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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