Calling all rear axle experts! Knocking noise coming from rear axle

[mcgarrett]

I did some troubleshooting again on my '40 Tudor Sedan today hoping to identify an annoying clunking/knocking noise coming from the right rear axle area and FINALLY isolated where it is coming from. The right rear axle shaft had just enough axial play to make a knocking noise when going over potholes and choppy roads. It might be somewhere around .015" to .020" but just enough to allow a bumping or clunking sound over certain road surfaces. The bad news is that it won't be an easy fix. I'll have to pull the rear axle assembly

Will I have to replace the right axle shaft or can it be shimmed?

The axle nut has been tightened to the specified torque and the key is very tight in the keyway. The drum tightens down like it should, but there is that pesky little play in the axle that is causing the noise.

Appreciate any input from all the rear axle specialist here on The Barn.

[Bored&Stroked]

The axle itself is really not responsible for controlling the axial play - unless it is bent and/or isn't correctly mounted/seated on the taper. So, I doubt the axle is your problem (best guess!).

What WOULD cause this is related to the bearing inside the rear hub and the bearing surface it rides on. If the axle "snout" is worn, or the bearing is shot, then the whole drum/axle assembly can move up and down. I'd pull the drum and inspect the bearings and the axle snout.

Note: There are TWO bearing surfaces for each hub - both need to be in spec. 1) Inside the rear hub itself - the OD of the roller bearing rides on it. 2) The bearing snout of the axle tube - the ID of the roller bearing rides on it.

It is not uncommon for the bearing snout of the axle tube to be worn, pitted, etc.. Folks have dealt with this for years. The whole housing can be machined (the snout end) partway down (on the OD) and a special repair sleeve pressed onto it. The repair sleeves are sold a variety of places - they are bearing quality (finish ground and hardened). The challenge is finding a place that can do this work. If that is the case, you'll need to ask folks on this forum for recommendations. Also, you could contact HotRodWorks to see if they can do it - or recommend somebody who can.

You can purchase the sleeve at ThirdGen Auto. If this is your problem, you should call Michael and see if he does this work, or knows somebody who does.

Best of luck!

[mcgarrett]

I pulled the rear drum and all looked fine there. Don't see any evidence of improper fit or looseness. Put it all back together and torqued down the axle nut again and still had a small amount of freeplay. I don't know what it would take to eliminate it. It feels like the axle itself is moving back and forth (horizonally) only by a few thousandths.

[deuce_roadster]

What is being described sounds to me like it is not the axle but maybe the pinion bearings in the banjo or the bearings the ring gear rotates on which are on the inner ends of the axle housings. If it was mine, I would take it apart now before something catastrophic happens. If it is making a clunk now, it is only going to get worse and may wipe out your ring and pinion. You would also have the opportunity to check the spider gears when apart and the spline connection to the driveline and the U-joint. Noises can fool you as to where they are coming from.

[Charlie ny]

Like B&S suggested is the snout on the axle housing good all around ? Next time the
drum is off run your fingers around the snout. Obviously the snout is the inner bearing

race. Don't be shocked if the snout diameter is torn up from 5 to 7 o'clock.
Charlie ny

[mcgarrett]

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Just to make sure we're all on the same page...when the axle nut is tight and I grasp the drum at the 3 o'clock and 9 o'clock positions and move the drum aggressively in and out on the same plane as the axle (horizontally), that's when I detect that small amount of freeplay and hear the bumping noise. If I try to move the drum up and down (vertically), I don't feel any freeplay.

[cadillac512]

I'll suggest an alternate "test". Maybe drive on a road that causes the noise and step on the brake pedal enough to load the engine and require more throttle to maintain speed. This should keep the axle from moving in any direction and help prove or disprove the end-play theory. It'd sure be a shame if it turns out to be something like a shock absorber or exhaust pipe and you went to all the work to remove and disassemble the axle assembly.

I've been guilty of rushing to judgement on things in the past....


Terry

[mcgarrett]

cadillac512,
I did check for loose shocks and made sure the exhaust system wasn't making contact with the frame anywhere - all good there. I'm positive that I've isolated the problem with the right rear axle. By pushing the axle in and out the way I described above, I've been able to duplicate the exact sound I hear when driving on bumpy roads. Trust me, I'm not looking forward to an axle teardown!!

[bbrocksr]

I don't think its the endplay causing the noise. They all have endplay, something else is causing the noise and it sounds the same as when you move the axle in and out.
Bill

[mcgarrett]

Thanks for all the helpful feedback. I think I'll reach out to Mac Vanpelt next week and get his take on the situation.

[drolston]

When is the last time the rear end was apart? If the banjo gasket shims were left too thick, a little wear could have loosened the preload on the differential carrier bearings, leaving room for the axle to move longitudinally. Here is the test for this condition from the Mac VanPelt site:

"The differential bearing adjustment may now be checked. Two people are required for this operation. Each should turn one of the axle shafts in the same direction and at about the same speed. If the adjustment is correct, a heavy drag should be felt. If the shafts turn easily, without apparent drag, the gasket on the right axle housing should be replaced with a thinner one (.004 to .005" thick). Check the adjustment in the same manner. If satisfactory, check the backlash between the ring gear and pinion."

Whether or not that shows a problem, I would retorque both sides of the banjo and check again for your slack. Put a jack under the banjo to take some of the weight off of the wheels and reduce the leverage of the axle housings at the banjo.

Here is a link to the VanPelt document describing how to set up the differential carrier bearings and pinion backlash.

http://www.vanpeltsales.com/FH_web/f...le_service.htm

[mcgarrett]

drolston,
I have a strong feeling that you may be onto something here. I had the rear axle apart about 10 years ago when I swapped out the 3.78 to a 3.54. All seemed to button up well and the car has been driving just fine ever since until about a year ago when the bumping noise started. At the time I first heard it, I thought it was probably a loose shock, exhaust rattle, etc. Now that I have dug a little deeper and made this discovery, I'm thinking you're on the right track. Thanks for chiming in with your observations. I was hoping it wouldn't require pulling the axle.

[larrys40]

Originally Posted by deuce_roadster

What is being described sounds to me like it is not the axle but maybe the pinion bearings in the banjo or the bearings the ring gear rotates on which are on the inner ends of the axle housings. If it was mine, I would take it apart now before something catastrophic happens. If it is making a clunk now, it is only going to get worse and may wipe out your ring and pinion. You would also have the opportunity to check the spider gears when apart and the spline connection to the driveline and the U-joint. Noises can fool you as to where they are coming from.

I agree with the above comments. I have rebuilt hundreds of Flathead axles and have had a noise similar before and found a pinion tooth in the bottom of the lube . I would just tear it down and see what’s going on. I don’t agree with the “load test of someone on each side. The only way to do and and know when setting one up properly ia to put the axle carrier together without the pinion and check for correct preload with the applicable gasket thickness to determine your preload.
Once done and total gasket thickness determined then install pinion and check for proper tooth contact backlash . Adjust as necessary.

More to it than slapping it together for sure. It’s prudent to do a proper rebuild and setup. Having the tools and someone who’s schooled at it is best. See if there’s a schooled guy in your area . Model A guys have done many as have I.

I have seen bearings and axles come apart from improper setup and installation.
I do agree don’t overlook some of the obvious other things like shock arms/links, etc. But if you know it’s in the axle it isn’t going to fix itself.
Larry

[Mart]

What is important is when the noise occurs and what sort of noise it is.
Axial end play is normal and will not generate a noise.
Pinion wear and loose bearings may generate a noise but it would be a drone that varies with speed and whether accelerating or decelerating.
If the noise occurs when stepping on or lifting off the gas (drive to overrun or vice versa) then gear mesh or bearings may be the culprit.
If the noise is a knock or rattle that occurs when going over a bumpy road then it is most likely suspension related.
It would be a pain to tear your axle down and find nothing then later find a loosely mounted shock or spring U bolt.

So when does the noise occur, and what sort of noise is it?

Mart.

[corvette8n]

You could always get one of these 6 channel sound detectors.

[Frank Miller]

You say you can replicate the noise by pulling the wheel in and out. So what is hitting to make this noise. Typically when the differential is loaded the axle is pushed outward due to the angled gears. When hitting a bump the wheel is unloaded and can move so this is when you are hearing the noise. Look for anything that could be rubbing inside the drum as well as checking stuff mentioned earlier.

[Bored&Stroked]

It is possible that the drive teeth on the axle and the spider gears are worn, but you should be able to easily reproduce a noise/issue by letting on/off the accelerator to load/unload the meshing of them. Given ALL the possible issues - including incorrectly setup preload (bell gaskets) on the 3.54 gear swap, it will probably need to come part.

[Ol' Ron]

It's time to consider up grading the drive train to something newer. An 8" open drove with a T-170 trans is a good start, and probably not much more that fixing the old one, A friend of mine has an AOD behind his flatty, and it a pressure to ride in. I have a great deal of respect for those that like to keep their car original, But I can't afford it.
Gramps

[mcgarrett]

I appreciate and respect all the various suggestions and viewpoints offered here. I've been working a great deal on originality and period correctness on this car and still have a way to go, but with that in mind I want to keep the stock rear axle & torque tube. I'll have to pull it and see what's going on.

[Brian]

I've been following this thread. You could also have wear inside the carrier where the end of the RH axle rubs. This would permit the end play you speak of and also make the noise as you go into and out of turns as the thrust is taken up/ eased off.