Author Topic: Troubleshooting high speed vibration  (Read 1020 times)

Rolo

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Troubleshooting high speed vibration
« on: 11 August 2020, 05:14 PM »
This has been a frustrating period for my old car.  We have changed out the floppy BF Goodrichs for nice round tires.  We have rebalanced tires twice.  We checked the propeller shaft support bearing.  Flex discs are new.  I've run it up to speed in 2nd at high revs and it's all smooth.

Then you hit an indicated 85 mph and a strong vibration starts coming through the seat.  Gets worse as speed increases.  The transmission and differential mounts appear to be in good shape.  I've searched older threads.  What are we missing?  Thanks.

daantjie

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Re: Troubleshooting high speed vibration
« Reply #1 on: 11 August 2020, 06:36 PM »
Engine mountings?
Daniel
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Jed

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Re: Troubleshooting high speed vibration
« Reply #2 on: 11 August 2020, 06:42 PM »
Hmm. At 85 mph every time?! Makes me think wheels/tires.

I am sure you tried this but rotate you tires front to back and see if it changes. Does the vibration now show up more in the steering than the seat? 
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revilla

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Re: Troubleshooting high speed vibration
« Reply #3 on: 12 August 2020, 01:12 AM »
Hi
If it started after changing the flex discs, I would look into the drive shaft mounted in a different configuration relative to the original causing therefore an out-of-balance condition that reaches its resonance frequency at 85 km/h. The fact that it vibrates at the same speed constantly implies a rotational assy that’s not well weight-balanced. All that assuming you have balanced all 4 wheels, which you say you have done twice.
Also, when you changed the flexs, did you also replace the central bearing?
Robert
W116 1977 280SEL & 1979 280SE

Rolo

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Re: Troubleshooting high speed vibration
« Reply #4 on: 12 August 2020, 01:31 PM »
Some good pointers.  The vibration becomes noticeable at 85 MPH and gets progressively worse, so it's not resonance.  At 95 MPH, the frequency of the vibration is higher and the amplitude greater.  This used to be a fun high speed car.

What are the symptoms of shot motor mounts.

UTn_boy

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Re: Troubleshooting high speed vibration
« Reply #5 on: 12 August 2020, 01:34 PM »
In addition to what the others state, be aware that W116 cars are really sensitive to out of round tires.  A tire can be well balanced but still not be perfectly round.  This is a common problem with inexpensive tires.  So ensure that you have Michelin, Vredestein, or AVON tires. 

As Revilla suggests, the issue is more likely in your drivetrain.  Since the vibration is felt in the seat that tells us that the issue could only be the tires and/or the driveshaft.  If you didn't renew the center support bearing and center support bushing on the driveshaft then I'd start there. 

Also, some aftermarket flex discs will cause vibration.  Many will wince at that remark, as they believe that aftermarket and genuine Mercedes are one in the same.  I just never could believe that, so I contacted four manufacturers of these flex discs.   Meyle, FEBI, SGF, and Jurid.  Jurid and SGF are who make them for Mercedes, while the other two are merely aftermarket manufacturers. 

I explained my imbalance issues to all three companies, and I asked them if I was doing something wrong or maybe installing them backwards.  Sadly, no one could answer any of those questions.  But it's the last question I asked that they DID answer, and two companies (Jurid and SGF) gave pretty much the same answer.  I asked them how/why they're different from the genuine Mercedes ones, and why quality is so diverse.  The unanimous answer among the two companies was something along the lines of:

"We can't make them the same way Mercedes does for copyright reasons.  Since physical shape is important for fitment, we have to sacrifice material quality.  We use less expensive metal barrels that the bolts go through, less expensive thread that goes in the rubber, and we have to use a lesser quality rubber material.  Since Mercedes lets us and a few other use their original molds, we are required by Mercedes to grind/scratch off the Mercedes part number and Mercedes star if present after we make our own versions.  People often mistake our products for genuine Mercedes because of the part number being scratched off, but the reality is that what we make is not anywhere close to a genuine Mercedes part.  We're not even allowed to sell genuine Mercedes discs even with the numbers and Star scratched off. If we did we'd be paying large fines and/or be in jail.  That's not to say that we don't make a good product, but our viewpoint is that we want to offer a product that is affordable to the masses, and if it vibrates a little at high speeds then that has to be better than a damaged/broken disc." 


Take that for what you will.....that's just what I was told.
« Last Edit: 12 August 2020, 02:07 PM by UTn_boy »
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Rolo

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Re: Troubleshooting high speed vibration
« Reply #6 on: 18 August 2020, 08:53 AM »
Tires are balanced and round.  We checked for run out after the experience with the floppy BFGs.  I also have 2 sets of rims and tires which I've swapped and rotated to confirm it's not tires.

The aftermarket flex disc is something to look at.   That's what I got.


UTn_boy

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Re: Troubleshooting high speed vibration
« Reply #7 on: 18 August 2020, 12:22 PM »
What about your center support bushing and bearing for the driveshaft? 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex

ptashek

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Re: Troubleshooting high speed vibration
« Reply #8 on: 18 August 2020, 12:46 PM »
The aftermarket flex disc is something to look at.   That's what I got.

I've got FEBI ones on my car, and they're made by SGF (Süddeutsche Gelenkscheibenfabrik). The exact same company which makes them for MB.
I've done 25k miles on them so far, at very high speeds for hours on end. Not a single issue with vibration in the drive train.

I'd start with the centre support bearing if original, and then checking the shaft assembly for balance if it was taken apart before.
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ptashek

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Re: Troubleshooting high speed vibration
« Reply #9 on: 18 August 2020, 01:02 PM »
"We can't make them the same way Mercedes does for copyright reasons.  Since physical shape is important for fitment, we have to sacrifice material quality.  We use less expensive metal barrels that the bolts go through, less expensive thread that goes in the rubber, and we have to use a lesser quality rubber material.  Since Mercedes lets us and a few other use their original molds, we are required by Mercedes to grind/scratch off the Mercedes part number and Mercedes star if present after we make our own versions.  People often mistake our products for genuine Mercedes because of the part number being scratched off, but the reality is that what we make is not anywhere close to a genuine Mercedes part.  We're not even allowed to sell genuine Mercedes discs even with the numbers and Star scratched off. If we did we'd be paying large fines and/or be in jail.  That's not to say that we don't make a good product, but our viewpoint is that we want to offer a product that is affordable to the masses, and if it vibrates a little at high speeds then that has to be better than a damaged/broken disc." 

I've worked in the industry for a few years. Not a single company, especially what can be considered a Tier-1 supplier, would ever issue a statement like this to a random person, let alone disclose such detail. This is an extremely hermetic world, especially when it comes to anything IP related. Unless you can furnish verifiable proof that these companies said this, I'm calling bullshit on this one. I'll happily eat my hat and apologise if you do, and we'll have this debate settled once and for all.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

revilla

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Re: Troubleshooting high speed vibration
« Reply #10 on: 18 August 2020, 11:05 PM »
I don’t see how discs can be replaced without taking apart the shaft. If it’s not marked prior, out-of-balance is HIGHLY  probable.
Shot engine mounts will never produce the symptoms described, they don’t rotate, so they can’t generate vibration at a given (vehicle) speed.  They could help reducing feeling the vibration, but the vibration shouldn’t be there to begin with.
Robert
W116 1977 280SEL & 1979 280SE

daantjie

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Re: Troubleshooting high speed vibration
« Reply #11 on: 18 August 2020, 11:25 PM »
You can replace the flex disks with the drive shaft in situ as it telescopes once you loosen the collar nut.  You need a long prybar and lots of clearance underneath though to work the flex disks off their mounting.
Agree to take a good look at carrier bearing too and yes if the shaft was put back by 1 tooth off then for sure you'll get vibration.
Daniel
1977 450 SEL 6.9 - Astralsilber

revilla

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Re: Troubleshooting high speed vibration
« Reply #12 on: 19 August 2020, 01:22 AM »
Careful, a recipe for troubles!
Again, once you lose the 46mm nut and fail to mark the relative position of the 2 pieces, chances are high the factory-balance of the assy will be lost with all the force needed to remove the flexs with the shaft still in the car.  Such locking nut should not be re-tighten but once the car is on its own weight and after pushing the car back and forward a few meters.

« Last Edit: 19 August 2020, 01:30 AM by revilla »
Robert
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Rolo

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Re: Troubleshooting high speed vibration
« Reply #13 on: 19 August 2020, 03:18 PM »
Very good point to raise with my shop about flex disc replacement.  I seem to recall we did the discs when the transmission got new bands and circlips.  As far as motor mounts, the vibration is worse under load, which there is a lot of at 95 mph.  Still present off throttle, but not nearly as bad.

UTn_boy

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Re: Troubleshooting high speed vibration
« Reply #14 on: 19 August 2020, 03:55 PM »
"We can't make them the same way Mercedes does for copyright reasons.  Since physical shape is important for fitment, we have to sacrifice material quality.  We use less expensive metal barrels that the bolts go through, less expensive thread that goes in the rubber, and we have to use a lesser quality rubber material.  Since Mercedes lets us and a few other use their original molds, we are required by Mercedes to grind/scratch off the Mercedes part number and Mercedes star if present after we make our own versions.  People often mistake our products for genuine Mercedes because of the part number being scratched off, but the reality is that what we make is not anywhere close to a genuine Mercedes part.  We're not even allowed to sell genuine Mercedes discs even with the numbers and Star scratched off. If we did we'd be paying large fines and/or be in jail.  That's not to say that we don't make a good product, but our viewpoint is that we want to offer a product that is affordable to the masses, and if it vibrates a little at high speeds then that has to be better than a damaged/broken disc." 

I've worked in the industry for a few years. Not a single company, especially what can be considered a Tier-1 supplier, would ever issue a statement like this to a random person, let alone disclose such detail. This is an extremely hermetic world, especially when it comes to anything IP related. Unless you can furnish verifiable proof that these companies said this, I'm calling bullshit on this one. I'll happily eat my hat and apologise if you do, and we'll have this debate settled once and for all.

Lucas, given your age and exposure, you should know that experience doesn't always make us the wiser.   I have no idea why they were so open with me....maybe because I questioned them about why the Mercedes and aftermarket ones were made from different materials but had their company name on them?  Even the Shore hardness was off between the two.  One would bend easily, and the other one was hard as a brick.  With your credentials, I'm very shocked that you don't know that what they make aftermarket is never the same as what they make for Mercedes Proper.  It's common knowledge that on something like this that the same mold is used, but different materials are used. 

These emails took place one year to one and a half years ago, and I cannot place them at the moment,and I may not even be able to, as I delete emails regularly after they're a month old.  So there is no way I can show you proof of the correspondence.  It really bothers me that you feel I'd make something like this up.  I ask is that you give me and everyone else the benefit of the doubt before you call bulls*&t.  However, if you leave this conversation thinking as such, then there is nothing I can do.   I realize that my presence on here annoys you to no end....and I'm not even sure why....but do know that I care.  I wouldn't purposely lead anyone astray on a subject matter such as this.  It's just not who I am or what I'm about. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex