[Vwdiesel] Brake boost failure.... Lazy pump Update.

brian gochnauer brian at gochnauer.net
Sun Dec 21 19:56:50 PST 2008

Nice pics!  Doesn't look likely to be a dry style pump.
You were not concerned with using gasoline to wash out the pump (into the
sump) ?

On 12/21/08, mark shepherd <mark at shepher.fsnet.co.uk> wrote:
> New update on lazy pump:
> I cured the vacuum leak showing on the gauge. This appeared to be in the
> join of the tubing leading into the car. So now gauge holds pressure for
> hours. Thus, braking system good and both oneway valves good.
> I stripped the pump down, as far as easily achievable. [ Lid off pump out,
> and vanes out.]
> http://img67.imageshack.us/img67/8562/vacuumpumpah0.jpg
> http://img78.imageshack.us:80/img78/4862/vacuumpumpcloseupwb3.jpg
> The two seals under the 'foot' of the pump seem fine.
> Seal under the barbed lid looks a little poor; but is still standing proud
> of its recess and soft enough to be sealing. Gauze in middle of pump hides
> a
> tube down through and apparently open to sump. It was not blocked. I rinsed
> the pump out with gasoline. The vanes are of carbon type material... In
> fact
> I'd go so far as to say they look more of a brown bakalite to me. They have
> slight wear, and some pitting.
> http://img389.imageshack.us/img389/6167/pumpvaneiz4.jpg
> Their edge is essentially semicircular, and not contoured to the shape of
> the pump bore. They weren't excessively sticky, but then again being almost
> weightless, probably not much needed to restrict them. After cleaning, they
> were loose in their slots. I decided because of afore mentioned shape, that
> it would be fine to reverse them, [trailing edge to chip free leading
> edge].
> Reassembled pump started car up and immediate response. Left overnight and
> then popped out in morning on Saturday. Drove about 1/2 mile... Nothing. I
> parked up and shopped and came out again. I slackened the three lid bolts
> slightly and then started the engine. Immediate steady vacuum  rise to
> about
> 20" wg [23" but flickering previously] I retightened the bolts and vacuum
> remained. Pump body was warm to the touch. This must be the answer, the
> pump
> [vanes] must be binding until somewhere near blood warm.  If you look back
> at the lid under the vane picture; interference marks from the pump rotor
> can be seen. If the vanes are also touching the lid then they wont open
> IMO... [Look how the vanes point like cords, rather than radially, which
> mean they retract when they meet resistance and so, I guess less chips per
> year ;o)] Pump worked fine for rest of the day... I must find a way of
> reducing interference... I'll sleep on it...
> Saturday evening, I'm looking at how to quieten down the engine which seems
> to have become noisier than usual these past few weeks. Sump pressure may
> be
> slightly worse than recent times. oil droplets splashing around slightly,
> but oil baffle restricts view. Revving engine up and sump pressure drops
> off
> as perceived  through the oil filler hole. I'll just check the oil
> level....
> Holycrap the oil is off the dipstick and requires a pint and a half or more
> to get it back to it's correct level. H'mm no warning lamp. Engine off,
> ignition on... Still no oil light... heck... I wonder how long this has
> been
> the case...  I know only last month I checked head pressure and got about
> 25psi fully hot at idle, with 50+ at 200rpm. Topping engine up reduced some
> of the noise. Ticking sound that I've had for a year, receded to it usual
> level.  A friend's wife last week had  asked me if the engine was clockwork
> :o)
> Sorry about the essay, BUT, now for the interesting part...
> After topping oil up, I noticed the brake vacuum rose to 28" wg [up from
> the 'newly bedding in' reversed vanes value of 20"] Now this is even more
> interesting....
> Sunday morning:
> The gauge showed buildup of vacuum immediately. A lovely 28" wg. I did
> about
> 4 miles, and gauge barely dropped with single applications of foot pedal
> yipppeee!!!  The next few days will provide the proof of cure...
> My new questions might include; maybe the pump has the need for more than
> just vapour, thinking laterally, you might kill a pump if you used total
> seal otherwise!!!! The vanes fling out and in rotating squeeze the air out
> of the servo/booster line, and push it out of a drain on the side of the
> pump, but looking at the action of what is effectively a spinning disc on
> the side of the vanes, which my physics tells me creates an increase in
> pressure radially as the film of oil moves outwards and actually sucks oil
> up the centre past the gauze. Close inspection of the picture of the face
> of
> the rotor of the pump shows a recess that acts as an oil reservoir. So this
> then is spun out radially and drops in the gaps of the rotor behind the
> vanes and out at the bottom end too, keeping everything nice  for what is
> now 23 years for this particular engine... I don't suppose that the Quantum
> Bentley presently winging it's way across the pond towards me explains all
> this, or does it ;o)
> Essay over....
> Mark

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