Thread: Brake booster/servo - Series 3 but general query.

It should hold vacuum much longer, even overnight. Certainly shouldn't be dependent on vacuum in 'real time' such as driving uphill. There's generally enough in reserve for two or three brake applications with a stalled engine. But I'm sure you know all this. I'd start by checking the one-way valve in the vacuum line. Also you might consider blocking the vacuum line to the booster and see if the engine idles differently; the vacuum leak might not be enough to cause 'surging etc' but perhaps a change in idle speed. Probably not though if it's holding vacuum for a few minutes.

I'm reminded of funny story from a workmate in the 1970s, his mate fitted an aftermarket turbo kit in his backyard, don't recall the car make, but he went for a test drive and gave it everything as he took of up the street, went for the brakes only to find the vacuum booster was now pressurised by the turbo.

Another thing to look for is cracks in the booster, probably around the centre where it bolts on to the pedal box.

Off topic comment - many cars of the 1920s to 1940s used a vacuum wiper motor. These tended to stop working on hills, and would flap wildly as you slowed with the throttle closed. Post war, some cars had a vacuum pump on the bottom of the fuel pump to boost vacuum when the manifold vacuum dropped, Holden being one, I think.

In my S3 Lightweight the brake warning light comes on randomly, the problem is in the shuttle valve itself , it'll come on for a week then stay off for months, non issue for me , Im only leaving it there because its an original Lightweight item , Ironic since theres not much original left of my LW . Mine never had the vac warning switch on booster. Was an FFR .

In fact I've removed my booster as the 12v vac pump was too noisy . I made a 'booster delete' kit put a 120Y Master cylinder on it , works very well.

_DSF0786.jpg

Originally Posted by POD

It should hold vacuum much longer, even overnight. Certainly shouldn't be dependent on vacuum in 'real time' such as driving uphill. There's generally enough in reserve for two or three brake applications with a stalled engine. But I'm sure you know all this. I'd start by checking the one-way valve in the vacuum line. Also you might consider blocking the vacuum line to the booster and see if the engine idles differently; the vacuum leak might not be enough to cause 'surging etc' but perhaps a change in idle speed. Probably not though if it's holding vacuum for a few minutes.

I'm reminded of funny story from a workmate in the 1970s, his mate fitted an aftermarket turbo kit in his backyard, don't recall the car make, but he went for a test drive and gave it everything as he took of up the street, went for the brakes only to find the vacuum booster was now pressurised by the turbo.

Loving the turbo incident!

I think mine may have “inhaled” the old filter as it’s disintegrated…

I kind of doubt the diaphragm has gone, but there could be issues with the valves internally…
Might put out my feelers for an old one I can go over and put in. Loathe to go Communist model as it is an ex-NATO vehicle!
If anyone has a genuine STC1816 around, PM me! Great if it’s working but would not mind a leaking one I can try to rejuvenate and exchange… PM me if you have anything! Only interested if a genuine Girling type one…
Cheers,
Dave

Originally Posted by JDNSW

Another thing to look for is cracks in the booster, probably around the centre where it bolts on to the pedal box.

Off topic comment - many cars of the 1920s to 1940s used a vacuum wiper motor. These tended to stop working on hills, and would flap wildly as you slowed with the throttle closed. Post war, some cars had a vacuum pump on the bottom of the fuel pump to boost vacuum when the manifold vacuum dropped, Holden being one, I think.

No cracks I can see yet! You mean in the steel?

Yes RE the wipers. My mates old Falcon had that!
The Austin Champ I was doing up had that too - with a big vacuum reservoir tank for them! Quite intricate and innovative inside the “motors”.

Originally Posted by goingbush

In my S3 Lightweight the brake warning light comes on randomly, the problem is in the shuttle valve itself , it'll come on for a week then stay off for months, non issue for me , Im only leaving it there because its an original Lightweight item , Ironic since theres not much original left of my LW . Mine never had the vac warning switch on booster. Was an FFR .

In fact I've removed my booster as the 12v vac pump was too noisy . I made a 'booster delete' kit put a 120Y Master cylinder on it , works very well.

_DSF0786.jpg

Interesting!
Whilst I’m staying all original whilst we can still buy hydrocarbons, your vehicle is far more future-proofed!

I’m interested yours didn’t have the vacuum switch. Mine was FFR too. Winterised/deep wading. All kinds of odd little things I discover on it! Like the unprotected brushes on the 24v starter once the rubber bag over it fell apart!
Cheers,
Dave

Originally Posted by davros

No cracks I can see yet! You mean in the steel?

.......

Yes, I mean in the steel! I had this happen on my County, and I have heard of it from others. I doubt it is specific to the booster I have, but could potentially happen to any of them - the chamber is stressed and the stress released every brake application, so it is a fatigue failure.