Checking and Rebuilding the Brake Reservoir Float Switch
On the later models the brake fluid reservoir lid contains a float switch which should cause the brake
warning lamp to illuminate when the fluid level falls.
Testing the Switch
The level warning switch may be inoperative due to corrosion or general decrepitude,
so it's worth checking it by chocking the wheels,
releasing the handbrake (which incidentally should also cause the warning lamp to illuminate in the on position)
turning the ignition on and lifting the switch out of the reservoir, at which point the lamp should illuminate.
If it doesn't, you can establish that the switch is faulty by removing the spade connectors and shorting
them together with a paperclip or something similar, at which point the lamp should also illuminate.
As you can now appreciate, the switch is not fail safe
so although it's a nice idea it's not much use by today's standards.
Dismantling the Switch
If the float switch is faulty it can be repaired.
By careful examination you will realise that it's little more than a cork on a brass pin inside an aluminium sleeve.
The top of the pin has a metal disc fastened to it inside the polythene cap.
When the cork drops the disc shorts the contacts inside the cap and the circuit is completed.
The contact relies on the weight of the cork, which isn't much, so a small amount of oxidation will cause a bad contact.
The contacts are accessible by levering off the top part of the polythene cap which is held in position by two
round headed studs which are clearly visible.
The studs are fluted so twisting them while pulling will facilitate their removal.
Cleaning the Electrical terminals
These are silver plated. George Raicevich from Australia e-mailed to suggest that you should avoid sandpaper or
steel wool when cleaning these because it will destroy the silver coating.
Instead, clean them by soaking them in some Domestos (sodium hypochlorite).
This was evidently a trick used for cleaning medical ECG silver electrodes back in the days before disposable 3M
type skin electrodes where used!
The terminals should come up bright and clean. Test that the contact is good.
Replacing The Screw Ring
The aluminium screw ring tends to corrode badly. George also explained that this is due to galvanic corrosion
(the aluminium acts as a sacrificial anode because it is higher in the reactivity series than the steel of the canister).
The lid was originally made by "Tri-seal". Consequently he suggests a new lid made of tin plated iron
can be made from the lid from any "Tri-Seal" 1 gallon metal container
(lawn mower fuel can, old style 1 gallon metal oil can, etc).
They will usually be a little shallower than the original float reservoir version.
and to compensate you can remove the rubber washer in the lid assembly.
With this method you will also have to cut a hole in the new lid.
Use a metal hole saw cutter with a guide drill bit. (38mmdiameter - from memory).
Don't use the cheapy hole saws with multiple clip-in cutter blades, go out and buy one with the blade that goes all the
way around 360 degrees. The cheapies have a big gap in the blade and are inaccurate.
Cut the lid with the screw edge flange facing up and the lid flat against a piece of wood.
Drill down into the inside of the lid and
into the wood.
Another tin plated steel alternative is available from JEM.
See the SPARES AND SUPPLIES page.
These are as deep as the original and have a hole cut out already.
However this will still need enlarging to fit the switch body.
Replacing the Float
It may also be found that the cork is loose on the pin which can cause the warning light to come on too soon.
The aluminium sleeve must be removed to remedy this.
Luckily it is only secured to the underside of the polythene cap by a couple of centre punch dots and so can be
carefully twisted off. The cork can be replaced with a new (ie not Ex-Chateau-Whatnot) one by slitting
the new one end to end just over half way through, and "wrapping" it round the pin.
The slit can be wired closed in several places, thus gripping the pin firmly, when the sleeve can be replaced.
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