Is it correct to downshift to brake?

Question

I'm taking the driving license and my instructor told me that I have to downshift to slow down the car, without using brakes. He said that I have to use brakes only when needed (when I need to stop or in case of emergency).

Is it correct? Could downshifting without braking damage the clutch?

PS: I'm also doubtful about this because when you downshift without hitting the brake, the red lights on the back of the vehicle do not turn on, so people behind you cannot understand that you're slowing down.

Answer 1

So there are several aspects to keep in mind if you use engine braking.

1. No brake lights! Don´t do this when somebody sits at your back!
2. Don´t over-rev. Only downshift to an appropriate gear. Never use force to engage the gear.
3. Downshifting and releasing the clutch when cornering hard can lead to unexpected behavior. You are braking only one axle, you´ll get oversteer/understeer depending on the kind of drive-system. No Anti-lock!
4. You´ll trade clutch-lifetime against brake-lifetime. You can reduce wear on the clutch if you give the gas a little pinch before re-engaging the clutch. The clutch wear only happens during the short slipping moment upon engaging - so this is a good trade off when you are going downhill for example.
5. You use absolutely no fuel, when engine-braking as opposed to the motor idling while disc-braking.

This leads to using the engine brake only in certain situations. When you are cruising and see a red light or speed limit up ahead to gently slow down. Or when you go downhill, to save the brakes from overheating.

It´s not a good alternative in any situation where you need a swift or finely controlled slowdown!

Answer 2

Personally, I use engine braking in my current gear to slow the car down, essentially coasting, then use disc brakes (assuming I can plan ahead a bit). This reduces brake wear without increasing wear on the clutch.

I would not engine brake through all of the gears as this will significantly increase clutch wear. Clutch jobs are not fun, nor are they cheap.

Answer 3

It's strange that neither of the answers mentioned transmission synchronizer wear.

If you don't double-declutch (i.e. press the clutch, change to neutral, release clutch, blip the accelerator, press the clutch, switch to lower gear, release the clutch while rev-matching), you cause synchronizer wear to the transmission.

I would be more worried about synchronizer wear rather than clutch wear, as most manual transmission drivers know how to rev-match.

Worn synchronizers mean that gear-changing requires more force than it used to require, and in extreme cases, you can hear grinding sounds when changing gears.

Clutch replacement is cheap in comparison to fixing worn synchronizers.

The summary is: don't downshift at every intersection. Just let the RPMs fall below whatever RPM the injection starts at, then press the clutch.

Answer 4

People have not mentioned that you almost certainly have to downshift instead of braking when coming down a mountain pass say from 11,158 feet (3,401 m) to 5280 feet (1,609 m).