Brake fail sensor switch

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24 Feb 2014 14:27 #1 by Ralley
Ralley created the topic: Brake fail sensor switch
I picked the OKA up from the mechanic today after having it check for ADR compliance. The only thing needed was the brake fail switch in the bottom of the master cylinder was not working we checked the light and it works so we pulled the switch and it was seized. So we freed it up and we can't get it to make contact. The local brake place can't get them, so i'm open to ideas otherwise I will pull it apart.

Rob

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24 Feb 2014 14:37 #2 by PeteFox
PeteFox replied the topic: Brake fail sensor switch
Rob
They are a PBR part and were fitted to almost every 90's Holden. Definitely available.

After you remove the switch you should use a small pin (nail etc) to push up on the plunger in the valve above to reset it. It won't make contact until you do this.
Are we talking about the same thing?
Pete

Pete Fox OKA266 MultiCab
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www.byles.net/www.oka4wd.com/forum/membe...oka-266?limitstart=0

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24 Feb 2014 14:57 #3 by Ralley
Ralley replied the topic: Brake fail sensor switch
If it's the one screwed into the bottom of the master cylinder that's the one. We can't get it to work with a meter on the bench so we haven't tried it back together. It doesn't make contact when we move the pin.

Rob

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26 Feb 2014 07:11 - 26 Feb 2014 07:16 #4 by dandjcr
dandjcr replied the topic: Brake fail sensor switch
Pete, Rob, this is an area I've never investigated, so a dumb question or 2:

How does the brake fail sensor detect a brake failure?

How do you tell if the brake fail sensor is actually working unless the brakes have failed?

David and Janet Ribbans - Oka 148
Oka148 profile here.
Visit our technical and travel blogs: here.
Last Edit: 26 Feb 2014 07:16 by dandjcr.

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26 Feb 2014 08:02 - 26 Feb 2014 08:20 #5 by outyonda
outyonda replied the topic: Brake fail sensor switch
I think, it is a pressure switch.
the plunger is held in no mams land.
stand on the pedal too hard & it comes on & you get brake lockout until the pressure drops.
the valve in the master cylinder keeps a small amount of pressure at all times, 1atmosphere. . a leak or lack of fluid or too big a foot should set it off.

that is my theory, I could be wrong!!

OKAs 091, 093, 094, 113, 346x6 & 405
Last Edit: 26 Feb 2014 08:20 by outyonda.

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26 Feb 2014 08:41 - 26 Feb 2014 08:56 #6 by dandjcr
dandjcr replied the topic: Brake fail sensor switch
Brett, some of your theory could be partly right.

The sensor must sense a pressure differential somewhere, maybe between the front and rear brake lines?

Normally the plunger would be held in no mans land, irrespective of the pressure.

This website explains all.

How you test the sensor is still a question.

David and Janet Ribbans - Oka 148
Oka148 profile here.
Visit our technical and travel blogs: here.
Last Edit: 26 Feb 2014 08:56 by dandjcr.
The following user(s) said Thank You: DarrenWebster303

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26 Feb 2014 11:10 #7 by Ralley
Ralley replied the topic: Brake fail sensor switch
if you look straight above the your right knee you will see the sensor screwed in-between 2 brake hoses it measures the difference between front and back. it's just a plunger like a brake switch. Mine was gummed up.

Rob

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04 Aug 2017 16:51 #8 by Frank
Frank replied the topic: Brake fail sensor switch
has anyone got details of what seals are inside this unit?
are they O'rings or special seals?
thanks,
Frank

Frank & Christine Thomas

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05 Aug 2017 05:20 - 05 Aug 2017 05:28 #9 by Peter and Sandra OKA 374
Peter and Sandra OKA 374 replied the topic: Brake fail sensor switch
Frank
I've not pulled an Oka one apart but have done a few other brands over the years and they usually just have O rings or simple cup seals, as has been said they only indicate pressure differences between the front and rear brake systems so it is just a piston with fluid from either system at each end and the switch in the centre.

OKA 374 LT Van, converted to camper/motorhome,
400ah Lithiums, 1100w solar, diesel cooking heating and HWS,
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Last Edit: 05 Aug 2017 05:28 by Peter and Sandra OKA 374.

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