Clutchless shifting Q's

D

dcharnet

Member
I am installing a Quaife 4 spd Rocket Box (with dog rings, of course) in my MGB and want to return to left foot braking and clutchless shifting.

From my FF/Hewland days I recall quickly breathing the throttle for upshifts.

For downshifts, I recall moving the shifter into neutral immediately upon getting off the throttle at the start of the braking zone.

Then, to engage the lower gear, I remember waiting as long as possible to just before throttle application (when the car is at its slowest speed for that corner), then blipping the throttle maybe 12-1500 RPM to relieve pressure on the gears and almost simultaneously jamming into the lower gear to be used for the corner. All of this is with the left foot braking, of course.

Is this roughly it? If it matters, I have a 7 1/2 Tilton.

Also, is clutchless shifting likely to stress the box more, with negative implications for longevity?
 
I'm using a Datsun 1200 4speed converted to MK9 Hewland gears in my HP Sprite with a 5 clutch. I use the clutch for downshifts only. On the up shifts I only have to quickly lift off the throttle and again, very quickly select the next higher gear. I have had no reliability issue's in the trans. I found this article by William Hewland on the different techniques used to successfully shift a dog engagement transmission. Worth a read. http://www.hewland.com/svga/advice.html

Good luck. Kerry
 
Kerry and Jesse, thanks for the responses. I am familiar with the Hewland piece. Here is what confuses me:

"Whilst braking, the dogs must be unloaded by either touching the throttle pedal or- my preferred method- by dipping the clutch. However, one sharp dab of clutch or throttle is appropriate per shift. Continued pressure on either will cause dog damage for different reasons. `Blipping the throttle` just before engagement is advisable if the rev drops between gears are over 1300 rpm, as this will aid engagement and stabilise the car. "

If you are approaching a corner at full throttle and do not want to "dip the clutch" because you want to left foot brake, surely he is not suggesting that you blip the throttle while braking. He must mean that the car is in neutral when you blip before engaging the gear.

Jesse, I watched the video. Seamless! But can you explain what you are doing? I hear no blips. You just seem to be popping it in with no specific thing done to unload except be off the throttle. Any details would be appreciated.

Don
 
As you downshift, you blip. You do them concurrently. If you don't get the match right you might get wheel hop ( as the NASCAR boys say).

The blip is quite minimal when you are threshold braking. That's why you don't hear much.
 
As Eric said, there's a blip. It has to be quick and seamless. It's an all in one motion, hard on the brakes, slight blip and immediately into the next gear. It's not for everyone but in a level 2 prod car, you need to be able to drive it like this to make it worth the weight penalty.

All of this being said I do have some customers who use the clutch on the upshift. That is the shift that if you mess it up you're possibly going to overrev your engine big time. Shifting a dog box right requires big concentration and smoothness to never screw it up.
 
Another aspect of shifting without the clutch is that it's harder on the whole transmission/driveline, mostly the dogs. The clutch dampens the impact of the change. Without the clutch, it's a much sharper hit.

The trick to the clutchless downshift blip is that it's only effective in raising the RPM during the moment when the slider is between the dogs (neutral - otherwise you're accelerating the car). This is a very brief time. Thus the challenge. The upshift is the opposite challenge, you need to time the duration of the period in neutral to allow the motor to drop to the RPM of the next gear. This is an unconscious timing. It's too fast to think about.

Are flat shift ECUs legal in prod? They make the upshifts MUCH easier.

FWIW: I find the corners where you need to left foot brake (quick dabs on the brakes) you dont need to downshift. I prefer to take it easy to the driveline and use the clutch. I may give up .001 a lap, but I've got good luck with gearboxes.

-Kyle
 
James Rogerson":232f4ouv said:
At least I now know how to take the kink! I've obviously been screwing it up.

James
Click to expand...

Don't try it flat in an EP car. That was the first and maybe the last time I'll try it. I know some of the FP cars can do it and probably most of the HP cars but in an EP car it's right on the edge, as some of the other EP competitors have shown in the last few years by wrecking there. I actually turned in a tick too soon in the video and have since learned not to turn in until the 1 marker. There's a ton of time to be found there by going fast though as it leads alllll the way down to Canada.
 
EPrill":32gkjldk said:
Forgot to mention this but you'll love the Quaife! I had one in my Lotus and it was very smooth and precise. Be careful though as you first get used to it as the replacement parts are expensive compared to hewland pieces.

I had one in my Lotus. Here's a clip of it.

http://www.youtube.com/watch?v=MEyZZU5N ... ata_player
Click to expand...

That was a really good lap, nice and smooth. HPR is a fun track!

I need to learn how to shift my new dog box, so this thread is timely!
 
cpa7man":2b0ew234 said:
EPrill":2b0ew234 said:
Forgot to mention this but you'll love the Quaife! I had one in my Lotus and it was very smooth and precise. Be careful though as you first get used to it as the replacement parts are expensive compared to hewland pieces.

I had one in my Lotus. Here's a clip of it.

http://www.youtube.com/watch?v=MEyZZU5N ... ata_player
Click to expand...

That was a really good lap, nice and smooth. HPR is a fun track!

I need to learn how to shift my new dog box, so this thread is timely!
Click to expand...

Thanks Paul. Can't wait to see you in the new car. It's a beauty.
 
EPrill":6l2fgver said:
cpa7man":6l2fgver said:
EPrill":6l2fgver said:
Forgot to mention this but you'll love the Quaife! I had one in my Lotus and it was very smooth and precise. Be careful though as you first get used to it as the replacement parts are expensive compared to hewland pieces.

I had one in my Lotus. Here's a clip of it.

http://www.youtube.com/watch?v=MEyZZU5N ... ata_player
Click to expand...

That was a really good lap, nice and smooth. HPR is a fun track!

I need to learn how to shift my new dog box, so this thread is timely!
Click to expand...

Thanks Paul. Can't wait to see you in the new car. It's a beauty.
Click to expand...

It may even be too pretty, but thanks Eric! It's a big step up for me to an RX-8, I'll need to figure out how to get some poundage off of it.
 
My view is that the main reason to shift without the clutch is to left foot brake, and not the speed of downshifts. The length of time in the braking zone minimizes the importance of pure speed in downshifting.

There is some gain on upshifts, but the real benefit is much smoother transitions by better coordination of throttle and brake. This is so upon application of the brake, and even more so when the brake is eased and the throttle applied. Use two coordinated feet instead of one foot jumping from one pedal to the other. The ability to balance the car and not overload the tires when weight is moving back and out is maximized.

Do you all agree that clutchless shifting, even with skill, is harder on the box?
 
dcharnet":2vsbt23f said:
Do you all agree that clutchless shifting, even with skill, is harder on the box?
Click to expand...

Certainly, but a race car is designed to be abused. It's harder on the entire driveline. I would also comment that 50% of drivers are wasting their time with a dog box because they can't utilize it properly. One advantage would be the ability to change individual gear ratio's but a lot of dog boxes don't allow this either, like the Quaife. I'd suggest anyone thinking about it also think about a good synchro alternate ratio box as well. These can be cheaper and just as fast without the added weight penalty. You have to be able to utilize a dog box properly and it's not for everyone.
 
I have heard that the use of the ignition cut during upshifts all but eliminates the wear issues.
 
" You have to be able to utilize a dog box properly and it's not for everyone."

Jesse, please elaborate on how you think the dog box is "utilized effectively."
 
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