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-   -   The best way to use the clutch, gear and brakes (https://www.team-bhp.com/forum/technical-stuff/1708-best-way-use-clutch-gear-brakes-7.html)

Prateek, did you get the MASS technicians to accompany you on a test drive after the clutch assembly was changed? Aren't they finding any burning?

I agree that the low end torque of the 1.3 is, well, very low. But here I am talking about 3000 rpm which should be decent enough to upshift on most cars. So, the scene here is, the car can't pull very good and it gets angry when u push it too hard(it shouldn't be)! A double whammy?

I did not know this. I thought as long as the clutch is pressed (half or full), the clutch life is getting shorter and shorter.
Are you sure it is not the other way?

Even without downshifting, keeping the engine in the loop does provide a significant amount of braking.

I remember an incident I had when I had newly learnt to drive. It was my Maruti 800 (everybody knows the horrible manual powered brakes :eek: of a Maruti 800) and I was speeding along the highway at around 80 Kmph. Suddenly an Indica zipped past me and 50 metres ahead or so and made a screeching halt with tyres burning as some cattle had decided to cross the road.

I was still in top gear and having no time to downshift, braked hard with my full weight upon the brake pedal (no power brakes) and without depressing the clutch. Of course, the engine stalled but my car came to a stop inches behind the Indica.

I am pretty sure, had it been not for the engine braking, it would not have stopped with the brake power alone.

Since then, I always brake without depressing the clutch pedal and now depressing the pedal before the engine stalls comes automatically.

This is absolutely correct. The clutch is nothing but a slip disc. So if the clutch is engaged, both discs are rotating at same speed and hence, no friction. If the clutch is fully depressed, again there is no friction as the discs are separate.

But if the clutch is half pressed, both discs are partially in contact and rotating at different speeds which causes friction and wear.

I have two questions.
What happens in the car gearbox in the scenario listed below and does this lead to a strain on the gear box ?
Scenario : While driving, say a constant speed of 20 kph, I let go of the accelerator and leave the car in the required gear which could be 2nd or 3rd. Now the car still goes on an on moving ahead but at a constant speed limited to that gear.
Hope everyone understands what I mean. Sorry if I haven't used my words right.

I don't know what exactly happens in the gearbox, but I believe this does not lead to any strain on the mechanicals. Then again, considering you are driving in 2nd, if the road has even a slight uphill, and I'm assuming a hatch, the engine would start to struggle, and this will certainly put some strain on the drivetrain.
Please correct me if I am wrong somewhere.

I believe the ECU nowadays are intelligent enough to raise the throttle a bit to prevent the engine from struggling. I have even seen it cut the A/C automatically when there is not enough power to go around.

So what you are saying is, suppose I am driving up a slight slope in 2nd gear, without throttle input. The engine is around 1.5k RPM. If the car begins to struggle in climbing the slope, the ECU will raise the RPM to say 2k or more, without the driver providing any throttle input?

I am not aware of any such mechanism, and have never experienced this myself. However, I would be very interested to know about this if you can throw some more light on it.

No. It doesn't raise the RPM so much as by 500 as to be able to comfortably drive up a hill in the 2nd gear but yes, it does raise it a little when needed (there must be some limit upto which the ECU is allowed to raise throttle). It is hard to kill an engine while moving in 1st gear or reverse by stalling unless you are trying to climb up a steep slope.

Compare this to the old (M800 carburetor cars in particular) style cars, they needed a foot on the accelerator pedal even when slowly reversing, else it would stall.

The reverse is also true and I tried this in my car numerous times. When starting, the RPM of the car would be a bit high, but if left idle for around 1 minute in neutral, the RPM drops noticably. At this time, if you turn on the A/C, again there is a noticable increase in RPM from the added load.

I believe the increase when the AC is on, is due to the greater load that is affected onto the alternator.

Likewise, right after starting the car the alternator needs more juice to charge the battery (it lost some power due to ignition). To get more juice, it needs more rpms.

Not exactly. The load on the alternator is negligible. The bulk of the load when the AC is on is to drive the AC compressor. The compressor is connected to the engine by a belt, usually the same one connects the engine to the AC, the starter motor and alternator. There is an electro-mechanical clutch in the compressor that gets engaged when the AC is set to on and this sets the compressor working.

That sounds fair, but then what about the dip right after ignition? Similarly, the rise in rpm when turning on high beams, or some serious ICE.

Yep. When using heavy electrical stuff, there will be an increased load in the alternator and as a result, ECU raises RPM to increase the power.

But do you think the battery that got discharged while starting the car would get charged in just 1-2 mins? I think it'd take more than that, maybe like 20-30 mins to top it up completely. My explanation is that initially it takes some more amount of fuel to start the engine from a stop. Once it is running good, the fuel can be reduced. This happens in case of any type of engine. Even an electric water pump draws significant energy to start up and then the energy consumption decreases.

Some don'ts from my side, to improve clutch life, based on my experience :)

I had this habit of depressing the clutch pedal fully, or coasting in neutral, while going down the slopes at 100 kmph on highway runs in my Scorpio. I would then re-engage the clutch when speeds dropped down to 90 kmph. This would happen several times on my long highway runs, with an objective to increase the FE, but I ended up burning the clutch in less than 20k kms ! Re-engaging the clutch this way repeatedly at inappropriate speeds can really burn up the clutch pretty fast.

I am wiser with my new cars, with much lesser gear shifting even in city drives, just by maintaining a wider band of speed in each gear. For example, in slow moving traffic I would earlier keep shifting across 1st, 2nd and 3rd gears very often, but I now manage to keep moving only in 2nd gear in speed bands of 20 even upto 45 kmph, reducing the number of shifts / clutch operation by almost 50 % and thereby helping in increasing clutch life.

Hi I have a few queries.
1) I have seen maxi cab drivers while braking shift to neutral and when the speed is reduced downshifting. Is this method correct?
2) my liva GD does not have a tachometer. How do I know if the engine RPM is low or in the power band?