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  #1  
Old 05-27-2021, 12:51 PM
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W108 Front end shakes on the highway

So I did a good amount of work on my V8 W108 recently all because my steering coupler needed replacing so I figured I would do more while I'm there and have no record of when anything else was done on my car since my ownership of 8yrs.

All that was done is new OEM engine mounts, transmission mount, steering coupler, resealed the steering box and replaced the shocks with new Bilstein's. After this, the car has a front end shake on the highway between 70mph-80mph as if a wheel is loose (trying to describe the shake). The steering wheel also shakes sort of up and down and not side to side like it would on a newer car.

After that, I balanced and rotated the tires (still lots of even tread left), replaced the complete tie rod assemblies and steering dampener, wheel bearings and got an alignment.

After all this work and I still have the issue that I never had before with all the older parts. Anyone have an idea what else it could be?

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Old 05-27-2021, 02:13 PM
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Bent rim? Wheel balancing will not fix this problem.
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  #3  
Old 05-27-2021, 03:13 PM
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Sounds Like Tires : Get some Tire shop to spin Balance the "Tires On The Car" not off the car on a machine after explaining the issue to them first
As well Swap the rear tires to the front and try the car .
Also Carefully Check the Frame where the Steering Box bolts on. Look for Cracks . Best to pull the drivers side tire to really have a good look . Check the Inside frame rail as well
( sometimes undercoating hides such things )
Driveshaft Bering support bushings and driveshaft ( bent ) ? are you getting any vibration ?
such things can sometimes transfer all over the Car .
How about the front Wheel Bearings .
Those 108's do have frame cracks quite often I would have a close look at the frame
they can be fixed quite easily welding plates over such area's first welding the crack of course . Are some rubber Parts of the front superstition & steering check all that out . sometimes a Long look over finds things. Again#1 I would check the tires starting with a test rear to front swap as a test
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Old 05-27-2021, 04:20 PM
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Quote:
Originally Posted by Benz Dr. View Post
Bent rim? Wheel balancing will not fix this problem.
The rims are fine and never had an issue until the first amount of work was done and I drove it on the highway.
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Old 05-27-2021, 04:24 PM
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Quote:
Originally Posted by aluminum View Post
Sounds Like Tires : Get some Tire shop to spin Balance the "Tires On The Car" not off the car on a machine after explaining the issue to them first
As well Swap the rear tires to the front and try the car .
Also Carefully Check the Frame where the Steering Box bolts on. Look for Cracks . Best to pull the drivers side tire to really have a good look . Check the Inside frame rail as well
( sometimes undercoating hides such things )
Driveshaft Bering support bushings and driveshaft ( bent ) ? are you getting any vibration ?
such things can sometimes transfer all over the Car .
How about the front Wheel Bearings .
Those 108's do have frame cracks quite often I would have a close look at the frame
they can be fixed quite easily welding plates over such area's first welding the crack of course . Are some rubber Parts of the front superstition & steering check all that out . sometimes a Long look over finds things. Again#1 I would check the tires starting with a test rear to front swap as a test
I had the wheels/tires rotated and re-balanced because I thought that was the issue too but it wasn't.

I'll check the frame where the steering box bolts and see if I notice anything.

Drive shaft is fine too as the flex disc and bushing was replaced and the carrier bearing is still in good condition as well. And I replaced the front wheel bearings (see my original post).
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Old 05-27-2021, 07:06 PM
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There is a rod that attaches the subframe to the unibody rail on the passenger side. Is the rod loose, or perhaps snapped? These are known to break if your subframe mounts are shot.

How are your kingpins and eccentric bolts in the upper control arms?

If you have the front wheels off the ground (support the vehicle from the unibody rails by the subframe, not the subframe itself) can you move the wheels top to bottom, left to right? Any play in either or both? Can you shift the subframe in and out?

Lastly, when the front is in the air, can you see daylight through where the subframe bushings are (indicating they're shot)?
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  #7  
Old 05-28-2021, 11:42 AM
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Originally Posted by Tomguy View Post
There is a rod that attaches the subframe to the unibody rail on the passenger side. Is the rod loose, or perhaps snapped? These are known to break if your subframe mounts are shot.

How are your kingpins and eccentric bolts in the upper control arms?

If you have the front wheels off the ground (support the vehicle from the unibody rails by the subframe, not the subframe itself) can you move the wheels top to bottom, left to right? Any play in either or both? Can you shift the subframe in and out?

Lastly, when the front is in the air, can you see daylight through where the subframe bushings are (indicating they're shot)?
I know exactly which one you're referring to and mine is still good and I replaced the bushings in that lateral rod and the idler arm as well. And my subframe mounts are still good too.

The king pins were replaced about 8yrs ago and this is my weekend car so I feel they should still be good.

With the wheels off the ground, I did have a little play side to side (tie rods) before all the work in my first paragraph but didn't have any highway shake. So I thought since now the steering is tight (with the new coupler), maybe I feel the tie rod wear was more noticeable which is why I replaced them recently trying to chase down this recent shake AFTER the first work (mounts, coupler, shocks and resealed steering box) was done. Same with the wheel bearings, very little play but when I removed the old ones, they were still good as well as the races but I replaced the bearings anyway to try and narrow down what could be causing the recent shake.

Before all of this work, I didn't have any kind of highway shake (with collapsed engine mounts, no bushings in the coupler and worn shocks). I figured with the new engine mounts, coupler, resealed steering box and new shocks, things got tighter which would make the older/worn parts more noticeable to need replacing.

I had the car on a lift a couple days ago when I did the front wheel bearings and tried looking at what could have play or cause this shaking but nothing seems out of the ordinary (drag link/joints are still good as well). And I did an alignment after installing the new wheel bearings. Could something in the steering box be causing this? Or maybe the steering box was installed incorrectly? I had a mechanic do that part for me.
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Old 05-28-2021, 01:55 PM
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Humm your making me think about the R & R of the steering Box now yes they could have messed that up somehow perhaps
About the Wheel Balance , was that done right on the Car or on a off the car Balance machine :
Why ? : Because if their are any issues Tire wise or wheel wise , weird Bearing's or installed wrong all of that will show up with a " On the Car " Balance machine "
I would make sure to mention the speed as most operator's don't spin the Wheels that fast more like 60 MPH Max

As well you mention the Motor Mounts : Moving them to a New Height could in fact change something . Should be to the better but those are the things that have changes
something to ponder . The up and Down Movement is very unusual ? that's why I mentioned to look for any Frame Cracks / Damage ..
Yes I missed the new wheel Bearing install sorry about that . Something is not right that's for sure
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Old 05-28-2021, 02:20 PM
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tires? I've had two come apart recently good tread then tread came off. Have some one drive next to you?? Do check gear box bolts and frame.
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Old 05-28-2021, 02:24 PM
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Quote:
Originally Posted by w1083 View Post
the car has a front end shake on the highway between 70mph-80mph as if a wheel is loose (trying to describe the shake). The steering wheel also shakes sort of up and down and not side to side like it would on a newer car.
Can you expand on this a bit? Steering wheel motion is angular (rotation). If something is causing the road wheels to shake, that shaking will appear at the steering wheel as an angular oscillation. At the twelve o'clock and six o'clock positions on the steering wheel that oscillation will be perceived to be left/right. At three o'clock and nine o'clock the oscillation will be up/down.
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Old 05-28-2021, 04:01 PM
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Quote:
Originally Posted by aluminum View Post
Humm your making me think about the R & R of the steering Box now yes they could have messed that up somehow perhaps
About the Wheel Balance , was that done right on the Car or on a off the car Balance machine :
Why ? : Because if their are any issues Tire wise or wheel wise , weird Bearing's or installed wrong all of that will show up with a " On the Car " Balance machine "
I would make sure to mention the speed as most operator's don't spin the Wheels that fast more like 60 MPH Max

As well you mention the Motor Mounts : Moving them to a New Height could in fact change something . Should be to the better but those are the things that have changes
something to ponder . The up and Down Movement is very unusual ? that's why I mentioned to look for any Frame Cracks / Damage ..
Yes I missed the new wheel Bearing install sorry about that . Something is not right that's for sure
The steering box was only resealed and I'm hoping nothing got messed up.

The tire balancing was done off the car. I did mention to them I had a shake at those speeds and they insisted on the rotation and rebalancing rather than just rebalancing the fronts and putting them back on the front. The rear wheels were taken off, rebalanced and moved to the front of the car but the shaking is still there. I'll try another shop soon and see if they're slightly off balance due to a "rush job".

I'll also see if I can get under the car to inspect the area around the steering box.
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Old 05-28-2021, 04:02 PM
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Quote:
Originally Posted by 801mbz View Post
tires? I've had two come apart recently good tread then tread came off. Have some one drive next to you?? Do check gear box bolts and frame.
When I noticed the shake, I had a friend drive next to me on the highway but nothing looked odd as far as the wheels go. I'll check the gear box bolts and frame next time I'm under the car.
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Old 05-28-2021, 04:05 PM
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Originally Posted by Frank Reiner View Post
Can you expand on this a bit? Steering wheel motion is angular (rotation). If something is causing the road wheels to shake, that shaking will appear at the steering wheel as an angular oscillation. At the twelve o'clock and six o'clock positions on the steering wheel that oscillation will be perceived to be left/right. At three o'clock and nine o'clock the oscillation will be up/down.
The steering wheel/column shakes/vibrates up and down due to the front end shake. Maybe the front end shake is causing it to travel to the steering wheel/column?

I do know the other type of steering wheel shake you're referring to as I've had that happen on other cars for various reasons which I was able to diagnose and fix. But this, I can't seem to figure out. It's just weird it's happening after the coupler and steering box reseal.
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  #14  
Old 05-28-2021, 07:33 PM
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Mercedes frame Reinforcement at steering box
https://www.youtube.com/watch?v=cq4bUN0_JMw

its a 108

Last edited by aluminum; 05-28-2021 at 09:00 PM.
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  #15  
Old 05-28-2021, 09:01 PM
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foolish question, with slight pressure on the brake pedal, does the problem change? -CTH

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