Shudder from Spider rear

[Hirsch <Catenary@xxxxxxxxxxxxxx>]

Dear Alfisti,

I have a problem with a friend's car I'm trying to diagnose. Car is a '90=

Graduate with 35,000 miles. Car is not driven much and is not abused.

There is a low frequency shudder or rumble from the rear or center
of the car immediately before the car stops when the brakes are applied
hard. The clutch is in (disengaged) at this time. If I stop with light to=

moderate
braking, there is no shudder. The shudder seems to come from the
diff or driveshaft based on listening in the car.

I jacked up the rear of the car and pulled on a few things and the =

bushings and shock mounts seem OK.

Problem doesn't seem to be brake related as the rotor is smooth
and the sound is not metallic like brake pads worn down to the
metal. Also, the sound seems to come from the center of the car.

With the rear wheels off the ground, when I rotate a wheel back
and forth, the diff seems fairly noisy (clunking) and somewhat
loose, though doing the same thing to my *baseline* car ('78
Spider, 90,000 miles) gives about the same level of diff
looseness, but with less noise.

In terms of the driveshaft, the U-joints feel tight and all
bolts are tight. Looking around the driveshaft, I saw no
obvious evidence of rubbing. The center support may be
sagging a bit, but in my experience a bad center support
produces a shudder on takeoff from first gear and not with
heavy braking. Is this correct? Car only has 35K miles (thou
the car motor mounts and a muffler were replaced already).

Does anyone have any suggestions on what else to look for
or what might be causing this?

Thanks,

Rich
'87 Milano
'78 Spider
'67 Duetto
'66 Sprint GTV <- Cat daddy car
Editor, i Saluti, St Louis AROC
Website: http://www.catenary.com/victor/isaluti

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