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6.9 suspension collapse

Started by raftel, 26 March 2022, 11:12 AM

raftel

Took the 6.9 to a club event today. Leaving the rendezvous point, I noticed that the car was driving like a pogo stick, very bouncy and exaggerated movements. Took it slow, and on the last left turn into the stop I heard grinding from the front. I stopped, to find the front end completely down. It won't raise in any setting, and I never got a warning light. Spheres are all Mercedes and all two years old. I am currently waiting for a tow neck home.


So..... Where to start?

daantjie

At first glance this reads like a pump failure but it does seem a bit sudden for that.  Check fluid in tank.  Right level on stick?
Daniel
1977 450 SEL 6.9 - Astralsilber

daantjie

Another quick check is the little connecting arm on the front leveling valve connecting the valve to the sway bar.  Might have come off if the bushings are shot.
Daniel
1977 450 SEL 6.9 - Astralsilber

raftel

Fluid level is good. When I tried to raise the suspension, the back went up and the front stayed down. My first and best guess is the rod connecting the leveling valve to the suspension. Still waiting for the tow.

daantjie

Indeed that little rod/ram could cause this.  Luckily they are cheap and still readily available.  Good luck!
Daniel
1977 450 SEL 6.9 - Astralsilber

raftel

So just before the tow showed up, I was able to put hands on the broken rod.  I started the car, and manually pushed the rod.  The car rose up in time.  We still towed it. 

So I know I have to replace the rod.  I'll replace the one on the rear suspension out of caution.  Does anyone have recommendations on sources?  What is the correct part number?  Anything I have to worry about setting the length of the rod?

Once we got the car home I note that the front end is solid.  No give at all - did the new accumulators blow?  The rear is still soft and compliant, but the front, although raised, is solid as a rock.

rumb

I suspect that with the front rod missing the suspension isnt going to do anything other than just sit were it is.

https://www.mboemparts.com/oem-parts/mercedes-benz-link-1233201489
(nevermind the picture reference that is incorrect, this pn is item #7 in that drawing.


https://nemigaparts.com/cat_spares/epc/mercedes/1/fg/116036/040/32/001/
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS

raueda1

Quote from: raftel on 26 March 2022, 03:27 PMSo just before the tow showed up, I was able to put hands on the broken rod.  I started the car, and manually pushed the rod.  The car rose up in time.  We still towed it. 

So I know I have to replace the rod.  I'll replace the one on the rear suspension out of caution.  Does anyone have recommendations on sources?  What is the correct part number?  Anything I have to worry about setting the length of the rod?

Once we got the car home I note that the front end is solid.  No give at all - did the new accumulators blow?  The rear is still soft and compliant, but the front, although raised, is solid as a rock.

The rod adjusts ride height.  This process is from memory so somebody else might comment.  Anyway, take the rod off and move the valve lever to the middle.  Have somebody start the engine while you stay by the valve.  On one side off of the center the car will rise, on the other it will drop. Fiddle with it till you get the proper ride height.  I think it's 26" from ground to wheel arch to the ground.  Center the valve so it's not going up or down.  Turn the car off and install the arm without moving the valve.  Your ride height is now set.  It's basically the same on the rear.  Be extremely careful though - dropping the rear could squish you, so take appropriate precautions.  Good luck and cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raftel

Yes, I understand that the threading permits adjustment of the rod and in turn adjustment of the ride height.  Thanks for the guidance, I'll do the rear on a lift for safety.

Turns out my front spheres have blown as well.  Not sure what preceded what, but the back is nice and soft and the front has absolutely no give.  I replaced all the spheres in November 2020 with fresh Mercedes parts from the Classic Center, so I'm not sure if I got a bad batch or what.  I've emailed Tom Hanson at the Classic Center to see if he can help, turns out he is retiring at the end of the month.

daantjie

Are you sure the front spheres are toast?  As in have you removed them to see if the bladders have collapsed thus filling the sphere with oil?
In my experience a sudden failure of the spheres would be highly unusual.  Normally they fail over time with the slow migration of nitrogen into the fluid.
Daniel
1977 450 SEL 6.9 - Astralsilber

raftel

I can't say I'm sure, but I'm not sure of any other situation that would cause the suspension to lock up like that. i've been in touch with Martin Werminghausen, who services and rebuilds these suspensions, and he was pretty certain.  I've just ordered the rods for the front and rear suspension.  I'll put the rods in and see if anything changes, but I'm fairly sure I've experienced a sudden failure. I'd love to hear alternate theories, and I know this isn't the usual failure mode, but it is what it is.

Jed

Hard to believe they failed after just two years.  Change the rod up front.  Use the length of the old rod to estimate the length of then new rod. Its should get you very close even though the inside plastic ball sockets are probably shot. 

Let us know please

jed
1979 Mercedes 6.9 #5206 - restored
1979 Mercedes 6.9 #6424 - ongoing restoration
1976 Mercedes 6.9 #484 - restoration?

raftel

I reached out to Tom Hanson from the Classic Center (he is retiring this week).  Tom said the accumulators were under a 2 year warranty.  New ones are being shipped out under that warranty, and I've been asked to return the defective units.

I ordered new rods for front and back from FCP.  Now its a matter of time - time for the parts to ship, and me to find the time to do the work.

raftel

#13
Finally got back to doing some work on the 6.9, and I think I'm running into a snag.

The new rods I got from Mercedes each have a ball stud pressed into the adjustable arm, and a short threaded rod coming out to secure it to whatever with a washer and a nut.

That's fine on the suspension end of things.  But the level controller has a ball stud pressed into the arm, and I don't see how I am supposed to connect it.  I'll try to figure out how to upload the photos I took that might better present the situation, but if anyone can tell me what I'm missing, I'd appreciate it.  It seems I could try to pry out the ball joint stud in my new arm and press the socket on the arm it into what is there on the level controller, but before I do that i'd like to be sure.