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

mark shepherd mark at shepher.fsnet.co.uk
Wed Dec 17 07:50:31 PST 2008

Vac  holds  for hours. In fact there may be a residue overnight!  Plenty of lubrication in chamber.  This morning ran to town. No vaccuum on gauge, until driven  a mile or so , and then it returned completely within a few seconds. Operates every trip  immediately, and hot  or cold reaches about 23 in wg. Problem must be with the vanes somehow.  Temp this morning was around zero. Car windows iced yet no ground frost. 
Maybe there is too much oil? 
More pointers please.  

Sniped  a Quantum Bentley a few days ago  for $6, alas postage may kill me though!

----- Original Message ----- 
  From: brian gochnauer 
  To: mark shepherd 
  Sent: Tuesday, December 16, 2008 12:32 AM
  Subject: Re: [Vwdiesel] Brake boost failure....

  My son and I used a cheap brake bleader that had a gauge on it to suck/track down a vacuum leak.
  It was -4 F here today.! (Iowa)

  On 12/15/08, mark shepherd <mark at shepher.fsnet.co.uk> wrote: 
    Thanks for the response Doyt;
    my next test I suppose, is to run the vac gauge on a longer piece of pipe
    so that I can see it during 'dead mode' Replacing the brake servo is an
    upsidedown and legs around the headrest job... I do have a salvaged one if
    it comes to that.
    With engine off; depressing the brake with it still energized; I can hear
    the air whooshing in. I wonder if that hole is clogged? I've never actually
    looked at it  [if it exists that is...]

    ----- Original Message -----
    From: "Doyt W. Echelberger" <doyt at buckeye-express.com>
    To: "mark shepherd" <mark at shepher.fsnet.co.uk>
    Sent: Monday, December 15, 2008 3:28 PM
    Subject: Re: [Vwdiesel] Brake boost failure....

    > Brake function on my 84 Rabbit D is pretty much the same as you describe,
    > or worse. I suspect that the failure is probably located in the drum-like
    > brake booster device on the firewall.  When I replaced that drum-like
    > brake booster device last year on another diesel (85 Jetta TD) similar
    > faulty braking went away.
    > During the next failure incident, can you test the actual booster on the
    > firewall?
    > Doyt
    > Ohio, USA
    > >>>>>>>>>>>>>>>>>>
    > At 08:28 AM 12/15/2008, you wrote:
    >>A few days ago during some extremely cold weather [-4 deg C] I drove off
    >>in my car and found that 100 yards up the road at a junction, the brakes
    >>went hard, and I struggled to stop. Went about half a mile before they
    >>came back to their usual responsive form. My conclusion was that maybe
    >>there was some ice on the vane pump. It happened again a few days later.
    >>Still around 0 deg C. I had driven for about 1/2 mile at around 45mph
    >>before I noticed it at a junction. Driving 10mph  for 100 yards further to
    >>the next junction and the power came back.
    >>It seems to be the first drive of the day. It happened again this morning,
    >>but air temp is more like a chilly 5 deg C ;o)
    >>I took the vaccum pump off and then apart, and found a little smear of
    >>sump oil, and the vanes were free to slide and were well oiled. Blowing
    >>and sucking on the plastic barb seemed to tell me that the non return
    >>valve operated.  Air freely came out of the spline base. Nothing else to
    >>see really...Reassembled and ran the car[yesterday]
    >>After today's reoccurance; I did a vaccuum test.
    >>[Car had already recovered from fault at this point]
    >>It reached 20 to 25 inches watergauge quickly. I was attached to one of
    >>those normally capped twin little barbs.
    >>Switching engine off gauge dropped to zero rapidly. [I put this down to
    >>either my poor connections with the gauge and being below the valve in the
    >>servo line.]
    >>Further to this when reassembled, the brakes retain their power for at
    >>least a minute after engine turned off.
    >>Suggestions welcome. [Except for comments on my misunderstanding of the
    >>term 'cold weather'] ;op
    >>Vwdiesel mailing list
    >>Vwdiesel at vwfans.com

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