what I'm hearing and feeling.  Or perhaps if all the lug nuts were loose.

I've run out of things to check.   Universal joints, all components of the brake assemblies, leaf spring shackles, leaf springs for breaks, U-bolts that hold the differential to the leaf springs.  Plus I've given the suspension a complete grease job.   I've taken off the differential backing place and drained the differential oil, and checked the oil and the bottom of the differential housing for any metal. I've inspected the wear on the ring gear and pinion and that looks normal.  I'm about to check the pinion backlash, but just by moving the ring gear back and forth, it doesn't look suspicious.  I replaced the pinion/differential gear assembly last year and the pinion backlash was within specs.  I checked that before installing. 

 

To check the backlash while the differential assembly is still in the car, I'm assuming to get a proper reading I should at least lock the driveshaft in a fixed position.  But I'm not sure if I need to slide out both axles or not.  I think there might be enough free play with those cluster gears,  that it won't effect a reading.  But I might be wrong there.  My backlash spec is between .006th and .008th.  When I installed it the backlash was .007th.   I've tried to inspect the 4 cluster gears in the differential but that's really limited since it's difficult to view them completely, without pulling everything out completely and separating the differential halves.  But from what I can see as I rotate the wheels in a full rotation they all look pretty good.  No excessive wear.  

 

I recently had one axle out ( 100 miles ago) and the hardfacing on the end of it is still looking good and undisturbed.  I had both axles hardfaced when I installed the replacement differential/pinion assembly, so I could get the proper axle end play.

 

Now we come to the real puzzling part.   This "klunk" only happens when the car has been sitting for a number of hours.  Overnight for sure.  It will happen within a few hundred feet of taking off.  But then it won't happen again no matter how many stop signs I come to.  Or no matter how fast and hard I try to take off.  I can let it sit for at least a few hours and not get that "klunk" .  But if I'm in my shop all day, then when I leave I get the "klunk"

 

But,,,,  when I do take off for the first time, if I take off ever so slowly.  I'm talking really slow, slower than walking speed.  Just put the car in gear and let the engine pull it along without any gas for a hundred feet or so.  Then gradually try to increase speed without applying any torgue to the drive wheel by just barely touching the gas pedal.  Once I travel maybe the length of a football field and get up to 30 mph, then it's all good and after that I can stop the car and take off again without the "klunk" noise. 

 

This next theory might be stretching it a bit, but one thought is that one or more of the shocks might be making the noise.  They were all empty when I got the car and I filled them with hydraulic fluid.  But they all slowly leaked out.  I have a spare one that I have pulled apart to see how they work.  The problem is the shaft is worn on one side.  They have felt seals, so no wonder they leak.  To fix the problem, I have to fill the worn area on the shaft, and then turn them to match a speedie sleeve, and then install the matching modern seal to match that speedie sleeve.  I don't own a lathe,,,, yet.  But it's my next tool to buy.  The cost of a used lathe would probably be less than the labour bill at a machine shop to rebuild all 4 shocks.

Anyway, so maybe, just maybe, they are getting hung up when at rest and sort of break loose ("klunk") once torque is applied to the differential which the arm is attached to.  Like I said that's a bit of a stretch.  I've even tried rocking the car dramatically before I take off to get the shocks moving.  

 

Has anybody experienced such a thing?

[Restorer32]

Had a similar problem with an MGB years ago.  Turned out one of the rear shocks was a bit loose on the frame. Drove me nuts until I figured it out.

[28 Chrysler]

I have had a thump when the car sat and the brakes had been stuck to the drums, also on the old Chryslers the parking brake band would stick to the drum.

[JACK M]

I would open up the trunk and secure whatever is bouncing around in there.

[mikewest]

It might be a missing shock bushing . Sounds like  something that has lots of slack.. Maybe a screwed up shackle ..... 

[lump]

Many years ago I helped my dad restore a 28 Model A pickup, which he then drove to work every day for a couple of years, year-round (even in the snow). Shortly after we first got it on the road, he had a very similar "clunk" upon take-off from a stop. Friends who were Model A experts gave us several things to try. We had that rear end out of the truck about a dozen times, but nothing worked. Finally, after a couple of weeks of wasted efforts, Dad sat on the ground looking at the undercarriage, and thought about it for a while. He then removed the right rear wheel, got a huge wrench, and tightened the axle nut. We put the wheel back on, and the "clunk" was gone! This solution came as a surprise to the local Model A Ford experts in our circle of car friends, as none of them had ever experienced that "clunk," nor Dad's fix.  

 

Don't know if Hudsons even have a big nut on the end of the axle, though....🤔

Edited November 9, 2023 by lump (see edit history)

[timecapsule]

5 hours ago, lump said:

Many years ago I helped my dad restore a 28 Model A pickup, which he then drove to work every day for a couple of years, year-round (even in the snow). Shortly after we first got it on the road, he had a very similar "clunk" upon take-off from a stop. Friends who were Model A experts gave us several things to try. We had that rear end out of the truck about a dozen times, but nothing worked. Finally, after a couple of weeks of wasted efforts, Dad sat on the ground looking at the undercarriage, and thought about it for a while. He then removed the right rear wheel, got a huge wrench, and tightened the axle nut. We put the wheel back on, and the "clunk" was gone! This solution came as a surprise to the local Model A Ford experts in our circle of car friends, as none of them had ever experienced that "clunk," nor Dad's fix.  

 

Don't know if Hudsons even have a big nut on the end of the axle, though....🤔

Yes there is an axle nut.  But it is a castle nut with a cotter pin.  It has tapered axle ends on the rear like the front spindles with key/keyway front and back.    Awesome looking truck.  

Edited November 10, 2023 by timecapsule (see edit history)

[alsfarms]

Check your u-joints

Al

[timecapsule]

3 minutes ago, alsfarms said:

Check your u-joints

Al

The U-Joints were the first thing that I mentioned being checked in my original post.  Besides once U-joints go, it's a constant noise and or vibration. 

[alsfarms]

Good work. How about motor mounts and transmission mounts?

Al

[timecapsule]

6 minutes ago, alsfarms said:

Good work. How about motor mounts and transmission mounts?

Al

The noise if from the back and as I mentioned it only happens once, when I first take off after the car has been sitting for at least 4 hours or so.

[alsfarms]

Hmmmm

[JACK M]

I think Lump may be onto something.

[lump]

16 hours ago, timecapsule said:

Yes there is an axle nut.  But it is a castle nut with a cotter pin.  It has tapered axle ends on the rear like the front spindles with key/keyway front and back.    Awesome looking truck.  

Dad's Model A truck also had a castle nut, cotter pin, and tapered axle ends, as I recall. Just offering thoughts on my one-time experience from over 50 years ago. 

 

Good luck. Hope you find the solution. 

[timecapsule]

8 minutes ago, lump said:

Dad's Model A truck also had a castle nut, cotter pin, and tapered axle ends, as I recall. Just offering thoughts on my one-time experience from over 50 years ago. 

 

Good luck. Hope you find the solution. 

I honestly don't mean to criticize, so I apologize if my thoughts come off that way,  but I find it difficult to imagine how one could not tighten on the wheel appropriately with this set up.  Tighten the nut as tight as possible, then if the cotter pin won't line up, tighten more until it slides through. That nut has to move a fair bit from one opening to the next.  If it's too loose it's detectible right away.  

But for discussion sake, lets say the castle nut wasn't tight enough.  There would be a few detectible and obvious signs, I would think.  Even with the car on the ground, you would be able to move the top of the wheel in and out.  The other sign would be a badly damaged key and key way.  The other sign would be quite a shimmy as you drove the car. 

I designed and made a special wheel puller for getting the wheel off.  I never found any pictures or illustrations as to what they used originally.  I have read and heard that if you didn't have the appropriate tool you would remove the cotter pin, loosen the castle nut maybe half a turn, and drive the car slowly for a short distance while cranking the steering wheel, until the wheel worked it's way loose.  That method seems a bit strange, because then you'd have to drive the car, into the shop or garage where you wanted to work on it, like that.  I would think over time that would put significant wear marks on the tapered pieces (axle & hub).

Anyway, my point being that I have to use the wheel puller that I made to get the wheel off each time with significant effort, before the wheel breaks free from the axle.   I routinely pull all my wheels off to check on brake lining wear and just as a routine check on all the brake components.

But I do appreciate your thoughts and experience. 

[lump]

7 hours ago, timecapsule said:

I honestly don't mean to criticize, so I apologize if my thoughts come off that way,  but I find it difficult to imagine how one could not tighten on the wheel appropriately with this set up.  Tighten the nut as tight as possible, then if the cotter pin won't line up, tighten more until it slides through. That nut has to move a fair bit from one opening to the next.  If it's too loose it's detectible right away.  

But for discussion sake, lets say the castle nut wasn't tight enough.  There would be a few detectible and obvious signs, I would think.  Even with the car on the ground, you would be able to move the top of the wheel in and out.  The other sign would be a badly damaged key and key way.  The other sign would be quite a shimmy as you drove the car. 

I designed and made a special wheel puller for getting the wheel off.  I never found any pictures or illustrations as to what they used originally.  I have read and heard that if you didn't have the appropriate tool you would remove the cotter pin, loosen the castle nut maybe half a turn, and drive the car slowly for a short distance while cranking the steering wheel, until the wheel worked it's way loose.  That method seems a bit strange, because then you'd have to drive the car, into the shop or garage where you wanted to work on it, like that.  I would think over time that would put significant wear marks on the tapered pieces (axle & hub).

Anyway, my point being that I have to use the wheel puller that I made to get the wheel off each time with significant effort, before the wheel breaks free from the axle.   I routinely pull all my wheels off to check on brake lining wear and just as a routine check on all the brake components.

But I do appreciate your thoughts and experience. 

No worries. I understand. 

 

My experience with Dad's issue is firmly burned into my brain, because we had tried EVERYTHING else, to no avail. Dad took off the wheel, removed the cotter pin, and put some muscle into tightening that nut. Then he put in a new cotter pin, and like magic the problem was gone. And like I said before, Dad's old car buddies were a bit bewildered at the time, as none of them had ever experienced that problem/solution. I don't mean to suggest that your problem is exactly like Dad's, nor that tightening that nut will help at all. But it was the right solution all those years ago. And if I ever face a symptom like that, I'll absolutely have to try it for myself. 

 

I sincerely hope you will be able to solve the problem, and when you do, we would all like to know the solution. Cheers. 

[timecapsule]

On 11/9/2023 at 10:58 AM, mikewest said:

It might be a missing shock bushing . Sounds like  something that has lots of slack.. Maybe a screwed up shackle ..... 

If you mean the rubber bushings on the arm that attaches the shock arm to the differential, yes I replaced all those rubber bushings when I got the car, as you can see in the picture.  There really aren't any bushings inside the shock.  

[mikewest]

If my dear dad was alive , he would of had me remove the rear seat and stuck my head down in the hole while he drove to find the  clunk. I remember him telling me a  few times of him laying on the fender of a 30s car making adjustments while one of his boys at the garage drove. I had a 31  Hudson 8  but never had any problems with the Ujoints. Are they Spicer?/ I had a 31 Auburn 8 that had the old Chrysler  type joints with the cross pin, two balls and a spring that werent the best setup. Take the seat out and get someone to drive you around. You most likely cant find it on the lift, because the weight and flex of the springs is most likely causing whatever is bad to make it knock. My 2 cents.

Edited November 11, 2023 by mikewest (see edit history)

[timecapsule]

4 minutes ago, mikewest said:

If my dear dad was alive , he would of had me remove the rear seat and stuck my head down in the hole while he drove to find the  clunk. I remember him telling me a  few times of him laying on the fender of a 30s car making adjustments while one of his boys at the garage drove. I had a 31  Hudson 8  but never had any problems with the Ujoints. Are they Spicer?/ I had a 31 Auburn 8 that had the old Chrysler  type joints with the cross pin, two balls and a spring that werent the best setup. Take the seat out and get someone to drive you around. You most likely cant find it on the lift, because the weight and flex of the springs is most likely causing whatever is bad to make it knock. My 2 cents.

That's what kids are for,,,,  to do the dirty work.    hahaha!!

[mikewest]

This was my 31-8 It is a scarce car having the Murray body. It was called the Club sedan. all round lines, forward opening doors.  I sold it when my girls were in school and I needed the $. 

[mikewest]

Another though, Look over the springs good for a broken center bolt allowing a spring to move.

[timecapsule]

2 minutes ago, mikewest said:

This was my 31-8 It is a scarce car having the Murray body. It was called the Club sedan. all round lines, forward opening doors.  I sold it when my girls were in school and I needed the $. 

Very cool car!!

[timecapsule]

2 minutes ago, mikewest said:

Another though, Look over the springs good for a broken center bolt allowing a spring to move.

Yep I thought about that too.  I've looked them over as close as possible.  I've also looked for any fresh steel wear markings on or around the leaf springs.  I've inspected every inch under the car for any signs of anything that looks odd.  All rivets on the frame are super tight.

[mikewest]

56 minutes ago, timecapsule said:

Very cool car!!

It was a very good performer. I drove it to Cambridge Ontario Canada from home(Rochester NY) following my friend in a 1933 Auburn 8 and had no problems  running 55-60 mph on the highways. I had gone through the motor , had the rods fitted up close and a new water jacket on the side of the motor. It always ran cool when other cars were boiling or vapor locking. The vacuum tank never failed or acted up. 

[timecapsule]

6 minutes ago, mikewest said:

It was a very good performer. I drove it to Cambridge Ontario Canada from home(Rochester NY) following my friend in a 1933 Auburn 8 and had no problems  running 55-60 mph on the highways. I had gone through the motor , had the rods fitted up close and a new water jacket on the side of the motor. It always ran cool when other cars were boiling or vapor locking. The vacuum tank never failed or acted up. 

Great stuff!   My Mother lived in Cambridge.

[Laughing Coyote]

Just my thought, but could any of these rivets be worn or broken and causing the center section of the differential to move?

 

 

[paulrhd29nz]

I’ve been reading over this for a while now. Everyone has given great ideas to help out Timecapsule. It has me stumped for sure. Timecapsule has explained himself very very well and clear. 
my suggestion is a hidden under dash stereo with a big volume knob. 

[timecapsule]

1 hour ago, Laughing Coyote said:

Just my thought, but could any of these rivets be worn or broken and causing the center section of the differential to move?

 

 

I've inspected those areas very closely.  Tapped everywhere with a hammer to see if there was any movement or even a difference in sound.  

[timecapsule]

I disconnected the rear shock absorbers yesterday.  Still have the "klunk"

Next I'm going to try disconnecting the rear brake linkage.  

[timecapsule]

1 hour ago, paulrhd29nz said:

I’ve been reading over this for a while now. Everyone has given great ideas to help out Timecapsule. It has me stumped for sure. Timecapsule has explained himself very very well and clear. 
my suggestion is a hidden under dash stereo with a big volume knob. 

I'm thinking you have the best suggestion so far Paul   

[timecapsule]

13 minutes ago, timecapsule said:

I've inspected those areas very closely.  Tapped everywhere with a hammer to see if there was any movement or even a difference in sound.  But it's like I mentioned at the beginning.  The feeling is exactly what you'd expect from a shifting differential.  But even at that, why wouldn't it do it every time I take off from a stop sign.  Even putting the pedal to the medal to try and make it happen has no effect once I'm driving for a few hundred feet or more.  Quiet as a mouse until the car sits for some time.

 

Edited November 12, 2023 by timecapsule (see edit history)

[edinmass]

With everything else checked and no apparent reason, I would bet a month’s wages it a brake hanging up and then releasing. Carefully disconnect the rear brake cables or rods, keeping only front brakes……..and road test the car for the noise. Lots of things like cross shafts, cables, adjusters, equalizers, there is a bunch of stuff that will cause a klunk when releasing. Also, do not set the emergency brake when you stop. Try this test first……leave the emergency brake off for a few drive cycles……….I have a tool called a chassis ear…………they make cheap ones and expensive ones…….but they work great for finding noises. Look it up. Good luck, Ed.

Edited November 12, 2023 by edinmass (see edit history)

[timecapsule]

One of the things Edinmass suggested, I actually suspected might be the problem today.  There is a round bar running from side to side in about the middle of the car that goes through holes in the frame.  It's purpose is to connect the centre point of the mechanical brake rods and make everything move at once by rotating slightly when you apply the brakes.  Hudson's method of providing that rotation to that bar, was to surround that rod with 3 round washer like pieces about 1/4" thick.  2 of them are bolted in a fixed place to the frame, but able to rotate.  The third washer is mounted using a cam shaped bolt.  This allows for adjustment.  While wiggling the brake arms today for the umpteenth time, I noticed that bar had significant side motion.  I convinced myself that the noise when I moved that round bar was similar to the noise I hear.   After taking the cam action washer like roller out and cleaning it, I could see how it works.  The end of the threaded bolt coming through has a portion without threads and two flats on it for a 1/4" wrench to fit on. ( see arrow in one of the pictures).  By loosening the nut and rotating the bolt with a wrench,  I took up the slack and I was hopeful that that was the culprit.  Which of course still wouldn't explain why this noise only happens on start up.  So I wasn't really surprised to still hear the noise on my test drive.

 

However I did learn something about the car, and I made an appropriate adjustment that needed to be done, and I checked off one of the things from my "rattle" list, that happen as I go over ruts in the road.

[EmTee]

Aren't antique car scavenger hunts fun!? 

 

Glad to hear that you're not giving up and the search continues.  Picking up on something else Ed mentioned, maybe ask someone else to ride in the back seat when you expect the noise to occur.  I have been fooled before by similar situations where I thought I knew where the sound was coming from, only to discover the source was somewhere else.  Sometimes sound travels through the body or frame in a way that changes the apparent location.  A dedicated observer is also free to move around to better localize the source of the noise.

[Jack Bennett]

On 11/8/2023 at 9:52 PM, timecapsule said:

For several months I've been hearing and feeling a "klunk" noise when I take off in my 1930 Hudson.  It's coming from the rear of the car.  Imagine replacing the leaf spring shackle pin/bolt with one much smaller in diameter.  When you'd take off all those components (shackles, pin, leaf spring) would make a similar sound to what I'm hearing and feeling.  Or perhaps if all the lug nuts were loose.

I've run out of things to check.   Universal joints, all components of the brake assemblies, leaf spring shackles, leaf springs for breaks, U-bolts that hold the differential to the leaf springs.  Plus I've given the suspension a complete grease job.   I've taken off the differential backing place and drained the differential oil, and checked the oil and the bottom of the differential housing for any metal. I've inspected the wear on the ring gear and pinion and that looks normal.  I'm about to check the pinion backlash, but just by moving the ring gear back and forth, it doesn't look suspicious.  I replaced the pinion/differential gear assembly last year and the pinion backlash was within specs.  I checked that before installing. 

 

To check the backlash while the differential assembly is still in the car, I'm assuming to get a proper reading I should at least lock the driveshaft in a fixed position.  But I'm not sure if I need to slide out both axles or not.  I think there might be enough free play with those cluster gears,  that it won't effect a reading.  But I might be wrong there.  My backlash spec is between .006th and .008th.  When I installed it the backlash was .007th.   I've tried to inspect the 4 cluster gears in the differential but that's really limited since it's difficult to view them completely, without pulling everything out completely and separating the differential halves.  But from what I can see as I rotate the wheels in a full rotation they all look pretty good.  No excessive wear.  

 

I recently had one axle out ( 100 miles ago) and the hardfacing on the end of it is still looking good and undisturbed.  I had both axles hardfaced when I installed the replacement differential/pinion assembly, so I could get the proper axle end play.

 

Now we come to the real puzzling part.   This "klunk" only happens when the car has been sitting for a number of hours.  Overnight for sure.  It will happen within a few hundred feet of taking off.  But then it won't happen again no matter how many stop signs I come to.  Or no matter how fast and hard I try to take off.  I can let it sit for at least a few hours and not get that "klunk" .  But if I'm in my shop all day, then when I leave I get the "klunk"

 

But,,,,  when I do take off for the first time, if I take off ever so slowly.  I'm talking really slow, slower than walking speed.  Just put the car in gear and let the engine pull it along without any gas for a hundred feet or so.  Then gradually try to increase speed without applying any torgue to the drive wheel by just barely touching the gas pedal.  Once I travel maybe the length of a football field and get up to 30 mph, then it's all good and after that I can stop the car and take off again without the "klunk” noise.

 

Has anybody experienced such a thing?

Hi timecapsule…….Nope……your 1930 Hudson has progressed into a age of technology which, I’m sorry to say, bores me.

But, it is neither a new Mercedes nor a Tesla, so I suppose the old rule KISS (keep it simple stupid) applies when working with your relatively antique vehicle.

Check simple stuff, which actually is under stress, when the car is powered up.

A universal joint which is cold my “clunk” as may a worn ring and pinion gear, un lubricated because the 600W or 1500 lube has drained back into the pumpkin.

Or, it may be an exhaust pipe or muffler “clunking” because the rubber hanger has stiffened up while sitting, or a “U” bolt has loosened over time…..remember, even though not a “brass era” car, a lot of water has been passed since 1930 too.

Good luck with your “clunk”! 
And, out of consideration for what can suddenly go wrong with these old buggies, be thankful it’s not a “clunk……clunk……..clunk” coming from the crankcase 🤪.

Jack

[timecapsule]

15 hours ago, edinmass said:

With everything else checked and no apparent reason, I would bet a month’s wages it a brake hanging up and then releasing. Carefully disconnect the rear brake cables or rods, keeping only front brakes……..and road test the car for the noise. Lots of things like cross shafts, cables, adjusters, equalizers, there is a bunch of stuff that will cause a klunk when releasing. Also, do not set the emergency brake when you stop. Try this test first……leave the emergency brake off for a few drive cycles……….I have a tool called a chassis ear…………they make cheap ones and expensive ones…….but they work great for finding noises. Look it up. Good luck, Ed.

That chassis ear sounds like a good idea. Any particular make and model that you recommend?  Looks like Steelman is the front runner.  Actually it's the only one I could find without going down the internet rabbit hole.   But the 60605 is $399 US.  so that's around a million CA.  Even at that, Amazon says it's not available here in Canada.  But Amazon has the 60635-00 and it's $160 CA.  So what's that, about 5 bucks US.  lol!  Anyways that's a huge difference in price between models.  I would think since it's made in China that the 60635-00 is a cheap toy compared to the 60605.  But then again maybe the 60605 is overkill for what I need.  But it sounds like a better idea than dangling a kid through a hole in the floor.  

[Zimm63]

1 hour ago, timecapsule said:

That chassis ear sounds like a good idea. Any particular make and model that you recommend?  Looks like Steelman is the front runner.  Actually it's the only one I could find without going down the internet rabbit hole.   But the 60605 is $399 US.  so that's around a million CA.  Even at that, Amazon says it's not available here in Canada.  But Amazon has the 60635-00 and it's $160 CA.  So what's that, about 5 bucks US.  lol!  Anyways that's a huge difference in price between models.  I would think since it's made in China that the 60635-00 is a cheap toy compared to the 60605.  But then again maybe the 60605 is overkill for what I need.  But it sounds like a better idea than dangling a kid through a hole in the floor.  

 

Dangling a kid through a hole in the floor could very well pinpoint the problem, as well as create a lifetime memory.  

 

[timecapsule]

3 hours ago, Zimm63 said:

 

Dangling a kid through a hole in the floor could very well pinpoint the problem, as well as create a lifetime memory.  

 

I agree.  Any volunteers out there?

[Hemi Joel]

Have you seen your bowling ball lately? 😃

[Highlander160]

Something is cooling since you state that it's a 1 time noise. Cpl hrs ok, all day not so much. Any noise in the drive system will "end" at the final point, the axle. I'll bet you feel it in the shifter and gas pedal too, yes? Having done such a thorough exam of usual suspects to find nothing, what else could shock the driveline with a clunk? Can you access the slide for the throwout brg easy enuff? If it were to stick a little the force could possibly send a shockwave down the line. You said all the mounts were good, so if the motor/trans can't move what can? Lots of force on the avg pressure plate. If the parts warm up a little then some clearance is gained. You can baby it to make it not happen as well. Raw thoughts...