w123 horrible shake over 70
 

My 84 300td has a horrible shake over 70mph, which is a bit hard for me to diagnose since I live almost an hour from the interstate... I have to drive out to closed course (or something like that) :rolleyes:

None of my tires are missing their weights. The shake isn't really in the steering wheel, rather than in the whole body of the car, doesn't matter if I'm accelerating or in neutral.

Recently I replaced my giubos and center bearing/support. The previous mechanic put the driveshaft together 90 degrees out of alignment, so that vibration is gone now. But the horrible shake in the body is still present. Two years ago I replaced one axle with a napa reman, a couple weeks ago I replaced the other with a Duralast Gold. I'm not sure if the issue could be an axle or not.

I'm out of ideas here, any suggestions?

I would still suspect wheel balance (imbalance), or possibly a bad shock absorber. A driveshaft or axle imbalance would be more of a vibration than a shake.

I forgot to mention, I replaced the front shocks which made the car handle much better around corners, but didn't touch this problem. The rear has SLS which works correctly. I put new accumulators in it a couple years ago, and the back isn't bouncy or anything.

Maybe the back tires lost their balance? They only have a few thousand miles on them and aren't missing the weights, who knows. I'd doubt front tires are out of balance since that usually shakes the steering wheel pretty bad before it shakes the whole car.

Wheel balance, tire fault, bad shock. They can all cause vibrations. They will be at relatively low frequency, about the speed the tires are going around. If you have a problem in the driveshaft, it will be much higher frequency, more of a vibration than a shake.

I had a bad vibration on my wagon, then when I swapped my wheels and tires over to my coupe, the vibration moved with the tires! had one way off balance and once redone, it cleared right up. I think my issue was the tires had been sitting for awhile and developed a flat spot the caused the balance to move once the tires were run for awhile and had a few heat cycles.

If it is low frequency and is so strong it throws the car about, I'd be looking at the steering dampener/shock. $30 and two bolts. Good luck!!!

This one was frustrating me since it's a 20 minute round trip to my err... "test track", so making a change and not having it solve anything is annoying.

My front tires were more worn than my back tires due to a bad alignment which I fixed a few days ago to no avail. I hate making more than one change at a time because I end up not knowing which change fixed the problem...

I swapped front and back tires and also found the back left caliper to be somewhat frozen and dragging really bad, weird since I changed the axle on that side 3 weeks ago and it was fine. I blocked off the line and removed the caliper. So either the caliper sticking or something to do with tires was causing the issue, I got up to 85mph and it's like driving a brand new car.

After the issues with the driveshaft and CV axles, this vibration, and other broken stuff I've honestly been pretty down about this car. Now that it cruises down the road silky smooth it has pretty much made my week (until something else expensive breaks...)

We're having the same problem with my roommate's 1991 W126 350SDL. At 70 MPH the front end shakes badly, and at 75 MPH it's too much to drive it that way. The front left tire's outer tread completely wore off in less than a year from new.

The tires on the car were less than a year old. Walmart said they balanced them then. My roommate took it back and they said the balance was fine. We swapped the front wheels to the rear to prevent further wear of the front left tire and it has the same shake.

I took the car to an alignment shop that was recommended by the local independent Mercedes repair shop that does all their alignments (dealer wanted $300) and the shop mechanic shook his head at me when I told him that the front end shakes. He told me that front end shaking NEVER has anything to do with alignment and I'd be wasting my money. He said it's wheels and tires. But Walmart says that the wheels and tires are balanced and fine.

I had them look at the car anyway because of the front left tire wearing out so fast. A couple minutes later he came back and said, "Nope! We're not touching your car. It needs everything replaced." I asked what exactly needed replacing, and he said, "It needs a new steering box, all subframe mounts, all tie rods NOT just the tie rod ends, center link, all upper and lower control arms, ball joints, and guide rods. And find someone else to do it."

The steering doesn't have any noticeable slop in the wheel and I didn't find any slop when I did a shake-down of each part. The only things that looked out of place to me were the leaking steering box seal and the squishy subframe mount from the steering box leaking onto it.

That's my experience with the issue you are having. His car also still has the original shock absorbers which squeak loudly. Some time next year I'll probably end up replacing the entire front end parts and shocks and get it aligned. If that doesn't work, it has to be wheels and tires, so I guess we'll have to take it somewhere other than Walmart because they claim the balance is perfect.

Have a shop that isn't walmart check the tire balance? A bad alignment and especially bad shocks can cause front end shakes, that's why it was my first step in finding the problem. I have replaced every bushing, balljoint, and tierod in my front end, except the LCA bushings. I also replaced the steering idler, which is really easy.
I don't have a suitable spring compressor for the massive front coil springs, otherwise it's actually fairly easy to rebuild the front end on these cars.

Two things will commonly cause excessive tire wear on the outside of the tire, excessive positive camber (which is doubtful since these go negative as the LCA bushings wear out), and excessive toe. If the car doesn't pull to one side, it's likely one side has more negative camber than the other side which is being offset by tires being toed in. You can get the alignment really, really close yourself with a laser level and a tape measure.

The front end certainly could be worn out if it has never been refurbished. You can test for tie rods by grabbing the wheel at 3:00 & 9:00 and determining whether there is any play. Ask Mr. Duck Duck Go for destructions. He is less likely to track you than is Professor Google.

If everything is worn out, repairing piece meal is an exercise in futility because parts will keep failing untill all are renewed. You need a new alignment after each part install which gets expensive.

Check the shop's diagnosis. With wheels on the ground, have your friend turn the steering wheel slightly back and forth. Look and feel for any play in the steering linkage and tire rod ends. Then, jack the front up and support it on the frame rails, w/ tires on for safety. Try forcing the tires back and forth, looking for play in the ball joints and control arms. Measure the toe-in w/ a tape measure (front tires: aft track width - fwd track width).

In my limited experience, worn lower ball joints don't cause vibrations while driving. One of my 300D's had one so worn that the ball could almost pull out of the socket, yet it drove fine. Similar for worn rubber control arm bushings, though they will give clunks over railroad tracks. My guess would be something in the upper control arms, like a broken sway bar end or bad rubber bushings on it (secures upper spindle) or excessive tow-out (causes car to wander). These cars also have complicated independent rear suspensions (requires alignment), though I haven't read of wear there causing such vibrations. I never touched my IRS parts.

Please let us know what you find.

Mr. Google has been busted deprecating sites too. So much for 'Don't Be Evil'

I try not to google out of principle but google and microsoft have become as intrusive (almost but not quite) as a virus.

here is one source of opinions. https://stallman.org/

What's odd is that in my case, I could not find play in any single component, yet the alignment shop said everything was sloppy and worn-out. So it seems that diagnosing slop oneself isn't very accurate.

You actually need to check balljoint play without the suspension drooped, jack the car up by the control arm and check for up/down play in the wheel. It helps to use a pry bar or something to lift the wheel since it's a heavy assembly.

The balljoints are under load when the suspension is at full droop and you may not notice play in them even if they're bad.

Here's a quick video on youtube https://www.youtube.com/watch?v=93ib1nxE0Ao