True. Great thread everyone!

 

You are doing it correctly.

In theory you can shift w/o the clutch but it does put addition wear on the synchros.

 

With proper 'Rev-Matching' there should be almost no wear on the Clutch Plate anyway. Clutch face only involves friction while accelerating from a dead stop.

Which is more cost/trouble, replacing clutch or syncros?

Think that most large trucks only use their clutch from inital start and don't know if they even have syncromesh.

 

I don't know how I feel about shifting into gear without the clutch...just seems risky. I hate the sound of grinding gears.

From what I've been told by Phil Wicks, he said that double clutching reduces wear and tear on the clutch itself. I honestly don't know. I just take people's advice who are wiser than me. You could be right as well.

The thing is, when accelerating, if I don't let the clutch slip a little, the shift seems "jerky" or makes it lurch a little. If not double-clutching, are you supposed to push clutch in, shift from gear to gear (no neutral), clutch out, then throttle? Or, give it some throttle as the clutch is disengaging? kind of like at the last second type of thing.

 

While this might be a little easier on the clutch, isn't it a lot harder on the syncros?

 

I wish I understood what you mean by 'slipping the clutch.' Do you mean letting it out slowing to feel the gear engage and make for a smoother transition?

 

Theoretically yes, but not a lot harder. Modern syncros are so good that I almost dismiss their need to be saved. Not to say I should do so because any wear on anything that is saved is always a good thing

 

Double clutching is basically doubling the work the clutch is doing and does put additional wear and tear on it.

You need to let out the clutch in such a way as to smoothly transition from gear to gear. This would normally be a slow release of the clutch, not a sudden action. So in essence you are "slipping" the clutch a bit as you re-engage the tranny.

 

Perhaps, but it doubles the actuation of the springs that force the friction material and the pressure plate together. This is why you should minimize the time that you have your foot on the clutch (such as sitting at a traffic light with the car in gear).

 

No idea about the R56 transmissions, but the Getrag syncros in the R53 cannot be sourced separately. As with any BMW, I bet they'd have you buy a whole new transmission because the syncros are held up in red tape, so you'd best preserve them.


Double clutch = bad
Rev-match and heel-toe = best

 

Ive had my doubts in when to shift when im racing against another car. <<<<at how many rev should i shift gears to get maximum performance out of my mini s jcw. thanks alot. if possible can u send me and email with the reply i dont know how to use this site much

 

Ive had my doubts in when to shift when im racing against another car. <<<<at how many rev should i shift gears to get maximum performance out of my mini s jcw. thanks alot. if possible can u send me and email with the reply i dont know how to use this site much

 

oh i'll bite...

i double clutch up and down, unless in a hurry (not often)

my theory is it saved the synchros, and i learned it on an XK 150 Jag with no synchros left in the bottom three gears...

the drive train is three parts, and the trick is matching their momentum.

take a downshift for example.

3k in fourth, the engine is at 3k, the input shaft including the clutch plate is at 3k, and the final drive is at whatever it's at (wheel speed derivative)

1. shift to neutral and release the clutch (step 1 of the double), while
2. blipping to add 6-700 revs, which accelerates the input shaft to match the rpm of the next lowest gear in the box (3rd in this case)
3. shift to 3rd with clutch in (step 2 of the double) which is easy as the synchros have no work to do - the two gears ar already rev matched
4. release the clutch

it's controlling the speed of that middle section, from clutch plate to input shaft, that matters. that's a pretty hefty collection of steel and i prefer not to rely on the synchros to accelerate or slow it down if i can avoid it.

i've 126k on the gearbox, and it shifts as if new -- but this winter the car will see a full teardown and so then i'll know for sure if there is any merit to all this tomfoolery

cheers,

charlie

 

Ive owned my mcs jcw for about 2 weeks. Any know when should i shift gears racing? i mean starting from cero. At first gear how many revs should i get to before i change to second gear to get max performance, from second to third so on so on! I hope to get a reply with your help and if possible anyother tecniques i should know about to get the mac potencial out of my mini. Thanks

 

two thoughts:

1. max power means shifting at redline. there is a thrust chart in my gallery for proof if you're curious.
2. don't make a habit of it...

;-0

 

thanks alot cmt52663 il check it out.

 

What's your thrust chart actually telling you?

My calculations indicate the shift point is a bit below redline in higher gears for the Cooper-S, about 5600 for 3rd-4th. I don't know about a JCW though.

 

it tells me that there is never any point in any gear (between 2k and redline) where selecting the next highest gear will actually increase the thrust measured at the contact patch

although there is more torque available at lower rpms, the mechanical advantage conferred by the lower gear always provides more thrust despite the declining torque available at the highest rpms

 

I'm not sure what you mean by thrust, it sounds like you're just considering torque, which doesn't tell the whole story. What actually accelerates you is power, and that's torque multiplied by revs. The power graphs tend to overlap at higher revs, giving you shift points before the red line.

Edit: We may be talking about different generation here. I thought I'd done this for the 1st gen, but never did, it does seem to be shift at redline. For the 2nd gen there's over lap for the higher gears. That's part of what people don't like about the new engine, it runs out of puff sooner.

 

so with your experience. When do you think its best to change gears in a r53 jcw. Thanks

 

I've never driven a JCW so I wouldn't know, but finding a dyno graph for a R53 JCW, it looks like red line is the optimal place to shift.

 

Been practicing a bit. I only double clutch when downshifting. I rev-match when upshifting as well but what I do is hold the clutch pedal in until the RPM go down to an appropriate speed then smoothly release clutch pedal and then hit the thottle again.
I no longer use the clutch to disengage gears. For instance, if I am coming to a complete stop, I'll break and once the RPM reach 1k I'll pull the shifter out of gear and into neutral. I feel no resistance but just wanted to make sure this isn't stressing the tranny. It feels very smooth and just slips right out.

Do have another question though. Not sure how to describe it but I'll try. When shifting, especially gears 1-3, I'll notice a slight bit of friction whien shifting. Well, it's not really friction but almost like a catchy feeling? Like it's rubbiing against the wall or teeth? I'm not familiar with the parts of a transmission. It still goes into gear without any extra effort. I'm not sure if it's me putting too much pressure to the left side of if it's the transmission. (I think I have a tendancy to pull the shifter towards me when shifting). It doesn't make any grinding or howling sounds. I've noticed this in other cars I just want to make sure it's not a future failure warning or bad technique or something.
Anyone else know what I am talking about?

When to shift:
You want to shift when the car hits its peak HP which is around 5,900 RPM or right at redline.

 

Relax your grip on the shifter a bit. You can't force the shifter to where it is not designed to go. The shifter is not a baseball bat...

 

For some reason I've been avoiding this thread, perhaps because I knew some of it would be over my head. As a new manual owner (almost been driving manual mini 1 year), I have my doubts when driving about whether or not I'm doing things correctly. I have been downshifting to slowdown, usually to 3rd and let the brakes do the rest. It seems to be working. After reading this thread, I'm still blurry on what double clutching and clutch slip are. I guess I'll read a couple more times to figure it out. Thanks for everyones in depth knowledge! It helps us manual noobs.

 

just remember don't rest your foot on the clutch pedal.....