Return of the Rear Axle Clackity Sound

[warbirdphotog]

COMPLETE UPDATE AS OF JUNE 8, 2021



THANK YOU to everyone who has tried to help so far! It is much appreciated. Since I've noticed a few people bringing up tests that have been already done, I figured I'd do another 'state of the rear axle' update and quickly point out everything I've done so far. We're narrowing down the list to only really one thing left to check at this point.

This started in mid December of 2020

• CJ AXLES: My Jeep had post-war CJ axles when I got it in October 2018. I wanted wartime axles.
• GPW AXLES: I was given a pair of GPW wartime axles from a fellow G503 member in November 2019. I spent a good part of 2020 restoring the two axles to spec. The front axle looked nearly NOS. The rear axle, however, had a major spider gear explosion in its life and damaged the Ring, Pinion, Carrier, and Housing. The brake drums were way out of spec as well and unusable. Axle shafts, brake plates, yoke, and cover were in perfect shape. I repaired the housing on the rear axle, got a take-off GPW carrier, and a NOS GPW ring and pinion set. Both axles get brand new bearings/races throughout, new shims, etc.
• GPW AXLES FINISHED & REPLACEMENT BEGINS: I finished the axle restoration (with my expert jeep mechanic friend who set the ring and pinion on both axles) in December 2020, and started the CJ replacement.
  • SPRINGS: I took off the springs, cleaned them up, replaced the bushings, and repainted them. They are original GPW springs and original to my Jeep. The pivot pins were replaced in all four springs.
  • SHOCKS: The shocks are also original GPW Gabriel shocks, all four work great with resistance when pushing in and pulling out. All four were cleaned up and repainted.
  • DRIVE SHAFTS: Both driveshafts were determined to be GPW, and both looked to be in good shape (though, at the time I didn't check for straightness in them). They both were cleaned up, repainted, and regreased. I did notice that I had to extend the rear driveshaft slightly longer than it was before as the CJ axles are wider overall. But, that being said, the driveshaft does NOT extend beyond the teeth. The teeth from the long shaft of the driveshaft do no come out of the end flange at all.
  • SHACKLES: All four shackles were in great shape, as were the end cap nuts. They were cleaned up, repainted, and reinstalled.
  • LEAF PLATES/U-BOLTS: The leaf plates for the CJ axles and the connecting U-Bolts are NOT compatible with wartime axles, so I got four repro leaf plates and a U-bolt set (GPW) from Ron.
  • WHEELS & RIMS: I got a set of Firestone Tires 600-16 (Coker made) with the correct TR-15 Tubes and Flaps which were paired with (due to possible litigation this name has been blocked) Combat Rims (MD Juan made) to replace the no-name brand tires I had and M38 rims.
  • REAR SHOCK BRACKETS: My Jeep was missing the rear shock brackets on the frame. I found two take-off GPW ones and used the 'bolt rivets' to attach it to the frame, then welded the imitation rivets and the back of the brackets to the frame as it would be.
• That IS ALL that was done. The Transmission/Transfer case were not changed. The flywheel/clutch were not changed. The engine was not changed. Frame was not changed other than adding the rear shock brackets.

Axles are completely installed just after New Years 2021. The first test drive produced the clackity sound.

• THE FIRST TESTS BEGIN: At first, we thought it was something wrong with the ring and pinion. I was 'hearing' the sound coming from the rear of the Jeep. First step was to inspect the rear axle (which we'll call Rear Axle #1).
  • INSPECTED INSIDE THE REAR AXLE #1: There are metal shavings in the oil. Quite a bit of them after just 5 miles of test driving. This is concerning.
  • RING AND PINION INSPECTION: There doesn't seem to be anything wrong with the ring and pinion. The grease test still shows a good contact. The corner edge of the ring appeared to be worn down slightly, but this was explained as possibly the NOS ring and pinion 'adjusting' to eachother. No other strike marks are seen on the housing or on the ring/pinion/carrier.
  • SPIDER GEARS: This was the first idea for the problem, so I pulled out the carrier and completely replaced the spider gears, thrust washers, and main pin. This didn't change the sound.
  • ON JACKS: I tested the sound on jacks with my Jeep in 1st, 2nd, and 3rd. It was at this point we discovered the Jeep HAS to be under a load. If the wheels are not on the ground, the sound will NOT occur.
  • REMOVE THE DRIVESHAFTS: I then removed the rear Driveshaft a put it in 4WD. The sound went away. I then removed the front driveshaft and put the rear back on. The sound came back.
  • CARRIER RUNOUT: We tested the carrier runout and realized that either the carrier or the ring had a pretty significant runout. BUT, it didn't seem to strike anything on the housing or cover. Still, this would bring me to the point (after the next part) to where I decided to get another rear axle.

• TRANSMISSION REBUILD: Thinking that the problem was somewhere in the transmission or transfer case, I started on a mutli-week journey of restoring and rebuilding my T-84 and D-18.
  • T-84 TRANSMISSION: I took everything apart, replaced the 1st/2nd gears, new blocking rings, new bearings, new shifter shafts, etc. A lot of the T-84 had been replaced before me, there were only a few items F stamped. All put back together it was as perfect as perfect could be.
  • D-18 TRANSFER CASE: I then went to work doing the same thing to the D-18 Transfer case. Unlike the T-84, this looked like it had NEVER been opened since the factory. Everything was F stamped down to the gaskets and washers. It was also in perfect shape, with all the gears looking near brand new. I replaced all the bearings, the 999 gear shaft, thrust washers, oil seals, safety wire, etc. The shimming that was on the transfer case was way off before, and there was quite a bit of backlash. I got that thing perfectly shimmed (and I mean perfect, using dial indicators to check everything!). All went back together and was sealed really nicely with new gaskets.
  • EXTERNAL E-BRAKE: I had rebuilt my E-Brake once already before I changed out the axles as the drum I had was warped. New repro drum and restored GPW brake band with new brake pads. But I took everything apart again for a second time and carefully inspected everything. I got that band dialed in nearly perfect on the drum. I did replace the companion flange with a brand new repro just in case as some people said that could be the problem (and it was leaking oil).
• The result? The sound did NOT change at all. I'm happy I did it though, as it needed to be done and the Jeep shifts like a dream now. Plus, now pretty much no oil leaks vs like several before.

It was about this time after so much frustration and putting in months of work with no difference in the clackity sound to make the decision that I was giving up with this GPW rear axle. A friend had a spare GPW rear axle (no brake drums, brake plates, axle shafts, or cover) that I was given in April 2021.

• REAR AXLE #2 BEGINS: I spent the next few weeks restoring/rebuilding the SECOND GPW rear axle.
  • CARRIER, RING, & PINION: Axle #2 came with a carrier, ring, and pinion. They were in good shape, and I decided to use those. Checking the runout on the carrier, it was well within spec. This isn't a new Ring and Pinion, they were a matching pair with the carrier that have been in that axle for years.
  • BEARINGS: I got new all new bearings for Axle #2 including the carrier, pinion, etc.
  • SETTING THE RING AND PINION: I went to my Jeep mechanic friend again (who is just as frustrated as me) and another Jeep expert was there the day we set the Ring and Pinion on this second axle. We used dial indicators, checked every little thing along the way, and had three 'I concur' agreements between myself and the two others on everything. That's three people (2 Jeep experts and me) that were doing/watching over the process. Since we were all frustrated with the first axle, we wanted to get this one perfect. As the mechanic said 'I think this is one of the most perfect rear axles I've done'.
  • REUSED PARTS: Because there were some items missing from this axle #2, I had to borrow some things from the first axle. This included the cover, the axle shafts, the brake plates (and brake parts), the brake drums, and the yoke.
  • REAR SPRINGS/SHOCKS/SHACKLES: While I had them off, I inspected them all again and found nothing out of the ordinary with them.
• The result? The sound was STILL there on the test drive. I'm sure you can imagine my frustration. So, I went back to more testing these last two months:
  • WHEELS: We thought, maybe there's an issue with the combat rims. So, I took off the wheels from the rear and rotated them with the front wheels in an X pattern. So the front driver's wheel/rim went to the rear passenger. And so on. No Change in the Sound.
  • REAR DRIVESHAFT: We discovered that my rear driveshaft had a significant wobble, so I took it in and had it straightened. But, just to make SURE that wasn't the cause of all this, I borrowed two rear driveshafts (MB and early MB) from a friend and tried them on my Jeep. Both the borrowed driveshafts and my now straightened driveshaft didn't change a thing. Sound was still there.
  • DRIVESHAFT U BOLTS/UNIVERSAL JOINT: Some thought it was the rear driveshaft U-bolts or the universal joint. So, I replaced the U-Joint and U-Bolts on my rear driveshaft with brand new ones. Sound was still there.
  • BRAKE DRUMS #1: Thinking maybe there was an issue with the drums, I took them off and went to a brake shop and had them resurfaced on the inside. I then readjusted the brakes after I got them back. Sound was still there.
  • BRAKE DRUMS #2: Thinking maybe it was the whole drums giving issues, I took one of the original well out-of-spec GPW drums I got with Axle #1 and, one at a time (so I had three drums with good brakes) I swapped the rear drums. Sound was still there both times.
  • REOPENED THE DIFFERENTIAL: Just recently, I drained the oil and checked the inside of Axle #2. There was some very slight metal shavings (a ton less than Axle #1 had, and I'd driven Axle #2 over 25 miles vs only 5 miles with Axle #1). The metal shavings were determined to be a correct amount based on setting a ring and pinion. Other than that, there were no signs of anything striking the housing, no signs of anything like the carrier bolts/lock straps hitting the housing, no sign of the carrier or ring hitting anything, and the pinion looked like it did when I installed it. Nothing seemed out of the ordinary.
• It was during all those tests that I got myself a GoPro camera to mount under the Jeep. I spend several weeks mounting it all over the Jeep and doing the same drive through the area. This determined that the sound is for sure coming from the rear axle.
  • AXLE WEDGES: A few people suggested that it appeared that my rear axle was dipping too far downward when I was decelerating, which could put stress on the pinion and move it to strike the ring. So, I went out and got 4 degree axle wedges, which I put between the axle and the springs. If my springs were worn out, this could be the cause for the axle rotating too far forward. Axle wedges would prove this and at the very least, make the sound either less loud or less often... but sound was still there and didn't change at all.

So, this is where we are now. The ONLY thing that has not been checked is the rear axle yoke, which I just got a different one (needs a speedi sleeve) from eBay yesterday. I plan to do that this week/weekend depending on the speedi sleeve arrival. I'm not holding my breath at this point, as I don't think that will solve the issue. This problem has stumped every Jeep expert/mechanic I know including Ron! At this point, I've been told by several people to just 'drive it and ignore the sound'... as either it'll eventually go away wearing down whatever is contacting, or something will break and I'll know exactly what the problem is. Not very reassuring. Maybe I should have stayed with my CJ axles.

TLDR: Axles are the worst.

[jnissen]

Metal shavings in the oil does not mean the ring and pinion are OK. In five miles driving to see noticeable shavings is something I’d be concerned with. You seem to be dismissing the obvious.


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[warbirdphotog]

Metal shavings in the oil does not mean the ring and pinion are OK. In five miles driving to see noticeable shavings is something I’d be concerned with. You seem to be dismissing the obvious.


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We didn't ignore it. That was one of the reasons went to a second axle. We determined the carrier runout was out of spec and that, we think, was the cause of the metal shavings.

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[Wolfman]

That is quite an in-depth and thorough update.
I have spent some time going over pictures and videos. Looking for anything.
Only thing I have spotted is, on page 4, toward the top, there is a picture of the rear differential yoke, without the drive shaft in place.
The yoke looks to be freshly painted in this picture.
At the bottom of the saddle, next to the nut and cotter pin, the yoke saddle looks all beat up. Like something has been hitting it. ???
We know the sound only happens on deceleration, rear drive shaft installed with the jeep in gear and at this time, the differential tips down, increasing the center line angle between the drive shaft and differential pinion.
At this time, it also moves the drive shaft yoke closer to the differential yoke at the top of shaft rotation. Maybe closing up the gap between the drive shaft and differential yoke to make contact ??
This does not happen on acceleration. Diff. nose raises. The gap gets wider and would not be an issue at all with the drive shaft removed.
This same yoke has been in place since the noise started.
But the speed of the clank and the speed of the rotating drive shaft doesn't match. ??
Although if the contact was only made on one side, that would cut rhythm of the contact in half, but still ??
I have been of the opinion all along that the tipping down of the differential nose plays into this.
Latest idea I can come up with. Still thinking.

[W. Winget]

Is there any local shop you might be able to use a lift at and place it on while running gear is engaged, then do a listen/feel for the noise.

Failing that my only thought is to tie the front bumper to an imovable object (car or truck with parking brake set) raise the body, disconnect the springs,raise the axle onto seperate stands, start the engine put it in gear and slowly rotate the spring/axle assembly to hear (and feel) the clackity sound.

Wish you were near me we could knock it out in a few hours on the lift, or replace it entirely with an axle I might have off another GPW residue.
V/R W. Winget

[Wolfman]

The lift idea makes sense, LTC.
Lifting the jeep off it's wheels would allow the entire differential to drop. Increasing the angle of the rear drive shaft. Making the drive shaft angle similar to how it moves during deceleration.
Turn the drive shaft by hand and see what happens.

[Michael O.]

So I got another GPW carrier, and then a NOS GPW ring and pinion set (all matching numbers).

So the ring a pinion gears came as a matched set then? I’m not sure what you mean by “matching numbers”. As you know, each individual ring and pinion must be machined to match each other, specifically. Any random ring gear installed with any given random pinion may lead to the issues you are describing.

[Joe Gopan]

Is your Parking Brake installed and adjusted correctly?

[Bruce W]

“ RING AND PINION INSPECTION: There doesn't seem to be anything wrong with the ring and pinion. The grease test still shows a good contact. The corner edge of the ring appeared to be worn down slightly, but this was explained as possibly the NOS ring and pinion 'adjusting' to eachother. No other strike marks are seen on the housing or on the ring/pinion/carrier.”

The ring gear and pinion are “adjusted” to each other when they are manufactured. No further break-in should be needed. This is the reason for the tooth contact pattern check (your “grease test” I guess, although I don’t believe grease is a good marking compound). We want to be sure our installed tooth contact pattern is as close as possible to the one put in the gears by the gear grinder/lapper.
I’m disturbed by two “experts” who think that shavings in the oil after 5 miles is ok, normal, or expected. The same goes for damage on the edge of the ring gear.
I know you said there is no sign of pinion gear contact on the case (“carrier”) but have you taken a good look at the ends of the differential pinion (“spider”) cross shaft? I’ve seen some and heard of some replacements that were longer than the originals and may strike the drive pinion gear on the head. Do the shaft ends extend beyond the case?
BW

[warbirdphotog]

Only thing I have spotted is, on page 4, toward the top, there is a picture of the rear differential yoke, without the drive shaft in place. The yoke looks to be freshly painted in this picture. At the bottom of the saddle, next to the nut and cotter pin, the yoke saddle looks all beat up. Like something has been hitting it. ???

After hunting for NOS/Take-Off yokes the last few days, I will say that nearly all yokes I've seen have that wear in that same area. I think it's more of the casting rather than something hitting it, personally. I could be wrong, but that's just based on all the ones I've seen on eBay so far. I wish someone made a correct repro Yoke, not these modern ones that look nothing like the WW2 yokes.

Although if the contact was only made on one side, that would cut rhythm of the contact in half, but still ?? I have been of the opinion all along that the tipping down of the differential nose plays into this. Latest idea I can come up with. Still thinking.

I think we're all going through the same list and coming up empty as well. It was hoped that the axle wedges would be the key here, the one last glimmer of hope. But when that didn't change the sound at all (and it should have even slightly as the axle tipping was reduced), that ruled out that being the issue. I could go out and get higher degree wedges, but seeing as the sound didn't change at 4 degrees, I can't imagine it would change any more with just 4 more degrees. The same with changing out my springs, it's expensive and the axle wedges would have demonstrated that as the issue here, but I'm thinking it's a waste of (lots) money to go after the springs.

Is there any local shop you might be able to use a lift at and place it on while running gear is engaged, then do a listen/feel for the noise.

Do you mean like a wheel treadmill? Because we know that the Jeep has to be under load for the sound. If the wheels are not on the ground, it seems, the sound won't appear. Sadly, I can't think of any shops around here that could do that. A wheel treadmill is the only thing that might work as it's under load and stationary. But not sure if anyone around here has one.

Failing that my only thought is to tie the front bumper to an imovable object (car or truck with parking brake set) raise the body, disconnect the springs,raise the axle onto seperate stands, start the engine put it in gear and slowly rotate the spring/axle assembly to hear (and feel) the clackity sound.

I see where you're going with this. Just to test the angle of the axle. In theory, I could use my 1 ton crane to lift up the back of the Jeep (with two jack stands forward of the springs on the frame as safety), disconnect the springs from the shackles and lay them on the ground, have the axle on jackstands up in the air still attached to the driveshaft, and drive the Jeep in 2WD as someone rotates the axle carefully (if they can). That might be a bit dangerous, I'd be afraid something would go wrong. Ha ha. But I get the idea!

Wish you were near me we could knock it out in a few hours on the lift, or replace it entirely with an axle I might have off another GPW residue.

But remember, this is the second GPW axle now on the Jeep! Other than having someone else set the ring and pinion, I'm not sure a third GPW axle would do any different. But I really appreciate the ideas!

The lift idea makes sense, LTC. Lifting the jeep off it's wheels would allow the entire differential to drop. Increasing the angle of the rear drive shaft. Making the drive shaft angle similar to how it moves during deceleration. Turn the drive shaft by hand and see what happens.

When I put the Jeep up on jacks, I put the jacks under the frame so the axle/wheels are airborne and the axle is resting down on the springs. I've ran that twice now in gear, and without that load on the wheels (and perhaps the movement with the load), the sound is not there. I would have to do like LTC said and disconnect the axle from the springs, lower the springs, put jackstands on the wheels to hold them up, and have someone force tip the axle. I'm still thinking that might be pretty dangerous overall.

So the ring a pinion gears came as a matched set then? I’m not sure what you mean by “matching numbers”. As you know, each individual ring and pinion must be machined to match each other, specifically. Any random ring gear installed with any given random pinion may lead to the issues you are describing.

I'm very mindful of the golden rule that ring and pinions are a matching set and cannot be mixed and matched. The first NOS set I got was a matching numbered pair, meaning the number on both the ring and pinion matched (they do this so you can keep track). It was a 4 digit number like 437. That NOS set I got was still wrapped in the wax paper and cosmoline and still sealed in the original package. The second ring and pinion set (the one that came with the second axle) was also a matching pair based on the 3 digit number. I would never mix ring and pinions as that would be a serious issue right there! Thanks for checking.

Is your Parking Brake installed and adjusted correctly?

Yes, I mentioned that in my latest update. It has been thoroughly tested. It is not contacting/holding up the drum. I even loosened it a few months ago to the point it was totally away from the drum, no change in anything.

[warbirdphotog]

The ring gear and pinion are “adjusted” to each other when they are manufactured. No further break-in should be needed. This is the reason for the tooth contact pattern check (your “grease test” I guess, although I don’t believe grease is a good marking compound). We want to be sure our installed tooth contact pattern is as close as possible to the one put in the gears by the gear grinder/lapper.

I believe Grease is considered the standard for testing ring and pinion setting (it's in manuals, youtube videos, mentioned all the time here on the G, etc). And we checked it in several spots on the ring, and we'd often do more than one rotation after the initial check just to be sure. Remember, this was done on my front axle as well the same way and it's fine. My friend has probably done more ring and pinion settings than most restoration places have! This is the first time he's had an issue like this. He just set a MB ring and pinion a few months ago, no issues with their axles. I know not everyone is perfect, but I think if you met him and knew his background in auto restoration (especially Jeeps, everyone takes his Jeep here in the OC/LA/Riverside area to him) you'd agree that he's not one to get it wrong. Especially twice in a row with two rear axles. He's the type of Jeep restorer that can tell you if something is wrong or right just based on feeling it alone. I believe he's got 30+ years experience.

I know you said there is no sign of pinion gear contact on the case (“carrier”) but have you taken a good look at the ends of the differential pinion (“spider”) cross shaft? I’ve seen some and heard of some replacements that were longer than the originals and may strike the drive pinion gear on the head. Do the shaft ends extend beyond the case?

The shaft does not extend beyond the carrier. And remember, two different carriers, three sets of spider gears. For the first take-off GPW carrier I used the original spider gear cross shaft (and original GPW) that it came with. I then replaced the shaft with a repro from Ron. The second carrier that came with the second axle had its own shaft I used. None of them extended to the point it would cause any hangups that I could see. Plus, the end of the shafts had no scarring marks. The pinion head, which I would imagine would be what it strikes, has no scarring marks.

[Bruce W]

Grease may be alright, but it’s not in any of my manuals and it’s not what I use. I use red lead, white lead (I don’t think you can get them anymore but I still have some) or Prussian blue. Sounds like your man knows what he is doing and if grease works for him, more power to him. “I believe he's got 30+ years experience.” Should be enough. I’ve got 50 plus.
I wondered about the cross shaft since you mentioned replacing the spider gears, and wasn’t sure if you said that the shaft was new too or not. Now we can cross that off the list.
Good luck with this problem. I wish I could help.
BW

[jnissen]

What about the U-joint at the rear? Does it have a grease zerk? Verify under a binding condition like deceleration that that zerk isn’t interfering. Some modern joints with zerks are not the same assembled height and perhaps it’s excessively long and hits only under deceleration?


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[Wolfman]

I have been watching the last videos on page 4 of the two side angles of the differential.
The speed of the clack is not in tempo with anything.
The pinion & drive shaft is rotating much faster than the clack, and the wheels ( axles and differential carrier ) are rotating much slower.
One chalk line or a piece of tape on the inside of the tire so the rotation speed of the tire could be compared to the tempo of the knock would help.
Don't think the knock tempo is going to match the rotating speed of anything in the video.
That would cross off metal to metal contact between two rotating parts.
So, what is rotating at a different speed than the pinion and carrier ??
Bearing cones in races. Would be slower in any position.
But why only knock in one direction ??
Side load between the pinion and ring gear teeth.
Side load forcing the carrier to one side would be the same going forward or backward.
But the pinion. Angle of the gear teeth. Going one direction, the pinion is being forced forward, and load being against the front bearing and in the the other direction, the pinion is being forced to the rear and the load being on the rear bearing.
?????
At times in the video it seemed like I could hear the clank in both directions, this included while backing up at a slow speed, it is most dominant decelerating going forward at a higher speed.
Just thinking on line again.
Brain lapse, but are these the same pinion bearings and races that have been moved to different axle housings, even though they were new to start with ??
And did the knock start after the new bearings were installed ???
This was listed with a color code somewhere in the last 8 pages.
And the small amount of shavings ???
Those apparently did not come from anything visible in the diff. when the cover was removed.
Where did they come from ???
I am wondering about a pinion bearing cone & race ???

[dcrawford]

Just a thought. And this may already have been addressed. Inside the axle tubes, just outboard of the inner oil seals near the differential, there is a stamped, formed sheet metal ring that smooths the corner transition from the actual axle tube to the diff housing. When the inner oil seal is pressed in, it pushes up against this piece. I'm working on an axle now and that formed piece was loose and popped out when I removed the seal. Could this piece be rotating inside the tube? I understand that the noise is with two different axles, so it's not likely, but worth a consideration.
Dave