For the second time in just a couple of months the rubber bushing in the Nippodenso A/C compressor clutch has torn in my '86 300 SDL. The result is the part connected to the fan belt pully spins freely, whilst the rest of the clutch doesn't move, even when engaged. The clutch itself has not seized. Originally I took it into my A/C service guy, who suggested the rubber melted and tore due heat exacerbated by my (then) poorly functioning auxillary fan and viscous fan clutch. At his insistence, I replaced both the aux. fan and the viscous clutch (lots of $$, even at FastLane) prior to his replacing the entire compressor clutch assembly with a factory rebuild.

Here is the fun part. The engine now runs about 5° cooler now with the new parts. However, the rubber bushing in the clutch gave way on a warm (though not hot day), with the engine at normal temperature - 82° C, right when I went over the freeway lane marker. The only symptom I had prior to that is that I could feel the compressor "wobble" when it engaged while I was at idle. This was a pronounced wobble and is more than the expected drop in engine RPM when the compressor engages. According to my A/C guy's logic, though, this should not have gone out since there is less heat, which leaves me wondering if there is another culprit.

In another thread I searched on, Steve Brotherton suggested the rubber in these compressors is prone to tearing, causing the symptoms I described. Is there anything that causes these clutches to go bad? My A/C guy, who is trustworthy and otherwise quite knowledgable is surprised by this.

Just a couple more symptoms to add. My A/C was functioning OK, but not great. Apparently, the clutch rubber problem has caused no other problems in the system. Also, I had the wobble when my compressor engaged during idle and what seemed an unusual strain on the engine with the A/C going.

I appreciate any help or insights.

__________________
Casey Cooper
"From a long line of Mercedes ownership"

'86 300SDL 250K miles (Gone, but not forgotten); best diesel I have ever driven, too bad about the Achilles heel.

'81 240D 370K miles (Sold to my brother after 9 years and 150K miles of reliable driving!)

[Five other Mercedes in family clipped for less length.]

Sounds like the A/C compressor may be contributing to the premature failure of the drive clutch. You mentioned and unusual amount of engine strain is/was noticeable when the A/C compressor was engaged, I am curious is the compressor noisy when it is engaged? After a couple of clutch failures on the same compressor I would be inclined to focus my attention on the compressor to determine if it is the cause of the failure. My .02


PS: I regret sacrificing my 1987 300 TDT, what a wagon.

Looks like that's where this is heading; a bad compressor. It is a rebuilt compressor, but now outside the warrantee. The compressor did not make any unusual noises. It would have been to easy to diagnose otherwise ...

MrCjames - bummer about the TD. If I could, I would get my hands on one. I can't believe they made them only one year. I guess I'll settle for the SDL.

__________________
Casey Cooper
"From a long line of Mercedes ownership"

'86 300SDL 250K miles (Gone, but not forgotten); best diesel I have ever driven, too bad about the Achilles heel.

'81 240D 370K miles (Sold to my brother after 9 years and 150K miles of reliable driving!)

[Five other Mercedes in family clipped for less length.]