XK140 turn signal control
XK140 Turn Signal Control
Dear Experts: does any one have a tip on improving the performance of
the dreaded Lucas 31250/A-TPS.1 turn signal switch with built-in, delayed
self-canceling action? Mine's canceling much too quickly.I've not checked
it out yet, I'm told it's oil-damped, is that true? The unit is fitted
to an XK 140 ots, the part # is C.10830 - Regards, John Morgan
John, I have the same problem, so I took the switch apart for a look-see.
Remove the 3 screws through the front (knob side) and the switch can be
pushed out of the outer shell. Now you'll see the contact points and 3
more screws that hold the body of the switch together and attach the 3
brass wire connections to the back of assembly. Proceed with care! There's
a potent spring inside that's poised to launch the contents across the
kitchen as those 3 screws are removed. Back those 3 out while you hold
the switch together. Inside is the spring, a cylinder with a V-groove,
and a pinned dowel on the knob shaft that rides in the V-groove. When the
knob is turned to one side, the dowel forces the cylinder against the spring.
Spring pressure on the cylinder forces the cylinder to return to the neutral
position. Sounds confusing, but you'll see when you open it up. Anyway,
the system appears to be oil-damped. The back end of the cylinder is fitted
with a friction collar or gasket that resembles the diaphragm in a bicycle
pump. There is a trace of heavy oil in the body of the switch. My guess
is that the oil serves to allow the friction collar to rotate inside the
switch body at the desired rate to control the signal time. I wrapped one
turn of adhesive metal tape between the cylinder and the friction collar.
It slowed the return time, but I don't know how long the tape adhesive
will last. Let me know if you come up with another solution. - Sam Bell
John, I am pleased to report that I have had recent experience with
this clever device with a successful outcome. The mechanism is based on
air not on oil! Turning the signal lever causes the piston to move toward
the cylinder end which has a bleed screw. The spring is forcing the piston
back to the original position, however when working properly, a vacuum
is formed behind the piston and the rate of return is determined by the
amount of air through the bleed screw. The problem with the rapid return
is the seal between the piston and the bakelite cylinder. Mine appeared
to be leather. I cleaned all the parts and soaked the piston in motor oil
for a day. You will know if you are successful when the piston does not
return because the bleed screw is shut and the piston seal is forming and
holding a vacuum. I was able to adjust the bleed screw for a return of
1 second to 40 seconds. I chose 15 seconds. Please let me know if you need
any additional info. - Regards, Walter Hickman 140DHC
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