Questions about components and sources of vibration - PeachParts Mercedes-Benz Forum

guyonabuffalo · #1 10-06-2015, 02:21 AM

Hi folks,
I have a few questions for both my peace of mind and understanding of things.

Last night on a 20+ mile drive home, I noticed a kind of slow wobble/vibration under my foot. Like the car was going over equally spaced bumps. This seemed to happen consistently around 60-65mph. At first I thought it was the road surface but later I realized, it felt like the throttle pedal assembly and other front end components were being shaken- at a slower rate than engine wobble motion (which is why i suspected road surface). I timed it and it had a pulse of about 130bpm.

1. Does this sound like some sort of front end issue?
2. Or could it be that now that my mounts are better and stiffer, some kind of engine vibration is being transferred to the linkages and such and the problems is in the engine?
3. What does a failing anti-roll bar feel/sound like?
4. Harmonic Balancer. I understand its purpose but how would one know if its on the way out?
5. Can the harmonic balancer cause slow vibration?

I ve recently managed to make my car modestly pleasant to drive and live with. OFV spring, fuel system cleaning, lift/primer pump, mounts, linkages etc. I really hope its nothing and just my imagination and road bumps.

Your help and suggestions are greatly appreciated.

cooljjay · #2 10-06-2015, 02:28 PM

Letting us know the make n model of the car would help?

First thing I would do is check the tires for a bubble or something worse.....

Partscarver · #3 10-06-2015, 03:17 PM

X2
look for tread delamination, some times it's really hard to spot
or wait till it gets worse...but that can be a bother.

leathermang · #4 10-06-2015, 03:52 PM

Fastest way is to get another car to drive behind and to the side of you...on both sides... you can see the tire moving if that is causing it...

Diesel911 · #5 10-06-2015, 03:52 PM

One way to see if it the Tires might be to get the Car going and briefly put the moving car in neutral and see if that changes the resonance. If it does not it is likely related to your Wheels. If the resonance changes then it could be some Drive Shaft or Mount issue.

After the tires check the Flex Discs and the Motor Mounts and the Drive Shaft Support.

guyonabuffalo · #6 10-07-2015, 01:41 AM

Thanks for the responses folks. My car is a 1978 300D. From what I have learnt through available literature as well as physically comparing with a friends car, many of the details on my car are more like the W115 300D I tried a few things from the suggestions above.
My tires are about 1 month old, they were balanced when installed. All front suspension components were changed with Lemfoerder parts earlier this year.
I drove it on the flattest piece of highway I could find close to me today and think I have narrowed it down to two separate things.

1. Tires need better balancing. There is vibration between approx. 75 - 80mph, it goes away below and above that range. This I can get checked and if necessary, fixed soon.

2. My throttle control mechanism is like that in a W115, as in throttle pedal connects to a spring that connects to a rod that goes across along the firewall etc. Kind of like this
http://www.benzworld.org/forums/attachments/vintage-mercedes-benz/327370d1282910094-throttle-linkage-bushings-under-hood-30_002.jpg
except a few differences since this picture is from an SL I believe.

If you look at the picture in the link, I tried jiggling rod number 186 by hand and turns out I can move it from side to side about 1/2 inch with little effort.
I am assuming this is not normal and is probably because the bushing no. 138 is worn out. Given the way the engine normally vibrates, this much play in the throttle controls might be what I am sensing. Keep in mind, the play is side to side. About two weeks ago, i noticed my throttle pedal rattling so I replaced the plastic bushing (no. 54) behind it. It stopped the rattle but I definitely feel vibration on the accelerator pedal if I keep my foot on it at idle. Is it possible to disassemble this linkage? If so, where would I look for this bushing? I checked a few sites and I m not really even sure what its called. Most throttle linkage bushing searches result in bushings for newer 1980 + model year linkages, which are totally different from mine.

What do you folks think? Am I on to something or is this a negligible problem?

Thanks

mannys9130 · #7 10-07-2015, 03:12 AM

Shifting to neutral while the car is moving won't change anything. The wheels, axles,and driveshaft will all still be turning.

Inspect your wheels inside and outside rims. Make sure a wheel weight didn't fling off. After stopping coworkers from almost using the wrong wheel weights during a balance, I put a lot of stress on it.

Stretch · #8 10-07-2015, 04:30 AM

I've heard that it is still possible to get "one side wheel balancing" done in the US. If you have weights only on one side of the wheel then you might be suffering from an inferior calculation...

...have you checked your wheel bearing clearance a la FSM? Have you got relatively new engine mounts?

leathermang · #9 10-07-2015, 10:01 AM

Wheel weights can be knocked off by hitting baby armadillos so small you won't even feel the impact...
I do not know what speed computer balanced tires are balanced at.. but when I was working in a front front end shop and they used the Hunter wheels which clipped to the actual wheel... they used about 45 mph ... I would sit in the car with my fingernails close to the dash and tell them when they got to smoothest setting...
Another thing I hate about computer , off the car, balancing..
is that the possibility of cumulative ' error' is possible... the discs or brake drums and the tires and wheels are dealt with as a UNIT with the old style balancing... hard to know if ' clocking' your tire on your axle will help or not without a lot of work...

Zacharias · #10 10-07-2015, 11:50 AM

Most shops balance the wheel and tire off the car for normal tire installs. THat is an imperfect system at best. I had a Volvo 240 that I had to take to the nearest Chrysler dealer, as they were the only shop with an on-car system (and someone competent to operate it).

The fact your tires are new doesn't negate the possibility one or more is failing. You could also have picked up a nasty nail or piece of debris that has self-sealed the hole it's made, but is heavy enough to cause that sort of symptom (nice big construction nail, for example... happened to me).

The early w123s, through model year 1980, have a different linkage and throttle firewall bushing setup than the later turbo models.

I would suggest you try raising the tire a bit using the jack, and spin each side then examine the tread surface. Watch for any wobble or sign of a bulge or bubble on the sidewalls (inside and out). Obviously look for foreign objects in the tread, but watch for a cut/slice (coke bottles do a lovely job of that). Actually look for slicing on the sidewalls as well.. this can be hard to spot.

guyonabuffalo · #11 10-07-2015, 12:11 PM

Checked tires today. No visible signs of damage or nails etc. However I think I will try to get an on car balance done. Just have to find a place that does it.

Have any of you with the older W123 cars ever messed with the linkages? There doesn't seem to be any pictorials or any relevant info since I assume they are fairly uncommon.
My mounts are brand new and since installing them two weeks ago, the car is significantly smoother and generally quieter.
Based on my personal experience in previous cars, the vibration at specific speeds was almost always related to tires and/or balancing. So that's something I will look at.

For those who know about this, what are some symptoms of driveshaft mount failure? I have been planning it for a while, maybe it's time I got it done.

Does the rear sub frame mount contribute to vibrations?

Maybe I m looking for trouble where there isn't any but I m sure most of these rubber parts are old and rotten by now.I will try to post a photo of the throttle linkages today.
I really appreciate all your input.

cooljjay · #12 10-07-2015, 01:47 PM

It is an old car, there are many things that can cause vibration...Just like many things can cause rough idle...

What brand mounts did you use? Did you also replace the trans mount?

Only one who can tell you if the driveshaft mount or flex disc are causing the issues....is you....You need to get under the car and inspect things....Then tell us so n so is cracked/bad/gone...

Here are PDF's about the linkage....but remember this transmission is all manually controlled meaning if you mess with the linkages, you will change shift points...That is if they are correct to begin with...

Removal and installation of accelerator pedal
http://mb.bolinko.org/wis/w123/CD02/Engine/615/30-330.pdf

Removal, installation and adjustment of front wall regulating shaft
http://mb.bolinko.org/wis/w123/CD02/Engine/615/30-320.pdf

Removal and installation of engine longitudunal regulating shaft
http://mb.bolinko.org/wis/w123/CD02/Engine/615/30-310.pdf

adjusting regulating linkage,
http://mb.bolinko.org/wis/w123/CD02/Engine/615/30-300.pdf

The whole FSM Manuals...Start reading...
W123-dokumentacja cz. 2

leathermang · #13 10-07-2015, 02:23 PM

Driveshaft vibrations will generally be about 3 times the rate of wheel vibrations.

Jarod · #14 10-07-2015, 03:31 PM

Just an odd thought as I've been chasing vibration in my 82 300D, check your axle shafts.

I had a torn cv boot and it had obviously been that way for a while, didnt cause any noise until about 45-55 mph, when it would shake the car very noticibly, felt like a lost wheel weight to me.

replaced them, I'd say 90% of the vibration is gone. I'm thinking the very slight vibration is from a driveshaft centering busing, I replaced the center support bearing, the flex discs and now the axle shafts, but was unaware of the little centering bushings.

guyonabuffalo · #15 10-07-2015, 04:42 PM

Thanks a lot Jay! Those links are excellent. I adjusted all linkages to fsm. Currently the car shifts great. It's just that there's play in the cross sectional rod which causes vibration and noise. I will attempt to fix/tighten things and see if that makes a difference. Once this is fixed I will post back with how the car feels. Thanks to you all for the excellent suggestions and especially to Jay for the awesome links.