84 126 metallic popping sound rear axle area - PeachParts Mercedes-Benz Forum

kerry · #1 04-22-2017, 08:42 PM

Daughter's car. 84 SD. A few months ago had left rear trailing arm replaced since it had a rust hole. Drove the car around town for months. Smooth as silk.. While we were out of town daughter took it on interstate and reported popcorn noises from back seat area. I thought ruptured boot and dry cv. Everything is intact. Daughter and wive took it on highway today and wife recorded the sound. Loud metallic popping which she recorded. I took it out and couldn't get it to repeat. I thought maybe shop didn't put the axle bolt back in axle thru the hub and a bump at higher speeds was pulling the axle out of the hub and splines were popping in and out. checked the bolt. Got about 1/4 of a turn on it but it was pretty tight. Any body have any hypothesis on the problem? Wife and daughter disagreed on which side it was coming from. So no sound under 40mph at all. Sudden onset at higher speeds. Not sure what initiates it as I couldn't get it to repeat. But definitely loud enough that my wife said she would have pulled over and driven no further.

kerry · #2 04-22-2017, 09:01 PM

Wife says live sound was louder than it sounds on the video

https://www.youtube.com/watch?v=jX1YQhsE1vg&feature=youtu.be

barry12345 · #3 04-23-2017, 10:41 AM

Not exactly the noise I would expect. Still typical of a cv joint once it heats up with little to no lubrication present. As far as this relates to the typical onset of the noise you are experiencing. Personally I would remove the clamps on the inboard side of the outer boots and inject some really heavy oil into each side.

As the parts get hot with no lubrication they expand. The popcorn noise could be them breaking loose to serve their function. Means they should not be worn a lot.

At worse you want this done as it also falls into the sphere of maintenance for reliability. Over the years we seem to have many cases where oil is lost in those joints even with good boots. It may not be the issue but a man has to know. It is the best bet probably if uncertain. If it were say the axle securing bolt was very loose I would expect a constant noise issue.

Again the time required to heat a dry cv joint usually means some highway running. Before the onset of any noises. If that does not do it then check the rear end oil level. I cannot see a dry one making that noise but you never know in life.

We have had a rash of dry cv joints over the years. I would expect more and more as these cars get even older. Preventative in nature for those using their cars a lot on the highway this upcoming year. Is adding a little oil to each outer joint. I am not quite sure why there are far less issues with the inner joints.

Also watch out for a loose inner joint although it should not be intermittent like this. The noise just does not sound clunky enough to me either.

kerry · #4 04-23-2017, 12:30 PM

Thanks. What kind of oil do you use? 90w gear oil?

kerry · #5 04-23-2017, 01:03 PM

Also, do you just replace the original clamp with a geared hose clamp? Or are the original clamps removable and replaceable?

kerry · #6 04-23-2017, 03:00 PM

From this thread it looks like it's one cup of oil per can.

http://www.peachparts.com/shopforum/diesel-discussion/380467-rebooting-pair-axle-shafts-how-much-oil-required-each-can.html

barry12345 · #7 04-24-2017, 08:23 AM

I never really decided what should be added for a top up.. Maybe 4-5 ounces first. A screw clamp is fine.

I like the ideal of snaking a small hose in the boot gap to axle and squirting the oil in. Less stress on the old boot. There probably is a spec for the oil type somewhere. I just never have seen it.

The 75-90 weight is a good choice to me though. Because it is a heavy load bearing lubricant. I also used to wonder about the possible effect of too much oil relating to balance. Then I decided the diameter of the boot is not that large. So it is not important. .

You can design for forced recirculation though a bearing. In this case I think since the boot runs at an angle the oil is just thrown all over the bearing surfaces all the time. Centrifical force cannot really function to keep the oil pinned to the inner surface of the boot. Because of the angle. A very clever setup.

mytimeyet · #8 04-24-2017, 11:16 AM

From the sound, I'll take a guess... Starting with simplest, something stuck under the car that is flapping around once the wind turbulence under the car is great enough (highway speed) - CV, maybe - Flex disk, frayed bit hitting the tunnel? or something attached to the drive line. Center support bearing? All guesses though.

kerry · #9 04-24-2017, 12:41 PM

Since there was evidence of leakage on the driver's side outer can I decided to refill that one and test it to see if that was the problem. Original clamp is easily removable without cutting. Put a narrow bladed straight screwdriver in the crimped portion, wiggle it back and forth to loosen the crimp and then the ear which catches on a slot can be slid out and clamp unwound. I then slid two flat bladed screwdrivers inside the boot end with a space between them. Then, using the $14.99 (not the $5.99) meat flavor injector from Bed Bath and Beyond I injected about 6 oz of synthetic 90w gear oil into the boot and put a new hose clamp on it. Standard hose clamps are wider than the original and don't fit nicely in the boot groove. I don't like that and may look for a narrower clamp. I haven't road tested it yet. I will. I also took some pictures of the process, tools and clamps which I will post later.

kerry · #10 04-24-2017, 01:22 PM

OK. Test drive complete. No more noises. I'm declaring Barry's hypothesis correct and problem solved. We'll see how long the oil stays in the boot. Everything looks original under there and there's 317k miles on the car. Outer boot seems better than the inner boot.

kerry · #11 04-24-2017, 01:31 PM

Pictures.

Only one screwdriver was in place when I took the photo. After some thought I decided two would make the job easier.

kerry · #12 04-25-2017, 09:01 AM

More thought and closer inspection leads me to think that the leak may be coming from the connection between the can and the axle shaft, perhaps damaged in the control arm replacement process. If that's true, the oil I added will also leak out in the near future. If that happens, I will likely remove the clamp from the large end of the boot and pack the joint and can with grease since it is less likely to leak out.

kerry · #13 05-07-2017, 03:26 PM

I've driven it a couple of time since doing this with no further noise. However, my wife and daughter were driving it today and they said they heard a single pop twice when making a turn on the interstate. Any hypotheses about that? Not enough oil causing excessive heat and expansion? Add more oil?

barry12345 · #14 05-07-2017, 04:53 PM

Any chance the oil you added has leaked out? You may consider removing both boot clamps and inspecting for lubrication. Depending on how the can may have been damaged. Centrifical force could remove oil faster than one would think. Perhaps your ideal of packing that one with grease is sound.

Any ideal of about the miles in service after the trailing arm was changed? Before the noise started? May indicate a leakage rate.

kerry · #15 05-07-2017, 05:03 PM

Less than 200 miles before noise started I think. It doesn't get driven much. I can't see any evidence of substanstial leakage although I will check again. I took it to a car wash and cleaned all the oil off after I added the new oil so perhaps a close inspection will reveal more leakage. A quick glance a few days ago and it didn't look like any had leaked out.

Just checked. A slight wetness on the brake backing plate. Perhaps a spot I missed at the car wash or a little new oil leaked out. I'll continue monitoring.