So... I've had this '83 300d turbo w123 for about a year and have put about 50k miles on it commuting. (90 miles one way, over a 4000 foot high mountain.) I drive it fairly hard and do some towing on that route. I have a truck for the heavy stuff but really appreciate the mileage of the Mercedes. (2-3 mpg drop for a 1000-1500 pound trailer.) I recently tried to tow closer to 2500 pounds and ended up letting a little smoke out of the transmission. I removed the load before it got very bad but I did smoke it enough to smell/see a bit of smoke (not out of the tailpipe)

My first question: How do these transmissions fail? Is it likely to be sudden or can I run it for a while as symptoms increase? (Drove to work ok today) basically I want to know if it's likely to leave me stranded or if I'll be able to limp it when it finally goes. I'm not worried about running the trans into the ground, I just don't want to have to pay for a tow truck or rent a car to go get my truck and trailer.

Secondly: I am planning to try to put a M5OD-R2 light truck transmission (available in junkyards) in it with an adapter kit from Mercedes Diesel 4x4.com (no affiliation). Has anyone on this forum ever tried to use one of their kits in a Mercedes chasis? The vendor told me that someone had once asked about it but they have no info on such a swap. (They put om617 engines in jeeps mostly) I've browsed this and other forums, but never seen anything posted about this type of swap.

Any info would be helpful.

Thanks

I have had a 722.x grenade on me with no warning before. It wouldn't go forward or backward. I wasn't even working it hard. I just started it up, threw her in reverse, heard a loud clunk and that was all she wrote.

I haven't messed with their adapter kits, but the oil filter housing relocation kit I ordered from mercedesdiesel4x4 was very nice and as I recall their customer service was very helpful as well.

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1984 300TD - der Landstreicher

Typically these transmissions run many miles with no symptoms, develop issues and fail catastrophically at the most I opportune time....unfortunately not necessarily in that order.

...which is of course a cute way of saying it's anyone's guess. At some point they will need a rebuild as they don't last forever. The need for a rebuild is escalated by lack of maintenance, abuse, overheating and other adverse conditions.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Thanks for the quick responses. I guess I'll start trying to get parts together sooner than later.

I had about 5 years warning when the auto in my 240D failed and had just returned home from a 1200 mile road trip in the 300TE when it's transmission failed with no warning. Both have now been converted to manual.

TRk:

Regarding the M5 box, try to find one from the Thunderbird/Cougar application with the supercharged V6 (Thunderbird SC). The top cover places the shifter farther aft than in the truck applications. The box is known as an M5RKE.

Also, should you require one, I have a manual trans W123 pedal assembly available.

Frank R-

Thanks for the info. After some research, it appears (correct me if I am wrong) that my current transmission has a 3.68 1st gear. The M5OD-R2 truck transmission has 3.91 and the M5R2-RKE has a 3.75.

I'm due for an oil change so I think I'll take a tape measure down there with me and see where the shifters will land and how much work I'd have to do to get the 3.91 first gear.

what about putting a proper atf cooler on your car? i bet with a load that torque converter is making a ton of heat and the little one in the rad is a joke!

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83 300CD- sanden, dual p/f condensers, 160a alternator, ect
91 300TD- 722.6, #22 head, 3.5L IP, w140 manifolds, ect

Good point. I'd also suggest putting a transmission temp gauge on it. You'd be surprised how much the temps vary. I've had one on mine for some time and I don't even tow. Pulls up a serious grade especially in the summer can really get the temps up there! I can't imagine what they'd be pulling a load. I'm in San Diego, so I think I know the grades you're talking about.

__________________
Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

on my w124 300td before i put my 722.6 in, the metal atf cooler line runs above the radiator and i'd always joke with my buddies that i was pretty sure lava ran through it lol. If you sprayed water on it after a good drive, it would turn to steam quickly. That transmission had a real slushy torque converter anyways so all it was good for was warming up the car faster on a cold day

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83 300CD- sanden, dual p/f condensers, 160a alternator, ect
91 300TD- 722.6, #22 head, 3.5L IP, w140 manifolds, ect

Benzturbo- I've thought about a cooler but don't really want to invest in the auto when I plan to swap to manual.

Mach4- I drive from Ocotillo Wells to La Jolla, so there's the climb to Ramona and of course Banner Grade...

TRk:

To the best of my knowledge you are correct on the ratios. With a 3.07 final drive ratio, the .8 overdrive yields a 2.46:1 5th gear, and a 3.91 x 3.07 gives a 12:1 1st gear. Quite friendly (4.89:1 ratio spread).

I was thinking I-8 but Banner Grade would be several times worse due to the slower speed and constant acceleration and deceleration going around the curves. It's no wonder you (likely) smoked the tranny.

__________________
Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica