In these models when the wiring is intact, the light should be lit if the key is in the run position, regardless of what gear you are in. With earlier models, which have the sliding switch won't hear a relay, because there isn't one. Replacement is one solution, but if you're clever with a soldering iron, you may be able to repair this kind of fault yourself.Īssuming the wiring is in order and the relay is clicking happily when you press the switch, you should have a light in the instrumentcluster telling you that the OD is on. It is also worth noting that OD relays have sometimes been found to have aging cold solder joints that allow for intermittent operation. The wires that travel from the shifter and travel under the carpet are often suspect, as are any wires that have had to flex repeatedly. If the OD relay isn't doing its thing, the fault could be in the relay (P/N 1259750-6) but before you rush off to spend money on a new relay, be sure the wiring that goes up to and through the shift lever is intact. Nonetheless, after 10 or 15 years, moving wires can break. The harness was upgraded in 1978, and later cars may be less prone to this fault.
If the fuse has blown from a circuit overload, look for damaged wiring in and around the shift lever shorting to ground. In my 1980 GT, the OD shares a fuse (#11) with the rear window de-mister, for what it's worth. It's an awful thing to spend time fault tracing only to end up finding a blown fuse. If your car is 1981 or newer, listen for the soft click of the relay, which is behind the vent directly to the left of the glove box (left hand drive).ĭon't forget that the circuit is fused. Disassemble carefully, and use electrical contact cleaner with caution - This stuff is generally super toxic. Less common, but possible, is that the switch itself is gummed up. You can check the switch for continuity Switch off - open circuit = no continuity Switch on - continuity = ~0 ohms. I have seen cases where the wires that go to either kind of switch have become disconnected, and a little fussy work with needle nose pliers will allow the overdrive to operate. Older 240s have a sliding switch in the shift knob to actuate the overdrive while the newer ones have a momentary contact switch that triggers a relay. If your overdrive unit isn't working at all, with no OD light in the instrument cluster, the chances are good that you have an electrical problem. Excluding major mechanical damage and worn internal parts, the usual suspects are electrical faults and slipping or failing to engage or remain in overdrive due to hydraulic problems. In my experience, the most common problems are fairly easy to diagnose and repair. Of course, a number of things that can go wrong with the J-type overdrive units. Volvo does have the distinction of being the only non-British marque to have used them in such great numbers. Jaguar, Austin Healy, Alpine, Hillman, Triumph, MG and others used them, as well as the French Facel-Vega III, which used the B18/M41 combo. Volvo was not the only company to use the Laycock overdrive units. In fact, quite apart from improved fuel economy and allowing the car to sustain high speeds with lower engine RPM, hitting that switch and feeling my car slip into overdrive is one of my favorite driving delights. Often thought to be troublesome and unreliable by its detractors, I have found the M46 to be durable and really quite satisfying when its basic hydraulic and electrical needs are met. When out of overdrive, the power comes by way of the transmission output shaft through the one way clutch internal to the annulus gear (output shaft) of the planetary gear set. In overdrive, the planetary gears are driven by the stopped sun gear on the transmission output shaft which drives the annulus gear faster than the output shaft of the transmission. It contains a sun wheel with a sliding cone clutch and a planetary gear set that run in an internally toothed annulus with a uni-directional clutch that drives the output allowing for 0.8:1 gear reduction when overdrive is engaged. The invention of Edgar de Normanville, it was originally called the de Normanville epicyclic gearbox. It's such a French sounding name from such a distinctly British company. There's something about the Laycock de Normanville mystique that I just love. The J-type overdrive is said to be stronger and able to withstand higher torque than the older D-type. The M46 is the younger sibling of the venerable M41 found in 1800 and in some 140 and Amazons and the more robust M410 found in the 1 E/ES. It is found in both 240 and 260 from 1975 through 1986.
Laycock overdrive yoke conversion manual#
The overdrive unit on the M46 manual transmission is surely one of the most maligned and misunderstood parts in the Volvo 200 series.
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