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Handbrake / brake test / twin res - help please
wombat - 23/5/13 at 06:44 AM

Morning folks, having got nearly all of the loom sorted I am stuck with the brake test illumination and switching, so if you could spare a moment I would appreciate it :-

I have the following set up:-
Twin master cylinders (OBP )with fluid sensors fitted into the caps
Standard Sierra handbrake with switch
Warning light for dash
Test switch (not purchased yet - what have you used?)

Am I correct that I just need to t- off the black/white handbrake wire and use this T to link reservoirs to test switch then to its original spade on the warning light?

Confused.wom

big_wasa - 23/5/13 at 07:49 AM

You don't need a test switch you can just pull the handbrake to test it.

wombat - 23/5/13 at 08:45 AM

Really ?

I understood from various searches that there has to be a test other than the handbrake?
Like a push button on top of the master cylinder for example............

loggyboy - 23/5/13 at 09:38 AM

quote:
Originally posted by wombat
Really ?

I understood from various searches that there has to be a test other than the handbrake?
Like a push button on top of the master cylinder for example............


The test switch needs to be from the drivers seat.
The idea behind the warning light is that it will act as a low fluid warning AND a failure warning. (there are two IVA RS's to meet - one for low fluid, the other for brake failure/pressure loss). You can meet the first RS by having your fluid level visable through the side of the MC reservoir, but you will still need either a hydraulic pressure sensor (expensive) or a fluid level sensor to show any possible failure in the system).

The test switch CAN be the handbrake (as long as its connected to a switch) as the hand brake warning light can be combined with the low fluid light as a 'general' brake warning light. Theres nothing to stop you having both.

The test switch is not to test that there is fluid, its to test the warning light bulb hasnt blown.


[Edited on 23-5-13 by loggyboy]

wombat - 23/5/13 at 10:01 AM

Thx Loggy, thought you might respond too, nearly contacted you direct instead of posting !

So:-

1. I mis-understood the switch part, didnt realise the handbrake could be THE switch (duh.....)
2. But I will need an hydraulic switch for my foot brake still
3. As OP - If I break into the B/W from the hanbrake wire going to the warning light, and link the resevoirs in series, this should do the trick?

Amazing that I have built it all so far without any form of manual (lots of help from LCB to be fair), but cant get my head around this.............

matt_gsxr - 23/5/13 at 10:18 AM

You will need to have the handbrake switch, Reservoir 1 switch and Reservoir 2 switch all IN PARALLEL.
Any one of them must switch the warning light on.


If you have them all in series, then you would have to have run out of brake fluid in both reservoirs and have your handbrake on for it to light!!!!

loggyboy - 23/5/13 at 10:20 AM

quote:
Originally posted by wombat
Thx Loggy, thought you might respond too, nearly contacted you direct instead of posting !

So:-

1. I mis-understood the switch part, didnt realise the handbrake could be THE switch (duh.....)
2. But I will need an hydraulic switch for my foot brake still
3. As OP - If I break into the B/W from the hanbrake wire going to the warning light, and link the resevoirs in series, this should do the trick?

Amazing that I have built it all so far without any form of manual (lots of help from LCB to be fair), but cant get my head around this.............


You will need something to make the brake lights come on, this can either my a hydraulic brake switch which is connected to the brake lines via T-peice. (there have been some who have found these unreliable and prone to being air traps) the alternative is a mechanical switch connected to the brake pedal, which is the common OE way of doing things. (usually these are push to break, not push to make)

You dont want to break the cable from the fluid level sensor warning light, the test switch needs to be in parallel, other wise it will only work when both the hand brake switch is used AND the fluid is low, you want it to be OR.

Worth having a run through the manual, theres alot there but 90% of it is not relevant to our cars or fairly obvious, its just a matter of reading it 3 or 4 times to get the gist of what they want.

loggyboy - 23/5/13 at 12:08 PM

Basic diagram of how you could wire it, im sure there other ways but this is the most straight forward IMO

Brake Warning Wiring
Brake Warning Wiring

[Edited on 23-5-13 by loggyboy]

wombat - 23/5/13 at 06:00 PM

Thx for the drawing Loggy but I am still confused....

Handbrake switch is one cable b/w which I believe to be "switched to earth"

Warning Light - has b/w wire - assume this goes directly to above
2x green wires(joined)- I believe this is supply - this according to diagrams is supply to various warning lights

Aaaaargh .............

snowy2 - 26/5/13 at 06:05 AM

i have used hydraulic brake switches on every kit i have built (now at 10 cars.... no kids :-( ) and replaced the pedal switch on those part built cars i buy when they went faulty, i have never had a problem with the hydraulic switches. i hear folks have problems but its always a mate of a friend says they have a problem, never a first hand account.
i would say they are reliable and easy to fit. on a restricted pedal box the mechanical switches can be a royal pain to set up in an area where they wont get constantly kicked and dislodged...they (the two basic types of brake switch) each have their merits.

snowy2 - 26/5/13 at 06:37 AM

the green wire will supply various lights, in exactly the same way as your battery supplies all circuits but the battery should have ideally one connection to it not dozens......
the supply for the brake switch can come from ANY suitable ignition supplied source, a single wire can supply the master cyls and the hand brake sw.
the simplest method is take a live wire from the ignition switched source of choice and connect it to the bulb. then connect TWO wires to the other side of the bulb, one goes to the master cyls (one terminal only then linked to the other master cyl) the other wire from the bulb goes to the hand brake switch. the master cyls need BOTH to be earthed.....
Thus when the hand brake is on the light illuminates OR if either master cyl is low the bulb will illuminate