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Old 17th May 2011, 21:31   #16
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Default Re: Emergency driving - Without clutch

An idle question. Does it help in changing gears without the clutch if your car has an RPM meter and you generally know the RPMs for each gear's change?

By the way, I am pretty sure the Indica NAs had no synchros in the 1st gear either. Its just a terrible fight with lot of grinding noise if you try slotting first in a moving Indica NA. Only when the speed has slowed down a lot on the second (threshold for the 1st -> 2nd shift can) one shift down to the first gear in this car. This is my personal observation with multiple NAs though never got down to check this spec.
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Old 17th May 2011, 21:53   #17
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Default Re: Emergency driving - Without clutch

Better not to try these experiments. Except in case of emergency.
With reference to clutch and gears, I had read that if on a slope car is moving in forward direction, brakes and also the hand brake malfunctions then as a emergency situation car can be put in reverse gear and the clutch pedal is to be released. this causes the gears to lock themselves and car stops with a jerk The gears may also break in the process but the car will stop for sure.
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Old 17th May 2011, 22:06   #18
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Default Re: Emergency driving - Without clutch

There is a sweet band of revs for all cars and a sweet band of speed for each gears in a car. Now it is your car so you are familiar with it. Typically the second gear takes on at about 20kmph~30kmph.

So you were in first gear. Get your car at the sweet speed for changing in to second gear. Now simultaneously lift off you right foot from accelerator and shift to neutral. Give it a second in neutral and then push the gear lever towards the second gear slot and keep slight pressure on the lever. Nothing more. Within a second you would feel it slotting in to the second gear. Slight pressure on accelerators at this time will help slot the gears quickly.

Simple!! try it. And repeat for next and next gear.

What happened inside the gear box was that the syncromesh rings came together when you pushed the gear towards second gear slot. And as soon as the revvs matched the gears slotted.

Why a wait for a second or so?? Well in first gear the engine was revving much higher than what it should be in second gear fro speed of 20~30kmph. So this momentary stop in neutral allows the engine side gear to slow down before pressure is borne by synchromesh rings.

Try it and use clutch (dummy you were only pretending it is not working) to shift down and try again shifting up without clutch.

Next step to shift down without clutch.

Last edited by sudev : 17th May 2011 at 22:07.
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Old 17th May 2011, 22:20   #19
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Default Re: Emergency driving - Without clutch

Shall we say 'double declutch, but don't use the clutch'.

Regards
Sutripta
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Old 17th May 2011, 22:48   #20
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Default Re: Emergency driving - Without clutch

Quote:
Originally Posted by Zappo View Post
An idle question. Does it help in changing gears without the clutch if your car has an RPM meter and you generally know the RPMs for each gear's change?

By the way, I am pretty sure the Indica NAs had no synchros in the 1st gear either. Its just a terrible fight with lot of grinding noise if you try slotting first in a moving Indica NA. Only when the speed has slowed down a lot on the second (threshold for the 1st -> 2nd shift can) one shift down to the first gear in this car. This is my personal observation with multiple NAs though never got down to check this spec.
I used to rely a lot on my Bajaj Pulsar's tachometer for the gear shifts. If you understand your vehicles power curves well then knowing the right RPM to shift up (or for that matter shift down) is quite easy. Found its more useful on a two-wheeler with the higher revs.
On the clutch action-loss scenario, I think the tachometer would be of great help! Layman's words :P

My old M800 (1997 model) does not have synchromesh for sure!! Haven't checked the specs though, based on my driving experience.
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Old 17th May 2011, 23:24   #21
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Default Re: Emergency driving - Without clutch

Sorry for being slightly off-topic but have just gotten back home after a similar clutch related issue. Just got out of the building and when i pressed the clutch to engage the second gear and clutch just went in and didnt bounce back as usual. The car did get slotted in second gear and was moving. I just pressed the clutch as hard as i could brought it to neutral and safely parked. The clutch pedal for some reason has become totally soft. The clutch pedal is connected with the clutch cylinder and there seems to a small pin/bolt assembly which holds them together. Don't know how or when but this pin/bolt assembly had come off. Road assistance didnt have the assembly and the search within the cabin was futile so used couple of inches of hard wire to tie them together. Took the car for a short spin, everything seems to be ok. Couple of Questions

1. Can someone shed more light on this pin/bolt assembly. Is this assembly available separately or will the A.S.S push me to replace the clutch cylinder assembly.
2. What could be the approx expenses for replacing the cylinder assembly. It is a fiesta petrol 1.4.
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Old 18th May 2011, 05:47   #22
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Default Re: Emergency driving - Without clutch

Quote:
Originally Posted by Sutripta View Post
Shall we say 'double declutch, but don't use the clutch'.
Aaahhhhhaa. Welcome Professori. I was expecting you to shed more tech insight in to what I am flippantly describing.

Dounle de-clutch. Yes those with greying hair or no hair would remember double de-clutching actions in for non syncromesh gear boxes. Even now used by truck and bus drivers.

Please contribute more.

Quote:
Originally Posted by bzr77k View Post
My old M800 (1997 model) does not have synchromesh for sure!! Haven't checked the specs though, based on my driving experience.
On the contrary M800 is one of the first cars that also had first gear synchromeshed. And I have driven that model in a rally stage without clutch!

@ashish1965 : When emergency happens you will not have experience to tackles it. That's is why it is useful to practise this when you have time. This will not harm the gear box if done a few times.

Putting the forward moving car to a full stop by slotting in to reverse!! I'd wait to hear if some one has already experienced this???!!!

@zappo : I'd help to have a ROM meter but if you know your car you know the speed and engine sound can tell you when to shift.

Yes it is easy to do so in bikes as you already have gear lever setup in sequential shift pattern. But even in cars it is pretty easy when you know how.

Not something that should be done regularly.
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Old 18th May 2011, 05:51   #23
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Default Re: Emergency driving - Without clutch

Quote:
Originally Posted by cyberwhizs View Post
Sorry for being slightly off-topic but have just gotten back home after a similar clutch related issue. Just got out of the building and when i pressed the clutch to engage the second gear and clutch just went in and didnt bounce back as usual. The car did get slotted in second gear and was moving. I just pressed the clutch as hard as i could brought it to neutral and safely parked. The clutch pedal for some reason has become totally soft. The clutch pedal is connected with the clutch cylinder and there seems to a small pin/bolt assembly which holds them together. Don't know how or when but this pin/bolt assembly had come off. Road assistance didnt have the assembly and the search within the cabin was futile so used couple of inches of hard wire to tie them together. Took the car for a short spin, everything seems to be ok. Couple of Questions

1. Can someone shed more light on this pin/bolt assembly. Is this assembly available separately or will the A.S.S push me to replace the clutch cylinder assembly.
2. What could be the approx expenses for replacing the cylinder assembly. It is a fiesta petrol 1.4.
Yes this is OT here. Perhaps the original topic that set this thread off is a better place for this query. Clearly the mechanical inkage has dropped off. Wonder why you could not find it inside the car!
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Old 18th May 2011, 08:11   #24
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Default Re: Emergency driving - Without clutch

Quote:
Originally Posted by ashish1965 View Post
Better not to try these experiments. Except in case of emergency.
With reference to clutch and gears, I had read that if on a slope car is moving in forward direction, brakes and also the hand brake malfunctions then as a emergency situation car can be put in reverse gear and the clutch pedal is to be released. this causes the gears to lock themselves and car stops with a jerk The gears may also break in the process but the car will stop for sure.

I doubt if one could engage the reverse gear in a car moving forward But I did hear this theory before.
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Old 18th May 2011, 11:08   #25
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Default Re: Emergency driving - Without clutch

As the thread title states this is only for an emergency that one needs to know its possible to drive and change gears without a clutch.

For those who are curious a few points must be noted as it helps in carrying out this action as efficiently as possible. Please note that in cars equipped with synchronisers you can quite easily change gears up and down without gears grinding each other. Before I explain how this can be done please try to understand some basic elements in a car's drivetrain.

The clutch in a car connects the flywheel to the input drive gear of a gearbox. As you depress the clutch you are basically disengaging the positive drive from the engine to the input drive gear.

Within the gearbox the act of changing gears has nothing to do with a failed clutch. You will slot out of a gear and slot into a gear just like when you do with a working clutch.

In a failed clutch situation you basically come up with a problem of mismatched gear revs. A gear meshes with another gear smoothly when they are either both idle or revving at same speed. A mismatch in revs causes the grinding teeth.

When driving smoothly gearbox ratios are designed in a way to cause a smooth blend in revs of the engine and final drive connect. As a result of this design blend you can shift from first to second to thrid etc quite smoothly when you do it quickly without depressing a clutch. There is a small band of revs for each gear within which it will mesh easily with the engine connected input drive gear without clashing. Remember its all about matching the engine revs to final drive gear revs

When changing down a better way to do this is to shift out of the gear and tap the throttle gently to then slot into a lower gear. This you do to bring the engine revs up to a natural high when you change down. You can gently push the lever into the lower gear slot and tap the throttle, as the appropriate rev band arrives the gear meshes in smoothly. Try not to force the gears in when you hear a grind. Just tap the throttle again and try again

Once again this action is recommended only when you are in a crisis situation where the safety/health of your family is comprimised and you need to get to a town urgently.

Please do not try this now when you don't need to, just to practice. You WILL damage your synchroniser rings as they will get ground out as they are not designed to handle the kind of torque the rings/plates are subjected to when the entire crank/flywheel weights are in action. Synchroniser metallurgy is designed only for the mass of the input drive gear of a gearbox. The work it has to do deals only with that mass when its either braking the input drive gear or stepping up its revs when changing down.

Just know that its possible to drive your car despite clutch failure and its possible to do so without grinding your gears. You will sustain additional wear on your synchroniser rings/plates when you drive a car without using the clutch. Its recommended to have your car recovered by a service technician using either a tow truck or recovery vehicle. As far as possible try to avoid this action of driving when your clutch fails. That said, in an emergency where your reaching a town is imperative the option to do so always remains albeit causing slight (can be severe) damage to your synchronisers and eventually your gears.

Last edited by DKG : 18th May 2011 at 11:31.
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Old 18th May 2011, 12:18   #26
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Quote:
Originally Posted by DKG View Post
Please do not try this now when you don't need to, just to practice. You WILL damage your synchroniser rings as they will get ground out as they are not designed to handle the kind of torque the rings/plates are subjected to when the entire crank/flywheel weights are in action. Synchroniser metallurgy is designed only for the mass of the input drive gear of a gearbox. The work it has to do deals only with that mass when its either braking the input drive gear or stepping up its revs when changing down.
Exactly what I was wondering. An attempt at 'partial recovery' due to a lost clutch should not result in more severe failure such as a damager gear box!
If I had to take such a decision, it would probably be only in case of an absolute emergency (more like a life or death scenario)

Quote:
Originally Posted by sudev View Post

On the contrary M800 is one of the first cars that also had first gear synchromeshed. And I have driven that model in a rally stage without clutch!
Are you sure it was the 1997 model? or a later one?

Last edited by Zappo : 18th May 2011 at 20:39.
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Old 18th May 2011, 15:21   #27
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Default Re: Emergency driving - Without clutch

Once I stranded for the same reason, what I did is, I pushed a car little and in the slow moving car, I jumped in, cranked the engine, slots the gear without accelerating the engine and moved on. It worked perfect for me.
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Old 18th May 2011, 17:41   #28
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Default Re: Emergency driving - Without clutch

Quote:
Originally Posted by bzr77k View Post
Are you sure it was the 1997 model? or a later one?
Right from 1984 the old model M800 had synchro on all forward gears.

Thanks DKG for giving out details of down shifting. So people can now practise down shifting without using clutch. And as you rightly mentioned do not over use this method. One or two practise will not hurt your car but prepare you to do this if and when needed.

Caveat if you are expecting to drive through heavy traffic do not shift to fourth or even third gear. Go on at reduced speeds in third or second gear. This will help you navigate properly.

Questions?
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Old 18th May 2011, 19:47   #29
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Default Re: Emergency driving - Without clutch

Some race cars are meant to be upshifted & downshifted without declutching, simply because it saves you the time & also because the dog teeth (gear teeth) in race cars are more widely spaced (almost like the trannys on trucks). Hence, it is easier for the non meshed teeth to fall into place.

A regular car has the teeth placed as closely as possible for Fuel efficiency reasons. Therefore, it is

1) Difficult to find the sweet spot for shifting. A couple of revs short & you get the famed grinding noise.

2) If you manage to do so, even in the ideal range, the synchro-rings will keep rubbing & the result is an overheated transmission(if done for long).

This tech is popularly known as Revvmatching & is usually done on non-synchro truck gearboxes. (Remember how they give a little throttle just before downshifting)

Last edited by JustCause : 18th May 2011 at 19:49.
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Old 18th May 2011, 20:05   #30
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Default Re: Emergency driving - Without clutch

revving to the right level and then shifting up or down is possible quite easily in these synchromesh gearboxes
indeed in the old days people used to sometimes to this kind of advanced "racing change" while driving their heralds, gazels, fiats and ambys as well as the mahindra jeeps in the hills. my dad taught me this trick a long time ago and its quite good fun - provided you get the revs right.
however i would not recommend these tricks for daily use since as has been mentioned one is more likely to grind and gnash one's gears to dust over time on account of "mis-hits" with constant usage of this racing change.
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