[Vwdiesel] Vacuum Pump problems

Roger Brown r.c.brown at ieee.org
Tue Mar 23 15:15:17 EST 2004

Gary Shea wrote:
> Hey guys.  More on the vacuum pump rebuild problem.  I _think_ my second
> replacement shredded a few hours after I installed it, and that's after
> taking Sandy's advice and 'pre-tensioning' it.  So... I must be doing
> something really stupid but... what?
> You'll recall the diaphragm has a flat lip and bubbles up in the middle.
> I'm putting the bubble on the same side as the screw heads (I think of
> that side as 'up').  There are two plates (like Loren describes below),
> one on each side of the diaphragm.  Each plate has a dished edge and the
> dished edges are turned away from the diaphragm, so the plates are
> concave in opposite directions away from the diaphragm.  On the first
> replacement diaphragm I tightened the nut down tight so the plates
> gripped the diaphragm firmly; this time I left 'em kind of loose.  Last
> time I think the diaphragm lasted like two days instead of a few hours.
> I would say tha the bushings are pretty tight, at least to
> finger-wiggling.
> I'm baffled...

Is there any sign of oil in the pump?  If so, you may be getting blowby out of the crank case feeding up the tube to the pump outlet.  One thing to try is disconnecting that tube and just run a bit of cloth over the outlet for a filter and see if it lasts
longer.  My old '81 would chew through pump parts (diaphrams and the plastic check valves) randomly, seemed to be a blowby issue, but it was only intermittent.  Almost like a ring would stick for a second or two then free up.  I found that fi I hooked the
crank to the pump with a tee up to the valve cover breather tube, it all worked fine, no pressure buildup in the pump.


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