Brake booster info needed.

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Chockster

Chockster

Member
Posts
88
Location
The Lake District
Hello all.
I have a series 3 I am going over at the minute. It is converted with a 2.5 dihatsu diesel. Found the brake vacuum pump to be completely knackered and spewing oil. It was powered from a spline on the back of the alternator and oil lubricated from the engine. Anyway after failing to find a replacement I bought a generic VW 12v vacuum pump of eBay. Came from an Audi TT and was only a tenner!
Simple wiring positive and earth.
Makes a big difference to breaking!
Anyway I have it wired up to run when the ignition is on but it constantly runs as I’m using the vehicle. So here is my question.
Is that bad? Will the pump burn out quick rather than having a vacuum sensor to regulate when the pump switches on or off? I would like to wire in a regulator but can’t find anything for love nor money to fit.
The brake servo has a non return valve so when the vacuum level is hit it will retain until the pedal is depressed. So I don’t need to be running it all the time.
Anyway. Thought, ideas and recommendations welcome.
Thanks in advance.
 
Chockster said:
The brake servo has a non return valve so when the vacuum level is hit it will retain until the pedal is depressed. So I don’t need to be running it all the time.
Click to expand...

The VAG system uses a vacuum switch which controls the running of the pump, making sure it only runs when needed.
 
Europa486 said:
On my small aircraft I had a vacuum system to run some of the instruments and used
A vacuum switch to put on a light if I should get a vacuum pump failure,
So shouldn’t be to difficult to wire up to your pump through a relay,
This was similar to what I used,

https://www.ebay.co.uk/itm/38252964...B6neJsP0jlyEFIFWIMJUI2qWET3u9yiYaAgo0EALw_wcB
Click to expand...

Hi thanks for your response. Is this a switch which is fed from the vacuum line to regulate the pump running?
If it is it could be just what I'm looking for!!!
 
Hi Nodge suggested using the VAG vacuum switch, it would be exactly the same principle as using the
One I suggested,
The switch is plumbed into the vacuum line, power is supplied to it, when low vacuum the switch
Detect a low vacuum and allows power to the pump, as the pump vacuum increases to a set value the switch would
Shut of power to the pump, you would need a relay to take the amps the pump would require,
 
Winner winner chicken dinner! This is amazing stuff. Thanks for the info. Ill be giving this a go and would you know what size relay to stick in? I’ve just hard wired the pump in at the moment.
 
I have been looking at this for my classic car and there is a kit you can get with a small vacume cylinder and switch i will have a look for it.
 
Having a look on the bay they seam to be missing nearest i can find is this cylinder
https://www.ebay.co.uk/itm/Chrome-Universal-5-x-7-Vacuum-Storage-Canister-SBC-Chevy-BBC-SB-Ford-Mopar-V8/123820878037?_trkparms=aid=1110006&algo=HOMESPLICE.SIM&ao=1&asc=20201210111314&meid=b740348aa23240e6948e98f0fc08d81f&pid=101195&rk=5&rkt=12&mehot=pf&sd=224299203495&itm=123820878037&pmt=1&noa=0&pg=2047675&algv=SimplAMLv5PairwiseWebWithDarwoV3BBEV2b&_trksid=p2047675.c101195.m1851

And this switch before covid there were kits for about £35 with tank and switch and all the tee pieces and hose

https://www.ebay.co.uk/itm/Electric-Brake-Vacuum-Pump-Switch-for-Booster-28146/224097319103?_trkparms=aid=1110006&algo=HOMESPLICE.SIM&ao=1&asc=20201210111314&meid=029c74071bd84812b14c3bdf17322f30&pid=101195&rk=1&rkt=12&mehot=pf&sd=224018885622&itm=224097319103&pmt=1&noa=0&pg=2047675&algv=SimplAMLv5PairwiseWebWithDarwoV3BBEV2b&_trksid=p2047675.c101195.m1851
 
I seem to recall that the "best" solution is to have it wired to a vacuum pressure switch so it maintains vacuum but also to the brake lights so it comes on immediately you start braking and gets a bit of a head start. Sorry i can't find where I read that.
 
rob1miles said:
I seem to recall that the "best" solution is to have it wired to a vacuum pressure switch so it maintains vacuum but also to the brake lights so it comes on immediately you start braking and gets a bit of a head start. Sorry i can't find where I read that.
Click to expand...
On ere probably. ;)
Takes about one second to reach full vacuum if the pipe is short enough.
 
Chockster said:
Hmm wiring it in to the break lights seems like a cost effective solution
Click to expand...

Only if you want boost after you need it.
All electric boost systems use a small vacuum vessel and some form vacuum pump control for a reason.
I suspect a pump on the brake lights won't pass an MOT, as vacuum can't be assured from the first press of the pedal.
 
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