560SL Rear Subframe Question - Is this correct? - PeachParts Mercedes-Benz Forum

red560SL · #1 10-16-2006, 07:30 PM

I am replacing the rear subframe bushings in my 1987 560SL. I'm doing one side at a time. After extracting the old bushing and cleaning things up, I have the following question. I notice the hole on the top of the subframe to the top bushing doesn't appear to be correct. Could it be that the top bolt shaft has pushed against the subframe and bent this? I don't know if this is how it was made or if this vehicle slammed into a curb or something that may have caused this or that this is how it was made. I have a shop manual, but it does not show any of this in detail.

Thanks in advance,
-Tony-

whunter · #2 10-16-2006, 08:15 PM

This is massive sub frame side stress trauma.

If the factory differential mount was subjected to this, it is junk now.

Strife · #3 10-16-2006, 08:45 PM

Mine was symmetrical and did not look like this.

t walgamuth · #4 10-16-2006, 09:47 PM

did your car track straightly before tearing it all apart?

if so, perhaps you can take a large drift and drive it back to its original position.

tom w

red560SL · #5 10-16-2006, 10:06 PM

Thanks guys!

I find no evidence of any other damage anywhere. A full report shows this vehicle has never been in an accident (reported anyway) and I see no evidence to support that it has. I've inspected the rear differential mount and other than being dried out and rotted (I was planning on replacing anyway) it all looks fine to me. I've inspected all mounting areas on the entire subframe to see if I can see any wrinkle in the body or some kind of evidence of paint stress and I can't find a thing. All the differential mounts look fine too. The vehicle tracks perfectly as far as I remember. I did follow the wife in another vehicle and I didn't notice any problem.

The stress (stretched part) is toward the front of the car. That would mean that the subframe would have had to slide toward the back of the car which seems almost impossible to me. How in the world could the subframe move toward the back of the car in some kind of collision? Pushed to the front by rear impact maybe, but to the back?

I do have another theory. What I suspect is that the vehicle was towed incorrectly. My guess is some jerk attached cables to the trailing arms and pulled it up on a flatbed truck. Nothing else that I can think of makes sense otherwise. If the damage was on the back of the subframe then I could imagine a rear collision of some kind, but damage in the front? Just doesn't make sense.

I think what I'll do is drop the differential and pull out the entire subframe and do a real good inspection. I'll take some measurements and check for square. If I can't find anything else wrong with it I'll straighten this out with a pin and maybe some heat. I'm hoping the passenger side has the same exact thing. This would at least help confirm my theory. Either way I know I need to yank it all out and have a real good look at it.

Later,
-Tony-

whunter · #6 10-17-2006, 01:35 PM

Quote:

Originally Posted by red560SL

The stress (stretched part) is toward the front of the car. That would mean that the sub frame would have had to slide toward the back of the car which seems almost impossible to me. How in the world could the sub frame move toward the back of the car in some kind of collision? Pushed to the front by rear impact maybe, but to the back?

I do have another theory. What I suspect is that the vehicle was towed incorrectly. My guess is some jerk attached cables to the trailing arms and pulled it up on a flatbed truck. Nothing else that I can think of makes sense otherwise. If the damage was on the back of the sub frame then I could imagine a rear collision of some kind, but damage in the front? Just doesn't make sense.

I think what I'll do is drop the differential and pull out the entire sub frame and do a real good inspection. I'll take some measurements and check for square. If I can't find anything else wrong with it I'll straighten this out with a pin and maybe some heat. I'm hoping the passenger side has the same exact thing. This would at least help confirm my theory. Either way I know I need to yank it all out and have a real good look at it.

Later,
-Tony-

The stress (stretched part) is in the forward sub frame mount ears...

Note:
This is a wish bone sub frame = two points forward, and one point rear.

This single traumatic stress appears DIRECTLY to the left or right (could not determine from the picture).

An out of control spin/slide which was stopped by impacting a rear wheel, could cause this (the wheel rim would have been wrecked (easily replaced).

I suggest extreme inspection of trailing arm bushings for trauma, and verification that they have not been replaced by the previous owner.

Trailing Arm Bushing W126 1985 300SD DIY
http://www.peachparts.com/shopforum/showthread.php?t=111052

The differential mount will need to be replaced, the rotting/impact trauma combination will have ruined it = sagging, excess movement.

red560SL · #7 10-17-2006, 06:05 PM

Thanks whunter,

I completed the removal of the differential and axles. The rear (third point) bolt was locktite'd in and even while being careful I ended up stripping the star socket bolt. I ended up chipping away the rubber mount so that I could attach a vice grip to it and eventually I was able to remove the bolt (took well over an hour). I'll have to find one of these bolts for the reinstallation. Other than that this was an easy task. In fact I believe the job would have been easier in the first place if I had removed the differential to begin with.

The reason I started this job was because I needed to replace the subframe mounts, trailing arm bushings, rear wheel bearings, rebuild the calipers, new rotors and pads, rear differential mount and all other differential rubber mounts. My initial task was to do one side at a time so I would always have one for reference, but when I noticed the trauma on the subframe I new I needed to ask here and make sure before I started putting things back together.

Now that the differential is out I still see no other trauma anywhere. Even the pins coming down from the body/frame that attach to the subframe mounts are straight with no visible signs of stress. I pressure washed and degreased the differential and I carefully inspected the mounting areas of the differential to subframe and I can not find any cracks or other signs of stress. I drove the car once before and no noises were heard from the differential either so I'm sure everything there is OK.

I have not yet completed the removal of the passenger side trailing arm. I'm working on that now and once I get that removed I'll drop the subframe out and start inspecting it. I'll pressure wash and degrease everything and take a magnifying glass to all areas that I can think of that would be affected by this. If I can't find anything wrong I'll straighten the holes and put it all back in. Right now I don't even see a paint chip, but who knows until I get everything out. This really does look like something dragged the vehicle from the trailing arms rather than an actual accident (see updated pic). The impact that could cause this would have to shift the subframe toward the rear of the car. I can't see how any side impact could do this, but hey, I'm no accident investigator

I've completely rebuilt the entire front end of the car. Virtually everything is new. After I get everything back together it's going to Mercedes for a final inspection and alignment. At that time I'll also ask them to verify the tracking and make sure the rear subframe is within specs. If it is, I'm good to go. If not then I'll have to purchase a rear subframe and do this all again. At least now I know how to do it so it won't be so bad the next time. hahahaha

Thanks again,
-Tony-

red560SL · #8 10-17-2006, 09:30 PM

I have removed the rear subframe and bushings. The exact same thing on the passenger side as on the driver's side. In fact I measured the indentation and it is exactly the same size. The rear differential mount was not broken and none of the other mounts were broken. I have pressure washed the entire subframe and degreased it. I visually inspected all welds and joints for any sign of fatigue, cracking or stress and was unable to find anything wrong. To make absolutely sure I used a jeweler's magifying googles to inspect the entire subframe and it's all clear.

This leads me to believe that my theory of the vehicle being drug by the subframe/trailing arms is the most likely cause of the damage. The flex within the rubber mounts appears to be just enough to allow the pins coming down from the top to dent the top flange of the subframe. I can't see anything that would lead me to believe this was caused by some kind of accident or blunt trauma.

Even though there appears to not be any kind of damage, I'm still glad I removed the subframe. It gave me the opportunity to clean everything and gave me piece of mind. I also believe it will be easier to re-install the trailing arms in the long run. It also makes it easier to replace all the other bushings on the differential mounts. And since the entire differential is out, I'm also going to replace the driveshaft bearing and the CV boots. The boots are not dried out, but they are a bit stiff and I do see some signs of cracking. Nothing is leaking yet so for the few bucks it costs for the boots I'm not going to skimp at this point in the game. Obviously this takes all kinds of special tools too. So my plan is to take it to the European transmission place in town. I'm sure they can do this in no time.

Tomorrow I'll get the hammer out and fix the flanges and paint the subframe. I have the driver's side trailing arm all ready and have completed the bearing replacement. I'll start on the passenger's side trailing arm and replace those bearings and races as well. Once these two trailing arms are done I'll attach them to the subframe and lift her up in place and complete all the brakes and everything else.

I want to thank everyone for their input. It helped me take the extra steps needed to confirm the problem. I think at this point I'm good to go, but I will of course still have Mercedes check eveything once it's ready for the alignment.

Thanks again,
-Tony-