Which is best, brakes or transmission going down hill?

My son in law says I should use my brakes when going down a hill, but I was taught (about 60 years ago) to use the transmission to slow the car down. Who is right?

You are, as long as you’re not slipping the clutch to do it.

Here we go. I say use the brakes on regular hills. If it’s a mountain pass, then use both. But remember, brake pads are a wear item, meant to be replaced pretty easily and cheaply. You are supposed to wear them out. Transmissions are not so easy to replace, and clutches are tough, too. Wouldn’t you rather do the brakes occasionally than a transmission repair?

You’re right, it all depends on the length. If brakes are needed only occaisionally, the brakes. If more, then downshift (no wear on an AT, match revs on an MT), use the engine to slow. Once you’re in the lower gear, no additional wear should occur. Opposite rule for a stop sign, just use brakes.

What was right 60 years ago is still right today. However even 60 years ago, they would not bother to shift to a lower gear for a short hill, it just is not worth the bother. Long hill 100% downshift as needed and then if you need more use the brakes. Doing otherwise is dangerous.

Depends on the hill.

You are partially correct. The issue is not just wear on the brakes though. Long hills can cause overheating of the brakes if you don’t use engine braking to help keep the vehicle at speed. The brakes should be used only to augment the engine braking. Overheated brakes can be lethal if you suddenly have to stop, or slow down even more.

Your not using the transmission to control your speed, but the engine. Use the free engine braking to keep control. Riding the brakes downhill will cause overheating and brake failure. The clutch and transmission WILL NOT WEAR when doing this. The clutch only wears when you release and re-engage the clutch. There is no clutch wear when it is fully engaged and not slipping. Automatics are the same way. The parts inside the transmission that are wearing will wear anyways, as the axle is going to turn them whenever the car is moving.

As an extreme example, tractor-trailers use an exhaust braking as a rule down hills. Using the brakes is a strict no-no, and has caused severe accidents and deaths when the brakes overheat and fail. All tractors use an exhaust brake, because the diesel engines have no vacuum resistance. But, gasoline engines do, and using it to control your down hill speed is the safest and best way to go.

What about automatic transmissions and steep, short hills, such as those in San Francisco? Should I downshift as I start to descend and let the engine act as a brake?

Yes. Some of those hills aren’t as short as you think. Using the engine as a brake is just as effective as on long down grades, like we have in Tennessee.

On long hills, absolutely use the transmission (engine) to help control speed.

You may have seen pictures of race cars with glowing red brake rotors showing through the wheels. That does not work with ‘street’ rotors and pads. Brake fade is terrifying and can kill you and others. In case you are wondering, no, you don’t want to put racing brakes on your street car. You would not be happy with the results.

I advise that you downshift at the crest of the hill. Don’t wait until you are halfway down the hill and realize that you are going 90 mph and then downshift. This is sound advice whether you have a manual or automatic transmission. Downshifting at high speed is hard on an array of different parts, from your differential to your valve train.

On a side note- it is illegal (at least in the states with which I am familiar) put the vehicle in neutral and coast down hill in neutral in an effort to save fuel.