My 1992 500SEL has a noisy strut problem. The bushing at the bottom of the rear strut sounded like an old bedspring creaking along down the road. I hated to spend the money on a new pair of struts when the old ones don't leak and otherwise work just fine. No 'clunking" sound, but man did it ever 'creak."
Today I attempted a fix. It started by pulling the struts. Before I'm done, all the rubber grommets on the rear of the car will be renewed. What a messy job. Cardboard was used to contain the oil spray as we broke the lines. It wasn't that bad but the floor would have been soaked but for the copious amounts of cardboard scattered about. Even with the cardboard it was difficult to contain the spewing strut after removal. More than once I nearly blasted myself in the face with fluid.
The bottom bushing is not a bushing actually. It looks to be 'rubber' like an ordinary shock but it's not. What you see is a rubber boot covering the bearing. It's a very complex and precision made nylon bearing designed to swivel to allow for the very complex motion of the strut. Imagine a ball-and-socket with a bolt sleeve running through it. The total throw on the strut is only about 3", which compounds to the travel of the wheel by means of the mechancal advantage afforded any lever. If you have 'clunking', you have a failed nylon bearing which would require a 3 or 4 axis mill to replicate. As luck would have it, mine were intact--WHEW! Any clunking noise would come from the strut banging on the through bolt due to the disintegrated nylon bearing.
It may not be nylon by the way. It looks like nylon but it may be a more substantial plastic like Delrin or some other type. I'm calling it nylon because people are familiar with that material. It's milky white in color and looks and feels like nylon.
At the factory, the bottom of the strut is assembled as a package. The aluminum socket is pressed onto the steel sleeve of the actuator. The assembly is placed into a press and struck to bend the ends around the bottom assembly and crimp the socket unto a mushroomed actuator end. I could place the end in a vice and use a pipe wrench to spin it, but it is NOT threaded. Removal would destroy the end.
Each side of the bottom assembly has a lip that contains the bearing on both sides. Removal requires that the lip be removed. I used my vertical mill and just free-hand removed about 1/8" of aluminum. Striking the sleeve with a hammer forced out the assembly.
The assembly is a sandwich of layers. Removing the spring allowed me to remove the boot and expose the bearings. What a grubby mess!
The 'fix' was to place the sleeve into the lathe and use emery cloth to remove all the accumulated rust. The creaking was due to the accumulation of rust in the small pockets of the nylon designed to hold the rust. Once it was packed full, it was using the rust as a lubricant of sorts, which clearly does not work well for the bearing. Left to its own, the nylon would fail most certainly.
I cleaned it all up, used copious amounts of moly grease, and put it back together. The trick of course comes from fabricating a new 'keeper' for the bearing.
The sandwich includes a washer, which was pressed into the aluminum and unsalvagable, and the bearing assembly. Once removed, a small 'lip' remained on the stut bottom. So I fabricated two large washers. One to replace that original washer (1/16" thick) and made to the exact inside and outside dimension as the original, and a second to be the size of the strut bottom to act as a keeper.
I drilled a pattern of 6 - 4-40 x 1/2" screws. I drilled the holes 3/4" deep and ran the tap all the way to the bottom. On each strut I broke the tap in one of the holes and had to drill another slightly off the pattern of the original. I wanted to use 6-32 but there is simply not that much material left. There doesn't appear to be any shear stress on the screws so I think it's going to hold.
I have a $20 bet with a local mechanic that it will make it just fine. He has 'bet' is that it will fail in <1000 miles. Obviously, this bearing has to hold the weight of the car bouncing off pot-holes. I'm not sure where the weakest link might be. The screws? The removed aluminum around the bearing? Time will tell. What I do know is that this is a fix requiring labor but not money. Although if you were going to ask a machinist to fabricate those washers, he's going to charge you for an hour or two of work.
So what do the rest of you think? Did I make a good bet?
Thank you for this. I say to myself everyday I drive my car with it's creaky rear, why on earth are those bearings non-serviceable, not even a grease fitting, good precise design but I would have went with a pure spherical bearing with no plastic sleeve around the ball, the strut is isolated again at the top anyhow.
I'd like to do this but the downtime of the vehicle may hinder me to do so, say I run into and issue, I just wish there was a way to loop the hydro lines but in a way so I can use them again, say in the mean time I put standard dampers in whilist I do my fabrications. I was thinking having my machine guy Take the measurements of the bottom joint and replicate them and then install a one piece desing after gutting the joint like you did. He would just weld it back in place.
The thing is my car doesn't sag a great amount when the system is fully depressurized like lets say a W126 rear does when the hyrdos fail. So having standard damper in there wouldn't be a problem.
Great effort IMHO
"However, not the the aesthetic masterpiece you might have expected for a billion dollars, but all of them, and this one in particular, justifies it's price through sheer attention to detail." -Jeremy Clarkson
I beg to differ. The entire strut is available as a part number, but the bushings and nylon appear to be unavailable. I can get the part numbers off the individual parts if you like, but the repair involves destroying the strut--e.g. removing the flange pressed at manufacture. I defy you to locate the spherical sleeve, and the nylon 1/2s that encase it, plus the boots that contain the system. Of course, the wire-like springs have no part number, and none is listed in the STAR software.
I beg you, produce a link to the part as you suggest.
Meanwhile, most are faced with a $1500 or more repair, while I am suggesting a $60 repair (the price of the dang fluid Errgghhhh!)
Does anybody know of a substitute fluid for the 'leveling' system? MB gets absolutely stupid money because they don't specify a lube. So you have to buy theirs.
I have read that John Deere hydraulic fluid would work just fine, but considering that the piston clearance of the strut is infinitely structured, I'd stick with the MB fluid. Actually DOT 4 brake fluid would work, but it would be a big mistake to use it because it is so hydroscopic.
Congratulations on your attempt to solve this common and dispiriting hydraulic strut problem.
Your commentary and pictorial presentation give new hope and knowledge to all of us dealing or who will eventually deal with this issue.
I can't say if your bet will pay off for you. Only time will tell. Please keep us informed.
Last edited by drcharlesatlas; 09-14-2009 at 06:39 AM.
I was thinking having my machine guy Take the measurements of the bottom joint and replicate them and then install a one piece desing after gutting the joint like you did. He would just weld it back in place.
I think welding would be a mistake. Why? Because the entire arrangement needs to be under a good deal of pressure to secure it back into its permanent prison cell. And the heat of the welding would destroy the boot covering the joint, which is part of the sandwich and in direct contact with that washer on the end. Excessive heat would turn the whole assembly to peanut butter.
Before replacing the strut, I'm going to swap out the screws and use stainless with loc-tite. I don't want to lose my $20 bet to something really simple.
In a private email I was queried about the possibility of soaking the bearing to eliminate squeaks. I'd like to comment on the failure mode observed.
I should have taken a better picture of the inside of the bearing. The one below is about as good an example as I've got. So I'll reference that one.
The peanut butter-like paste you see on my fingers is actually rust. The nylon bearing is in two halves. Each half is a cup that encases the bolt sleeve. The rust appears to be an accumulation of surface rust. What at first appeared to be pitting was actually layers of rust pressed to the surface. The nylon cups have grooves, which I presume are designed to draw the oxide out of the way. Frankly, they looked like they worked very well until the system was overwhelmed with the amount of rust accumulated.
While the system is considered "sealed," it's not. To make a true seal it would have to be impervious to the passage of air. Any air exposure to the steel is going to cause rust. No getting around it. I don't care how well you seal something to eliminate water, if it allows the passage of air it will condense when the temperature of the metal drops below the dew point of the air.
With that being said, the system is quite impenetrable to liquid. In my opinion, soaking it in a lubricant is a waste of time. Until the excessive rust oxides can be removed from the joint, and a proper grease applied to reduce the exposure to air (and the associated moisture that comes with air), adding a lubricant is simply changing the viscosity of the abrasive materials. The rust had the consistancy of pencil graphite dust. Imagine an oil mixed with grit. That's how they polish gems and stones. I've heard of people using a hypodermic needle to inject oil into the rubber seals, but I seriously believe it to be a waste of time and good grease.
Last edited by rightstuff4u; 09-14-2009 at 07:39 PM.
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