I have a 1991 300Sl with no reverse ... brought the car in for a rumbling sound and then the check engine light came on. It was a simple thing, at 15 years old the rubber on these (and most anything) cracks and breaks. The flex disc which is where a universal joint would be, had broken, spun around and unplugged the oxygen sensor. A $130 part and I thought I was on my way. Now I have no reverse. I brought it back to that dealer and they said all the linkage is correctly installed and they assume it's internal. They suggested a remanufactured trans.... and the answer is... NO!!
There has to be something simple wrong because worked when I drove it to them. All 5 forward speeds work perfect. If a spring broke, or piston is stuck in the valve body, which would engage reverse, then I need disassembly help. To the best of my knowledge there still are no manuals available on this car so where do I go???
Please help me with this one...
A link to a site for transmission disassembly would be nice.

Its internal, the transmission has to be removed, B3 clutch failure.
Initial Symptoms are delay reverse engagements.

Another symptom I have seen a couple times recently is a vibration. Gotta come apart.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician