I'm going through the brakes of my 1979 1500cc Midget. As part of the
process, I dismounted the brake pressure warning valve, also known as
pressure differential warning actuator -- or brake failure switch. (In years
to come, someone Googling for info will thank me for using all those
phrases.)
In the process of disassembly, I broke the actual nylon switch that screws
into the housing. To be fair: I *was* following the step-by-step, which said
to remove the endplug and copper washer first. The problem was those parts
were torqued in at over 80 foot-pounds: far exceeding specs of 16
foot-pounds. So I had to put the assembly in a vice between wood blocks to
keep from deforming the housing. I should have removed the plastic switch
*before* putting the housing in a vice. The housing twisted and sheared off
the plastic switch.
This is where the real problem comes in. The shuttle valve piston I took
out of the assembly doesn't resemble the one illustrated in my 1982 Haynes
manual. It is spring loaded. The nylon switch works opposite of the one
described in the book. The plunger of my switch rides on a ridge on the
shuttle valve piston. When one brake circuit fails, pressure forces the
piston against its spring to one side or the other and the ridge moves out
from under the plunger. The plunger drives home, locking the switch on.
Bleeding the system won't unlock the switch. It has to be reset by hand, by
unscrewing the nylon switch. This allows the plunger to centralize itself on
its spring.
Although this is a 1979 model year car, the housing (the bit with all the
brake-pipe holes in it) is made of brass. The Moss catalog says that it
should be cast iron. Moss says brass was used through 1975. There are two
different switches listed, determined by whether the housing is brass or
cast iron.
The question is, which one do I need? Do I go by model year or housing
material? Or is mine some sort of wierd one-off. I am the original owner of
this car, so if it is a one-off, it's a factory job. The number on the
plastic switch is: 4177-716. Three numbers stamped on the brass housing are
obscured. Here's what I can make out: 3214224; 656; 162 G26.
In the archives, there are some postings from 1999 from a fellow who
refurbed his brake failure switch, but without any description. Is he still
here?
Can someone here with a 1979 Midget go take a look at his or her car and
see if the housing is brass?
Thanks,
Rick in MD
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