c230_kS

i am just curious .... it says on the manual about the first 1000 mile. they tell you do not attempt to stop the car by shifting down gears, and so wat's the possible problem it might lead to if people really did it.

adamrs80

I think they are concerned that if you are not careful when downshifting you will cause the engine to rev really high, or redline when the car is new. I don't think this would be a good thing to do ever so just be careful. Also when I had just gotten my coupe, I used to slow down alot by downshifting, if you get in the habit of doing this just remember that you're putting wear and tear on your clutch and syncros just so you can slow down whereas you could be wearing down something much less valuable being your brakepads. Sorry I went off on a tangent but we discussed this topic a while back on the forum. Enjo your new car and break it in properly. Some people will tell you not to worry about breaking it in but it's a good idea and will help determine how well your car performs in the future. It's important to vary your engine speed when driving on the highway and not keep the car at a certian RPM for an extended period of time.

Mike T.

If you downshift using a double-declutching technique you will not be wearing either the clutch disc or the gearbox synchromesh. The release bearing will get a small workout but hey, it's a bearing and I've not had one ever fail on me in about 1 million km of driving, despite having had some high mileage cars. For example, my 405 has 292,500 km on it and the entire clutch is original. Oh and the gearbox is fine too.

Gratuitous double-declutch downshifting for a light or stop sign is unnecessary, but in fast driving and severe mountain descents it really is a good thing to do.

I've run out of brakes on a modern disc brake-equipped car descending the Grossglockner pass in Austria. So it's not always true that modern cars should just be slowed with their brakes.

nukblazi

Hey MikeT, could you put a definition to this action?

I've only heard the term used in two places before. Old three-on-the-tree american manuals, and the movie "the fast and the furious". The later seemed to be used in error?

Mike T.

Simply stated, a double-declutching technique is where the following sequence of events occurs:

1. clutch pedal depressed
2. with clutch pedal depressed, gearlever moved from higher gear to neutral
3. throttle blipped
4. with gearlever in neutral, clutch pedal is released
5. clutch pedal depressed a second time
6. lower gear engaged
7. clutch pedal released a second time

All this happens in a fraction of a second if you are practised at it, and the amount of the throttle blipping needed is a function of how quickly you can complete the above sequence. When you're quick, the blipping required will only be slightly more rpms that the engine would be spinning once the lower gear is engaged.

Some people rev-match on downshifts, which saves clutch disc wear but does not save the synchros. If you rev-match, then take the few days needed to learn double-declutching.

The purpose of the release of the clutch pedal in the middle of the shift combined with the throttle blip is to match the speeds of the mainshaft and layshaft inside the gearbox. If you don't double declutch, the synchromeshes do this gearbox shaft synchronisation for you. And this causes the synchromesh dogs to wear. Usually the second gear synchro is the first to go. A chronic downshifter who does not double-declutch can destroy a synchromesh unit in under 100,000 km (60,000 miles).

So if you do the above-noted actions properly, the input shaft and flywheel will be at almost exactly the same rpm when the clutch pedal is finally released, so the re-loaded clutch at the end of the shift will not wear appreciably since it does not have to drag the engine rpm up.

Hope that makes sense. It's easy to do but hard to write about.

nukblazi

It makes perfect sense as my '49 Ford Tudor required double clutching. I had just never heard of it used on a modern day car.

My MB C230 Sport Coupe crunches EVERY 1 - 2 shift. I am a chronic downshifter, I actually downshift more then I brake using throttle blipping to ease the lurching forward when downshifting.

I have 28k on my car and as I have said in earlier posts, it feels like my shifter is getting sloppier, much sloppier and as I said, it literally cruches every 1 - 2 shift more so when cold but becoming closer to every shift unless I double clutch it.

Any advice would be appreciated. (When I go to speak to my service dept. what do I say?)

kingkong

"It's important to vary your engine speed when driving on the highway and not keep the car at a certian RPM for an extended period of time." by adamrs80

could some 1 pls explain to me why is that?
what about old cars?

Paul Le Corre

@Mike T: your 405?? do you speak about the peugeot 405??

SB-ziV

So.. when do i exactly blip the throttle?
when clutch is still depressed?
or when cluth is released?

what i do when i downshift is, just keep depressing clutch, blip it, and to the lower gear.. so I only depress clutch once..
is that what u refer to rev-match?

Lynn

This is only for the breakin period. This is done to prevent the engine acquiring wear patterns for a certain rpm.

Matt230K

To answer the second question, yes, that is rev-matching. It makes it feel smoother even though you are still wearing the synchros.

Mike, I also want clarification on the first question. Aren't you supposed to blip the throttle after you release the clutch in neutral??

Mike T.

Absolument Paul, régardez ma signature!

It's a Canadian model 405, originally called "405 DL" here but most similar to the 405 SRI in France. To confuse the curious, I placed a 405 SRI badge on it.

My favourite Peugeot is the 404 Coupé with Kugelfischer fuel injection, année modèle 1966, which is a restoration project.

Are you a Peugeot owner too?

Mike T.

Well the bottom line is that the engine has to be spinning sufficiently fast when the clutch pedal is momentarily released in the middle of the shift to spin the gearbox's main shaft up to the speed of the output shaft if the synchros are not going to have to do any work. God I answered that question like a politician.

OK, try again. Yes!

If you were only going to blip after the second declutching movement has begun, you are effectively doing a rev match, not a double-declutch. In order for the gearbox input shaft to be sped up, the engine needs to be blipped before/simultaneously with the momentary clutch release. That is what spins the input shaft up to the correct speed for the lower gear.

Told you it was hard to write about...

oggle

I used to switch gears without engaging the clutch at all by pulling out the gear right after I take my foot off the throttle, revematch, then throw the gear into place. Not always possible to do in all situations, but does that wear out the synchros too?

Matt230K

When the clutch is in, the engine is completely disconnected from the gearbox, right? So if you rev the engine and then release clutch, it will connect with gearbox shaft and spin it up to the same speed? If this is true, wouldn't blipping the throttle with the clutch out make the engine and the gearbox shaft spin up simultaneously, accomplishing the same thing? It seems like this would cause less wear???

Yes, hard to write about. Especially since I'm not completely familiar with the internals of a gearbox.

Mike T.

Not if you can get the car into the lower gear without grinding. Obviously it's easier to upshift without the clutch, rev matching on a downshift without using the clutch is more nerve-wracking, but it is not too difficult.

Shifting without a clutch is a good thing to know how to do in an emergency, but it's not good for the gearbox, especially when you make several mistakes...

vadim

Am I the only one to find this not too easy in the C Coupe? Is it drive-by-wire or the inertia of the M111 or something else? It sure is more difficult compared to other manual cars I've had (including 2 bimmers).

Mike T.

You're right, whether you blip before or after the pedal's out in the middle of the shift, it still must spin the shaft up to the right speed, and it's more efficient to blip as the clutch is released in the middle of the shift.

In any case, were almost dealing in hundredths of a second, so it all happens more or less at the same time anyway...

shkeller55

For another explanation with drawings showing foot-on-pedal placements, check this link to the TurnFast! web site. Read all the way down to get to the double-clutch section:

http://www.turnfast.com/tech_driving..._heeltoe.lasso

A good explanation with pictures can also be found in the book, "Bob Bondurant on High Performance Driving". It's been revised several times; I have an edition from about 25 years ago which I had my 16-year-old son read as part of his driver's education.

oggle

Saved me once when the clutch was leaking and lost all pressure. Pumping it didn't help either and I was very close to a railroad track too.

nukblazi

Just to point out, this article is about heel-toe technique, which is very different from double clutching. The article describes the blip being referenced.

Anyway, double clutching did nothing for my gear grinding issue. I have an appointment for June 11th figure out what's going on with the trans. However, the past two days, the issue has happened once.

For the clutch gurus, I've been practicing another shifting technique and I am curious of your anticipated effects. Basically it is designed to shave time off lap or drag slips. It's been refered to as speed shifting.

For upshifting.
basically, when you are shifting, you simply don't lift of the gas pedal. You depress the clutch just enough to make your shift, leaving the gas pedal mashed to the floor. It makes for super quick shifts, the car sort of jumps forward, but I am sure it can't good for the mechanical components.

Lynn

That technique is nothing new. It is called power shifting. Welcome to the world of blown engines, clutches, transmissions, broken u-joints and cv-joints. It is going to get expensive, if you continue to do this.

shkeller55

"Just to point out, this article is about heel-toe technique, which is very different from double clutching. The article describes the blip being referenced. "

If you had read all the way to the bottom of the article you would have seen that it does indeed describe double-clutching. And heel-toe technique is not "very" different; it is in fact very related in that you can't double-clutch properly if you don't employ the heel-toe technique properly.

nlk10010

thread. Just a couple of questions, if the posters would be so kind.

First, the just-referenced site (and I've always thought this) indicates that the "blipping" should be done with the clutch released. Now perhaps it makes no difference if the clutch is in, on the way out or fully out, and I'm no expert, but I really do think the clutch needs to be out when one blips in order to synchronize all the shafts.

Next, what do most people take as a "blip"? I double-clutched while downshifting for thirty years (don't know how well, though, although I never had to replace a clutch or gearbox), and blipped meant press and quick release of the throttle. After a brief sojourn with autos I just picked up my new manual car and everything I read now indicates "blip" means depress-and-hold throttle (until clutch is released). Perhaps it doesn't make any difference, I don't know.

Any pointers would be appreciated.

=NLK=

nukblazi

Err- I did read all the way to the bottom, then when I didn't see double-clutch, I tried skimming through again looking for it. I must have missed it.

In regards to technique, individually, and conceptually, they seem distinctly different. One requiring the other doesn't merge the techniques or make them the same.

Heel-toe technique is operating the brake and gas at the same time when braking into a turn. So as you employ heel-toe going into the corner, you use you heel to blip the gas while double-clutching. This is employing two techniques at the same time, not one. No?

We are discussing street cars here right?