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How to bypass o/d & high altitude switch?


claysspot

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Have you learned the quirks of the A43D transmission yet. It doesn't have a locking torque converter and slippage when overdrive is on can cause overheating and fry your trannie. Some add extra coolers and you still can really use it only on very flat or slightly downhill grades. I find that even on flat grades the wind at 55 to 60 will slow me down if I use overdrive and my rig is the smallest Sunrader. I have done several tests to see if overdrive improves mileage driving on highway 5 in California. Very long. very flat road. My mileage was worse with overdrive. You slow down and have to step on gas to maintain speed and lose fuel efficiancy. I would think that the power loss that comes with driving at high alttude would only make this worse. This engine is very happy running at high RPM's and I have been driving mine with the overdrive off for over nine years. If nothing but overdrive on will do I've heard it's underneath the kick plate on the drivers side. I'm sure some of the guys will jump in and give you the details.

Linda S

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The engine has barely enough power to use od at sealevel, in Denver you have even less. I live in Wy and never use od. If you just gotta use od then plan on changing the rear axle raito to something like 4:88.

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The OD is controlled by a relay that's mounted on the brake pedal support bracket, if i remember correctly the relay is blue and may even say overdrive on it. I am not sure there is a separate altitude switch i think the altitude control is part of the engine ECM as it is a necessary condition for the ECM to control the fuel injection system. To enable the OD you could install a switch to bypass the relay but if your main concern is operating at high altitudes i doubt it would be worth the effort as the higher you go the less power your engine develops and it does not have any excess of power even at sea level.

When we had a 4cyl 86 mini cruiser in areas that were pretty much level or near level roads and not much above sea level i found the overdrive to be useful and used it a lot. I had installed an aftermarket oil cooler and a trans temp gauge and never saw temps above 190f and most of the time it ran at 180f. With everything as it should, be trans cable adjusted properly, relay functional, etc; the computer is smart enough to shift to 3rd when the load is too great for the OD. When operating in an area that causes frequent in and out of OD you just switch it off and run in 3rd. A change to 4.56 or even 4.88 rear gear as suggested by WME would be a real benefit if you will be operating primarily at high altitudes and will make the OD much more useful at lower altitudes as well.

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