W123 Shimmy at ~60+ mph - PeachParts Mercedes-Benz Forum

Demothen · #1 10-03-2016, 11:41 AM

I'm getting a shimmy at around 60 mph and up in my w123 300D. It seems to come through the steering wheel the most, but I can also feel it in the pedals. I noticed that my driver's side mirror shakes, but do not notice it in the passenger's side much.

I've rebuild the entire front end, all new bushings, tie rods, balljoints, steering damper. I am noticing a occasional clunking at low speed cornering from the front though. I need to try to figure what that is. I used lower priced parts instead of all top-end stuff, so I suppose something could have failed - but it's only been a thousand miles or so since I rebuilt it. Alignment has been done and checked once or twice.

I have replaced the tires, <3000 miles on the tires, which have been balanced and re-balanced.

The front brakes are also new.

I've also got new motor mounts and transmission mount, though engine RPM does not seem to affect it.

At this point, my only real thoughts are:

The low speed clunking is related to this.
My tires are garbage and won't balance (possible, they're moderately priced, and I've been chasing a "tire pull" that seems to follow one of the tires, been meaning to swap that for the spare).
Some level of vibration is normal, and that should be absorbed by the steering coupler, which could stand to be replaced (I feel this is unlikely).
I have a vibration somewhere in the driveline. I need to get the car up in the air and inspect the driveshaft supports and couplings, but if I recall they looked like they could use some attention.

Assuming the driveshaft is the culprit, what all should I replace while I'm doing the work? I'm thinking U joints, supports, bushings, boots, and flex joints?

leathermang · #2 10-03-2016, 12:05 PM

Did this start immediately after you got it back on the road after you replaced all those front suspension and steering parts ?
The word ' shimmy' does not bring to my mind driveshaft...
and does not go along with the speed it starts at to me...

You have already determined that the tires will not balance...but are not blaming them ?

How did you , or someone , set the toe in ?

Go ahead and swap that spare to where you think you need to.... no need to jump over what you suspect already... eliminate that first..

Demothen · #3 10-03-2016, 12:08 PM

Honestly I'm not sure. Before I replaced the suspension it was in really rough shape. I know when I bought the car it was even worse because I had a wheel missing all it's balance weights. I think it's shimmied the entire time i've owned the car, but I can't swear to it.

leathermang · #4 10-03-2016, 12:12 PM

Ok... get someone to drive the car and you drive beside it and see if you can see any vibration in the wheels at any speed... this is easy compared to lots of other stuff.. a vibrating wheel can easily be seen...

Demothen · #5 10-03-2016, 12:21 PM

Good tip! Thanks!

charmalu · #6 10-03-2016, 12:50 PM

You mentioned clunking, did you replace the Guide Rod Mounts?

Pelican Parts - European Automotive Parts and Accessories - Porsche • BMW • Mercedes • Volkswagen • Audi • Saab • Volvo • MINI

Raise her back up securely of Jack Stands with the front suspension hanging,
and move the tires back and forth on each side to see if you notice any slop in the
Steering components.
Using a Pry Bar under each tire, move it up and down to check for slop in Ball Joints, Upper Control arms etc...

Did you replace the Idler Arm Bushings?
How are the Wheel bearings?

I know you replaced everything, but can`t hurt to recheck things.

Demothen · #7 10-03-2016, 12:55 PM

Oh good call, I did not replace the guide rod mounts now that I think about it. I checked them at the time and they seemed good, but it's worth double checking for sure. That could be the clunking.
I'll check with a pry bar again as well.
Idler arm bushings and wheel bearings are new.
Would guide rod mounts cause a shimmy? They control caster right?

leathermang · #8 10-03-2016, 01:06 PM

I am surprised you did not replace them with all the other stuff...
they do not cause shimmy by themselves..
but if your wheel is vibrating then a worn guide rod mount will allow movement fore and aft... the same effect when you put on the brakes... which can cause a ' clunk'...
instead of trying to check them... suggest you just replace them... you said the car was worn a lot when you got it... so just assume these were worn as well....

Demothen · #9 10-03-2016, 01:14 PM

It won't cost me anything to check them, but yeah - I'll probably replace them. I think I forgot to order them when I was doing the previous work, and just decided to go with what I had to get the car back on the road. It looks like they can be changed without dismantling the suspension much, but I may have to use a ratchet strap to pull the LCA forward? I have a 3 year alignment plan, so at least I wont have to pay to have it aligned again. It sounds like that's a very likely place for my clunking to be coming from.

greazzer · #10 10-03-2016, 01:19 PM

Still could be the tires. Did they do a full dynamic balancing? Not just lower speeds, but at the 60 MPH range? I generally get my tires at Firestone who used to provide a superior service. Now, count on a re-do of virtually most services, to include tire balancing. Make sure they (whoever you go to) balances them at the 55-60 MPH range as well. The MB front end is pretty robust overall. Some cheaper cars I have driven in the past feel like at 80 MPH you're hitting an asteroid belt ... lol. The W123 holds its own well over 100 MPH and it just hums along ... so ...

Demothen · #11 10-03-2016, 01:38 PM

Good question Greazzer. I called the shop that did the balancing, they said they use a dynamic machine but had no idea what speed it runs at. They said it could be bad tire pressure (yeah, uh, I've checked that about a dozen times), or a bent wheel - which one would HOPE they would have noticed during the balance, but who knows..

Really not happy with that shop. I'll see if I can find a shop that knows what they're talking about and has the equipment to do a high speed balance.

greazzer · #12 10-03-2016, 01:43 PM

I can say this about tire balancing. Unless it's done, and really done correctly and at both speeds, e.g., low and high (the latter being 55-60 MPH), you will probably have a weird shimmy or something 'wrong' up front. Put truly top of the line tires on wife's car and it rode like shyte on the highway. Took it back for a re-do at Firestone and sure enough, they were not balanced correctly at high speeds. Well worth the $75 bucks to get a guarantee they are done correctly. That is why I force myself to pay the ransom for the 100% roadside / warranty deal at Firestone. Once you start coming back and back and back, they will recognize your name and will do the job correctly.

leathermang · #13 10-03-2016, 01:48 PM

I used to work at a front end shop..... I really do not know how you would properly test a guide rod ( used to be called a control arm ) mount... You can tell if they are plumb worn out... but otherwise.. with all the wear on the rest of the suspension.. suggest replacing it..
Given all you have said... I suggest you just put the new ones on..
Here is the problem with using a computer for tire balancing.... it only balances the wheel and tire... if you have a brake hub slightly out of round or balance... and you happen to put the tire on a certain way.. you can get what is called ' cumulative error' ... I hate that the old way of jacking the car up and spinning the entire mass to check for balance is not commonly available for cars ... I think they still use it for trucks...

Demothen · #14 10-03-2016, 01:48 PM

Called the local firestone, they do a high speed balance with road force to check the roundness of the tire for a reasonable price with 6 month guarantee. They dont do low speed balance though. I think that is probably my best bet, I wouldnt be surprised if one of my wheels or tires is out of round or bent.

Demothen · #15 10-03-2016, 01:52 PM

Yeah, LMG i wish i could get a shop to run it on a dyno and check the systems. I am tempted to find a sensitive accelerometer and do some data logging on various points of the car during driving. I would think i could chart each control arm, and maybe the transmission and floor pan near the driveshaft supports to look for an oscillation. The only problem with having someone else drive my car is that I hate having other people drive my vehicle, and finding a friend with time to help.