Hello all..

I have a 300SDL that is about to hit 300,000km (180,000 miles) and I don't think the motor mounts have ever been changed. The bills from the original owner don't show them being changed, and I haven't done them either. I bought the car at 225,000km (135,000 mi).

When do I need to replace these and is there any way to know if they're bad? I don't get any shaking at traffic lights but assume there is a useful lifespan to these things. Do I also need to change the engine shock at the same time?

Thanks!
Neal

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'83 300SD 335,000km (207k) mi SOLD
'87 560SL 163,000km (101k mi) SOLD
'86 300SDL 356,000km (220k mi) SOLD
'92 500SEL 250,000km (155k mi) SOLD
'90 300SL 140,000km (87k mi) SOLD
'01 S430 260,000km (161k mi) SOLD
'03 SL500 167,000km (104k mi) SOLD
'07 S550 4MATIC 235,000km (146k mi) SOLD
'07 GL320 CDI 4MATIC 348,000km (215k mi)
'13 GL350 BlueTec 4MATIC 170,000km (105k mi)
'14 SL550 72,000km (43k mi)

Engine mounts can usually be known as good/bad by visual inspection..... Am not familiar with later model cars after '83, but they switched from solid rubber to absurd fluid filled bladder engine mounts somewhere along the line. If you are stuck with those bladder mounts, known to crap out and leak, then you might opt for retro-upgrade to older solid rubber mounts.

If you're not shaking at idle why mess with it? Mine shakes some with the a/c off and a lot with the a/c on. I would wait until it gets that bad before replacing. One guy told me he has heard bare metal because the mounts were so wore out, so i'd run 'er---

Bill,

Normally I follow the "if it ain't broke.." rule, but I'm wondering if these motor mounts are anything like MB shocks.

I have replaced a few sets of 15+ year old shocks that worked just fine, and found an *amazing* difference in the way the car handles. I would never have thought to replace the shocks (thought they were perfectly fine) until someone told me to do it.

Neal

__________________
'83 300SD 335,000km (207k) mi SOLD
'87 560SL 163,000km (101k mi) SOLD
'86 300SDL 356,000km (220k mi) SOLD
'92 500SEL 250,000km (155k mi) SOLD
'90 300SL 140,000km (87k mi) SOLD
'01 S430 260,000km (161k mi) SOLD
'03 SL500 167,000km (104k mi) SOLD
'07 S550 4MATIC 235,000km (146k mi) SOLD
'07 GL320 CDI 4MATIC 348,000km (215k mi)
'13 GL350 BlueTec 4MATIC 170,000km (105k mi)
'14 SL550 72,000km (43k mi)

I believe that the rubber compresses over time without regard to the mileage. I had the mounts done by the indy when I originally brought the SDL up from Florida. One was flattened by over 1.25 inches when compared to a new replacement. The other was only flattened by about .50 inches.

I can tell you that the engine seemed quite a bit smoother after the mounts were replaced. If the existing mounts are the original mounts, they are most likely history.

Well hell, why not replace the tires every 20,000 too!! I do think bad motor mounts will eventually cause other problems and i do plan on changing mine but have got more pressing issues at the moment---

Bill

Mine will be done this fall, I think the car vibrates more than it should.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Eighteen year old motor mounts ARE bad. Even if they have not collapsed, they will be MUCH harder than they were designed to be.

Marshall

My thoughts exactly, rubber ages as a result of time.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200