> The auto in question is a 1985 380 SL
>
> A recent engine rattle has been isolated to the air pump. Bad clutch?
the vanes inside usually break.
> What's involved in repair, or are these swapped out? Cost?
Swapped out, ask your local Auto parts store for cost.
(call all of them, prices vary wildly)
> Can this be bypassed?
Yes, but you may burn up more parts (diverter valve,etc) that are kept
cool by the flow of air from the pump, if you disconnect, exhaust can go
backwards up the system.
Bernard
Air pump is mainly only used when engine is cold... after that, it is always
idle. Old cars like ours are super loud and noisy when on... it is normal.
I'd leave it alone... I know it is annoying.