New 1991 MB 350SD

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JHZR2

JHZR2

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Yes, the "rod bender" 3.5L turbo model - got a good deal and am willing to take the chance. Last of the W126 - admittedly I originally wanted an OM617.952 and MB tex (and 14" bundts), this one found me by accident and Im glad it did. 113k, very clean, no dash cracks, no rust, some signs of use but nothing major. One of ~2200 ever made, IIRC. Drives great, runs nice and smooth and quiet. Sound system surprisingly good. A few items to iron out - a vibration that starts around 50-55 MPH, felt in the floorboards, but no vibration in the steering wheel with either pair of tires on the front axle. Higher air pressure in the tires seems to help though FWIW. Some sideways motion over bumps at highway speeds. I think that means shocks??? Could bad shocks and the vibration be related?

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Quite the acquisition! Classic lines, very handsome. You clearly are well versed in the MB's should provide quite a bit of entertainment.

How old are the tires? Even tires with seemingly acceptable tread will sometimes go wonky and need replacing simply due to age deterioration. Just went through that on the Lincoln myself, had an old tire shudder/vibration.
 
Originally Posted by KCJeep
Quite the acquisition! Classic lines, very handsome. You clearly are well versed in the MB's should provide quite a bit of entertainment.

How old are the tires? Even tires with seemingly acceptable tread will sometimes go wonky and need replacing simply due to age deterioration. Just went through that on the Lincoln myself, had an old tire shudder/vibration.


Thanks! Rears are week 34 2017. Fronts had a 2004 date code and fairly low, but evenly worn tread. Just swapped them at Costco tonight, so now I have the same tires (Bridgestone Ecopia 422) all around.

Didnt change the vibration. In fact, Costco put the rear tires on the front, and the new ones on the rear. That didnt change anything either. I had them rebalance the tires I was keeping when they had them off as well...
 
Originally Posted by Chris142
Rod bender? How does that happen?


There are literally hundreds of pages of theory on the web on that. #1 and/or #6 rods bend, wear the bores oval, start consuming oil at a quart every 100-200 miles. Runs smooth and perfect up until it starts to consume.

The OM603 engine is a good design, but some early ones had head cracks, and these later ones have good heads, but bend rods.

Some theories include:
- HG issues and creepage of water or oil into the cylinders.
- Design got rid of the trap oxidizer, and so the more aggressive EGR forces oily soot in there at too great a level
- The block, which was originally a 3.0L was bored too much to get to 3.5L and has some flex.
- Rods are weaker in design (fatigue as a result), new versions have more metal and are heavier.

I may premptively do a HG, as it does seem like there is a decent incidence of that.

Its an iron block, aluminum head. There are tons that go to 300-500k documented. But lots of others that show issues at 80-100k.
 
Originally Posted by rubberchicken
Vibration- ujoints ? or possibly an out of balance drive shaft ?


Was thinking along the same lines.

The Flex Joints (rubber bushings in place of u-joints) are often a source of driveline vibration in this vintage of MB...
 
Definitely something to check. Think the shocks are needed regardless. None of my MB cars have ever needed a flex joint, but certainly have heard of the need, and so it's on my mind.
 
Originally Posted by Astro14
Originally Posted by rubberchicken
Vibration- ujoints ? or possibly an out of balance drive shaft ?


Was thinking along the same lines.

The Flex Joints (rubber bushings in place of u-joints) are often a source of driveline vibration in this vintage of MB...

BMW too
The U joints AND flex disk are usually the two main sources of the problem.

Considering this car probably has the original u joints, I can easily see the old grease drying up with age and the heat from the exhaust manifold.
 
That is an absolute beauty, congrats! I have been eyeing an 80s-early 90s MB as a fun weekend/project for some time now. Seeing a thread like this makes me even more interested in getting it going. Thanks for sharing
 
Nice! I would probably do the HG preemptively also along with shocks and a full steering and suspension go through and replace anything worn or suspect bushings.
 
im looking to get one as well but the 82-85 300-TD om617 flavor preferably a estate
is the power any better?
the om617 is the waste oil drinking champ. that i have found in my searches.
im looking for any thing that can run on WMO at the drop of a hat , if need be.
diesel just hit $3.45@gal here NW IN
 
you can always pick up another block and have the block sleeved( 3.5L block does not have sufficient bore material to allow for sleeving ....opps.....who knew lol
) on all 6 and install aftermarket connecting rods
modify the oil pan to hold more oil .

i would first delete and EGR systems and install a catch can and ditch the cat if eqpt.
 
Last edited:
Originally Posted by rubberchicken
Vibration- ujoints ? or possibly an out of balance drive shaft ?


Also what I was thinking .

Is it FWD , RWD or AWD ?
 
Not familiar with MB at all but if you are going to do the HG, how hard would it be to pop the pistons from underneath and change the rods while you are there?
 
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