Driveline Vibration - Page 3 - PeachParts Mercedes-Benz Forum

Zulfiqar · #31 03-02-2017, 11:36 AM

Quote:

Originally Posted by Stretch

The design of these propshafts and how they are fitted does not compare favourably with common driveshaft / propshaft knowledge.

(Let the lecture begin!)

This system relies on everything being in line - once you've got that idea fixed in your head the planets start to align and problems can be solved!

Think of an imaginary line that runs from the front of the engine at the crankshaft pulley that runs along the centre line of the crank through the centre of the flywheel - through the centre of the transmission - through the transmission yoke - through the flex discs - through the centre propshaft bearing - through the input yoke on the differential and out through the differential pinion...

...this imaginary line needs to be a straight line - it needs to be constant and unwavering in the vertical (y-axis) and the horizontal (x-axis) => this line needs to exist only in the z-axis (one dimensional)...

...the existence of a single universal joint is misleading. This needs to be set in the straight - zero degree - no bend position to stop any inherent induced vibrations. This configuration is less than ideal for a universal joint as it encourages "flattening" or Brinelling of the joint. All Mercedes UJs in this set up will end up being notchy.

The effects of a notchy UJ are amplified when this imaginary line - the alignment between each part of the driveline - is not just quite right.

The message is:

Consider the relative heights and positions of each resilient component of the driveline. Motor mounts at the front - transmission mount at the back - centre propshaft bearing - differential / subframe mounts at the rear. If one (or more) of these heights is not aligned with the others then you get a bend in the propshaft <= And in this system it should not happen!

(in addition to the resilient mounts flexdisc health is important)

Thats why the U joint has a flat spot in the middle position??

Diseasel300 · #32 03-02-2017, 02:37 PM

Quote:

Originally Posted by Stretch

The design of these propshafts and how they are fitted does not compare favourably with common driveshaft / propshaft knowledge.

(Let the lecture begin!)

This system relies on everything being in line - once you've got that idea fixed in your head the planets start to align and problems can be solved!

Think of an imaginary line that runs from the front of the engine at the crankshaft pulley that runs along the centre line of the crank through the centre of the flywheel - through the centre of the transmission - through the transmission yoke - through the flex discs - through the centre propshaft bearing - through the input yoke on the differential and out through the differential pinion...

...this imaginary line needs to be a straight line - it needs to be constant and unwavering in the vertical (y-axis) and the horizontal (x-axis) => this line needs to exist only in the z-axis (one dimensional)...

...the existence of a single universal joint is misleading. This needs to be set in the straight - zero degree - no bend position to stop any inherent induced vibrations. This configuration is less than ideal for a universal joint as it encourages "flattening" or Brinelling of the joint. All Mercedes UJs in this set up will end up being notchy.

The effects of a notchy UJ are amplified when this imaginary line - the alignment between each part of the driveline - is not just quite right.

The message is:

Consider the relative heights and positions of each resilient component of the driveline. Motor mounts at the front - transmission mount at the back - centre propshaft bearing - differential / subframe mounts at the rear. If one (or more) of these heights is not aligned with the others then you get a bend in the propshaft <= And in this system it should not happen!

(in addition to the resilient mounts flexdisc health is important)

This makes a lot of sense. Between the wear in the U-joint and the sagging rubber bits, things can get out of kilter over the years and miles. I'm sure replacing the engine and transmission mounts helped contribute to the vibration as well. The original mounts were completely collapsed (metal to frame).

The idea from this point onward is to R&R the rear diff mounts (Anyone got a GOOD DIY article on this?) and replace the DS with a rebuilt.

On a sidenote- I'm surprised how long this thread has gotten!

SD Blue · #33 03-02-2017, 04:56 PM

Are you talking about the differential mount or subframe mount. The rear differential mount is pretty straightforward with a jack under the differential. Loosen the 2 differential bolts first and then unbolt the mount from the frame.

If you are talking about the forward subframe mounts, then it is a little bit more. The easiest thing to do with them is to get a longer center bolt to get it lined up then raise it into place, then install the correct length bolt. Getting things to line up can be a bear sometimes. I used a come-along to help position the subframe.

https://www.startekinfo.com/StarTek/outside/12253/program/Chassis/35-010.pdf

Diseasel300 · #34 03-02-2017, 07:56 PM

I guess my confusion comes from a lack of understanding how the diff is actually mounted to the car. I'm aware of the big "square" mount in the rear, which seems pretty straight forward to replace, but what else attaches the diff to the car? I mean there has to be more than just that square rubber hanger?

The FSM isn't clear on it, I haven't found a good writeup, and I haven't spent enough time looking at the diff itself to figure out how it's mounted and what I need to order to refresh.

To make matters worse, the diff and it's mounting seems to be completely missing from the EPC for whatever reason, so no exploded parts diagram either. If all I need to worry about at the moment is the square hanger, great, that's easy. I'm not ready to do the subframe (another battle for another day, month, or year...)

SD Blue · #35 03-02-2017, 08:24 PM

Actually, the big u-shape mount in the rear is it. Ensure the jack is carrying a bit of the weight when you unbolt it.

Diseasel300 · #36 03-02-2017, 10:22 PM

Easy enough, we'll start there for sure.

Stretch · #37 03-08-2017, 05:47 AM

Quote:

Originally Posted by Zulfiqar

Thats why the U joint has a flat spot in the middle position??

Yep - essentially the needle roller bearings are always "getting bashed" in the same place. Conventional UJ usage allows for more movement so the loads get spread through and around the supporting needle bearings.

####

I think it was diesel911 who came across some old guru who said you could free up this notchiness by bashing the caps one way - penetrating oil - bash caps back again.

I've not tried it - the staking looks too stubborn for this to work.

Whilst the UJ notchiness is a concern I've actually detected more movement in the splines of some propshafts => I'm pretty sure that's the main cause of the distinctive W201 clunk and the "wow I'm pretty sure I released the clutch half an hour ago - are we moving already?" effect...

Stretch · #38 03-08-2017, 05:48 AM

Quote:

Originally Posted by Diseasel300

...
On a sidenote- I'm surprised how long this thread has gotten!

Ha! You ain't seen nothing yet!

Alec300SD · #39 03-08-2017, 10:49 AM

Quote:

Originally Posted by Diseasel300

I guess my confusion comes from a lack of understanding how the diff is actually mounted to the car. I'm aware of the big "square" mount in the rear, which seems pretty straight forward to replace, but what else attaches the diff to the car? I mean there has to be more than just that square rubber hanger?

The FSM isn't clear on it, I haven't found a good writeup, and I haven't spent enough time looking at the diff itself to figure out how it's mounted and what I need to order to refresh.

To make matters worse, the diff and it's mounting seems to be completely missing from the EPC for whatever reason, so no exploded parts diagram either. If all I need to worry about at the moment is the square hanger, great, that's easy. I'm not ready to do the subframe (another battle for another day, month, or year...)

Exploded diagram of differential

Differential mount 1233511142
"This product fits 196 vehicle variants.
Mercedes: 27 models, 196 variants between 1971 and 2010."

Mercedes-Benz W123 Differential Mount or Bushing Replacement | W123 (1977-1985) | Pelican Parts DIY Maintenance Article

Video of removing old (and installing new) differential mount starts at 2:14
https://www.youtube.com/watch?v=m2Xp9OzoeWU
I'm sure there are better videos out there.

Very straightforward job.
Just be safe, don't work alone, wheel chocks on either side of both front wheels, spare(s) under side(s) of vehicle in case car slips off jack stands, safety eyewear, etc.

Stretch · #40 03-08-2017, 11:19 AM

Quote:

Originally Posted by Alec300SD

...

Mercedes-Benz W123 Differential Mount or Bushing Replacement | W123 (1977-1985) | Pelican Parts DIY Maintenance Article

...

It probably isn't deemed to be polite to say this about the site sponsor's DIY pages but I don't rate them. They often contain weird or just plain wrong information. That link is a classic example =>

Quote:

If you are getting sounds from the rear of your vehicle while accelerating, going around corners or a bump or when you take your foot off the throttle, it's time to check and perhaps replace the differential mount or bushing.

I don't know if that part of the blurb is a result of a cut and paste from another DIY for a different car (perhaps a Porsche?) but a W114/5/6 / W123 / W126 differential mount in my experience isn't going to make noises like that under those circumstances. Now a broken rusted out trailing arm or utterly knackered trailing arm bushings - perhaps

I think the old community organised wikki pages were much better. The best bit was that they also linked to the original thread so you could continue the discussion and ask questions.

Ultimately the best source for DIY information (in my opinion) is the FSM

Alec300SD · #41 03-08-2017, 03:51 PM

I agree, the FSM is usually the best source, but it wasn't clear enough for the OP.
More info from other DIY's can be helpful, even if inexact.

If the DIY has an image you can right click on and press the "Search Google for image" button and the links to source pages can be found.

Doing this for the third image of the Pelican Parts DIY Maintenance Article, brings up 6 page links including dmorrison's original post from his 04-20-2008 thread and the PeachPart Wiki based on that thread.

Diseasel300 · #42 03-08-2017, 04:10 PM

I like the FSM for most jobs since it's from the manufacturer of the car. I'd expect them to know what they're doing! However, in this case, the detail is a bit lacking, especially for someone not familiar with how the independent rear suspension is set up on these cars.

I haven't been real impressed with Pelican's DIY articles either. There seems to be steps left out or things applied that don't necessarily line up with the vehicles they claim they cover. I tend to use the FSM or writeups from here or BW for most of the jobs I do. Sometimes a combination of both!

In other news, new DS should be here tomorrow and the diff mount whenever Pelican gets around to shipping it. DS will go in this weekend most likely so that I can get the core turned around and sent back to the rebuilder. Will follow up when the deed is done...

Diseasel300 · #43 03-09-2017, 05:14 PM

DS arrived today. MARKED difference in feel of the U-Joint compared to the original DS on the car. Pretty sure the issue is clear as day. We'll know on Sunday.

SD Blue · #44 03-09-2017, 05:23 PM

Quote:

Originally Posted by Stretch

It probably isn't deemed to be polite to say this about the site sponsor's DIY pages but I don't rate them. They often contain weird or just plain wrong information. That link is a classic example =>

I don't know if that part of the blurb is a result of a cut and paste from another DIY for a different car (perhaps a Porsche?) but a W114/5/6 / W123 / W126 differential mount in my experience isn't going to make noises like that under those circumstances. Now a broken rusted out trailing arm or utterly knackered trailing arm bushings - perhaps

I think the old community organised wikki pages were much better. The best bit was that they also linked to the original thread so you could continue the discussion and ask questions.

Ultimately the best source for DIY information (in my opinion) is the FSM

Agreed, the symptoms for a differential mount problem are a rear end squat when placing it in Drive and lift when placed in Reverse.

Diseasel300 · #45 03-12-2017, 07:18 PM

This car definitely had the squat/lift issues. Diff mount was very tired. Replacing it jacked the whole ass end of the car up about half an inch.

Replaced the driveshaft today and I'm happy to report that the vibration is gone. Smooth as silk and silent all the way up to 90 (as fast as I took it out on the interstate). I'm really surprised how well the car holds up on the highway, I was expecting to have to keep my foot in it on all the hills to maintain the 75mph speed limit, but it had no problem at all maintaining speed. Today was the first time it had ever been driven over 60 for any period since I've owned the car (and probably since it was parked in 2007!)

I feel a weekend roadtrip in my near future...