Use of OD-Off for its braking ability

My viewpoint...

- brakes are a lot cheaper then transmissions so I always use the brakes unless there is REALLY a need for engine braking.

- OD bands seem to be a weak link in many transmissions (at least those with OD bands instead of clutches) so if I'm going to be manually shifting a tranny the OD would be my least favorite gear to play with.

- an automatic tranny was designed to shift itself automatically, the less I interfere with it's automatic operation the longer it's likely to last.

I think the thing that does in most transmissions is shock loads (rev it up and drop it into gear) and reverse loading (poorly executed manual shifts that make the tranny go "CLUNK").

-- Elbridge Gerry, of Massachusetts:

"What, sir, is the use of militia? It is to prevent the establishment of a standing army, the bane of liberty. . . Whenever Government means to invade the rights and liberties of the people, they always attempt to destroy the militia, in order to raise a standing army upon its ruins." -- Debate, U.S. House of Representatives, August 17, 1789

If you're shifting out of OD to come down a big grade it's a good idea, otherwise you are better off just using the brakes. Bob

AZGuy opined in news: snipped-for-privacy@4ax.com:

Correct me if I'm wrong - trans being my least knowledgable area - but OD on/off is nothing but a switch for all intents, right? And the pattern of daily driving would see OD shifting much more than would be practical to do it by hand.

I cant see using this as a matter of course in daily driving but for long grades it seems to me it'd be a good idea.

If you engine brake down to the point where the OD would drop out anyway, I cant see the wear factor.

Of course, when towing or carrying a very heavy load OD should be off at all times.

MORE likely in daily use would be wearing out the switch.

I was taught "gears are for going, brakes are for slowing," but also to use the same gear doing down a gradient as I would going up it. However, I was taught not to change down just for the purpose of braking. Brake first, then change, not t'other way around.

I'd imagine that there are all sorts of reasons for this, such as the brakes work on all wheels (this is true of an all wheel drive vehicle using the engine as a brake), brakes are cheaper than transmission or clutches, and you have more control when using the brakes rather than the engine.

In our manual car, if I'd be using third gear for a certain gradient on the way up, I should be using third on the way down. Of course, sometimes I'm in a higher gear anyway and relying on the brakes...

Manually disabling the overdrive for downhill engine braking has the benefit of not heating up your brakes, but it reads as though you downshift (effectively) on the approach to a hazard, even on the flat, and so use the donk as a brake. It may be more prudent to lift off sooner and let the transmission figure out what it needs to?

If you have a long grade, and use shift out of OD to keep your speed down, this is perfectly acceptable. Why use the cars brakes? Wear and tear on the trans from using engine braking to keep the vehicle speed down on a downgrade is nothing compared to wear and tear when you step on the gas to merge.

Changing your trans fluid annually is the best way to fight transmission wear and failure.

Ya, that's right, on the assumption that you'd not be using OD on the way up of course (and to be fair, I'd expect not, unless you're hooning along, in which case slowing down probably isn't in mind).

I guess not. When you're accelerating, the engine is driving the transmission and when you're decelerating, the transmission is driving the engine. But I'm no expert in automatics, not having owned one yet.

The OD is just another mechanical part. In most transmissions they have chosen to control it's application thru an electric solenoid rather then just the hydraulic valves in the valve body but aside from using the solenoid it's still just a mechanical issue. When it comes to downgrades, It's not the use of OD or not using OD, it's the shifting in and out of it that's potentially hard on the tranny. The transmission will ideally be doing up shifts under FORWARD load. If you are shifting your OD on and off and some of that consists of turning it ON while coasting or feathering the throttle, you put a BACKWARD load on the band, many people will then give it another jolt by giving it the gas and snapping it into forward load mode. Except for occasional odd situations, there's really no point in doing that, just let the transmission shift itself. Here's another way to view this - stomp the pedal and force a "passing gear" downshift, in most vehicles that will be relatively smooth with no reverse loading on anything. But if you decide you can "do it better myself" so you figure 3/4 throttle is all you really need but you are still going to drop it into a lower gear you often get a heck of a CLUNK because at

3/4 throttle the engine isn't going fast enough to apply forward load on the tranny and you wind up with the reverse load on it. Of course as soon as you feel that the engines going too slow you give it more gas and snap all the internals into forward mode. Since this could be loading the sprag (one way clutches) rather heavily, not to mention the possible reverse loading on the bands, it's not likely to be any good for the transmission. Will it break the first time you do it? Probably not. How about the 50th time?? How many shock loads will the sprag clutch take before it galls?

When towing, yes, just turn OD off and forget about it till you get there and unhook the trailer, assuming that's what the owners manual says. Some of the newer transmissions claim it's not a problem to tow in OD with them. I'd still worry on upgrades and turn it off. I'd rather pay for a little more gas just like I'd rather pay for brakes.

-- Elbridge Gerry, of Massachusetts:

"What, sir, is the use of militia? It is to prevent the establishment of a standing army, the bane of liberty. . . Whenever Government means to invade the rights and liberties of the people, they always attempt to destroy the militia, in order to raise a standing army upon its ruins." -- Debate, U.S. House of Representatives, August 17, 1789