I have a C6 Z51. If I read the owner's manual correctly, it explains the transmission should not be double clutched during a downshift. In driving schools, I learned to downshift by pushing in the clutch, pulling the trans to neutral, letting out the clutch, then hitting the accelerator to help the transmission speed match the engine speed, then pushing in the clutch and downshifting.

The manual says to just downshift it. Is this correct? If so, why should it be done this way?

Thanks.

 

I read the complete manual and did not interpret as you did. Double-clutching matches gear speeds and eliminates the shock of mis-matched rpms. This results in less stress on the drive-train which is not a bad thing. I always double-clutch when down-shifting unless my speed is very low. A long time ago I used to double-clutch on an up-shift but without blipping the throttle in neutral. Without syncronizers all this was necessary to keep from breaking gear teeth on the older trucks.

 

imo, 95% of the time there isn't a need to double clutch with the c6.
just keep the rpms in a reasonable range when you shift and it should be fine.

 

If there was a need to double-clutch on a particular transmission and one did not do it, wouldn't there be some type of unfavorable effect, like a clunk or grinding noise, or...? I downshift my C6 without double-clutching and do not observe any unfavorable effects. Am I missing something?

 

I usually double clutch out of habit on downshifts. It's not necessary, but it makes me feel better to baby the tranny to make up for the other 95% of the time I'm abusing the car

 

this aint no truck

 

I agree with the no need to double clutch on down shifting as long as the RPM's are where they should be. It is no fun to miss a gear when down shifting, especially when you have your wife in the car....that conversation last all the way home....

 

There is absoultly NO reason to double clutch !

 

Doubleclutching made sense with the older non-synchro and crude synchro transmissions but isn't needed on the C6. You can "rev match" without double clutching but there's no need for rev matching with street driving. Maybe if you were cruising in 6th at 1000 RPM and got challenged by a ricer you would want to downshift to second and bury him but even then there's no need for double clutching, C6's have good synchros.

 

You can get a much smoother and quicker downshift by using the "heel and toe" method to blip the throttle. Similar to double clutching in the fact that you are matching engine revs - but you eliminate the movement of the shifter to neutral and then again to the selected gear. Instead, just blip the throttle and downshift all in one motion. With practice it becomes second nature.

 

WE SEPND ALL THIS MONEY ON A CAR AND THIS IS HOW YOU TREAT IT?!??!

 

Actually, there is! If you want the synchros to last 300K miles then double clutching takes the load off of these devices. If you don't care about 'doing' a tranny afte 150K miles or you are not going to keep the car this long, then does it not matter.

{Rev matching takes a lot of the load off of they synchros, double clutching takes the rest of the load off of them. Not that they are fragile or anything}

 

 

I have double clutched on every downshift on just about every standard shift car I have owned for several years. It is probably unnecessary in a lot of cases, but there is no doubt that it is easier on the mechanicals, i.e. I have never had to replace a clutch or ever have to repair a gearbox.

Once you learn the procedure it becomes second nature, you can do it without thinking and that is good for you and good for the car. If you don't want to learn how to double clutch (mentally challenged or lazy), at least learn to blip the throttle in neutral as you go down a gear to better sync the engine speed to the gearbox.

If you put your car on the track it is helpful to learn how to double clutch for those situations where you skip a gear, i.e. 4th to 2nd without going into 3rd. In that situation it seems much smoother to double clutch, than just downshifting normally and letting the syncros take the burden.

 

This is how I was taught to shift years ago by my uncle who raced his '58 FI Corvette professionally. Could you be referring to the section regarding the 500-mile break-in period? Matching engine speed to the trans will certainly save the tranny over time.

 

First of all, the entire purpose of synchros is so that you don't have to double clutch. That is why they were even created, if you always double clutch it you don't need synchros. Synchos slow down the output gear, input gear, and input shaft (layshaft) to match the speed of the collers, output gears, and output shaft to linup the engagment between the collers (locked to output shaft) and output gears (locked to input gears). They do this by making frictional contact as you slide the shifter over, but that is what they are designed to do. Unless they screwed up their engineering design, they should not wear out from this and the ones I've seen show very little wear. They aren't made of friction material like clutches and brakes and are designed to last the life of the vehicle. So, in a sense you would be saving your synchos by double clutching it, but that would eliminate their entire purpose of existance, destroying their spirit and will to live....

Also, there is nothing magical about downshifting, you use the synchros when you upshift as well. If you believe you should double clutch when downshifting, you should do it when upshifting as well. Remember though, you are depriving your synchos of their purpose in this world
...

Checkout how stuff works for more information

http://auto.howstuffworks.com/transmission1.htm

...and no, it no longer matters if you put it in neutral or keep the clutch in when stopped at a light either

 

Your comment about double clutching on the upshift is not correct. In the upshift situation the input shaft needs to slow down somewhat in order to syncronize with the next highest gear ratio and this happens naturally as you back off the throttle and depress the clutch.
Anyone who has ever driven a real racing car with a non syncro gearbox knows that downshifts should be double clutched or alternatively you can blip the throttle in neutral as you goto the lower gear; but, upshifts can be made normally with no blipping or double clutching.

I also do not agree with your comment about syncros not wearing out. Ther are a lot of older performance cars around with weak syncros. Cars that have been tracked extensively or used hard, will wear out syncros, because downshifting at high speed to a lower gear will take its toll after a time. For just driving around town the syncros may last the life of the car, but many people who own a performance car will use it for the purpose it was intended and the syncros may not last.

 

Double clutching means extra wear on the clutch disc,pressure plate and throwout bearing. Normal driving it's not needed. If you double clutch downshifts you are adding 1/3 more wear to the clutch assembly.

 

Very good point... especially if double-clutching is really not needed. Guess it just depends on what type of driving you're doing. A racer is going to be beating the heck out of the clutch and everything else anyway so it doesn't matter. But for legal street driving, it seems that double-clutching might wear the clutch, throw-out bear etc before the benefit to the syncros would ever be realized. Just a speculation anyway. I find double-clutcing to be a pain, just slows down your shift... call me lazy, maybe I am, but I certainly would not want to double-clutch if not necessary. If I thought it would prolong the life of my tranny from 100k miles to 200k, I would probably do it... but if it's more a matter of prolonging from 175k miles to 300k miles, it doesn't matter... I, nor most other people will have their C6 past 175k miles. Finally, you can always just swap in a rebuilt tranny after ten years or whatever, not the end of the world.

 

Just learn to heel/tow and you will be fine.