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?

tjts1 · #9 10-08-2015, 04:25 AM

Quote:

Originally Posted by Stretch

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...

I had a tire shop do this to my Volvo a few years back and they even argued with me that this is the CORRECT method to balance tires. I've ****ing had it with tire shops and finally decided to mount and balance my own tires using this method.
AircoledTech.com's "Tools-On-The-Cheap" Wheel balancing With Beads
This yields by far the smoothest ride I've ever had. It never goes out of balance and theres no wheel weights to lose.

Mxfrank · #10 10-08-2015, 07:18 AM

One of the things I've discovered is that since the shops in NY have moved away from lead weights, wheel weights are larger than they used to be. The significance of that is that when they put clip on weights on the inside of my wheels, they sometimes interfere with the outer tie rod ends. Not only does this produce a regular vibration, it can tear the rod end boots to shreds. And sometimes the weights are just knocked off the wheel. When I have my wheels balanced, I now ask that they use adhesive weights on the inside of the rim.

guyonabuffalo · #11 10-08-2015, 09:39 PM

Quote:

Originally Posted by tjts1

I had a tire shop do this to my Volvo a few years back and they even argued with me that this is the CORRECT method to balance tires. I've ****ing had it with tire shops and finally decided to mount and balance my own tires using this method.
AircoledTech.com's "Tools-On-The-Cheap" Wheel balancing With Beads
This yields by far the smoothest ride I've ever had. It never goes out of balance and theres no wheel weights to lose.

TjTs1, I have never heard of this technique but sounds awesome. I wish I had known about this a few weeks earlier when I put new tires on. Maybe I will get lucky and find some sharp objects to drive over so my tires will need replacing.

BTW, I am in Glendale. If you are free, we can meet and race 0-25 and see who gets there last.

Thanks for the links Jay, really helped. I think I will order whatever parts I can find for the linkages. Many of the things that I think are bad are unavailable - which isnt the end of the world. The way I see it, if I can at least change the regulating rod mounts and tighten everything up, it should stop the rod from jiggling about at speed or at least make movement difficult. If not, I will leave good enough alone. Since installing Greazzers OFV spring and cleaning my fuel system, the car feels great. Its nothing like a 2015 Mercedes or a W210 with an OM606 turbo (both of which I drove recently) but nice!
BTW, my mounts are Lemfoerder. I ordered Phoenix from PP but they sent me Lemfoerder. I assume either one is OEM.
Thank you all for your help and suggestions.

Sorry I didnt get a chance to take a video of the loose regulating rod. I will try to remember tomorrow.

Stretch · #12 10-09-2015, 01:24 PM

Quote:

Originally Posted by tjts1

I had a tire shop do this to my Volvo a few years back and they even argued with me that this is the CORRECT method to balance tires. I've ****ing had it with tire shops and finally decided to mount and balance my own tires using this method.
AircoledTech.com's "Tools-On-The-Cheap" Wheel balancing With Beads
This yields by far the smoothest ride I've ever had. It never goes out of balance and theres no wheel weights to lose.

Interesting - thanks for the link.

tjts1 · #13 10-09-2015, 11:19 PM

Quote:

Originally Posted by guyonabuffalo

TjTs1, I have never heard of this technique but sounds awesome. I wish I had known about this a few weeks earlier when I put new tires on. Maybe I will get lucky and find some sharp objects to drive over so my tires will need replacing.

BTW, I am in Glendale. If you are free, we can meet and race 0-25 and see who gets there last.

That sounds fun, I'm in Brentwood but I split my time between the Bay and LA. Let me know when you find yourself on the west side.

Quote:

Originally Posted by Stretch

Interesting - thanks for the link.

This video demonstrates the principle of how it work (obviously 3.5oz worth of airsoft bbs in the tires isn't exactly the same but you get the picture). From what I've read it doesn't work well on low profile tires. I've done it on 195/65R15 and 195/60R15 tires with good results.
https://youtu.be/ullnFQD4F1I

leathermang · #14 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 · #15 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.