[edm]

- Like the topic states, the problem occurs only when the A/C is ON and I am stopped at a traffic light or at a complete stop ( traffic), but when moving no problems. With the A/C is OFF, engine is smooth. 1993 Cab Tiptronic.

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[gbarrier]

What's idle rpm with A/C on and off?

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[94SilverCab]

I'm betting it is one of the "ears" on the compressor that cracked and is causing vibration. Fortunately, I installed the D1R solution for this very common problem.



Jay

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[flash]

yup. happens all the time from people adjusting their belt without first loosening the mounting bolts for the compressor and/or forgetting to tighten them back up.

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[edm]

I'll check on it tomorrow. Thanks for the input guys.

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[MB968]

Yeah, check the compressor mounting. I found a broken front bolt on mine.

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[tamathumper]

Is the vibration constant when the AC is on, or only when the compressor clutch is engaged?

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[968Syncro]

My Tiptronic 968 shows the same symptom, just like you stated it. It goes away when I shift into neutral, but the RPM stays the same in neutral or drive -- about 9500. The vibration is also a bit less if I shift into 1st gear while stopped. Not sure it is a broken mount, it is almost like a binding or shuddering, it seems like the broken compressor mount would be subject to RPM but not drive vs. neutral.

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[tamathumper]

I've just noticed mine has a slight "shudder" the past few weeks, but I attribute it to the low vacuum I'm experiencing. It never had a shudder before, and now I can watch the tach needle move slowly up and down from 900-950 (ish) as the idle (and vacuum) slowly rises and falls. The shudder is when the idle is at its lowest, IIRC.

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[rl968]

Vibration on these cars can be deadly...think pick-up tube.

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[Cloud9...68]

[quote name='rl968' timestamp='1373138785' post='145288']

Vibration on these cars can be deadly...think pick-up tube.

[/quote]

Yep - one of these cracking due to vibration car really ruin your whole day. That's why I had mine reinforced with a small piece of metal bridging the tube to the back of the mounting surface. It was done by my machinist, using some sort of low-temperature welding technique (I know nothing about welding, but he assured me it would not distort of harm the tube in any way, which of course would have been worse than not doing anything at all).

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[ds968]

Education time for me :-) .. What is a pick-up tube ( what does it do ) and where exaftly is it ??

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[tamathumper]

It's in the oil sump - it sticks down from the engine to near the bottom of the sump, and to make matters worse it has a big puck with a screen on the end of it. When the engine vibrates, it wags that puck back and forth on the end of that slender curved tube, and if the tube cracks as a result your oil pressure goes down.

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[rl968]

The metal on that tube is not that thick. I suspect breaking these is going to be more common as the cars age. If anyone ever has to open up the pan (for rod bearings or to change a leaky gasket,) the tube should be replaced.

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