[Vwdiesel] Brake boost failure....

[mark shepherd]

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...]
Mark




----- 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
>>
>>Mark
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>>Vwdiesel at vwfans.com
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>
>
>