8

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.

closed as off-topic by Solar Mike, raydowe, GdD, Chenmunka, Pᴀᴜʟsᴛᴇʀ2 Jul 17 '18 at 19:52

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on driving techniques are off-topic unless asked in regard to a specific mechanical problem. See: Are driving questions on-topic?" – Solar Mike, raydowe, GdD, Chenmunka, Pᴀᴜʟsᴛᴇʀ2
If this question can be reworded to fit the rules in the help center, please edit the question.

  • 3
    I suppose his intention was to tell you about engine breaking. That is really important for prolonged descents as overheating brakes tend to "fade", reducing braking effectiveness up to the point where you could loose control of your car. – Martin Jul 17 '18 at 14:28
  • 3
    Your clutch is expensive and hard to replace. Your brakes are cheaper and easy to replace, what with being at the wheels instead of between the engine and transmission. Which one would you rather wear out first? (Every time you shift, some wear on the clutch disc occurs.) – 3Dave Jul 17 '18 at 15:31
  • 1
    @3Dave: A set of rotors and pads for my front brakes costs me 250€ - A new clutch 50€... Also, with engine braking my clutch held for 100.000 km and counting, whereas I had to change the brake at ~80.000 ... – Daniel Jul 17 '18 at 15:33
  • 2
    @Daniel And how much does it cost do have the clutch installed? On one of my cars, it's close to 1000 USD. Brake install cost is 100USD around here. (I do this stuff myself, but not everyone does.) – 3Dave Jul 17 '18 at 15:35
  • 1
    @Daniel The $1000 - actually, about $950 - was on a C5 Corvette, about 15 years ago. But, given that car's unconventional drive train (front-engine, rear transmission), it's a little harder to do. I imagine it would be much less on the Solstice, but even the clutch on that car cost me about $350. (But it's an upgraded clutch, so... not apples-to-apples.) – 3Dave Jul 17 '18 at 15:52
9

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!

  • So given the number of tailgaters then you won’t be using engine braking.... – Solar Mike Jul 17 '18 at 15:05
  • @Solar Mike: not much during rush hour at least :) – Daniel Jul 17 '18 at 15:34
  • I have heard that it is good to use in Icy Conditions because it doesn't risk the lock up like brakes traditionally would. Is that true? – Nick Jul 17 '18 at 16:32
  • 1
    @Acccumulation: The energy for turning the engine is comeing from the momentum of your car, so you do´t need fuel to keep it running - that´s actually the foce that you feel as engine braking - the force your motor normally needs to burn fuel for when ideling. – Daniel Jul 17 '18 at 21:43
  • 3
    @Nigel Touch: Maybe you should read the whole post again. Engine braking is still essential when going downhill. You should understand the whole mechanics behind it - there is no simple No or Yes. If it´s too complicated, one should refrain from operating a car. Moving two tons of metal in public at deadly speeds should be accompanied by some basic understanding of its modes of operation. – Daniel Jul 17 '18 at 22:12
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.

  • 2
    You can shift down, match engine speed with road & gearbox speed without having to slip the clutch at all. And, if you are any good you can change up or down through the ‘box without even using the clutch... – Solar Mike Jul 17 '18 at 15:09
  • Clutch jobs are not fun, nor are they cheap. Depends on the model. Older Opels/Vauxhalls used to have a clutch that you could slide in with little effort and was dirt cheap... – Daniel Jul 17 '18 at 15:11
  • @Solar Mike: I've only done it on my motorcycle for convenience\speed, but doesn't clutchless shifting put a ton of extra wear on the synchronizers, even if it feels smooth? – SyntheticAbyss Jul 17 '18 at 15:54
  • 1
    Done it on a gearbox that did not have synchros to get worn - if it ain’t right the teeth tell you.... – Solar Mike Jul 17 '18 at 16:11
  • @Solar Mike: That's certainly true. It takes more effort, but your point is 100% valid. – masospaghetti Jul 18 '18 at 15:45
1

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.

  • One other aspect to consider, the cost of replacing a worn clutch is substantially greater than the cost to replace worn brakes! – fred_dot_u Jul 17 '18 at 14:30
  • Can you find any source that concludes that downshifting actually wears synchronizers? From my understanding, correct shifting will not wear a synchro ring at all, since the synchronizers don't actually touch (the oil has enough hydrostatic pressure to match the speeds as the synchronizers get closer). Assuming the car is properly driven and maintained, i.e. proper rev-matched shifts and gear-oil changed as specified, the synchronizers shouldn't wear. – Shamtam Jul 17 '18 at 18:11
  • It's from my experience of driving a 1989 Opel Vectra, with transmission oil never changed. The wear was very noticeable and prompted me to change my driving habits. Perhaps it was due to the old transmission oil? – juhist Jul 17 '18 at 18:13
  • I've not encountered a need to double clutch in any vehicle with syncros. (Read: anything that is likely to still be on the road that's worth less than $1M and isn't pulling a 40-ton trailer.) In 25 years of driving manuals, I have yet to have a transmission blow due to this. – 3Dave Jul 17 '18 at 19:16
  • @juhist Yes, very likely. Just because the transmission isn't shifting as smoothly doesn't mean the synchronizers have worn. I (and many others) have great luck with smoother shifting after changing the gearbox oil. Oil breaks down and can potentially lose viscosity over time, which will show the symptoms you describe in your answer. – Shamtam Jul 17 '18 at 20:29
0

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).

  • Almost? According to dictionary, that means very close to downshift, but not quite downshift. I certainly wouldn't almost downshift; I would downshift. – juhist Jul 17 '18 at 18:04
  • 3
    @juhist instead of being snarky you could simply use the edit button to fix it. – Sam Jul 17 '18 at 18:40
  • Sam, I almost never use the edit button to modify content, just spelling and such. If you agree with @juhist, edit your answer. Otherwise... – 3Dave Jul 17 '18 at 19:18
  • @3Dave, I have edited it, and it was a missed word, well within the uses of the edit button. If juhist had not wanted to use the "edit" button he could have, like most civil people simply said "your grammar makes no sense, I think you missed a word" – Sam Jul 17 '18 at 19:21
  • 1
    Well... we try (here) not to put words in other's mouths. I would not presume to speak for you or to alter your speech (posts) as that feels like over-stepping. Something that looks like a mistake to me may not, in fact, be a mistake. – 3Dave Jul 17 '18 at 19:23

Not the answer you're looking for? Browse other questions tagged or ask your own question.